Initial Phosphorus Concentration Research Articles

Machine learning assisted prediction and process validation of electrochemically induced phosphorus recovery from wastewater

The disturbance in the natural phosphorus cycle has enhanced the problem of depletion of phosphorus rocks and its overabundance in the wastewater, leading to various environmental problems. Electrochemical phosphorus recovery from wastewater has gained attention due to the production of high-purity phosphorus precipitates that can be utilized to relieve the pressure on natural sources. However, its commercialization needs to be planned and predicted using modern machine learning algorithms. Hence, this study aims to predict electrochemical phosphorus recovery using different machine learning (ML) models: Linear regression, Lasso regression, Ridge regression, Adaboost, eXtreme Gradient Boost (XGB), Random Forest, and Support Vector Regression. The dataset for 16 input parameters considering the wastewater parameters, reactor, and reaction characteristics from the literature was used to envisage its influence on electrochemical phosphorus recovery. XGB was the robust ML model that outperformed other models in testing with R2 (0.98) and RMSE (33.54). The influence of the input parameters was studied using the feature importance, dependence plot and summary plot. Current density, pH, inter-electrode distance, electrolysis time and initial phosphorus concentration were some of the most influential input parameters affecting the phosphorous recovery. The process validation shows the R2 of 0.78 between the predicted values from the model and the experimental result. Overall, this study could help to predict electrochemical phosphorus recovery from the wastewater to facilitate optimization, upscaling, and commercialization of the technology to close the phosphorus loop.

Simultaneous nitrogen and phosphorus removal by immobilized bacterial particles of denitrifying phosphorus accumulating microorganisms and its application

Enterobacter cloacae G, a novel denitrifying phosphorus-accumulating bacterial strain, was isolated from anaerobic sludge tank of a wastewater treatment plant used for pig farms. It was discovered that a pH of 7, a temperature of 30°C, an initial phosphorus concentration of 8 mg/L, and a C/N ratio of 10 were the strain's ideal growth conditions. To ensure the stability of strain G in wastewater treatment, strain G was immobilized by 5 % polyvinyl alcohol, 2 % sodium alginate, and 0.6 g of biochar and crosslinked for 9 h in 4 % calcium chloride saturated boric acid solution via an orthogonal test. After the immobilized microspheres were introduced into the sequencing batch reactor (SBR), the nitrate and phosphate removal rates achieved were 89.36 % and 65.53 %, respectively, with a hydraulic retention time (HRT) of 8 hours, a pH of 7.5, and a C/N ratio of 4.5. The immobilized microspheres containing strain G demonstrated potential for the treatment of nitrogen-rich and phosphorus-rich wastewater.

Vachellia nilotica sawdust-derived polymeric and magnetic biocomposites for phosphate ions removal: Kinetics, isothermal, and thermodynamic studies

Phosphorus is an important element for both animals and plants, but its excess can cause eutrophication in water. Excess phosphorus is present in wastewater mainly due to acid rain, the dissolving of rocks, and agricultural waste. There are many methods for the elimination of Phosphorus from aqueous solution, but their use is finite because of the high operational cost. Adsorption is a productive and popular method for removing phosphorus from aqueous solution. In this study, Vachellia nilotica sawdust and its different composites (Ppy/SD and MG/SD) were utilized for the effective adsorption of phosphorus from the solution. Prepared sorbents were characterized via BET, SEM, FTIR and XRD for their surface area and morphological, functional and crystallinity attributes. Adsorption tests were carried out to identify the optimal working parameters such as adsorbent dose, temperature, initial phosphorus concentration, pH, and contact time. Adsorption isotherm and kinetic model were accurately explained by the Langmuir model and pseudo 2nd order kinetics. The maximal adsorption capacity for Phosphate was 4.803, 5.32, and 6.27 mg/g for Native/SD, Ppy/SD, and MG/SD, respectively. Thermodynamic characteristics confirmed that the phosphorus adsorption was endothermic and spontaneous. Thus, sawdust is an eco-friendly and inexpensive adsorbent for phosphorus removal from wastewater.

Recycling of sludge residue as a coagulant for phosphorus removal from aqueous solutions.

Phosphorus pollution poses a significant challenge in addressing water contamination. The coagulant is one of the effective methods to remove phosphorus from wastewater. Abundant Al and Fe oxides in sludge residue make it have great potential to synthesize water treatment coagulants. However, the utilization of sludge residue for preparation of coagulant was seldom investigated. In this study, we fabricated a novel coagulant, polyaluminum ferric chloride (SM-PAC), using sludge residue as a raw material through acid leaching and polymerization processes. Characterization results confirm that the parameters of SM-PAC meet the specifications outlined in the national standard (GB/T 22627-2022). We investigated the effects of pH, dosage, initial phosphorus concentration, and contact time on the removal efficiency of SM-PAC. As anticipated, the prepared SM-PAC exhibited a significant efficacy in removing phosphorus, meeting the discharge standards set for municipal sewage. Furthermore, the adsorption kinetics analysis suggests that the predominant mode of phosphorus adsorption on SM-PAC is chemical adsorption. Furthermore, the SM-PAC was employed in the actual wastewater treatment plant and exhibited excellent efficiency in phosphorus removal. The utilization of SM-PAC can not only effectively address the issue of sludge disposal but also achieve the goal of "treating waste with waste." It is expected that the proposed method of reusing sludge residue as a resource can provide a sustainable way to synthesize a coagulant for phosphorus removal.

Factors affecting phosphorus uptake/dissolution during slaking and causticizing

Hydroxide is regenerated in the recovery cycle of kraft pulp mills by the addition of lime (CaO) to green liquor. Phosphate in green liquor can react with the lime during slaking/causticizing. Total titratable alkali (TTA), sulfidity, the concentration of phosphate in the green liquor, temperature, and the liming ratio were all vari-ables explored in this work to determine their influence on phosphorus uptake and dissolution. Experiments were also run in which the lime was slaked before being added to the green liquor to separate reactions with phosphate during slaking and reactions that occur during causticizing. Both reburnt lime and technical grade CaO were used. The experiment results indicate that phosphorus primarily reacts with slaked lime (Ca(OH)2), and that the final con-centration of phosphate in the white liquor at the end of slaking and causticizing is nearly independent of the initial concentration of phosphorus and only mildly dependent on the carbonate concentration in the green liquor. There do appear to be differences in the rate at which phosphate reacts with reburnt lime and technical grade CaO, though the reason for this was not determined.

Engineered algal systems for the treatment of anaerobic digestate: A meta-analysis

The objective of this review was to provide quantitative insights into algal growth and nutrient removal in anaerobic digestate. To synthesize the relevant literature, a meta-analysis was conducted using data from 58 articles to elucidate key factors that impact algal biomass productivity and nutrient removal from anaerobic digestate. On average, algal biomass productivity in anaerobic digestate was significantly lower than that in synthetic control media (p < 0.05) but large variation in productivity was observed. A mixed-effects multiple regression model across study revealed that biological or chemical pretreatment of digestate significantly increase productivity (p < 0.001). In contrast, the commonly used practice of digestate dilution was not a significant factor in the model. High initial total ammonia nitrogen suppressed algal growth (p = 0.036) whereas initial total phosphorus concentration, digestate sterilization, CO2 supplementation, and temperature were not statistically significant factors. Higher growth corresponded with significantly higher NH4–N and phosphorus removal with a linear relationship of 6.4 mg NH4–N and 0.73 mg P removed per 100 mg of algal biomass growth (p < 0.001). The literature suggests that suboptimal algal growth in anaerobic digestate could be due to factors such as turbidity, high free ammonia, and residual organic compounds. This analysis shows that non-dilution approaches, such as biological or chemical pretreatment, for alleviating algal inhibition are recommended for algal digestate treatment systems.

Phosphorus recovery from sewage sludge via Mg-air battery system

A pressing issue in contemporary society is the resource scarcity of phosphorus. Operating on the principle of electrochemical reactions between Mg as the anode and oxygen from air as the cathode, Mg-air batteries (MAB) have been employed to provide new prospects for phosphorus recovery in struvite form. Different phosphorus concentrations and reaction time impact struvite generation in MAB systems; however, the exact mechanism has rarely been investigated. We investigated how varying the initial phosphorus concentration and the reaction time affects phosphorus recovery, electricity generation, and the efficiency of struvite production in MAB. Additionally, we examine the impact of solid carbon sources on phosphorus transformation in sludge. The findings revealed that the incorporation of solid carbon sources facilitated the release of phosphate by changing phosphorus speciation. The electrolyte derived from the conditioned sludge filtrate exhibited a remarkable phosphorus removal efficiency of 91.7 % within 1 h, yielding the highest struvite purity of ∼70 %, whereas that using raw sludge filtrate or extending the reaction time was found to be less effective, even reducing struvite formation. Furthermore, different electrolytes influence the system's ability to passivate anode, and electrolytes with higher phosphorus concentrations have better electricity production performance. The results by Visual MINTEQ model confirmed that longer reaction times and lower initial phosphorus concentrations can negatively affect struvite formation by introducing Mg3(PO4)2 and Mg(OH)2. The integration of agricultural waste as carbon sources with MAB for phosphorus recovery represents a potential methodology for struvite recuperation from sewage sludge, thereby heralding a sustainable strategy for resource recovery.

Efficient phosphorus removal from ultra-low concentration wastewater by flow-electrode capacitive deionization

During the 14th Five-Year period, the stringent phosphorus emission standard puts forward higher requirements for the phosphorus removal. In this study, lotus leaf-based biochars were prepared by hydrothermal carbonization method and used as low-cost FCDI electrode materials to remove ultra-low concentration phosphorus in wastewater at the first time. The governing factors and optimal adsorption conditions were systematically investigated as 1.2 V applied voltage, 24 s HRT, 10 wt% content of biochars. The maximum removal efficiency reached 98.55 % under 20 mg/L initial phosphorus concentration, which ensured that the phosphorus concentration of the effluent could meet discharge standard (0.3 mg/L) of WWTPs. Furthermore, the microscopic and spectroscopic characterization revealed that phorphorus removal mechanism included physical adsorption, electrosorption, ion exchange, precipitation and ligand exchange, which may take place simultaneously or supplementing each other. Using in situ potential measurement method, the potential gradient and energy consumption contribution of each FCDI component were described. The results showed that total specific energy consumption was very low and the flow electrodes modules dominated (more than 50 %) in all FCDI components. The findings opened up a promising way for managing biowastes and confimed the application of engineering biochar in environmental pollution treatment field.

Removal of phosphorus from water bodies using high-performance ceramsite prepared from solid wastes

This study successfully prepared a high-performance ceramsite for phosphorus adsorption using the sintering method, incorporating regolith granite sand-washing sludge (RGSWS) and phosphate tailings as raw materials. The optimal conditions for ceramsite preparation were determined as a ratio of RGSWS to phosphate tailings at 6:4, and sintering at 900 °C for 30 min. The impacts of various factors, such as the prepared ceramsite dosage, different initial phosphorus concentrations, temperature, pH, and co-existing ions were explored, and the reusability and safety of the ceramsite were also investigated. The results show that the ceramsite has a high adsorption capacity for phosphorus (20.40 mg/g) at pH 7 with broad applicability in the pH range of 3–11 and good selective adsorption in the presence of coexisting ions. Additionally, the application of ceramsite does not cause secondary pollution, and the ceramsite still maintains a high removal rate after being reused five times. XRD, FT-IR, XPS, and SEM-EDS analysis showed that chemical precipitation, surface complexation, and electrostatic attraction were involved in the adsorption process. It can be well described by the pseudo-second-order kinetic model and the Langmuir model, and the phosphorus adsorption by ceramsite was a spontaneous endothermic reaction process with increasing chaos. This research presents an effective solution for phosphorus removal from water bodies and offers a sustainable approach toward solid waste utilization.

Electrochemical activity of electroless Ni-P coatings in the hydrogen evolution reaction

The purpose of this study was investigation of the electrochemical activity of Ni-P coatings, differing in phosphorus content and structure, in the hydrogen evolution reaction (HER) and the identification of the reasons for their high activity in the reaction being studied. The coatings were deposited from an electroless nickel plating solution, the phosphorus content in the coatings (from 4.8 to 8.0 wt. %) varied by changing the pH of the solution. It was found that during cathodic polarization in 0.5 M H2SO4 additional surface activation occurs as a result of dissolution of the surface layer of the coating, removal of phosphorus from the surface layer, and development of the electrode surface. Of all the coatings studied coatings containing 4.8% phosphorus were most susceptible to cathodic activation. Coatings with a phosphorus content of 8.0% were least susceptible to cathodic activation. The similar electrochemical activity of the studied coatings (taking into account the roughness factor) in HER indicates that, as a result of cathodic polarization, the composition of the thin surface layer on which the cathodic reaction occurs is approximately the same, regardless of the initial phosphorus content

Removal of phosphorus by modified bentonite:polyvinylidene fluoride membrane-study of adsorption performance and mechanism.

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

Study on the dynamic adsorption and recycling of phosphorus by Fe–Mn oxide/mulberry branch biochar composite adsorbent

In this study, the Fe–Mn oxide/mulberry stem biochar composite adsorbent (FM-MBC) was prepared and fully characterized by SEM-EDS, XRD, BET, and XPS. The solution pH (3.0, 4.5, and 6.0), initial concentration of phosphorus (10, 20, and 30 mg L−1), adsorbent bed height (2, 3, and 4 cm), and solution flow rate (1, 2, and 3 mL min−1) were investigated to analyze the breakthrough curves. The results showed that the breakthrough time was shortened as the initial phosphorus concentration, the flow rate increased and the bed height decreased. Higher initial phosphorus concentrations, flow rates, and lower bed heights, led to a faster breakthrough of phosphate ions in the FM-MBC adsorbent. Additionally, it was observed that increasing the pH value was not conducive to the adsorption of phosphorus by the FM-MBC adsorbent. Dynamic adsorption data were fitted to four models (Yoon-Nelson, Thomas, Adams-Bohart, and Bed Depth Service Time), and the R2 values of the Thomas and Yoon-Nelson models exhibited minimal variation, suggesting that the dynamic adsorption process of FM-MBC was rather intricate. The saturated fixed-bed column (including FM-MBC) was regenerated with NaOH or HCl, and it was found that a 0.1 mol L−1 NaOH solution had the best regeneration effect. XRD analysis showed that the reaction product between the FM-MBC composite and phosphate anions was Fe3(PO4)2·H2O. Moreover, the experimental results that FM-MBC can successfully be used to remove phosphorus from actual wastewater.

Optimization of phosphorus adsorption on honeycomb briquette ash by application of response surface methodology

Honeycomb coal ash was selected as phosphorus adsorbent to explore the influence of different factors on phosphorus adsorption performance for phosphorus containing wastewater. The structural, physical and chemical properties of coal ash were determined by SEM, BET and XRF analysis methods. The response surface methodology (RSM) was applied for experimental design of phosphorus adsorbent. The effect of five independent variables including initial concentration of phosphorus, coal ash dosage, coal ash particle size, adsorption time and pH on the phosphorus removal efficiency (R (%)) was studied in the ranges of 5–7 mg/L, 6–10 g, 180–220 mesh, 20–30 min and 6.12–6.92 respectively. 46 runs of experiments were designed by the Design-Expert software. The optimum conditions for initial concentration of phosphorus, coal ash dosage, coal ash particle size, adsorption time and pH were found as 6.34 mg/L, 8.17 g, 207.97 mesh, 23.33 min and 6.64, respectively. At these conditions, removal efficiency and desirability function were found to be 96% and 1.000, respectively. The results of kinetic model reveals that the adsorption process conforms to Pseudo-first-order kinetics Equation (R2 =0.9991). The briquette ash has a good application prospect for the actual treatment of phosphorus containing wastewater, which provides a certain treatment strategy for the restoration of damaged water environment.

Physiological and Biochemical State of Green Microalgae (Chlorophyta) under Different Nutrients' Content in the Cultural Medium

The physiological and biochemical state of green microalgae &lt;i&gt;Tetradesmus dimorphus&lt;/i&gt; (Turpin) M.J. Wynne and &lt;i&gt;Desmodesmus brasiliensis&lt;/i&gt; (Bohlin) E. Hegew at different growth phases depending on the nutrients' content in the cultural medium was investigated. Maximal cell numbers, specific growth rate and biomass increment in &lt;i&gt;T. dimorphus&lt;/i&gt; were recorded at the exponential stage under high concentrations of nitrate nitrogen and phosphorus of phosphates, and in &lt;i&gt;D. brasiliensis&lt;/i&gt; - under low. The increase of the cells' division frequency resulted in their lesser size and increase of length/width ratio. Maximal content of lipids and carbohydrates in the cells of &lt;i&gt;T. dimorphus &lt;/i&gt;was recorded at the end of the exponential stage over cultivation in the medium with low initial concentrations of nitrate nitrogen and phosphorus of phosphates, and in &lt;i&gt;D. brasiliensis&lt;/i&gt; -with high content. At this is no difference in the proteins' content in their cells was revealed.

Application of Anaerobic-Aerobic Combined Bioreactor in Phosphorus Removal

A two-stage anaerobic-aerobic sequencing reactor system was developed in order to enhance the removal of biological phosphorus in the sequencing of combined reactors. Combining both aerobic and anaerobic designs in one reactor improved the efficiency and reduced the construction and operating costs. The combination of an upflow anaerobic fixed bed (UAFB) and a floating activated sludge aerobic bioreactor was designed with respective Kaldnes packing ratios of 90 and 30% for the anaerobic and aerobic sections. The controlled parameters were pH levels within a neutral range, a temperature of 37°C, mixed liquor suspended solids (MLSS) of 1220 and 1030 mg/L for the aerobic and anaerobic sections, respectively, and an attached growth that was equal of 743 and 1190 mg/L for the aerobic and anaerobic sections, respectively. Tests were conducted for three different initial phosphorus concentrations (12.8, 32.0, and 44.8 mg/L), two different volumes for each section, and four chemical oxygen demands (CODs) (500, 1000, 1200, and 1400 mg/L). The results demonstrated that, generally, the phosphorus removal in the anaerobic section fell significantly by increasing the inlet COD, and the maximum removal occurred at COD = 500 mg/L. More than 90% of the phosphorus was removed in the aerobic section at COD = 500 mg/L. In other words, the best performance of the reactor was when the ratio of the COD : N : P = 100 : 5 : 2, composition of phosphorus in industrial wastewater.

Phosphorus Recovery from Wastewater Aiming Fertilizer Production: Struvite Precipitation Optimization Using a Sequential Plackett–Burman and Doehlert Design

The precipitation of struvite from wastewater is a potential alternative for the recovery of nutrients, especially phosphorus, which is an essential macronutrient for agriculture but can be harmful to the environment when improperly disposed of in water bodies. In addition, struvite has elements of great added value for agricultural activity (P, N, and Mg) and is, therefore, considered a sustainable alternative fertilizer. In its formation process, several intervening physicochemical factors may be responsible for the production yield levels. Optimization processes can help to define and direct the factors that truly matter for precipitation. In this context, a sequential design of experiments (DOE) methodology was applied to select and optimize the main struvite precipitation factors in wastewater. Initially, a screening was performed with eight factors with the aid of Plackett–Burman design, and the factors with a real influence on the process were identified. Then, a Doehlert design was used for optimization by applying the response surface methodology and the desirability function. The results were used to identify the optimal points of the pH (10.2), N/P ratio (≥4), and initial phosphorus concentration (183.5 mg/L); these values had a greater effect on phosphorus recovery and the production of struvite, which was confirmed through thermochemical analysis of the decomposition of its structure by differential scanning calorimeter—glass transition temperature (DSC-TG) and phase identification by X-ray diffraction (XRD). The determination of the best synthesis conditions is an enormous contribution to the control of the process because these conditions lead to better yields and higher levels of phosphorus recovery.

Preparation of Fe/Zr bimetallic oxide beads and its performance and mechanism for advanced treatment of actual phosphorus-containing wastewater

Phosphorus removal by adsorption method has unique advantages in the wastewater treatment. The granulation and recycling performance of adsorbent are key factors restricting its practical application. To solve these problems, this study used an environmentally friendly binder to prepare Fe/Zr bimetallic oxide beads (Fe/Zr-Bead) with high mechanical strength and recyclability. The batch experiment results confirmed that the maximum adsorption capacity of Fe/Zr-Bead was 24.60 mg/g. During extended operational trials, the Fe/Zr-Bead-filled fixed-bed column enables unhindered flow of wastewater without blockages, effectively treating simulated wastewater with varying initial concentrations of phosphorus. Furthermore, Fe/Zr-Bead exhibits prominent performance in the treatment of real wastewater plant effluent, reducing the initial phosphorus concentration from 0.416 mg/L to below 0.05 mg/L. Even after undergoing 11 cycles of adsorption and desorption, the phosphorus removal capacity of Fe/Zr-Bead only decreased by 5.5 %. Moreover, the desorption solution, which contains phosphorus, can reach up to 57.93 mg/L, making it suitable for phosphorus resource recovery. Ligand exchange between hydroxyl oxygen and phosphorus was found the main mechanism for phosphorus removal by Fe/Zr-Bead. This study is valuable for overcoming the limitations of adsorption materials in practical applications and also provide practical and technical support for advancing phosphorus treatment in the future.

Synthesis of magnesium-modified ceramsite from iron tailings as efficient adsorbent for phosphorus removal

The preparation of ceramsite from iron tailings to remove phosphate can reduce environmental pollution and realize the sustainable development of “treating waste with waste”. This study prepared a modified ceramsite for phosphate removal in water bodies,with iron tailings as the main raw material and magnesium chloride as the modification agent. The optimal preparation conditions for the modified ceramsite were determined as follows: iron tailings: MgCl2 = 50:15, pre-heating at 300 °C for 10 min, and sintering at 800 °C for 60 min. The effects of factors such as adsorbent dosing, contact time, temperature, pH, NH4+ concentration, and coexisting ions were investigated, and the slow-release ability of modified ceramsite after phosphate adsorption was explored. The results show that the adsorption process best fit the pseudo-second-order model and the Sips model at a dose of 1 g/L and an initial phosphorus concentration of 100 mg/L, belonging to multilayer chemical adsorption. The phosphate adsorption was influenced significantly by pH, and the adsorption capacity reached the maximum of 10.24 mg/g at pH 6. The NH4+ concentration of 100 mg/L was favorable for the simultaneous removal of phosphorus and nitrogen. Coexisting anions in water have a minor effect on the adsorption process, while coexisting cations promote adsorption. The XRD, FTIR and XPS characterization results indicate that electrostatic attraction, internal complexation and chemical precipitation are the main mechanisms of action.

The effects of N-addition on litter mixture effects depend on decomposition time: A case from mixed-litter decomposition in the Gurbantunggut Desert.

Changes in nitrogen (N) deposition and litter mixtures have been shown to influence ecosystem processes such as litter decomposition. However, the interactive effects of litter mixing and N-deposition on decomposition process in desert regions remain poorly identified. We assessed the simultaneous effects of both N addition and litter mixture on mass loss in a litterbag decomposition experiment using six native plants in single-species samples with diverse quality and 14-species combinations in the Gurbantunggut Desert under two N addition treatments (control and N addition). The N addition had no significant effect on decomposition rate of single-species litter (expect Haloxylon ammodendron), whereas litter mass loss and decomposition rate differed significantly among species, with variations positively correlated with initial phosphorus concentration and negatively correlated with initial lignin concentration. After 18 months, the average mass loss across litter mixtures did not overall differ from those predicted from single species either in control or N addition treatments, that is, mixing of different species had no non-additive effects on decomposition. The N addition, however, did modify the direction of mixture effects and interacted with incubation time. Added N transformed synergistic effects of litter mixtures to antagonistic effects on mass loss after 1 month of decomposition, while transforming neutral effects of litter mixture to synergistic effects after 6 months of decomposition. Our results demonstrated that initial chemical properties played an important role in litter decomposition, while no effects of litter mixture on decomposition process in this desert region. The N addition altered the litter mixture effects on mass loss with incubation time, implying that increased N deposition in the future may have profound effects on carbon turnover to a greater extent than previously thought in desert ecosystems.

Enhanced Removal of Phosphorus from Aqueous Solutions by Cation-Modified Hydrochar

In this study, cassava stem-derived hydrochar was modified with sodium hydroxide (NaOH) treatment, followed by loading of minerals, was used to prepare cation-modified hydrochars with enhanced phosphate removal ability. Cassava stems were converted to hydrochar by hydrothermal carbonization at 240 °C for 60 min, then it was soaked in 2 M NaOH for 3 h. The NaOH-treated hydrochars were then loaded with iron (Fe), magnesium (Mg) and calcium (Ca). The cassava stems and the derived hydrochars were analyzed for carbon, hydrogen, nitrogen and oxygen content, surface morphology and elemental compositions. Methylene Blue Numbers (MBN) measured surface area and porosity, and pH at the point of zero charge (pHpzc) was determined. Modification with Fe, Mg and Ca improved phosphate removal efficiency of the resulting hydrochars. Treatment of synthetic wastewater containing 50 mg P/L at pH 7 with the dosage of 2 g/L of the cation-modified hydrochars for 360 min showed that phosphate removal efficiency of these modified hydrochars were - Fe-modified 81 %, Mg-modified 66 % and Ca-modified 56 %. When the adsorbent dosage increased to 20 g/L, more than 98 % of phosphate was removed by the hydrochars modified with Fe, Ca and Mg. In the same conditions, phosphate removal efficiency was for the NaOH-treated hydrochars - 89 %, hydrochar derived from cassava steam - 69 % and the starting material - 59 %. The phosphate removal ability of these cation-modified hydrochars increased even when initial phosphorus concentration was increased to 100 mg P/L. This work demonstrated that an abundant agricultural residue, cassava stems, can be converted into effective phosphate adsorbents. HIGHLIGHTS Cassava stem were converted to hydrochar by aqueous carbonization at elevated temperature and pressure - hydrothermal carbonization (HTC) Sequential steps of alkali treatment and chemical modification, following HTC, were used to improve the phosphate removal ability of the cassava stem-derived hydrochar Loading of minerals (Fe, Mg and Ca) was a vital way to increase the adsorption of phosphates on hydrochar Phosphorus removal efficiency of Fe-loaded hydrochar was better than Mg- and Ca-loaded hydrochars Cation-modified hydrochars showed good phosphate removal ability over a wider concentration range GRAPHICAL ABSTRACT