Ammonia Recovery Research Articles

Transitioning through the vapour-liquid equilibrium for low energy thermal stripping of ammonia from wastewater: Enabling transformation of NH3 into a zero-carbon fuel

Vacuum thermal stripping permits the recovery of ammonia from wastewater in a concentrated form, which is key to its exploitation in the circular economy, but the latent heat demand for thermal separation remains a critical barrier to exploitation. In this study, we investigate the vapor-liquid equilibrium (VLE) for ammonia-water as a mechanism to enhance recovered ammonia quality and minimise the thermal energy required for ammonia separation. Below the dew point (65 °C at 0.25 bar) a two-phase region of the VLE exists where 48 %wt gas-phase ammonia could be produced (61 °C) compared to only 2 %wt within the stripping region adopted widely in the literature. This was complemented by a 98 % reduction in thermal separation energy, since limited water vaporization can occur when the feed is maintained below the activation energy threshold for bulk evaporation. Operation within this practically unexplored region of the ammonia-water VLE fosters a gas-phase product suitable for energy generation in gas turbines or solid oxide fuel cells. Comparable product quality was achieved using concentrated wastewater, which validated the VLE for design in the presence of a broad range of dissolved gases and volatile inorganic compounds. Rapid desorption of CO2 occurred during vacuum stripping, subsequently increasing pH >9 without the requirement for alkali addition to shift the ammonia-ammonium equilibrium in favor of gaseous ammonia. Consequently, the two-phase region of the VLE defined for vacuum thermal stripping provides a synergistic strategy to mitigate chemical demand, minimise separation energy and recover gas-phase ammonia for zero carbon energy generation, constituting a significant advancement toward the net zero ambitions of the water sector.

End-to-end machine-learning for high-gravity ammonia stripping: Bridging the gap between scientific research and user-friendly applications

The removal and recovery of ammonia from wastewater are critical processes for achieving global environmental sustainability and promoting circular economic development. High-gravity technology is an advanced solution to achieve ammonia stripping from wastewater. This study used machine-learning (ML) techniques to provide more comprehensive insights on various influencing factors, including the operating parameters, wastewater characteristics, and design parameters of rotating packed beds. Bayesian auto-optimization combined with a boosting algorithm effectively overcame the challenges of modeling complex datasets with small sample sizes, multidimensional data, missing values, and skewed distributions. Accurate ML based predictive models for the ammonia removal efficiency (η) and mass transfer coefficient (KLa) were developed, the performance on the training set was R2 = 0.98 and R2 = 0.89, and on the testing set was R2 = 0.98 and R2 = 0.82. The developed model revealed that the stripping stage and gas-liquid ratio were the most influential features for predicting η, whereas the liquid flow and high-gravity factor were the most important features for predicting KLa. The well-trained model was then deployed in an online software application that could provide both predictive and auto-update functions for operators and managers, ensuring that practitioners could use the model. The end-to-end machine-learning approach used in this study—that is, covering data collection, model development, and application—could improve the availability of research results, providing valuable references for the further advancement of technology in the field of environmental.

Resource recovery from landfill leachate by two-stage of direct contact membrane distillation

Landfill leachate (LL) is a high organic matter and ammonia strength wastewater. The recovery of ammonia and water as by-products can be a path to a more sustainable management of LL. This study aims to evaluating the performance of a two-stage of Direct Contact Membrane Distillation for resource recovery from LL. In the first stage, the hot LL flows through the shell side of the polypropylene hollow fiber membrane module while the sulfuric acid solution passes through the lumen side. Ammonia is recovered as ammonium sulfate. In the second stage, the hot effluent from the first stage flows through the hot channel of the poly(tetrafluoroethylene) flat sheet membrane module, while cooled distillate water flows through the other side in countercurrent. The water evaporates and cross the membrane from the hot to the cold channel where it condenses. The results revealed the ammonia recovery rate was 87.38 % in the first stage, then, for each 1 m3 of LL, 2.20 kg of ammonia could be recovered. The water recovered (flux of 11.7 kg m−2 h−1) showed high quality, due to the great membrane rejection rate of colour (99.99 %), turbidity (99.88 %), TOC (99.98 %), NH3 (99.85 %) and phosphorus (99.88 %).

Enhanced ammonia recovery from strong ammonia wastewater via a transmembrane electro-chemisorption system with authigenic acid and base

A transmembrane electro-chemisorption system with authigenic acid and base was developed to enhance ammonia recovery from strong ammonia wastewater. The authigenic base from water electrolysis at the cathode could raise the wastewater pH, which transformed ammonium into free ammonia. Simultaneously, the authigenic acid from water electrolysis at the anode could adsorb free ammonia via transmembrane chemisorption. The recovered product was pure (NH4)2SO4, and two valued byproducts (pure H2 and pure O2) were obtained at the same time. Increasing applied voltage could promote the ammonia recovery. Keeping catholyte circulating flow or some headspace proportion in the cathode chamber was beneficial to the ammonia recovery. It took longer time for high influent NH4+-N concentration to achieve the same recovery efficiency with low influent NH4+-N concentration. Within the same operation time, the former could recover more amount of ammonia. Besides avoiding the addition of acid and base, the energy consumption of this system for ammonia recovery was low to 8.47 kWh/kg NH4+-N. Accordingly, the developed system showed good prospects in recovering ammonia from strong ammonia wastewater.

Novel membrane contactor-like bioreactor for selective separation and biodegradation of phenol and ammonium from coal chemical wastewater

The development of coal chemical industry usually generates high-concentrated wastewater containing phenol and ammonium, which requires deep treatment before disposal. Herein, a novel combined process of membrane contactor and bioreactor (MCBR) was established for the efficient treatment of phenol-ammonium wastewater for the first time. When pH was in the range of 8–13, the increase of pH weakened the transmembrane mass transfer of phenol and enhanced the mass transfer of ammonia, owing to their different existing forms at different pH values. At a temperature of 20–30 ℃, the transmembrane mass transfer of phenol and ammonia both increased with temperature increasing. Meanwhile, the established transmembrane mass transfer model reflected the same tendencies of phenol and ammonium recovery rates between experiment and theory. The precise control of concentrations of phenol and ammonium by membrane contactor ensured the safety and effectiveness of subsequent biodegradation process. After biodegradation, the concentrations of phenol and ammonium reduced from 120.1 and 78.9 mg/L to 7.8 and 2.5 mg/L, respectively. The volatile solid content of activated sludge remained relatively constant, while the settling ratio decreased from 39 % to 29 %. Overall, this study established a novel MCBR system for green and cost-effective treatment of high-concentrated coal chemistry wastewater.

Ammonium Recovery from Synthetic Wastewaters by Using Zeolitic Mixtures: A Desorption Batch-Study

Resource recovery from wastewater is very important in view of a circular economy approach in the water field. Among the different technologies applied to realize circular economy, an attractive option is the use of nutrient-enriched media that can be utilized as slow-release fertilizers. Zeolites have been re-discovered for their key role in ammonium (NH4+) adsorption from treated wastewater. Although many studies have been carried out to assess the ability of zeolites to adsorb NH4+, only few papers concerning NH4+ desorption from zeolites are available in the literature. Therefore, this study investigated NH4+ desorption from mineralogically different zeolites, before (ZNS and ZNC) and after (ZSS and ZSC) their treatment with sodium chloride. The zeolites differed in mordenite content. The amount of the desorbed NH4+ varied from 78 to 84% of the total NH4+ adsorbed. In particular, the NaCl-treated materials showed the largest desorption (27.6 ± 0.2 mg L−1, and 27.9 ± 0.7 mg L−1, ZSS, and ZSC, respectively) as compared to the untreated zeolites (22.9 ± 0.3 mg L−1, and 24.2 ± 0.3 mg L−1, ZNS, and ZNC, respectively) because of the different affinity of the cations for the zeolite surface. A monomodal pseudo-first-order model best approximated the desorption kinetics, suggesting only one mechanism of NH4+ desorption from zeolites. Such a mechanism is based on the ion exchange between dissolved Na+ and adsorbed NH4+. The desorption kinetics also showed that NH4+ desorbed slower from the NaCl-treated zeolites than the untreated ones. This effect was explained by the different affinity of Na+ and NH4+ for the zeolite surfaces as due to the diverse sizes of the Na+ and NH4+ hydration spheres. By revealing the effect of zeolite mineralogy and surface treatments in the desorption of NH4+, this study can suggest new and effective synthetic strategies for the achievement of cheap new materials to be applied in environmental remediation within a circular economy perspective.

Low-Temperature Vacuum Evaporation of Ammonia from Pig Slurry at Laboratory and Pilot-Plant Scale

Livestock manure has a high ammonium content that can limit its direct application on soil as a fertiliser in nitrate-vulnerable zones. Treatment technologies that are able to extract ammonium from livestock manure allow it to be concentrated in small volumes, making it cheaper and easier to transport and use as fertiliser in crop areas where there is a deficit of nitrogen. This study proposed using low-temperature vacuum evaporation to treat pig slurry in order to obtain marketable products that can be used as fertilisers and help close the nitrogen cycle. Two different configurations and scales were used. The first was a seven-litre laboratory-scale evaporator complemented with a condenser, a condensate trapper, an acid trap and a vacuum pump operated at −90 kPa vacuum pressure and at three different temperatures: 50.1 ± 0.2 °C, 46.0 ± 0.1 °C and 45.3 ± 1.3 °C. The second, Ammoneva, is an on-farm pilot-scale evaporator (6.4 m3), capable of working in four-hour batches of 1 t of liquid fraction of pig slurry with an operating temperature of 40–45 °C and −80 kPa vacuum pressure. The laboratory-scale evaporator, which features several novel improvements focused on increasing ammonia recovery, showed a higher nitrogen removal efficiency from the liquid fraction of pig slurry than the on-farm pilot plant, achieving 84% at 50.1 °C operation, and recovering most of it in ammonia solution (up to 77% of the initial nitrogen), with 7% of the ammonia not recovered. The Ammoneva pilot plant achieved a treated liquid fraction with 41% of initial nitrogen on average, recovering 15% in the ammonia solution in the acid trap; so, the NH3 gas absorption step needs to be further optimised. However, due to the simplicity of the Ammoneva pilot plant, which is easily placed inside a 20-foot container, and the complete automation of the process, it is suitable as an on-farm treatment for decentralised pig slurry management. The implementation of the novel design developed at laboratory-scale could help further increase recovery efficiencies at the pilot-plant scale.

Electrochemical Nitrate Reduction to Ammonia – Recent Progress

AbstractThe presence of nitrate in industrial, domestic and agricultural wastewater has a detrimental impact on both ecosystem and human health, as remediation and purification efforts are slow, challenging and difficult, given the high solubility and stability of this pollutant. Taking nitrate into high value‐added ammonia by electrochemical reduction can overcome high pollution and energy consumption limit of Haber‐Bosch process with long‐term significance of environmental protection and energy saving. This review summarized the research progress on the electrocatalytic reduction of nitrate to ammonia, with a focus on the reaction mechanisms, influencing factors, product detection methods, performance evaluation methods and the research status of electrocatalysts up to now. The review reported the latest strategies employed to design efficient electrocatalysts, such as pore structure regulation, alloying, heterostructure construction, defect and interface engineering, crystal surface regulation and microenvironment modulation of single‐atom catalysts. It highlights critical factors that determin the performance in terms of nitrate adsorption, exposed active sites, mass transfer rate, intermediates barrier and side reactions, as well as the stability of electrocatalysts and recovery of ammonia. In addition, the future direction of technology for electrocatalytic reduction of nitrate to ammonia has also been proposed.

Novel ammonia recovery from anaerobic digestion by integrating biogas stripping and gypsum absorption

Recovering ammonia from anaerobic digestion (AD) effluent offers the opportunity to produce a renewable fertilizer and reduce environmental impact. A novel process developed for such an application was evaluated during this study. The feature of the process is integrating biogas stripping and gypsum (CaSO4·2H2O) absorption. The result revealed that the lower CO2 content and the absorption temperature contributed the higher efficiency of ammonia recovery. The gypsum solution recovered around 95% of the stripped ammonia when the stripping gas contained 10% CO2 and it rose to 100% when the gas contained more than 30% CO2. Furthermore, a statistical model and genetic algorithm were applied to estimate the total ammonia recovery and optimize the operating parameters. The experimental and modeling results indicated that integrating biogas stripping with gypsum absorption can effectively harvest ammonia nitrogen and reduce CO2 emissions while producing (NH4)2SO4 fertilizer from AD effluent.

From waste to wealth: Using MgO nanoparticles to transform ammonium into a valuable resource

In this contribution, a versatile approach to the crystallization of ammonium carnallite is discussed through a highly efficient process of ammonium removal from an aqueous solution on MgO(111) surface through a rapid one-pot route. In addition to effective ammonium removal from the reaction environment and recovering it in the form of ammonium carnallite, another dual-purpose application of this approach is the recovery of magnesium in the form of carnallite crystals as a valuable metal with wide application in the industry. The MgO nanoparticles (MgO-NPs) showed high adsorption potential due to the presence of high index surfaces of (111) in the nanoparticle lattice due to the unsaturated valley and edge locations. The phase purity and crystallinity of MgO-NPs were investigated by XRD, and the planes' lattice was confirmed using SAED patterns, and lattice fringes from HRTEM images, while their acidic active sites led to high NH4+ removal using NH3-TPD analysis. A mechanism of ammonium adsorption on the active sites of the MgO(111) surface is proposed for the crystallization phenomenon. FESEM, EDS, HRTEM, XRD, FTIR, and BET analyses were evaluated to confirm the synthesis of single-crystal carnallite. Subsequently, TGA tests displayed the ammonium carnallite weight loss through decomposition to NH3 and HCl and proved the formation of MgO. Therefore, the high recovery rate of 100 mg/L ammonium within 30 min at neutral pH with 125 mg/L of MgO-NPs through the adsorption/crystallization process was revealed. Ammonium recovery from wastewater reduces the costs, energy, and environmental footprints associated with its removal processes.

Influence of feed salinity on ammonia recovery from high-strength effluents in transmembrane chemical absorption process

Transmembrane chemical absorption (TMCS) is a promising technology to recover ammonia from high-strength wastewater and sustainably produce fertilizers for agricultural propose. In this study, the effect of ionic strength was analyzed by modelling and experiments, to establish the impact of the salinity of the treated effluent on the performance (ammonia recovery and water vapour transfer). The non-ideality of the solution is considered and the effect of pH, ionic strength and temperature is analyzed by a thermodynamic model approach using Phreeqc software. Results reveal that high ionic strength can play a positive or negative role in ammonia recovery efficiency, depending on the pH of the solution. The salinity also influences water vapour diffusion through the membrane which can negatively impact the process by diluting the ammonium salt produced. Results show that water vapour transfer is linearly correlated to ionic strength. It can occur in both directions from effluent to acid or inversely depending on difference of ionic strength. The impact of salinity of the effluent on ammonia and water vapour transfer through gas-permeable membranes was theoretically and experimentally assessed.

Influence of pH on the performance of anaerobic piggery wastewater treatment coupled with membrane-based NH3 extraction

The influence of the pH of piggery wastewater (PWW) on both ammonia recovery and anaerobic digestion performance during PWW treatment was evaluated in a continuous stirred tank reactor coupled with a membrane-based extraction module. The anaerobic digester was operated at a hydraulic retention time of 20 days at 37 °C, while the flat sheet PTFE membrane module operated continuously at liquid recirculation rates of 250 mL min−1. The membrane module was able to gradually decrease the total ammoniacal concentration from 1.27 ± 0.01 to 0.62 ± 0.01 g L−1 after 360 days of operation. Membrane-based NH3 extraction induced a CH4 yield increase of 1.3-fold. Moreover, COD and VS removal efficiencies increased up to 1.2-fold and 1.5-fold, respectively, along with the increase in PWW pH from 7.5 to 12. Total VFAs removal efficiencies were higher at a PWW pH of 9.

Microaerophilic Activated Sludge System for Ammonia Retention toward Recovery from High-Strength Nitrogenous Wastewater: Performance and Microbial Communities.

A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia and organic carbon removal is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is based on conventional activated sludge (CAS) with aerobic and settling compartments. Low dissolved oxygen (DO) concentrations (<0.2 mg/L) and short solids retention times (SRTs) (<5 days) eliminated nitrifying bacteria. The two parallel MASs were successfully operated for 300 days and had ammonia retention of 101.7 ± 24.9% and organic carbon removal of 85.5 ± 8.9%. The MASs mitigated N2O emissions with an emission factor of <0.23%, much lower than the default value of CAS (1.6%). A short-term step-change test demonstrated that N2O indicated the initiation of nitrification and the completion of denitrification in the MAS. The parallel MASs had comparable microbial diversity, promoting organic carbon oxidation while inhibiting ammonia-oxidizing microorganisms (AOMs), as revealed by 16S rRNA gene amplicon sequencing, the quantitative polymerase chain reaction of functional genes, and fluorescence in situ hybridization of β-proteobacteria AOB. The microbial analyses also uncovered that filamentous bacteria were positively correlated with effluent turbidity. Together, controlling DO and SRT achieved organic carbon removal and successful ammonia retention, mainly by suppressing AOM activity. This process represents a new nitrogen management paradigm.

Electrochemically Mediated Ammonia Removal and Recovery from Wastewater Using Functional Membranes

Wastewater treatment plants (WWTPs) typically use anaerobic digestion (AD) to treat sludge, but ammonia produced during AD process returns to the headworks of WWTPs. The amount of ammonia in the liquid stream produced after dewatering the stabilized sludge, commonly referred to as dewatering sidestream, could contribute as high as 20% of the overall ammonia loading to WWTPs. Several sidestream treatment technologies are being developed not only to prevent additional ammonia inputs to WWTPs, but also to valorize ammonia for fertilizer production. Electrochemically mediated processes can achieve this goal in two simultaneous steps: (1) ammonium separation from wastewater through a cation-exchange membrane and (2) ammonium-to-ammonia conversion for its recovery by membrane stripping. Although electrochemical reactions in electrodialysis or flow-electrode capacitive deionization have been shown to drive the separation and increase the solution pH, an acid solution must be externally fed in the subsequent stripping process. Here, we demonstrated the use of bipolar membrane electrodialysis (BMED) to separate ammonium while simultaneously producing acid and base streams. Using a three-compartment BMED cell (effective repeating unit area = 29.2 cm2) with a synthetic sidestream containing 50 mM total ammonia nitrogen (TAN), we achieved TAN removal up to 80% with energy consumption less than 10 kWh kg−1 N at a productivity of 34.2 L m−2-repeating unit membrane area h−1 (LMH). The separated ammonia was recovered (>90%) in a subsequent membrane contactor that was fed with acid and base streams produced from the BMED cell. We specifically focused on increasing TAN concentration in the final product stream by changing relative flow rate of acid/base streams, which allowed for concentrating TAN nearly 8 times greater than the feed. These results show the use of BMED coupled with membrane stripping enables ammonia recovery without the need for chemical inputs, representing a promising sidestream treatment technology.

Ammonium Recovery from Manure Wastewater and Simultaneous Electrosynthesis Using Ammonium-Ion Selective Redox Material

The environmental pressure due to greenhouse gas emissions and water contamination generated by livestock manure motivates the development of new approaches to reduce their environmental impacts and improve sustainability. Effective approaches to recover nutrients, especially ammonium, from manure wastewater to produce fertilizer are needed. Here we develop a new electrochemical strategy to achieve simultaneous ammonium recovery and electrochemical synthesis using potassium nickel hexacyanoferrate (KNiHCF) as the ammonium ion-selective redox material to mediate the processes. The KNiHCF electrode spontaneously uptakes ammonium (and K+) from manure wastewater with a nutrient (NH4 + and K+) selectivity of ~100% and effective reduction of chemical oxygen demand (COD). The subsequent electrochemical process achieves the co-production of NH4 +-rich fertilizers and value-added chemicals, such as H2 as a green fuel and H2O2 as a disinfectant, without expensive ion-exchange membranes. These results provide a new conceptual strategy and insights for distributed electrochemical resource recovery and on-demand electrochemical manufacturing that can improve agricultural sustainability.

Scaling up an Electrochemical Nitrogen Recovery Process from Lab Benchtop to Pilot Wastewater Plant

Municipal wastewater and agricultural runoff contain large amounts of reactive nitrogen, which can pollute the environment upon release, leading to harmful algal blooms and poor drinking water quality. At the same time, these reactive nitrogen species are valuable and can be recycled to generate fertilizers and commodity chemicals; it has been estimated that doing so would offset the need for ~30% of global Haber-Bosch ammonia production. For this reason, both removal and recovery of active nitrogen from wastewaters are important goals. An electrochemical separations technique known as Electrochemical Stripping (ECS) has been developed to achieve selective ammonia recovery from wastewater.1 This technique leverages pH swings induced by water-splitting, coupled with appropriate cation- and gas-selective membranes, to remove and recover ammonia nitrogen from wastewaters. ECS has been demonstrated at the benchtop scale with relatively high efficiency (>90% total ammonia nitrogen [TAN] recovery) in various wastewaters, and the effects of certain process variables such as temperature, influent TAN concentration, and gas-permeable membrane material have previously been reported.2 Our goal with this work is to initiate ECS process scale-up by at least 3 orders of magnitude in order to match the scale of municipal wastewater treatment. In order to do this, we set out to build a more complete fundamental process model to inform our design decisions during scale-up. Here we will present results of exploratory tests varying multiple process parameters, including current density, relative electrolyte volumes, reactor residence time, catholyte solution chemistry, and reactor geometry. We then translate these results into a process model comprising thermodynamic relationships as well as kinetic equations, describing both the rates of species generation/consumption as well as transport between reactor compartments. This model, which yields molecular-level insights, is then used in an iterative fashion to first predict performance at small scales under new sets of conditions, and then ultimately inform the design of a ~1000 L/day ECS reactor at a pilot-scale wastewater treatment facility.In addition, we will discuss findings from stakeholder engagement conducted in parallel to lab-scale tests, indicating utility limitations, priorities, needs for certain effluent specs, desired product specs, cost bounds, and details around hydrogen coproduct handling. These discussions additionally feed into design decisions and are crucial for eventual technology deployment.

Recovery of ammonia and phosphate from aquaculture effluent using a reactive vacuum membrane distillation-vacuum membrane distillation/nanofiltration hybrid system

The primary obstacle to extracting nutrients from aquaculture effluent lies in the fact that they are present only in minuscule amounts, rendering the conventional recovery methods inefficient and economically unfeasible. To address the issue, a two-stage membrane system, reactive vacuum membrane distillation-vacuum membrane distillation/nanofiltration (RVMD-VMD/NF) was developed in this work to concentrate ammonia and phosphate simultaneously from low-nutrient fresh aquaculture effluent. RVMD was effective to recover ammonia to a higher concentration factor (59-fold) at 40 °C. The temperature was then increased to 70 °C to further concentrate phosphate using the VMD system, and the results were compared to the pressure-driven nanofiltration (NF) system. VMD demonstrated an excellent capability to concentrate phosphate without any loss to the recovered water and achieved a comparable concentrating effect based on theoretical volume reduction, while NF only achieved half of the targeted value. Considering low-nutrient sources for treatment, RVMD followed by the VMD is a better approach in concentrating both ammonia and phosphate than the RVMD-NF system but RVMD-VMD required a slightly higher total cost (RM 1.68/L) and energy usage (0.53 kWh/L) compared to RVMD-NF of RM 1.66/L and 0.53 kWh/L. The application of the RVMD-VMD system to the fresh aquaculture effluent resulted in a remarkable 77-fold of recovered ammonia (49.33–3790 mg/L) with a separation factor (SF) of 554 and up to 6 factors of phosphate (16.67–92.52 mg/L). Besides, clean water was produced as a by-product. This innovative system provides a sustainable and effective solution for managing aquaculture effluent, with the potential to achieve zero-waste discharge.

Short flow and green process for the production of V2O3 powder via ammonia reduction method

BackgroundThe NH3, a clean reductant, generated by the thermolysis of NH4VO3, is not effectively utilized in the conventional process of vanadium metallurgy. Additionally, the preparation process of V2O3 is both long and costly. Ammonia recovery is essential to prevent environmental issues resulting from ammonia release. By direct thermolysis of NH4VO3 and effectively utilizing of active NH3, it is possible to achieve the short flow and green process for the production of V2O3. MethodIn an open NH3 atmosphere, one end of the flange was connected to the liquid ammonia gas cylinder, while the other end was connected to the tail gas absorber. Furthermore, in a closed NH3 atmosphere, both ends of the tube furnace were sealed with flanges, and the initial atmosphere in the tube was pre-injection NH3. The products of NH4VO3 thermolysis were characterized using various techniques, including XRD, FT-IR, ICP-OES, SEM, XPS, and TG. Significant findingThe thermolysis process of NH4VO3 with pre-injection of NH3 under the sealed condition was a simulation of the continuous production process of V2O3 using a rotary kiln in industrial production. The rational utilization of ammonia resulted in the reduce of energy consumption, extra reductant consumption, and significant NH3 emissions compared to the traditional V2O3 production process. It was observed that V2O3 was easily obtained through the thermolysis of NH4VO3 with pre-injection of NH3 under the sealed condition at 600 °C for 3 h, using a dosage of NH4VO3 ranging from 2 g to 10 g. During this process, the NH4VO3 went through the phase transition as follows: NH4VO3→NH4V3O8→(NH4)0.38V2O5→V6O13→VO2→V4O7→V3O5→V2O3, and the relevant characterization of products showed that the V2O3 obtained was qualified. These experimental results were of great significance to the industrial practice of vanadium metallurgy. Based on these results, short flow and green process of V2O3 could be achieved in industry by partially improving the calcination process of NH4VO3 in large-scale rotary kilns.

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

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.

Ammonium nitrogen (NH4+-N) recovery from synthetic wastewater using biosolids-derived biochar

The nutrient removal in the wastewater treatment plant is a critical step before the treated water is either recycled or discharged into natural water bodies. The current work provides a low-cost and environmentally sustainable nitrogen recovery approach from wastewater using biosolids-derived biochar. The biochar, produced from the pyrolysis of biosolids, was tested for NH4+-N adsorption from a synthetic wastewater sample via a batch adsorption experiment and compared with biomass-derived biochar, cation exchange resin, zeolite, and activated carbon. The adsorption capacity of biochar produced at 500 °C was around 1.8 mg g−1 for an initial NH4+-N concentration of 50 mg L−1, which was half of the cation exchange resin and zeolite given the presence of sulfonate (-SO3H) and -OH groups on their surface to exchange H+ ion with NH4+-N ion. The external surface layer and intra-particle diffusion were the rate-controlling steps of the adsorption process, as reflected in the kinetic modelling results, where a pseudo first-order model could best describe the evolution of adsorption. The presence of active sites with varied affinities towards NH4+-N adsorption on the heterogeneous surface of the adsorbent and the occurrence of multilayer adsorption were implied by the acceptable fitting of isotherm experimental data to Freundlich and Temkin models, respectively. Biosolids-derived biochar may be an attractive adsorbent for ammonium recovery from wastewater in a circular economy concept.