Adsorption characteristics and mechanism of ammonia nitrogen and phosphate from biogas slurry by Ca2+-modified soybean straw biochar

Xiaomei Wu; Meifeng Ye; Jinglong Wang; Feilong Wu; Cenwei Liu; Zhangting Li; Daiyan Lin; Rilong Yang

doi:10.1371/journal.pone.0290714

Abstract

The utilization of biogas slurry is critical for the sustainable development of animal husbandry. Biomass carbon adsorption is a feasible method for the recycling of nutrients from biogas slurry. However, research on the co-adsorption of ammonia nitrogen and phosphate is scarce. Herein, soybean straw was utilized as the raw material to prepare Ca²⁺-modified biochar (CaSSB), which was investigated for its ammonia nitrogen and phosphate adsorption mechanisms. Compared with natural biochar (SSB), CaSSB possesses a high H/C ratio, larger surface area, high porosity and various functional groups. Ca²⁺-modified soybean straw biochar exhibited excellent adsorption performance for NH₄⁺–N (103.18 mg/g) and PO₄³⁻−P (9.75 mg/g) at pH = 6, using an adsorbent dosage of 2 g/L. The experimental adsorption data of ammonia nitrogen by CaSSB corresponded to pseudo-second-order kinetics and the Langmuir isotherm model, suggesting that the adsorption process was homogeneous and that electrostatic attraction might be the primary adsorption mechanism. Meanwhile, the adsorption of phosphate conformed to pseudo-second-order kinetics and the Langmuir–Freundlich model, whose mechanism might be attributed to ligand exchange and chemical precipitation. These results reveal the potential of CaSSBs as a cost-effective, efficient adsorbent for the recovery of ammonium and phosphate from biogas slurry.

Citation: Wu X, Ye M, Wang J, Wu F, Liu C, Li Z, et al. (2023) Adsorption characteristics and mechanism of ammonia nitrogen and phosphate from biogas slurry by Ca²⁺-modified soybean straw biochar. PLoS ONE 18(8): e0290714. https://doi.org/10.1371/journal.pone.0290714

Editor: Nor Adilla Rashidi, Universiti Teknologi Petronas: Universiti Teknologi PETRONAS, MALAYSIA

Received: April 19, 2023; Accepted: August 12, 2023; Published: August 25, 2023

Copyright: © 2023 Wu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information file.

Funding: This work was financially supported by grants from the Special Fund for Provicial Public Research Institute of Fujian Provice (Nos.2021R1032003), recipient: xiaomei wu, Natural Science Foundation of Fujian Province (Nos.2021J01497), recipient: xiaomei wu, and the Innovation Program of Fujian Academy of Agricultural Sciences (Nos.CXTD2021015-3), recipient: feilong wu, and International Cooperation projects of Fujian Academy of Agricultural Sciences (Nos. DWHZ-2022-16), recipient: cenwei liu. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Livestock and poultry manure production has increased as a result of advancements in intensive and large-scale farming. Anaerobic digestion has emerged as a popular technology for treating these manures, offering advantages such as low cost, high efficiency and ease of operation. In China, approximately 90% of farm manure is treated using biogas anaerobic digestion [1]. Nevertheless, the proliferation of biogas plants has led to an increase in the production of biogas slurry, posing a challenge for its harmless resource treatment [2]. Biogas slurry, a by-product of anaerobic fermentation, contains various biologically active substances, including nitrogen, phosphorus, potassium, amino acids, trace elements, organic acids and humic acids [3]. Discharging untreated biogas slurry into water causes environmental pollution and wastes valuable nitrogen and phosphorus resources [4]. Various treatment technologies have been previously utilised, including coagulation–flocculation, catalytic oxidation and A²/O. However, their widespread application has been hindered by several limitations, including high cost, unstable operation and inadequate phosphorus treatment [5–8]. In recent years, extensive attention has been paid to the recovery of nitrogen and phosphorus nutrients from biogas slurry, driven by policies promoting the resource utilisation of livestock and poultry manure.

There are several frequently-used technologies for recovering nitrogen and phosphorus from biogas slurry recovery, including crystallisation, ultrafiltration, filtration, reverse osmosis, phytoremediation, and so on [9, 10]. These methods offer a twofold advantage by facilitating nutrient recovery and generating clean water from biogas slurry. The resulting clean water can be either directly discharged into water bodies or used for non-domestic applications. Nevertheless, the high expenses and substantial chemical consumption pose obstacles to the extensive implementation of these technologies. Adsorption technology is a straightforward, effective and economical technique for nutrient recovery from biogas slurry. It reduces nitrogen and phosphorus efflux pollution, prevents resource waste and enables the reuse of the slurry as a soil conditioner [11]. However, commonly employed adsorbents, such as commercial activated carbon [12], minerals [13] and zeolites [14], are usually expensive and are limited in their potential applicability, characterised by low utilization value. The biological nutrient removal efficiency is considerably influenced by the choice of an appropriate adsorbent in this approach [15]. Therefore, it is highly desirable to develop a new type of adsorbent with low production cost and effective adsorption properties.

Biochar is a porous carbon-rich by-product generated via gasification or pyrolysis of agricultural and forestry biomass under anaerobic conditions [16]. Biochar has been widely adopted in the fields of water purification and soil amelioration owing to its high porosity, stable aromatic structure, excellent stability and rich functional groups [17–19]. The physicochemical properties of biochar are highly dependent on the biomass source and various carbonization processes. Thus, biochars derived from different raw materials exhibit varying adsorption capacities for nitrogen and phosphorus [20]. To achieve simultaneous adsorption, biochars have been modified with metal cations such as iron [21], calcium [22], aluminium [23] and magnesium [24], which remarkably enhance their pollutant adsorption capacity. Among them, calcium is a versatile resource known for its low cost and ease of operation, and it exhibits remarkable binding capabilities for phosphorus [25]. Furthermore, Ca²⁺ is a medium element required for plant growth. Liu [26] impregnated ramie stem biochar with calcium chloride, determining that biochar loaded with calcium facilitated the precipitation reaction between calcium and phosphorus, chemisorption being the primary mechanism behind this process. Antunes [27] reported that the phosphate adsorbed on Ca²⁺-doped biochar could be converted into hydroxyapatite crystals. Zhang et al. [20] found that the removal of ammonia nitrogen occurs mainly via ion exchange. Ca²⁺-modified biochar not only exhibits excellent adsorption capacity for nitrogen and phosphorus, but also exhibits environmental benefits [28, 29].

Selecting abundant and easily available biomass raw materials promotes the application of biochar. Soybean straw, the agricultural waste obtained after soybean harvest, is cost effective and easily available. Using soybean straw to produce biochar can reduce the production cost and decrease environmental pollution. Several studies reported the removal of heavy metals, dyes and organic matter using straw charcoal. However, studies reporting on the joint adsorption of ammonia nitrogen and phosphate in biogas slurry by calcium-impregnated biochar are scarce. Moreover, the specific mechanism of ammonium and phosphate removal through Ca²⁺-modified biochar derived from soybean straw remains unclear.

This study investigates the performance and mechanism of Ca²⁺-modified soybean straw–based biochar (CaSSB) in adsorbing and recovering ammonium and phosphorus from biogas slurry. The nitrogen and phosphorus pollution within the biogas slurry is primarily derived from ammonium and phosphate that facilitates the utilization of ammonia nitrogen and phosphate as inspection indicators [30]. The objectives of this study can be summarised as follows: (1) preparation of calcium chloride impregnated biochar; (2) characterisation of the physicochemical properties of Ca²⁺-modified soybean straw biochar via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer Emmett Teller (BET) and zero energy thermonuclear assembly analysis (zeta); (3) evaluating the effects of dosage, pH, coexisting ions, adsorption kinetic and adsorption isotherms on adsorption and recovery; (4) investigating the CaSSB adsorption mechanism of ammonium and phosphate. This study proposes a promising method to prepare an efficient absorbent based on agricultural waste for ammonia nitrogen and phosphate recovery from biogas slurry.

Materials and methods

Soybean straw (SS) and biogas slurry

Soybean straw was obtained from a farm in the suburb of Fuzhou City, Fujian Province, China. The biomass was chopped, soaked in deionized water and placed in an oven for drying at 105°C for 12 h until constant weight was achieved. The dried soybean straw was pulverized and sieved through a 30-mesh sieve (particle size of 0.6 mm). After grinding, the powder was dried at 105°C for 24 h in an oven and cooled in the desiccator before carbonization and impregnation. Results of the elemental and proximate analyses of the raw soybean straw and biochars are listed in Table 2. Biogas slurry was obtained from large-scale pig farms, Xingyuan agriculture and animal husbandry technology Corporation, located in in the suburb of Fuzhou City, Fujian Province, China. The biogas slurry was refrigerated prior to the experiment. Table 1 lists the chemical characteristics of the biogas slurry.

Download:

Table 1. Characteristics of biogas slurry (n = 3, SD).

https://doi.org/10.1371/journal.pone.0290714.t001

Chemical reagents

The chemical reagents involved in this work, including KH₂PO₄, NH₄Cl, NaOH, HCl, CaCl₂, CuCl₂, ZnCl₂, KNO₃, K₂SO₄, were all of analytical grade and purchased from the Shanghai Aladdin Chemical Reagent Company.

Preparation of biochars

Carbonization: A slow pyrolysis process was selected to increase the biochar yield. Soybean straw was processed in a vacuum tube furnace (DSK-60A, Dongguan, China) at a temperature of 350°C for 2 h under nitrogen atmosphere, and then cooled to room temperature under nitrogen protection. The heating rate was 10°C/min, and the nitrogen flow rate was 150 mL/min during the preparation of biochar. The biochar was designated as SSB.

Modification: The preparation of Ca²⁺-modified SSB (CaSSB) comprised two steps. First, the biochar was acid-washed with 6 mol/L hydrochloric acid for 1 h, and the solid–liquid ratio was 1:15 (m:v). Subsequently, the biochar was filtered and rinsed with deionized water five times to remove residual acid, and dried at 75°C for 12 h. Second, 100 mL of 1.5 mol/L CaCl₂ solution was added to 2.00 g of SSB to achieve a weight ratio of calcium to SSB (M(Ca)/M(SSB)) of 3.0. Then, the mixed solution was reacted in a magnetic stirrer for 24 h. Finally, the solid matter was dried at 75°C after removing the filtrate to obtain Ca²⁺-modified SSB (CaSSB).

Physicochemical characterisation

The organic composition in the biomass and biochar was analysed by the elemental analyser (LECO ONH2000, Elementar, USA). In a helium atmosphere, O was analysed at 1250°C; C, H and N were analysed at 1050°C and sulphur was analysed at 1350°C in an oxygen environment. The moisture and ash content were determined based on a dry basis. BET (APSP 2460, micromeritics, USA) was used to measure the specific surface area and total pore volume of the biochar, and BET and BJH model methods were employed for calculation and analysis. The zeta potential of SS, SSB and CaSSB were gauged using the Malvern Zetasizer Nano ZS90 (Malvern Instruments, UK, 2012). The surface morphology of the biochar was observed and characterized by SEM (TESCAN MIRA4). XRD (Panalytical X’Pert’3 Powder, Netherlands) was used to identify the crystallinities in the biochar after Ca²⁺ loading. FTIR (Thermo Fisher Scientific, Nicolet iS20, USA) was employed for infrared characterization of the biochar. The samples were qualitatively scanned by the potassium bromide solid tablet method under the conditions of scanning wave number 4000–400 cm⁻¹ and resolution of 1 cm⁻¹.

Adsorption experiment

Batch experiments were conducted to obtain adsorption data dependence on the pH and dose of CaSSB. The pH of ammonium phosphate solution was controlled with diluted HCl or NaOH, and the pH level was maintained throughout the entire absorption experiment. To select the optimal adsorption dosage, the adsorption capacity of CaSSB for ammonia and phosphate was tested using adsorption dosages of 0.05, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 g at a pH of 6. To investigate the influence of pH on ammonia nitrogen and phosphate, the initial pH was adjusted to 3, 4, 5, 6, 7, 8, 9 and 10 by HCl (0.1 M) and NaOH (0.1 M) at the CaSSB dosage of 2 g/L. The presence of various ions in the biogas slurry requires us to take into account the influence of common coexisting ions on the adsorption process. The various concentrations of K⁺, Ca²⁺, Cu²⁺, Zn²⁺, Cl⁻, CO₃²⁻, SO₄²⁻ and NO₃⁻ were respectively added into the 474.00 mg/L ammonium and 50.00 mg/L phosphate solution before the addition of 2 g/L CaSSB. To assess the applicability of the CaSSB adsorbent for actual wastewater, 0.1 g CaSSB was added to the 50 mL biogas slurry. A 250-mL glass Erlenmeyer flask test container and test adsorption solutions, each with a volume of 50 mL, was used. The adsorption process was carried out at room temperature with constant shaking at a speed of 150 r/min for 24 h. When the adsorption was complete, the sample to be tested was filtered by a 0.45-μm filter to assess ammonia nitrogen and phosphate quantities. All experiments in this study were conducted in triplicate to reduce errors. Eq (1) calculates the removal rate of ammonia nitrogen and phosphate by samples: (1)

Among them, x represents the removal rate (%), and S₀ and S_e represent the initial and equilibrium state concentrations of ammonia nitrogen and phosphate (mg/L), respectively.

The adsorption capacity of ammonia and phosphate can be calculated according to Eq (2): (2) where V represents the volume of reaction solution (mL) and m represents the weight of added biochar (g).

Nessler’s reagent was used to determine the concentration of ammonia nitrogen, and the phosphate concentration was determined by antimony–Mo blue.

Adsorption kinetic analysis

For the kinetic adsorption experiments, NH₄Cl and KH₂PO₄ were dissolved in deionized water to prepare the simulated sewage of ammonium and phosphate. The ammonia nitrogen concentration in the solution was 30 mg/L, whereas the phosphate concentration was 20 mg/L. To explore the adsorption kinetics of ammonia nitrogen and phosphate, batch experiments were conducted in triplicate. A total of 0.4 g of the adsorbent was introduced to 200 mL of ammonium phosphate solution. Prior to conducting the experiments, the pH_initial of the sorption solution was set at 6. The mechanical shaker was set at 150 r/min and the vessels were left to shake at room temperature. The collected suspension was filtered at specific times (ranging from 5 to 1440 min). To determine the ammonia nitrogen and phosphate adsorption kinetics of the CaSSB, three classical models the pseudo-first-order kinetics equation, pseudo-second-order kinetics and the intraparticle diffusion model were employed [31].

(3)

(4)

(5)

Herein, q_e (mg/g) and q_t (mg/g) respectively denote the quantity of ammonia nitrogen or phosphate adsorbed at equilibrium at a specific time t. k₁ (min⁻¹) and k₂ (g/(mg·min)) represent the reaction rate constants of the pseudo-first-order model and pseudo-second-order model, which are calculated from the plot of ln(q_e-q_t) versus t and t/q_t versus t, respectively. k₃ (mmol kg⁻¹ h^−0.5) denotes the intra-particle diffusion rate constant, and a (nmol/kg) is a constant.

Adsorption isotherm analysis

Herein, CaSSB (2 g/L) was mixed with seven groups of ammonium phosphate solutions, each with concentrations ranging from 0 to 100 mg/L. The mixture was placed in a shaking incubator at 25°C and 150 r/min. All samples were equilibrated for 24 h, and the concentrations of ammonia nitrogen and phosphate at equilibrium were measured. The Langmuir, Freundlich and Langmuir–Freundlich isotherm models were used for fitting the test data [32]. The Langmuir model, assuming uniform monolayer surface adsorption, can be expressed by Eq (6): (6)

The Freundlich model assumes that the adsorption behaviour on the adsorbent surface is heterogeneous, and its expression is given by Eq (7): (7)

The Langmuir–Freundlich is expressed as Eq (8): (8)

In this equation, q_max (mg/g) represents the maximum adsorption capacity; K_L is the affinity constant; K_F, K_LF and 1/n represent the constants.

Data analysis

Excel 2018 was used to summarize and organize the data, and Origins 8.0 was used to perform regression analysis and plot the data on the adsorption of ammonia nitrogen and phosphate by biochar. Error bars represent the standard deviation (SD), calculated from the experiments performed in triplicate.

Results and discussion

Characterisation of biochar

Elemental composition and Zeta potential of biochars.

The elemental composition of the pristine material and biochars used in this experiment are presented in Table 2. The results showed that charcoal was the major component of the biochars, indicating that the adsorbent had carbonaceous properties. After carbonization and modification of the soybean straw, the proportion of carbon and nitrogen content increased, while the proportion of oxygen and hydrogen elements decreased. Among them, the contents of oxygen and hydrogen in CaSSB were higher than those in SSB, whereas the contents of carbon and nitrogen exhibited the opposite trend. In addition, the ash content of CaSSB was lower than that of SSB, and the calcium content was 8.65 times as much as that of SSB, indicating that calcium was loaded on soybean straw carbon. The H/C and O/C ratios remained widely used as indicators for describing the degree of carbonization and evaluating the aromaticity and stability of biochar [33]. Compared with SSB, the H/C and O/C ratio of CaSSB increased by 0.23 and 0.21, respectively. Based on these results, CaSSB is likely to possess higher hydrophilicity than SSB, as it exhibits a higher O/C ratio (0.44 vs 0.23).

Download:

Table 2. Elemental analysis and proximate analysis (wt%) of raw SS and biochars.

https://doi.org/10.1371/journal.pone.0290714.t002

The zeta potential can be used to represent the strength of the inter-particle interaction force inside the samples [34]. As the absolute value of the zeta potential increases, the dispersed particles reduce in size and the entire system increases in stability. The zeta potentials of SS, SSB and CaSSB measured at a pH of 7 are shown in Table 2. The three materials were all negatively charged. Yao et al. [35] suggested that the increase in the zeta potential of carbon materials led to superior adsorption performance. From the absolute value of the zeta potential, the value of CaSSB was greater than that of SS and SSB, indicating that CaSSB had better dispersion and might exhibit excellent adsorption performance for ammonium.

SEM and XRD.

The surface morphologies of SS, SSB and CaSSB were assessed by SEM, as shown in Fig 1. The morphology of soybean straw before carbonization in Fig 1A shows wrinkles and some particles on the surface. After pyrolysis, the cellulose, hemicellulose and lignin of straw were destroyed, as they transformed into tar and other sediments, forming evident pores on the SSB (Fig 1B) [36]. As shown in Fig 1C, CaSSB exhibited a rough surface morphology with bulk particles. The forming processes may be described as follows: The calcium ions reacted on the surface of biochar to form particles during modified process, resulting in a rough surface, which increased the adsorption sites of biochar and improved its ion-exchange capacity. The calcium ions were embedded in the carbon structure, causing changes in the crystal structure and pore structure of biochar.

Download:

Fig 1.

SEM images of raw biomass and biochar: (a) SS; (b) SSB; (c) CaSSB.

https://doi.org/10.1371/journal.pone.0290714.g001

XRD analysis was used to clarify the crystal structure of SS, SSB and CaSSB. As shown in Fig 2, the XRD spectra of SS, SSB and CaSSB displayed a common diffraction peak at 2θ = 23°, which was indexed as the cellulose or amorphous nature of carbon [37]. The CaSSB contained five distinct wide peaks at 2θ = 32.4°, 37.6°, 54.1°, 64.6° and 67.8°, which putatively corresponded to CaO or Ca(OH)₂ [38]. These results imply that Ca²⁺ is loaded on the surface of the biochar.

Download:

Fig 2. XRD spectra of the SS, SSB and CaSSB.

https://doi.org/10.1371/journal.pone.0290714.g002

FTIR.

The FTIR spectra shown in Fig 3 reveal the presence of surface functional groups of samples at wavelengths of approximately 400–4000 cm⁻¹. The aromatic, phenolic and aliphatic groups were dominant. The stability of aliphatic carbon compounds was lower than that of aromatic carbon [39]. Therefore, after the carbonization of biomass materials, certain peaks decreased or even disappeared, such as cellulose, carbohydrates, methylene functional groups and so on. According to relevant literature, the absorption peak at 3200–3500 cm⁻¹ arose from the O–H stretching vibration of alcoholic or phenolic hydroxyl groups associated with intermolecular hydrogen bonds [40]. The bands in the range of 2856 to 3000 cm⁻¹ were produced by the C–H groups of aliphatic saturated. The bands in the range of 1596 to 1620 cm⁻¹ represented the aromatic C = O and C = C groups stretching vibration, implying the formation of initial aromatisation of the precursor and carbonyl-containing groups [41]. The bands in the range of 1080–1030 cm⁻¹ might be due to the C–O bending vibration in phenolic hydroxy groups. A peak identified at 875–755 cm⁻¹ might be attributed to furan CH₂ groups. The above functional groups in CaSSB also indicated that impregnating CaCl₂ did not affect the types and structures of the original organic functional groups in soybean biochar [42]. In addition, the bands below 800 cm⁻¹ were stronger after CaCl₂ modification, implying that Ca²⁺ was successfully grafted onto the surface of soybean straw biochar.

Download:

Fig 3. FTIR spectra of raw biomass and biochar.

https://doi.org/10.1371/journal.pone.0290714.g003

Specific surface area and pore structure

The pore structure and specific surface area of biochar are important factors for the facilitation of ammonia nitrogen and phosphate adsorption in the removal of ammonia nitrogen and phosphate from biogas slurry through biochar [43]. The pore structure characteristics of SS, SSB and CaSSB are listed in Table 3. The specific surface areas of SS, SSB and CaSSB were 1.03, 2.12 and 3.69 m²/g, respectively. The average pore diameters varied from 20.89 to 24.87 nm, indicating that most pores were mesopores. The total pore volumes of SS, SSB and CaSSB were 0.0016, 0.0027 and 0.0040 cm³/g, respectively. Compared with SS and SSB, CaSSB had a larger specific surface area and lower average pore size owing to the improvement in the pore structure of the biochar by the impregnation of calcium chloride [44].

Download:

Table 3. Comparisons of surface characteristics of biomass and biochar.

https://doi.org/10.1371/journal.pone.0290714.t003

Ammonia nitrogen and phosphate adsorption

Effect of pH.

The pH is a key factor for the adsorption performance of biochar, as it directly influences the chemical form of ammonia nitrogen and phosphate, surface charge and the ionization and formation of adsorbates [45]. Fig 4 shows the adsorption performance of ammonia and phosphate of CaSSB at the pH range of 3–10. CaSSB demonstrated the maximum adsorption capacity of ammonia nitrogen (102.21 mg/g) and phosphate (9.75 mg/g) at pH = 6. Strong acidic or alkaline condition would lead to a lower adsorption capacity. These results were similar to those reported by Cheng et al. [14]. Ammonia nitrogen occurs in varying forms of NH₄⁺–N and NH_3, depending on the pH value of the solution. Ammonia nitrogen exists in the form of NH₄⁺–N when the pH value of the solution is lower than 7, whereas it occurs in the form of NH₄⁺–N and NH₃ when the pH is between 7 and 10 [46]. Moreover, the higher the pH value, the higher the free ammonia content, which induces a weakened electrostatic interaction between ammonia and biochar and the inverse effects on the adsorption capacity of biochar [47]. Therefore, the adsorption amount of NH₄⁺–N by CaSSB increased with the increase in pH from 3–7, and the adsorption exhibited a downward trend at pH > 7.

Download:

Fig 4. Effect of solution pH_initial on adsorption of ammonia and phosphate by CaSSB.

https://doi.org/10.1371/journal.pone.0290714.g004

Phosphate in the solution occurred in the form of H₃PO₄, H₂PO₄⁻, HPO₄²⁻, PO₄³⁻, of which H₂PO₄⁻ is most likely to replace OH⁻ and combine with Ca²⁺, followed by HPO₄²⁻. Similarly, phosphorus exists in different forms, depending on the pH value: PO₄³⁻ at pH > 12.33; HPO₄²⁻ at 7.2 < pH < 12.33; H₂PO₄⁻ at pH < 7.2 [48]. Therefore, in acidic conditions, the amount of phosphate adsorbed by CaSSB increased with the increase in pH. Meanwhile, in alkaline conditions, the opposite is true. These results were similar to Wang [49] and Blaney [50].

Effect of dosage.

The impact of adsorbent dosage on the adsorption capacity of ammonia nitrogen and phosphate by CaSSB was investigated, and the results are shown in Fig 5. The adsorption capacity of ammonia and phosphate increased with the dosage of CaSSB. Specifically, the adsorption capacity of ammonia nitrogen increased from 65.73 to 100.43 mg/g with the increase in CaSSB dosage from 0.05 to 0.1 g. Similarly, the adsorption capacity of phosphate increased from 8.83 to 9.71 mg/g when the CaSSB dosage increased from 0.05 to 0.1 g. Nonetheless, when the CaSSB dosage was increased from 0.1 to 0.5 g, a slight reduction could be observed in the adsorption capacity of ammonia nitrogen and phosphate. The enhanced removal efficiency at lower adsorbent dosages might be attributed to an increase in the available active sorption sites on CaSSB. The decline in the unit adsorption capacity of ammonia nitrogen and phosphate was observed when the dosage exceeded 0.1 g. This phenomenon can be attributed to the fact that higher adsorbent dosages may lead to a reduction in the unsaturation of the ion-exchange sites on CaSSB, resulting in a decline in the amount of ion-exchange sites per unit mass. Considering the nutrient adsorption capacity, efficiency and economic factors, the optimal dosage for the CaSSB was determined to be 2 g/L.

Download:

Fig 5. Adsorption performance of CaSSB for ammonia nitrogen and phosphate under different dosages.

https://doi.org/10.1371/journal.pone.0290714.g005

Effect of coexisting anions

Biogas slurry usually contains metal ions and inorganic salts, and these ions may engage in competition with ammonia nitrogen and phosphate for the adsorption sites of CaSSB. As shown in Fig 6A, different ions exhibited varying degrees of effects on the adsorption performance of CaSSB. When the concentration of K⁺ and Ca²⁺ was lower than 40 mg/L, the ion concentrations had a negligible impact on the adsorption performance of CaSSB for the ammonia nitrogen. Cu²⁺ and Zn²⁺ exerted a greater influence on the adsorption process with the increase in concentration. This phenomenon is similar to the results obtained by Liu et al. [51]; it may be attributed to the competition between the metal cation with ammonium ions for the adsorption sites. For phosphate adsorption, Yao et al. [52] determined that when using a synthetic adsorption solution containing phosphate, Cl⁻, NO₃⁻, HCO₃⁻ and humic acid—similar to actual wastewater—the biochar’s phosphate adsorption capacity decreased by 40% compared to that in a pure phosphate solution. However, Cl⁻, CO₃²⁻, SO₄²⁻ and NO₃⁻ have a negligible impact on the phosphate adsorption by CaSSB when their concentrations are below 40 mg/L. On the contrary, the adsorption capacity of CaSSB for phosphate decreased when the concentration of coexisting anions increased. Among them, CO₃²⁻ and SO₄²⁻ exerted a greater negative impact. It is speculated that they can react with calcium to produce precipitation, which reduces the adsorption sites for phosphate.

Download:

Fig 6.

Coexisting ions effect on CaSSB adsorption performance: (a) ammonia nitrogen and (b) phosphate.

https://doi.org/10.1371/journal.pone.0290714.g006

Comparison of adsorption capacities of SSB and CaSSB

The maximum adsorption performances for ammonia nitrogen and phosphate obtained by CaSSB and SSB under optimal conditions are shown in Fig 7. The adsorption capacities of CaSSB for ammonia nitrogen and phosphate were 103.18 and 9.75 mg/g, respectively, remarkably higher values than those of SSB (31.0 and 6.69 mg/g, respectively). The maximum adsorption capacities of the CaSSB for ammonia nitrogen and phosphate were 3.33 and 1.45 times those of SSB. These results revealed that the adsorption performance of SSB for ammonia and phosphate in biogas slurry considerably improved after modification with the calcium ion. The adsorption capacity of CaSSB to ammonia nitrogen was remarkably greater than that of the phosphate. The adsorption capacity of ammonium increased as a result of the negative charge of biochar. Overall, negatively charged biochar underperformed in removing anionic pollutants. The high calcium content of CaSSB was responsible for its efficient removal of phosphate, as it could form metal bonds, such as Ca–O–P, through precipitation with phosphate acid. The adsorption effects of CaSSB and other adsorbents reported previously on ammonia and phosphate are listed in Table 4. Herein, the soybean straw–based biochar was modified with Ca²⁺, which exhibited high adsorption capacity for ammonia nitrogen and phosphate in comparison to most previously reported adsorbents. This result also suggested CaSSB could be used to recover ammonium and phosphate from biogas slurry.

Download:

Fig 7. Comparison of adsorption capacities of SSB and CaSSB for ammonia nitrogen and phosphate in biogas slurry.

https://doi.org/10.1371/journal.pone.0290714.g007

Download:

Table 4. Maximum ammonia nitrogen and phosphate adsorption capacity of CaSSB and other adsorbents.

https://doi.org/10.1371/journal.pone.0290714.t004

Adsorption kinetics

The adsorption kinetics of ammonia and phosphate on CaSSB were studied. The initial concentrations of ammonia nitrogen and phosphate were 30 and 20 mg/L, respectively. The initial pH of the solutions for the adsorption kinetics for both experiments was 6.0. The adsorption processes of CaSSB for ammonia and phosphate were recorded during 24 h tests. Fig 8 presents the ammonia and phosphate adsorption kinetics of CaSSB. The adsorption process of CaSSB for ammonia nitrogen followed a typical kinetic model, with a rapid sorption rate in the first 30 minutes, followed by an increase in the adsorption capacity as time progressed. The adsorption equilibrium time was found to be 24 hours, and therefore, all batch experiments were shaken for 24 h. To explore the reaction mechanisms, the pseudo-first-order, pseudo-second-order model and the intraparticle diffusion model were used to fit the experimental data. The corresponding kinetic parameters, k₁, k₂, k₃ and a, calculated q_e values and the correlation coefficients R², were shown in Table 5. The results suggested that q_e values of ammonia nitrogen and phosphate calculated using the pseudo-second order kinetics were more aligned with the experimental values than those of other models. The q_e values of ammonia nitrogen and phosphate calculated using the pseudo-second order kinetics were 10.811 and 4.547 mg/g, respectively. Compared to the pseudo-first order and intraparticle diffusion model, the correlation coefficients of the pseudo-second order kinetic equation was higher, suggesting its suitability for the entire adsorption process. These results also indicated that the adsorption of ammonia nitrogen and phosphate process might be dominated by chemical reactions, such as cation exchange, sedimentation and complexation. The maximum removal rates of CaSSB for ammonia nitrogen and phosphate were 71.87% and 45.80%, respectively. The saturated adsorption amount of CaSSB surpassed that of reported biochar materials derived from phytoremediation plants, cornstalk, wood chip and other sources [21, 53].

Download:

Fig 8.

Adsorption kinetics of ammonia nitrogen (a-c) and phosphate (d-f) on CaSSB: following pseudo-first-order kinetics for ammonia nitrogen (a) and phosphate (d); pseudo-second-order kinetics for ammonia nitrogen (b) and phosphate (e); intraparticle diffusion model for ammonia nitrogen (c) and phosphate (f).

https://doi.org/10.1371/journal.pone.0290714.g008

Download:

Table 5. Adsorption kinetic parameters for ammonia nitrogen and phosphate on CaSSB.

https://doi.org/10.1371/journal.pone.0290714.t005

Adsorption isotherm

As shown in Fig 9, the adsorption isotherms of CaSSB for ammonia and phosphate were tested with various initial concentrations in the range of 0–100 mg/L. The experimental data was modelled with Langmuir, Freundlich and Langmuir–Freundlich models. Table 6 presents the adsorption parameters and correlation coefficients for ammonia nitrogen and phosphate on CaSBB obtained from the three models. The correlation coefficient for the Langmuir model (R²: 0.972 for NH₄⁺–N) was slightly higher compared to those for the Freundlich (R²: 0.947 for NH₄⁺–N) and Langmuir–Freundlich models (R²: 0.941 for NH₄⁺–N), indicating a better fit for the Langmuir model. The Langmuir model may imply monolayer adsorption for ammonia nitrogen on the surface of homogeneous adsorbents [57]. The surface of CaSBB exhibited a potentially finite number of uniform adsorption sites with consistent ammonia adsorption affinities [58]. Hence, it is likely that the mechanism involved in the ammonia adsorption process was monolayer adsorption, primarily occurring on the surface-active regions of the CaSBB. However, among the three models, the Langmuir–Freundlich model provided the highest fitting accuracy (R²: 0.995 for PO₄³⁻–P) for the phosphate on CaSBB. It is deduced that the adsorption of phosphate on CaSSB is a physicochemical adsorption process. The dominant sorption mechanism of CaSSB for phosphate might be the reaction between Ca²⁺ and OH⁻ with PO₄³⁻ to generate Ca₅(PO₄)₃(OH) precipitation. The parameter K_L, which represents the affinity of the binding sites, enables a comparison of the biochar’s affinity towards ammonia and phosphate. The affinity of CaSBB for ammonia nitrogen (1.895 L/mg) was higher than that of phosphate (0.071 L/mg). It can be inferred from the obtained 1/n values of ammonia nitrogen and phosphate being <0.5, that CaSBB demonstrates superior adsorption performance for ammonia nitrogen and phosphate.

Download:

Fig 9.

Adsorption isotherms of ammonia nitrogen (a-c) and phosphate (d-f): following the Langmuir model for ammonia nitrogen (a) and phosphate (d); the Freundlich model for ammonia nitrogen (b) and phosphate (e); the Langmuir–Freundlich for ammonia nitrogen (c) and phosphate (f).

https://doi.org/10.1371/journal.pone.0290714.g009

Download:

Table 6. Adsorption isotherm parameters for ammonia nitrogen and phosphate sorption by CaSBB.

https://doi.org/10.1371/journal.pone.0290714.t006

Conclusions

The Ca²⁺-modified soybean straw biochar was prepared and used for adsorbing ammonia nitrogen and phosphate from biogas slurry. The zeta potential, BET surface area, elemental analysis and the adsorption capacity of the CaSSB were analysed and investigated. After modification with CaCl₂, the CaSSB derived from soybean straw exhibited a considerable adsorption capacity for ammonia nitrogen (103.18 mg/g) and phosphate (9.75 mg/g), demonstrating the feasibility of the proposed method for treating biogas slurry. In addition, the adsorption kinetics of ammonia and phosphate on CaSSB were examined using three kinetic models. The experimental results of CaSSB on ammonia nitrogen and phosphate conform to the pseudo-second-order kinetic model, indicating that chemical reactions might have taken place during the adsorption process. Furthermore, the maximum removal rates of ammonia nitrogen and phosphate by CaSBB were found to be 71.87% and 45.80%, respectively. In comparison with the Freundlich isotherm model, the Langmuir model was found to be more appropriate for characterising the adsorption of ammonia nitrogen on CaSSB, whereas the Langmuir–Freundlich model was more suitable for the adsorption of phosphate. These results suggest that the adsorption might be attributed to monolayer adsorption and involved the chemical process. The adsorption mechanisms of CaSSB could be Ca–P precipitation, ion exchange and electrostatic attraction. The results indicate that the modification of biochar by calcium chloride improves its adsorption capacity for biogas slurry nutrients, and that CaSBB is a promising material for biogas slurry resource treatment.

Supporting information

S1 File. Effect of coexisting anions and comparison of the adsorption capacity of the SSB and CaSSB.

https://doi.org/10.1371/journal.pone.0290714.s001

(DOC)

References

1. Duan N, Zhang D, Lin C, Zhang Y, Zhao L, Liu H, et al. Effect of organic loading rate on anaerobic digestion of pig manure: Methane production, mass flow, reactor scale and heating scenarios. Journal of Environmental Management. 2019; 231: 646–652. pmid:30390449
- View Article
- PubMed/NCBI
- Google Scholar
2. Scarlat N, Fahl F, Dallemand JF, Monforti F, Motola V. A spatial analysis of biogas potential from manure in Europe. Renew Sustain Energy Rev. 2018; 94: 915–930.
- View Article
- Google Scholar
3. Ding JT, Shen YJ, Ma Y R, Meng H B, Cheng H S, Zhang X, et al. Study on dynamic sorption characteristics of modified biochars for ammonium in biogas slurry. International Journal of Agricultural & Biological Engineering. 2020; 13: 234–240.
- View Article
- Google Scholar
4. Li BT, Jing FY, Hu Z Q, Liu YX, Xiao B, Guo D B. Simultaneous recovery of nitrogen and phosphorus from biogas slurry by Fe-modified biochar. Journal of Saudi Chemical Society. 2021; 25: 101213–101224.
- View Article
- Google Scholar
5. Zhang Q, Ye XZ, Li H, Chen D, Xiao WD, Zhao S P, et al. Cumulative effects of pyrolysis temperature and process on properties, chemical speciation, and environmental risks of heavy metals in magnetic biochar derived from coagulation-flocculation sludge of swine wastewater. Journal of Environmental Chemical Engineering. 2020; 8: 1–9.
- View Article
- Google Scholar
6. Wang TT, Kumar A, Wang X, Zhang D, Zheng Y, Wang GG, et al. Construction of activated biochar/Bi₂WO₆ and /Bi₂MoO₆ composites to enhance adsorption and photocatalysis performance for efcient application in the removal of pollutants and disinfection. Environmental Science and Pollution Research. 2023; 30: 30493–30513.
- View Article
- Google Scholar
7. Alberto CA, Santiago E, Carme S. Abatement of ozone-recalcitrant micropollutants during municipal wastewater ozonation: Kinetic modelling and surrogate-based control strategies. Chemical Engineering Journal. 2019; 360: 1092–1100.
- View Article
- Google Scholar
8. Park JG, Lee , Heo TY, Cheon AI, Jun HB. Metagenomics approach and canonical correspondence analysis of novel nitrifiers and ammonia-oxidizing archaea in full scale anaerobic-anoxic-oxic (A²/O) and oxidation ditch processes. Bioresource Technology. 2021; 319: 1–11.
- View Article
- Google Scholar
9. Luo X, Lin F, Zeng S, Luo Z, Chen, Tian G. Performance of a novel photobioreactor for nutrient removal from piggery biogas slurry: operation parameters, microbial diversity and nutrient recovery potential. Bioresource Technology. 2019; 272: 421–432.
- View Article
- Google Scholar
10. Han B, Butterly C, Zhang W, He JZ, Chen DL. Adsorbent materials for ammonium and ammonia removal: A review. Journal of Cleaner Production. 2020; 283: 124611.
- View Article
- Google Scholar
11. Shakoor MB, Ye Z, Chen S. Engineered biochars for recovering phosphate and ammonium from wastewater:a review. Science of the Total Environment. 2021; 779: 146240. pmid:33744573
- View Article
- PubMed/NCBI
- Google Scholar
12. Wang TT, Stadler FJ, Husein DZ, Zhang D, Cai J, Wang Y, et al. Comparative study of enhanced adsorption photodegradation activity using activated biochar composited with Ag₃PO₄ or Ag₆Si₂O₇ in wastewater treatment and disinfection: effects and mechanisms. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2022; 655:130235.
- View Article
- Google Scholar
13. Gupta S Sen Bhattacharyya KG. Adsorption of metal ions by clays and inorganic solids. RSC Advances. 2014; 4: 28537–28586.
- View Article
- Google Scholar
14. Cheng Q, Li H, Xu Y, Chen S, Liao Y, Deng . F Study on the adsorption of nitrogen and phosphorus from biogas slurry by NaCl-modified zeolite. Plos One. 2017; 5: 0176109.
- View Article
- Google Scholar
15. Wang TT, Li GL, Yang KQ, Zhang XY, Wang K, Cai JJ, et al. Enhanced ammonium removal on biochar from a new forestry waste by ultrasonic activation: characteristics, mechanisms and evaluation. Science of The Total Environment. 2021; 778, 146295. pmid:33721637
- View Article
- PubMed/NCBI
- Google Scholar
16. Wu P, Wang Z, Bolan NS, Wang H, Wang Y, Chen W. Visualzing the development trend and research frontiers of biochar in 2020: a scientometric perspective. Biochar. 2021; 4: 419–436.
- View Article
- Google Scholar
17. Wang TT, Zheng JY, Cai JJ, Liu QQ, Zhang XX. Visible-light-driven photocatalytic degradation of dye and antibiotics by activated biochar composited with K⁺ doped g-C₃N₄: Effects, mechanisms, actual wastewater treatment and disinfection. Science of The Total Environment. 2022; 839: 155955.
- View Article
- Google Scholar
18. Xiang W, Zhang X, Chen J, Zou W, He F, Hu X, et al. Biochar technology in wastewater treatment: a critical review. Chemosphere. 2020; 252: 126539. pmid:32220719
- View Article
- PubMed/NCBI
- Google Scholar
19. Liu Y, Zhu Z Q, He X S, Yang C, Qiong D Y, Huang Y D, et al. Mechanisms of rice straw biochar effects on phosphorus sorption characteristics of acid upland red soils. Chemosphere. 2018; 207: 267–277. pmid:29803158
- View Article
- PubMed/NCBI
- Google Scholar
20. Zhang M, Song G, Gelardi DL, Huang LB, Khan E, Masek O, et al. Evaluating biochar and its modifications for the removal of ammonium, nitrate, and phosphate in water. Water Research. 2020; 186: 116303. pmid:32841930
- View Article
- PubMed/NCBI
- Google Scholar
21. Barbora MR, Vladimír F, Martin P, Libor Ď, Eduardo MJ, Gerhard S. Iron impregnated biochars as effective phosphate sorption materials. Environmental Science and Pollution research. 2017; 24: 463–475. pmid:27730505
- View Article
- PubMed/NCBI
- Google Scholar
22. Wang S, Kong L, Long J, Su M, Diao Z, Chang X, et al. Adsorption of phosphorus by calcium-flour biochar: isotherm, kinetic and transformation studies. Chemosphere. 2018; 195: 666–672. pmid:29287274
- View Article
- PubMed/NCBI
- Google Scholar
23. Choi MY, Lee CG, Park SJ. Enhanced Fluoride Adsorption on Aluminum-Impregnated Kenaf Biochar: Adsorption Characteristics and Mechanism.Water Air Soil Pollute. 2022; 233: 435.
- View Article
- Google Scholar
24. He Q, Li X, Ren Y. Analysis of the simultaneous adsorption mechanism of ammonium and phosphate on magnesium-modified biochar and the slow release effect of fertiliser. Biochar. 2022; 1: 396–411.
- View Article
- Google Scholar
25. Yang HI, Lou KY, Rajapaksha AU, Ok YS, A AO, Chang SX. Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars. Environmental Science and Pollution Research. 2018; 25: 25638–25647. pmid:28229381
- View Article
- PubMed/NCBI
- Google Scholar
26. Liu S, Tan X, Liu Y, Gu Y, Zeng G, Hu X, et al. Production of biochars from Ca impregnated ramie biomass (Boehmeria nivea (L.) Gaud.) and their phosphate removal potential. RSC Advance. 2016; 6: 5871.
- View Article
- Google Scholar
27. Antunes E, Jacob MV, Brodie G, Schneider PA. Isotherms, kinetics and mechanism analysis of phosphorus recovery from aqueous solution by calcium-rich biochar produced from biosolids via microwave pyrolysis. Journal of Environmental Chemical Engineering. 2018, 6(1): 395–403.
- View Article
- Google Scholar
28. Wang Z, Bakshi S, Li C, Parikh SJ, Hsieh HS, Pignatello JJ. Modification of pyrogenic carbons for phosphate sorption through binding of a cationic polymer. Jouranl of Colloid and Interface Science. 2020; 579: 258–268. pmid:32592991
- View Article
- PubMed/NCBI
- Google Scholar
29. Wang TT, Cai JJ, Zheng JY, Fang KK, Hussain I, Husein DZ. Facile synthesis of activated biochar/BiVO4 heterojunction photocatalyst to enhance visible light efficient degradation for dye and antibiotics: applications and mechanisms. Journal of Materials Research and Technology. 2022; 19: 5017–5036.
- View Article
- Google Scholar
30. Dai Y, Wang W, Lu L, Yan L, Yu D. Utilization of biochar for the removal nitrogen and phosphorus. Journal of Cleaner Production. 2020; 257: 120573.
- View Article
- Google Scholar
31. Inyang MI, Gao B, Yao Y, Xue Y, Zimmerman A, Mosa A, et al. A review of biochar as a low-cost adsorbent for aqueous heavy metal removal. Critical Reviews in Environmental Science and Technology. 2015; 46(4): 406–433.
- View Article
- Google Scholar
32. Tümsek F, Avcı Ö. Investigation of Kinetics and Isotherm Models for the Acid Orange 95 Adsorption from Aqueous Solution onto Natural Minerals. Journal of chenical and engineering Data. 2013; 58(3): 551–559.
- View Article
- Google Scholar
33. EBC. European Biochar Certificate—Guidelines for a Sustainable Production of Biochar’, Eur. Biochar Found. Arbaz, Switzerland. 2015. 1–22.
34. Cheng N, Wang B, Feng Q,Zhuang XY, Chen M. Co-adsorption performance and mechanism of nitrogen and phosphorus onto Eupatorium adenophorum biochar in water. Bioresource Technology. 2021; 340: 125696. pmid:34385126
- View Article
- PubMed/NCBI
- Google Scholar
35. Yao Y, Gao B, Inyang M, Zimmerman AR, Cao XD, Pullammanappallil P, et al. Biochar derived from anaerobically digested sugar beet tailings: characterization and phosphate removal potential. Bioresource Technology. 2011; 102: 6273–6278. pmid:21450461
- View Article
- PubMed/NCBI
- Google Scholar
36. Zhuang Z, Wang L, Tang J. Efficient removal of volatile organic compound by ball-milled biochars from different preparing conditions. Journal of Hazardous Materials. 2021; 406: 124676. pmid:33310330
- View Article
- PubMed/NCBI
- Google Scholar
37. Li RH, Wang JJ, Zhou B, Zhang Z, Liu S, Lei S, et al. Simultaneous capture removal of phosphate, ammonium and organic substances by MgO impregnated biochar and its potential use in swine wastewater treatment. Journal of Cleaner Production. 2017; 147: 96–107.
- View Article
- Google Scholar
38. Yang F, Sui L, Tang C, Li J, Cheng K, Xue Q. Sustainable advances on phosphorus utilization in soil via addition of biochar and humic substances. Science of The Total Environment. 2021; 768: 145106. pmid:33736348
- View Article
- PubMed/NCBI
- Google Scholar
39. Cheng CH, Lehmann J, Thies JE, Burton SD, Engelhard MH. Oxidation of black carbon by biotic and abiotic processes, organic geochemistry. 2006; 37: 1477–1488.
- View Article
- Google Scholar
40. Rapacz-Kmita A, Paluszkiewicz C, Ślósarczyk A, Paszkiewicz Z. FTIR and XRD investigations on the thermal stability of hydroxyapatite during hot pressing and pressureless sintering processes. Journal of Molecular Structure. 2005; 744: 653–656.
- View Article
- Google Scholar
41. Guo Y, Rockstraw DA. Physical and chemical properties of carbons synthesized from xylan, cellulose, and Kraft lignin by H₃PO₄ activation. Carbon. 2006; 44: 1464–1475.
- View Article
- Google Scholar
42. He X, Zhang T, Ren H, Li G, Ding L, Pawlowski L. Phosphorus recovery from biogas slurry by ultrasound/H₂O₂ digestion coupled with HFO/biochar adsorption process. Waste Manage. 2017; 60: 219–229.
- View Article
- Google Scholar
43. Yin Q, Zhang B, Wang R, Zhao ZH. Biochar as an adsorbent for inorganic nitrogen and phosphorus removal from water: a review. Environmental Science and Pollution Research. 2017; 24: 26297–26309. pmid:29039039
- View Article
- PubMed/NCBI
- Google Scholar
44. Hu Y J, Tong X, Zhou H, Zhong L X, Peng XW, Wang S, et al. 3D hierarchical porous N-doped carbon aerogel from renewable cellulose: An attractive carbon for high-performance super capacitor electrode and CO₂ adsorption. RSC Advances. 2016; 6: 15788–15795.
- View Article
- Google Scholar
45. Li Y, Wang Z, Xie X, Zhu J, Li R, Qin T. Removal of Norfloxacin from aqueous solution by clay biochar composite prepared from potato stem and natural attapulgite. colloids and surfaces a physicochemical and engineering aspects. 2017; 514: 126–136.
- View Article
- Google Scholar
46. Saltalı K, Sarı A, Aydın M. Removal of ammonium ion from aqueous solution by natural Turkish (Yıldızeli) zeolite for environmental quality. Journal of Hazardous Materials. 2007; 141: 258–263.
- View Article
- Google Scholar
47. Yin Q, Liu M, Ren H. Biochar produced from the co-pyrolysis of sewage sludge and walnut shell for ammonium and phosphate adsorption from water. Journal of environmental management. 2019; 249: 109410. pmid:31446122
- View Article
- PubMed/NCBI
- Google Scholar
48. Mitrogiannis D, Psychoyou M, Baziotis I, Inglezakis VJ, Koukouzas N, Tsoukalas N, et al. Removal of phosphate from aqueous solutions by adsorption onto Ca(OH)₂ treated natural clinoptilolite. Chemical Engineering Journal. 2017; 320: 51–522.
- View Article
- Google Scholar
49. Wang SL, Cheng CY, Tzou YM, Liaw RB, Chang TW, Chen JH. Phosphate removal from water using lithium intercalated gibbsite.Jouranl of Hazardous Materials. 2007; 147: 205–212.
- View Article
- Google Scholar
50. Blaney L, Clinar S, Sengupta A. Hybrid anion on exchange for trace phosphate removal from water wastewater.Water Research. 2007; 41: 1603–1613.
- View Article
- Google Scholar
51. Liu HW, Dong YH, Wang HY, LiuY . Ammonium adsorption from aqueous solutions by strawberry leaf powder: equilibrium, kinetics and effects of coexisting ions. Desalination. 2010; 263: 70–75.
- View Article
- Google Scholar
52. Yao Y, Gao B, Chen JJ, Yang LY. Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slow-release fertilizer. Environmental Science Technology. 2013; 47: 8700–8708. pmid:23848524
- View Article
- PubMed/NCBI
- Google Scholar
53. Zeng Z, Zhang S D, Li T Q, Zhao FL, He ZL, Zhao HP. Sorption of ammonium and phosphate from aqueous solution by biochar derived from phytoremediation plants. Journal of Zhejiang University Science B. 2013; 14: 1152–1161. pmid:24302715
- View Article
- PubMed/NCBI
- Google Scholar
54. Zhang M, Gao B, Yao Y, Xue Y, Inyang M. Synthesis of porous MgO-biochar nanocomposites for removal of phosphate and nitrate from aqueous solutions. Chemical Engineering Journal. 2012; 210: 26–32.
- View Article
- Google Scholar
55. Sarkhot DV, Ghezzehei TA, Berhe AA. Effectiveness of biochar for sorption of ammonium and phosphate from dairy effluent. Journal of environmental quality. 2013; 42: 1545–1554. pmid:24216432
- View Article
- PubMed/NCBI
- Google Scholar
56. Munar-Florez DA, Varón-Cardenas DA, Ramírez-Contreras NE, García-Núñez JA. Adsorption of ammonium and phosphates by biochar produced from oil palm shells: Effects of production conditions.Results in Chemistry. 2021; 3: 100119.
- View Article
- Google Scholar
57. Zazycki MA, Godinho M, Perondi D, Foletto EL, Collazzo GC, Dotto GL. New biochar from pecan nutshells as an alternative adsorbent for removing reactive red 141 from aqueous solutions. Journal of Cleaner Production. 2018; 171: 57–65.
- View Article
- Google Scholar
58. Lin J, Zhan Y, Wang H, Chu M, Wang C, He Y, et al. Effect of calcium ion on phosphate adsorption onto hydrous zirconium oxide. Chemical Engineering Journal. 2017; 309: 118–129.
- View Article
- Google Scholar

[ref1] 1. Duan N, Zhang D, Lin C, Zhang Y, Zhao L, Liu H, et al. Effect of organic loading rate on anaerobic digestion of pig manure: Methane production, mass flow, reactor scale and heating scenarios. Journal of Environmental Management. 2019; 231: 646–652. pmid:30390449
View Article
PubMed/NCBI
Google Scholar

[2] View Article

[3] PubMed/NCBI

[4] Google Scholar

[ref2] 2. Scarlat N, Fahl F, Dallemand JF, Monforti F, Motola V. A spatial analysis of biogas potential from manure in Europe. Renew Sustain Energy Rev. 2018; 94: 915–930.
View Article
Google Scholar

[6] View Article

[7] Google Scholar

[ref3] 3. Ding JT, Shen YJ, Ma Y R, Meng H B, Cheng H S, Zhang X, et al. Study on dynamic sorption characteristics of modified biochars for ammonium in biogas slurry. International Journal of Agricultural & Biological Engineering. 2020; 13: 234–240.
View Article
Google Scholar

[9] View Article

[10] Google Scholar

[ref4] 4. Li BT, Jing FY, Hu Z Q, Liu YX, Xiao B, Guo D B. Simultaneous recovery of nitrogen and phosphorus from biogas slurry by Fe-modified biochar. Journal of Saudi Chemical Society. 2021; 25: 101213–101224.
View Article
Google Scholar

[12] View Article

[13] Google Scholar

[ref5] 5. Zhang Q, Ye XZ, Li H, Chen D, Xiao WD, Zhao S P, et al. Cumulative effects of pyrolysis temperature and process on properties, chemical speciation, and environmental risks of heavy metals in magnetic biochar derived from coagulation-flocculation sludge of swine wastewater. Journal of Environmental Chemical Engineering. 2020; 8: 1–9.
View Article
Google Scholar

[15] View Article

[16] Google Scholar

[ref6] 6. Wang TT, Kumar A, Wang X, Zhang D, Zheng Y, Wang GG, et al. Construction of activated biochar/Bi₂WO₆ and /Bi₂MoO₆ composites to enhance adsorption and photocatalysis performance for efcient application in the removal of pollutants and disinfection. Environmental Science and Pollution Research. 2023; 30: 30493–30513.
View Article
Google Scholar

[18] View Article

[19] Google Scholar

[ref7] 7. Alberto CA, Santiago E, Carme S. Abatement of ozone-recalcitrant micropollutants during municipal wastewater ozonation: Kinetic modelling and surrogate-based control strategies. Chemical Engineering Journal. 2019; 360: 1092–1100.
View Article
Google Scholar

[21] View Article

[22] Google Scholar

[ref8] 8. Park JG, Lee , Heo TY, Cheon AI, Jun HB. Metagenomics approach and canonical correspondence analysis of novel nitrifiers and ammonia-oxidizing archaea in full scale anaerobic-anoxic-oxic (A²/O) and oxidation ditch processes. Bioresource Technology. 2021; 319: 1–11.
View Article
Google Scholar

[24] View Article

[25] Google Scholar

[ref9] 9. Luo X, Lin F, Zeng S, Luo Z, Chen, Tian G. Performance of a novel photobioreactor for nutrient removal from piggery biogas slurry: operation parameters, microbial diversity and nutrient recovery potential. Bioresource Technology. 2019; 272: 421–432.
View Article
Google Scholar

[27] View Article

[28] Google Scholar

[ref10] 10. Han B, Butterly C, Zhang W, He JZ, Chen DL. Adsorbent materials for ammonium and ammonia removal: A review. Journal of Cleaner Production. 2020; 283: 124611.
View Article
Google Scholar

[30] View Article

[31] Google Scholar

[ref11] 11. Shakoor MB, Ye Z, Chen S. Engineered biochars for recovering phosphate and ammonium from wastewater:a review. Science of the Total Environment. 2021; 779: 146240. pmid:33744573
View Article
PubMed/NCBI
Google Scholar

[33] View Article

[34] PubMed/NCBI

[35] Google Scholar

[ref12] 12. Wang TT, Stadler FJ, Husein DZ, Zhang D, Cai J, Wang Y, et al. Comparative study of enhanced adsorption photodegradation activity using activated biochar composited with Ag₃PO₄ or Ag₆Si₂O₇ in wastewater treatment and disinfection: effects and mechanisms. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2022; 655:130235.
View Article
Google Scholar

[37] View Article

[38] Google Scholar

[ref13] 13. Gupta S Sen Bhattacharyya KG. Adsorption of metal ions by clays and inorganic solids. RSC Advances. 2014; 4: 28537–28586.
View Article
Google Scholar

[40] View Article

[41] Google Scholar

[ref14] 14. Cheng Q, Li H, Xu Y, Chen S, Liao Y, Deng . F Study on the adsorption of nitrogen and phosphorus from biogas slurry by NaCl-modified zeolite. Plos One. 2017; 5: 0176109.
View Article
Google Scholar

[43] View Article

[44] Google Scholar

[ref15] 15. Wang TT, Li GL, Yang KQ, Zhang XY, Wang K, Cai JJ, et al. Enhanced ammonium removal on biochar from a new forestry waste by ultrasonic activation: characteristics, mechanisms and evaluation. Science of The Total Environment. 2021; 778, 146295. pmid:33721637
View Article
PubMed/NCBI
Google Scholar

[46] View Article

[47] PubMed/NCBI

[48] Google Scholar

[ref16] 16. Wu P, Wang Z, Bolan NS, Wang H, Wang Y, Chen W. Visualzing the development trend and research frontiers of biochar in 2020: a scientometric perspective. Biochar. 2021; 4: 419–436.
View Article
Google Scholar

[50] View Article

[51] Google Scholar

[ref17] 17. Wang TT, Zheng JY, Cai JJ, Liu QQ, Zhang XX. Visible-light-driven photocatalytic degradation of dye and antibiotics by activated biochar composited with K⁺ doped g-C₃N₄: Effects, mechanisms, actual wastewater treatment and disinfection. Science of The Total Environment. 2022; 839: 155955.
View Article
Google Scholar

[53] View Article

[54] Google Scholar

[ref18] 18. Xiang W, Zhang X, Chen J, Zou W, He F, Hu X, et al. Biochar technology in wastewater treatment: a critical review. Chemosphere. 2020; 252: 126539. pmid:32220719
View Article
PubMed/NCBI
Google Scholar

[56] View Article

[57] PubMed/NCBI

[58] Google Scholar

[ref19] 19. Liu Y, Zhu Z Q, He X S, Yang C, Qiong D Y, Huang Y D, et al. Mechanisms of rice straw biochar effects on phosphorus sorption characteristics of acid upland red soils. Chemosphere. 2018; 207: 267–277. pmid:29803158
View Article
PubMed/NCBI
Google Scholar

[60] View Article

[61] PubMed/NCBI

[62] Google Scholar

[ref20] 20. Zhang M, Song G, Gelardi DL, Huang LB, Khan E, Masek O, et al. Evaluating biochar and its modifications for the removal of ammonium, nitrate, and phosphate in water. Water Research. 2020; 186: 116303. pmid:32841930
View Article
PubMed/NCBI
Google Scholar

[64] View Article

[65] PubMed/NCBI

[66] Google Scholar

[ref21] 21. Barbora MR, Vladimír F, Martin P, Libor Ď, Eduardo MJ, Gerhard S. Iron impregnated biochars as effective phosphate sorption materials. Environmental Science and Pollution research. 2017; 24: 463–475. pmid:27730505
View Article
PubMed/NCBI
Google Scholar

[68] View Article

[69] PubMed/NCBI

[70] Google Scholar

[ref22] 22. Wang S, Kong L, Long J, Su M, Diao Z, Chang X, et al. Adsorption of phosphorus by calcium-flour biochar: isotherm, kinetic and transformation studies. Chemosphere. 2018; 195: 666–672. pmid:29287274
View Article
PubMed/NCBI
Google Scholar

[72] View Article

[73] PubMed/NCBI

[74] Google Scholar

[ref23] 23. Choi MY, Lee CG, Park SJ. Enhanced Fluoride Adsorption on Aluminum-Impregnated Kenaf Biochar: Adsorption Characteristics and Mechanism.Water Air Soil Pollute. 2022; 233: 435.
View Article
Google Scholar

[76] View Article

[77] Google Scholar

[ref24] 24. He Q, Li X, Ren Y. Analysis of the simultaneous adsorption mechanism of ammonium and phosphate on magnesium-modified biochar and the slow release effect of fertiliser. Biochar. 2022; 1: 396–411.
View Article
Google Scholar

[79] View Article

[80] Google Scholar

[ref25] 25. Yang HI, Lou KY, Rajapaksha AU, Ok YS, A AO, Chang SX. Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars. Environmental Science and Pollution Research. 2018; 25: 25638–25647. pmid:28229381
View Article
PubMed/NCBI
Google Scholar

[82] View Article

[83] PubMed/NCBI

[84] Google Scholar

[ref26] 26. Liu S, Tan X, Liu Y, Gu Y, Zeng G, Hu X, et al. Production of biochars from Ca impregnated ramie biomass (Boehmeria nivea (L.) Gaud.) and their phosphate removal potential. RSC Advance. 2016; 6: 5871.
View Article
Google Scholar

[86] View Article

[87] Google Scholar

[ref27] 27. Antunes E, Jacob MV, Brodie G, Schneider PA. Isotherms, kinetics and mechanism analysis of phosphorus recovery from aqueous solution by calcium-rich biochar produced from biosolids via microwave pyrolysis. Journal of Environmental Chemical Engineering. 2018, 6(1): 395–403.
View Article
Google Scholar

[89] View Article

[90] Google Scholar

[ref28] 28. Wang Z, Bakshi S, Li C, Parikh SJ, Hsieh HS, Pignatello JJ. Modification of pyrogenic carbons for phosphate sorption through binding of a cationic polymer. Jouranl of Colloid and Interface Science. 2020; 579: 258–268. pmid:32592991
View Article
PubMed/NCBI
Google Scholar

[92] View Article

[93] PubMed/NCBI

[94] Google Scholar

[ref29] 29. Wang TT, Cai JJ, Zheng JY, Fang KK, Hussain I, Husein DZ. Facile synthesis of activated biochar/BiVO4 heterojunction photocatalyst to enhance visible light efficient degradation for dye and antibiotics: applications and mechanisms. Journal of Materials Research and Technology. 2022; 19: 5017–5036.
View Article
Google Scholar

[96] View Article

[97] Google Scholar

[ref30] 30. Dai Y, Wang W, Lu L, Yan L, Yu D. Utilization of biochar for the removal nitrogen and phosphorus. Journal of Cleaner Production. 2020; 257: 120573.
View Article
Google Scholar

[99] View Article

[100] Google Scholar

[ref31] 31. Inyang MI, Gao B, Yao Y, Xue Y, Zimmerman A, Mosa A, et al. A review of biochar as a low-cost adsorbent for aqueous heavy metal removal. Critical Reviews in Environmental Science and Technology. 2015; 46(4): 406–433.
View Article
Google Scholar

[102] View Article

[103] Google Scholar

[ref32] 32. Tümsek F, Avcı Ö. Investigation of Kinetics and Isotherm Models for the Acid Orange 95 Adsorption from Aqueous Solution onto Natural Minerals. Journal of chenical and engineering Data. 2013; 58(3): 551–559.
View Article
Google Scholar

[105] View Article

[106] Google Scholar

[ref33] 33. EBC. European Biochar Certificate—Guidelines for a Sustainable Production of Biochar’, Eur. Biochar Found. Arbaz, Switzerland. 2015. 1–22.

[ref34] 34. Cheng N, Wang B, Feng Q,Zhuang XY, Chen M. Co-adsorption performance and mechanism of nitrogen and phosphorus onto Eupatorium adenophorum biochar in water. Bioresource Technology. 2021; 340: 125696. pmid:34385126
View Article
PubMed/NCBI
Google Scholar

[109] View Article

[110] PubMed/NCBI

[111] Google Scholar

[ref35] 35. Yao Y, Gao B, Inyang M, Zimmerman AR, Cao XD, Pullammanappallil P, et al. Biochar derived from anaerobically digested sugar beet tailings: characterization and phosphate removal potential. Bioresource Technology. 2011; 102: 6273–6278. pmid:21450461
View Article
PubMed/NCBI
Google Scholar

[113] View Article

[114] PubMed/NCBI

[115] Google Scholar

[ref36] 36. Zhuang Z, Wang L, Tang J. Efficient removal of volatile organic compound by ball-milled biochars from different preparing conditions. Journal of Hazardous Materials. 2021; 406: 124676. pmid:33310330
View Article
PubMed/NCBI
Google Scholar

[117] View Article

[118] PubMed/NCBI

[119] Google Scholar

[ref37] 37. Li RH, Wang JJ, Zhou B, Zhang Z, Liu S, Lei S, et al. Simultaneous capture removal of phosphate, ammonium and organic substances by MgO impregnated biochar and its potential use in swine wastewater treatment. Journal of Cleaner Production. 2017; 147: 96–107.
View Article
Google Scholar

[121] View Article

[122] Google Scholar

[ref38] 38. Yang F, Sui L, Tang C, Li J, Cheng K, Xue Q. Sustainable advances on phosphorus utilization in soil via addition of biochar and humic substances. Science of The Total Environment. 2021; 768: 145106. pmid:33736348
View Article
PubMed/NCBI
Google Scholar

[124] View Article

[125] PubMed/NCBI

[126] Google Scholar

[ref39] 39. Cheng CH, Lehmann J, Thies JE, Burton SD, Engelhard MH. Oxidation of black carbon by biotic and abiotic processes, organic geochemistry. 2006; 37: 1477–1488.
View Article
Google Scholar

[128] View Article

[129] Google Scholar

[ref40] 40. Rapacz-Kmita A, Paluszkiewicz C, Ślósarczyk A, Paszkiewicz Z. FTIR and XRD investigations on the thermal stability of hydroxyapatite during hot pressing and pressureless sintering processes. Journal of Molecular Structure. 2005; 744: 653–656.
View Article
Google Scholar

[131] View Article

[132] Google Scholar

[ref41] 41. Guo Y, Rockstraw DA. Physical and chemical properties of carbons synthesized from xylan, cellulose, and Kraft lignin by H₃PO₄ activation. Carbon. 2006; 44: 1464–1475.
View Article
Google Scholar

[134] View Article

[135] Google Scholar

[ref42] 42. He X, Zhang T, Ren H, Li G, Ding L, Pawlowski L. Phosphorus recovery from biogas slurry by ultrasound/H₂O₂ digestion coupled with HFO/biochar adsorption process. Waste Manage. 2017; 60: 219–229.
View Article
Google Scholar

[137] View Article

[138] Google Scholar

[ref43] 43. Yin Q, Zhang B, Wang R, Zhao ZH. Biochar as an adsorbent for inorganic nitrogen and phosphorus removal from water: a review. Environmental Science and Pollution Research. 2017; 24: 26297–26309. pmid:29039039
View Article
PubMed/NCBI
Google Scholar

[140] View Article

[141] PubMed/NCBI

[142] Google Scholar

[ref44] 44. Hu Y J, Tong X, Zhou H, Zhong L X, Peng XW, Wang S, et al. 3D hierarchical porous N-doped carbon aerogel from renewable cellulose: An attractive carbon for high-performance super capacitor electrode and CO₂ adsorption. RSC Advances. 2016; 6: 15788–15795.
View Article
Google Scholar

[144] View Article

[145] Google Scholar

[ref45] 45. Li Y, Wang Z, Xie X, Zhu J, Li R, Qin T. Removal of Norfloxacin from aqueous solution by clay biochar composite prepared from potato stem and natural attapulgite. colloids and surfaces a physicochemical and engineering aspects. 2017; 514: 126–136.
View Article
Google Scholar

[147] View Article

[148] Google Scholar

[ref46] 46. Saltalı K, Sarı A, Aydın M. Removal of ammonium ion from aqueous solution by natural Turkish (Yıldızeli) zeolite for environmental quality. Journal of Hazardous Materials. 2007; 141: 258–263.
View Article
Google Scholar

[150] View Article

[151] Google Scholar

[ref47] 47. Yin Q, Liu M, Ren H. Biochar produced from the co-pyrolysis of sewage sludge and walnut shell for ammonium and phosphate adsorption from water. Journal of environmental management. 2019; 249: 109410. pmid:31446122
View Article
PubMed/NCBI
Google Scholar

[153] View Article

[154] PubMed/NCBI

[155] Google Scholar

[ref48] 48. Mitrogiannis D, Psychoyou M, Baziotis I, Inglezakis VJ, Koukouzas N, Tsoukalas N, et al. Removal of phosphate from aqueous solutions by adsorption onto Ca(OH)₂ treated natural clinoptilolite. Chemical Engineering Journal. 2017; 320: 51–522.
View Article
Google Scholar

[157] View Article

[158] Google Scholar

[ref49] 49. Wang SL, Cheng CY, Tzou YM, Liaw RB, Chang TW, Chen JH. Phosphate removal from water using lithium intercalated gibbsite.Jouranl of Hazardous Materials. 2007; 147: 205–212.
View Article
Google Scholar

[160] View Article

[161] Google Scholar

[ref50] 50. Blaney L, Clinar S, Sengupta A. Hybrid anion on exchange for trace phosphate removal from water wastewater.Water Research. 2007; 41: 1603–1613.
View Article
Google Scholar

[163] View Article

[164] Google Scholar

[ref51] 51. Liu HW, Dong YH, Wang HY, LiuY . Ammonium adsorption from aqueous solutions by strawberry leaf powder: equilibrium, kinetics and effects of coexisting ions. Desalination. 2010; 263: 70–75.
View Article
Google Scholar

[166] View Article

[167] Google Scholar

[ref52] 52. Yao Y, Gao B, Chen JJ, Yang LY. Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slow-release fertilizer. Environmental Science Technology. 2013; 47: 8700–8708. pmid:23848524
View Article
PubMed/NCBI
Google Scholar

[169] View Article

[170] PubMed/NCBI

[171] Google Scholar

[ref53] 53. Zeng Z, Zhang S D, Li T Q, Zhao FL, He ZL, Zhao HP. Sorption of ammonium and phosphate from aqueous solution by biochar derived from phytoremediation plants. Journal of Zhejiang University Science B. 2013; 14: 1152–1161. pmid:24302715
View Article
PubMed/NCBI
Google Scholar

[173] View Article

[174] PubMed/NCBI

[175] Google Scholar

[ref54] 54. Zhang M, Gao B, Yao Y, Xue Y, Inyang M. Synthesis of porous MgO-biochar nanocomposites for removal of phosphate and nitrate from aqueous solutions. Chemical Engineering Journal. 2012; 210: 26–32.
View Article
Google Scholar

[177] View Article

[178] Google Scholar

[ref55] 55. Sarkhot DV, Ghezzehei TA, Berhe AA. Effectiveness of biochar for sorption of ammonium and phosphate from dairy effluent. Journal of environmental quality. 2013; 42: 1545–1554. pmid:24216432
View Article
PubMed/NCBI
Google Scholar

[180] View Article

[181] PubMed/NCBI

[182] Google Scholar

[ref56] 56. Munar-Florez DA, Varón-Cardenas DA, Ramírez-Contreras NE, García-Núñez JA. Adsorption of ammonium and phosphates by biochar produced from oil palm shells: Effects of production conditions.Results in Chemistry. 2021; 3: 100119.
View Article
Google Scholar

[184] View Article

[185] Google Scholar

[ref57] 57. Zazycki MA, Godinho M, Perondi D, Foletto EL, Collazzo GC, Dotto GL. New biochar from pecan nutshells as an alternative adsorbent for removing reactive red 141 from aqueous solutions. Journal of Cleaner Production. 2018; 171: 57–65.
View Article
Google Scholar

[187] View Article

[188] Google Scholar

[ref58] 58. Lin J, Zhan Y, Wang H, Chu M, Wang C, He Y, et al. Effect of calcium ion on phosphate adsorption onto hydrous zirconium oxide. Chemical Engineering Journal. 2017; 309: 118–129.
View Article
Google Scholar

[190] View Article

[191] Google Scholar

Figures

Abstract

Introduction

Materials and methods

Soybean straw (SS) and biogas slurry

Chemical reagents

Preparation of biochars

Physicochemical characterisation

Adsorption experiment

Adsorption kinetic analysis

Adsorption isotherm analysis

Data analysis

Results and discussion

Characterisation of biochar

Elemental composition and Zeta potential of biochars.

SEM and XRD.

FTIR.

Specific surface area and pore structure

Ammonia nitrogen and phosphate adsorption

Effect of pH.

Effect of dosage.

Effect of coexisting anions

Comparison of adsorption capacities of SSB and CaSSB

Adsorption kinetics

Adsorption isotherm

Conclusions

Supporting information

S1 File. Effect of coexisting anions and comparison of the adsorption capacity of the SSB and CaSSB.

References