Recovery Of Ammonia Nitrogen Research Articles

Application of physicochemical techniques to the removal of ammonia nitrogen from water: a systematic review.

Ammonia nitrogen is a common pollutant in water and soil, known for its biological toxicity and complex removal process. Traditional biological methods for removing ammonia nitrogen are often inefficient, especially under varying temperature conditions. This study reviews physicochemical techniques for the treatment and recovery of ammonia nitrogen from water. Key methods analyzed include ion exchange, adsorption, membrane separation, struvite precipitation, and advanced oxidation processes (AOPs). Findings indicate that these methods not only remove ammonia nitrogen but also allow for nitrogen recovery. Ion exchange, adsorption, and membrane separation are effective in separating ammonia nitrogen, while AOPs generate reactive species for efficient degradation. Struvite precipitation offers dual benefits of removal and resource recovery. Despite their advantages, these methods face challenges such as secondary pollution and high energy consumption. This paper highlights the development principles, current challenges, and future prospects of physicochemical techniques, emphasizing the need for integrated approaches to enhance ammonia nitrogen removal efficiency.

Recovery of ammonia nitrogen from simulated reject water by bipolar membrane electrodialysis

ABSTRACT Ammonia monohydrate (NH3·H2O) is an important chemical widely used in industrial, agricultural, and pharmaceutical fields. Reject water is used as the raw material in self-built bipolar membrane electrodialysis (BMED) to produce NH3·H2O. The effects of electrode materials, membrane stack structure, and operating conditions (current density, initial concentrations of the reject water, and initial volume ratio) on the BMED process were investigated, and the economic costs were analyzed. The results showed that compared with graphite electrodes, ruthenium-iridium-titanium electrodes as electrode plates for BMED could increase current efficiency (25%) and reduce energy consumption (26%). Compared with two-compartment BMED, three-compartment BMED had a higher ammonia nitrogen conversion rate (86.6%) and lower energy consumption (3.5 kW· h/kg). Higher current density (15 mA/cm2) could achieve better current efficiency (79%). The BMED performances were improved when the initial NH 4 + concentrations of the reject water increased from 500 mg NH 4 + /L to 1000 mg NH 4 + /L, but the performance decreased as the concentration increased from 1000 mg NH 4 + /L to 1500 mg NH 4 + /L. High initial volume ratio of the salt compartment and product compartment was beneficial for reducing energy consumption. Under the optimal operating conditions, only 0.13 $/kg reject water was needed to eliminate the environmental impact of reject water accumulation. This work indicates that BMED can not only achieve desalination of reject water, but also generate products that alleviate the operational pressure of factories.

Optimization of Ammonia Nitrogen Removal and Recovery from Raw Liquid Dairy Manure Using Vacuum Thermal Stripping and Acid Absorption Process: A Modeling Approach Using Response Surface Methodology

Dairy manure adds a substantial amount of nitrogen to wastewater due to its high levels of associated nutrients. Removal and recovery of ammonia nitrogen (NH3-N) from raw liquid dairy manure (RLDM) is greatly valued. This study was focused on the vacuum thermal stripping–acid absorption (VTS-AA) process for NH3-N from RLDM, followed by modeling and optimization. Using the response surface methodology (RSM)-based central composite design (CCD) approach, the critical operational parameters of the vacuum thermal stripping process, including temperature (50–70 °C), pH (9–11), vacuum pressure (35–55 kPa), and treatment time (60–90 min), were optimized. With the specified parameters set at temperature 69.9 °C, pH 10.5, vacuum pressure 53.5 kPa, and treatment time 64.2 min, the NH3-N removal efficiency attained was 98.58 ± 1.05%, aligning closely with the model prediction. Furthermore, the recovered ammonium sulfate ((NH4)2SO4) closely matched their commercial counterparts, confirming the effectiveness of the VTS-AA process in recovering NH3-N from RLDM. The distinct advantage of the employed technology lies in the concurrent energy demand reduction achieved by introducing a vacuum system. These findings contribute valuable insights into the practical implementation of the VTS-AA process for treating raw dairy manure, particularly in large-scale operational contexts.

Improving ammonia nitrogen removal and recovery by BMED stack optimization: The effect of ion exchange membrane thickness

Bipolar membrane electrodialysis (BMED) has emerged as an efficient and promising technology for the removal and recovery of ammonia nitrogen. Despite its potential, the optimization of BMED systems for enhanced performance and energy efficiency remains a critical challenge, particularly in the context of varying ion exchange membrane (IEM) thicknesses. Membranes with a thickness of < 80 µm have low resistance and are mainly used for processes requiring low energy consumption. Membranes with a thickness of 80–250 µm have moderate resistance and high ion selectivity and are widely used for electrodialysis applications. Membranes with a thickness of > 250 µm have higher ion selectivity than commercial membranes with a thickness of 80–250 µm and are suitable for processes that demand high purity. This study investigates the effect of IEM thickness ranging from 16–400 µm on BMED performance for ammonia nitrogen removal and recovery, and energy consumption. The BMED configuration comprising five cell triplets consisting of a cation exchange membrane, bipolar membrane, and anion exchange membrane was employed. The thickness of IEMs was divided into three categories: 16–17 µm (PCEM/ PAEM), 100–150 µm (CD100/AD100, InnoSep-C/InnoSep-A), and 380–400 µm (MC-3470/MA-3475). In membranes with a thickness of 100–150 µm, the ammonia nitrogen removal was exceptionally high at 99.2 %, with a recovery of 98.7 % (CD100/AD100: 100 µm) at a current density of 80 mA/cm2, and the system exhibited low specific energy consumption (SEC) of 8.87 kWh/kg-N (InnoSep-C/InnoSep-A: 150 µm) at a current density of 20 mA/cm2. However, when using the thinnest IEMs (PCEM: 16 µm, PAEM: 17 µm), an increase in total ammonia nitrogen loss (10.21–22.01 %) led to a reduction in ammonia nitrogen recovery. Conversely, when using the thickest IEMs (MC-3470: 380 µm, MA-3475: 400 µm), the SEC was extremely high (30.98–126.67 kWh/kg-N), making them unsuitable for the BMED process for ammonia nitrogen removal and recovery. Based on these experimental results, it is suggested to use an optimal thickness of IEM within the range of 80–250 µm in the BMED systems to achieve a balanced performance, maximizing ammonia nitrogen removal and recovery while minimizing the SEC. Consequently, the present study provides a comprehensive understanding of the effects of the IEM thicknesses on the BMED systems and could offer a practical perspective for optimizing the BMED stack with respect to improving the removal and recovery rate of ammonia nitrogen and reducing the energy consumption.

The Simultaneous Efficient Recovery of Ammonia Nitrogen and Phosphate Resources in the Form of Struvite: Optimization and Potential Applications for the Electrochemical Reduction of NO3.

In response to the need for improvement in the utilization of ammonium-rich solutions after the electrochemical reduction of nitrate (NO3--RR), this study combined phosphorus-containing wastewater and adopted the electrochemical precipitation method for the preparation of struvite (MAP) to simultaneously recover nitrogen and phosphorus resources. At a current density of 5 mA·cm-2 and an initial solution pH of 7.0, the recovery efficiencies for nitrogen and phosphorus can reach 47.15% and 88.66%, respectively. Under various experimental conditions, the generated struvite (MgNH4PO4·6H2O) exhibits a typical long prismatic structure. In solutions containing nitrate and nitrite, the coexisting ions have no significant effect on the final product, struvite. Finally, the characterization of the precipitate product by X-ray diffraction (XRD) revealed that its main component is struvite, with a high purity reaching 93.24%. Overall, this system can effectively recover ammonium nitrogen from the NO3--RR solution system after nitrate reduction, with certain application prospects for the recovery of ammonium nitrogen and phosphate.

Boosting synergistic recovery of ammonia nitrogen and phosphate from phosphorus chemical wastewater by co-pyrolyzing the biomass and magnesite

In this study, biomass was co-pyrolyzed with the low-cost magnesite to prepare nano-MgO loaded biochar (n-MgO/biochar) composites for the simultaneous recovery of NH4+-N and PO43--P consisting in wastewater. It was found from the outcomes that the addition of biomass effectively reduced the pyrolysis temperature of magnesite, and the dispersion of biochar promoted the reactive activation of nano-scale MgO. The nano-MgO could provide Mg2+ and OH− simultaneously for the efficient recovery of NH4+-N and PO43--P. At a pH of approximately 9 and an N/P/Mg molar ratio of 1:2:1.5, the NH4+-N and PO43--P in the experimental wastewater were recovered by 93.7 % and 84.8 %, respectively. Mechanism analysis revealed that chemical adsorption, with the main product being MgNH4PO4·6H2O, predominantly controlled the recovery process. Furthermore, n-MgO/biochar demonstrated a successful recovery of NH4+-N and PO43--P consisting in the complex phosphogypsum leachate. What’s more, NaH2PO4, n-MgO/biochar/P, and raw phosphogypsum leachate could all serve as effective phosphorus sources for recovering NH4+-N consisting in nitrogenous wastewater with phosphorus deficiency. Conclusively, this study provides an alternative method for the simultaneous recovery of NH4+-N and PO43--P consisting in the wastewater.

Ligand Exchange Adsorbents for Selective Phosphate and Total Ammonia Nitrogen Recovery from Wastewaters

Ligand Exchange Adsorbents for Selective Phosphate and Total Ammonia Nitrogen Recovery from Wastewaters

Simultaneous water softening and selective ammonia nitrogen recovery from coal gasification gray water using an innovative four-chamber flow-electrode electrochemistry system

Capacitive deionization-based technologies such as flow electrode capacitive deionization (FCDI) have shown great promise for desalination and resource recovery, but simultaneous desalination and resource recovery using one FCDI device has thus far received minimal attention. In this study, a novel four-chamber FCDI coupled with a monovalent cation exchange membrane (MCEM) was proposed to realize simultaneous desalination (including water softening) and ammonia-rich solution production from coal gasification gray water (CGGW). The results showed that under optimal conditions, up to 91.2 ± 0.1 % ammonia nitrogen, 88.9 ± 1.0 % Ca2+, and 92.6 ± 5.5 % total organic carbon of real CGGW were removed by the desalination chamber. Furthermore, NH4+ passed through the MCEM and entered the recovery chamber, while Ca2+ was effectively blocked from entering the recovery chamber by MCEM. Thus, a multipurpose ammonia-rich solution with purity of 98.0 % was obtained. The process was superior since two typical FCDI cells are needed to realize water softening and recover ammonia-rich solutions. The mechanistic insights into the proposed four-chamber FCDI coupled with MCEM can be expanded to other simultaneous desalination, ion separation and recovery processes. Thus, the four-chamber FCDI is a promising technology for simultaneous desalination and resource recovery with the advantages of being chemical-free, capital efficient and operable.

Enhanced internal circulation for struvite crystallization in a novel air-lift circulation reactor with Venturi structure for ammonium recovery from wastewater

Nutrient recovery as struvite from wastewater in is quite feasible. The mystery of ammonia loss has received much attention, and inadequate struvite purity is frequently present. A struvite fluidized bed reactor (FBR) was constructed and operating conditions were optimized in order to minimize ammonia nitrogen loss. The properties of the struvite produced by the reactor and the optimum operating conditions for ammonia recovery were also assessed. According to simulations, the Venturi tube increased turbulent flow energy to 4.5 × 10−2 m2·s−2. This significantly improved the mass transfer efficiency. A significant difference between the wall shearing rate (50–319 s−1) and the fluid shearing rate (2–10 s−1) prevented the crystal particles from colliding with the vessel wall. The reactor reached stable operation under conditions of N/P = 1:1 and pH = 9.0. The purity of the obtained struvite was 96.5 %, with an ammonia nitrogen conversion rate of 89.67 %, where the struvite crystals could grow to 82 μm within 24 h. It was concluded that the new FBR with air-lift internal circulation function was feasible for improving struvite crystal growth and purification. It is possible to achieve high ammonia nitrogen recovery efficiency at low cost.

Recovery of ammonia nitrogen and phosphate from livestock farm wastewater by iron-magnesium oxide coupled lignite and its potential for resource utilization.

A new adsorbent called iron-magnesium oxide coupled lignite (CIMBC) was developed to address the challenges of recovering high concentrations of ammonia nitrogen and phosphate in livestock farm wastewater and improving the inefficient use of lignite (BC) with low calorific value. CIMBC was synthesized using the modified ferromagnesium salt double-coating method. The experiments demonstrated that Fe2O3 and MgO could be effectively loaded onto the surface of BC at a Fe/Mg molar ratio of 1:2 and pyrolysis temperature of 500°C. The optimal conditions for adsorption were determined to be an N/P concentration ratio of 2:1, adsorbent dosage of 1g/L, and pH of 7. The presence of coexisting cations (Ca2+ and Mg2+) inhibited the removal of ammonia nitrogen but enhanced the removal of phosphate. Likewise, the presence of coexisting anions (CO32- and SO42-) hindered the removal of both ammonia nitrogen and phosphate. The adsorption behavior followed the pseudo-second-order model and the Langmuir model, with a maximum adsorption capacity of 95.69mg N/g for ammonia nitrogen and 101.32mg P/g for phosphate. The adsorption process was a spontaneous endothermic process controlled by multiple levels. The main mechanisms of adsorption involved electrostatic attraction, intra-particle diffusion, ion exchange, chemical precipitation, and coordination exchange. After 5 times of adsorption-desorption, the recovery rate of CIMBC is less than 50%, and the removal rate of phosphate is less than 40%. Although the RCIMBC exhibited low reusability, but also it showed potential in removing heavy metals (Pb) from wastewater and for use as a slow-release fertilizer. CIMBC is a promising new adsorbent, which can realize resource utilization of lignite with low calorific value while removing nitrogen and phosphorus.

One-step green construction of granular composite hydrogels for ammonia nitrogen recovery from wastewater for crop growth promotion

The great application potential of hydrogel adsorbent in water treatment has been widely reported in recent years. However, practical application is severely restricted due to the tedious preparation procedures, high energy consumption, and potential environmental threat of spent adsorbent after adsorption. To address these challenges, a new method was proposed in this study to prepare granular hydrogel composites through one-step polymerization induced phase separation (PIPS), initiated via a redox reaction consisting with calcined oil shale semi-coke (COSSC) and active ingredients of in green tea (GT) at 40 °C. Then granular hydrogel was applied to remove NH4-N in wastewater, and the spent adsorbent after adsorbing was used as the medium for plant growth. The granular hydrogel exhibited a favorable swelling capacity of 205 g/g and excellent adsorption capacity of 40.2 mg/g for NH4-N. Remarkably, the adsorption process achieved equilibrium only within 30 min. To avoid the influence of soil and other factors, we conducted a soilless cultivation experiment, and the results showed that the total seed biomass of mung bean increased by 33.69% with adding 1% of spent hydrogels into the culture medium. Based on above excellent performance, this study presented a feasible idea for the green preparation granular hydrogel composites and offered a promising strategy for the sustainable utilization of spent adsorbent.

Graphene Oxide/Polyethyleneimine-Modified Cation Exchange Membrane for Efficient Selective Recovery of Ammonia Nitrogen from Wastewater.

Competition for the migration of interfering cations limits the scale-up and implementation of the Donnan dialysis process for the recovery of ammonia nitrogen (NH4+-N) from wastewater in practice. Highly efficient selective permeation of NH4+ through a cation exchange membrane (CEM) is expected to be modulated via tuning the surface charge and structure of CEM. In this work, a novel CEM was designed to form a graphene oxide (GO)-polyethyleneimine (PEI) cross-linked layer by introducing self-assembling layers of GO and PEI on the surface of a commercial CEM, which rationally regulates the surface charge and structure of the membrane. The resulting positively charged membrane surface exhibits stronger repulsion for divalent cations compared to monovalent cations according to Coulomb's law, while, simultaneously, GO forms π-metal cation conjugates between metal cations (e.g., Mg2+ and Ca2+), thus limiting metal cation transport across the membrane. During the DD process, higher NH4+ concentrations resulted in a longer time to reach Donnan equilibrium and higher NH4+ flux, while increased Mg2+ concentrations resulted in lower NH4+ flux (from 0.414 to 0.213 mol·m-2·h-1). Using the synergistic effect of electrostatic interaction and non-covalent cross-linking, the designed membrane, referred to as GO-PEI (20) and prepared by a 20 min impregnation in the GO-PEI mixture, exhibited an NH4+ transport rate of 0.429 mol·m-2·h-1 and a Mg2+ transport rate of 0.003 mol·m-2·h-1 in single-salt solution tests and an NH4+/Mg2+ selectivity of 15.46, outperforming those of the unmodified and PEI membranes (1.30 and 5.74, respectively). In mixed salt solution tests, the GO-PEI (20) membrane showed a selectivity of 15.46 (~1.36, the unmodified membrane) for NH4+/Mg2+ and a good structural stability after 72 h of continuous operation. Therefore, this facile surface charge modulation approach provides a promising avenue for achieving efficient NH4+-selective separation by modified CEMs.

Phosphate and ammonia nitrogen recovery from sewage sludge supernatants by coupled MgO-biomass ash and its potential as heavy metal adsorbent

Aiming at the problem of complex treatment for energy solid waste—biomass ash (BA) from thermal power plant and difficult recovery for phosphorus and ammonia nitrogen in sewage sludge supernatants, a coupled MgO-biomass ash (CMBA) was established. CMBA composites were synthesized by in situ thermal-precipitation modification method, which simultaneously achieved recovery of phosphorus and ammonia nitrogen and BA resource utilization, and explored the potential of recovered CMBA (RCMBA) containing phosphate and ammonia nitrogen to remove heavy metal from wastewater. The results showed that magnesium oxide could be effectively loaded on the surface of BA at an MgCl2 concentration of 1.25 M and calcination temperature of 400 °C. pH, adsorbent dosages and initial concentration affected the adsorption capacity of phosphate and ammonia nitrogen by 400CMBA. The existence of K+, Ca2+ and Mg2+ ions promoted the removal of phosphate by 400CMBA, but hindered the removal of ammonia nitrogen. The existence of Cl-, NO2- and SO42- ions affected the removal of phosphate by 400CMBA. The adsorption processes of 400CMBA for phosphate and ammonia nitrogen can be used with the Langmuir-Freundlich model and the pseudo-second-order model reaching a maximum adsorption capacity of 262.88 mg/g and 122.39 mg/g, respectively. The adsorption behavior was controlled by several processes, spontaneous and thermogenic chemisorption. The saturated adsorbent can be effectively regenerated in 0.1 M HCl solution. After the fifth regeneration, the phosphate and ammonia nitrogen removal rates were less than 50% and 25%, respectively. The adsorption mechanisms of phosphate and ammonia nitrogen by 400CMBA were mainly physical adsorption, electrostatic attraction, ion exchange, complexation reaction and chemical precipitation, among which chemical precipitation was dominated by struvite crystallization was dominant. In addition, RCMBA had a specific removal effect on heavy metal in solutions. Overall, this work provides a feasible way for the resource utilization of energy solid waste-BA from thermal power plant.

Harmless treatment of electrolytic manganese residue: Ammonia nitrogen recovery, preparation of struvite and nonsintered bricks

The ammonia nitrogen in electrolytic manganese residue (EMR) is easily transferred to water source, polluting the environment and endangering biological health. In this study, the ammonia nitrogen in EMR is removed by slaked lime, carbide slag (CS) and red mud (RM). The removal of ammonia nitrogen is influenced by the liquid–solid ratio, stirring time, and additives dosage. The removal efficiency of ammonia nitrogen of EMR pretreated with 7.4 % fresh CS for 15 min can reach 98.5 % when the liquid–solid ratio is 1.50. Under the synergistic effect of CS and RM, the ammonia nitrogen in EMR is quickly removed within 15 min, and the removal efficiency of ammonia nitrogen reaches 98.2 %. It is feasible to replace slaked lime with CS and RM to achieve the removal of ammonia nitrogen in EMR. Struvite has high quantity and good purity when the molar ratio of N, P and Mg is 1:1.6:1.6 and pH = 8.0. The remaining EMR after removal of ammonia nitrogen, blast furnace slag, Portland cement and aggregates was used as raw materials to prepare nonsintered bricks (NSB). The NSB according to the optimal formula after curing for 7 days had no free ammonia nitrogen detected. This study provided a new way to remove ammonium nitrogen in EMR by CS and RM, and demonstrated a solution to prepare struvite and nonsintered bricks.

Ammonia nitrogen recovery from biogas slurry by SCP production using Candida utilis

The safe and robust yeast Candida utilis was employed for nitrogen recovery as single cell protein from biogas slurry. The maximum biomass of 6.2 g/L with protein content of 53.5% was produced in batch cultivation with glucose as the carbon source, C/N ratio of 3:1, NH4+-N concentration of 3000 mg/L, initial pH of 8.0, and the addition of 0.35% (w/v) Na2HPO4. It was speculated that C. utilis can grow well with free ammonia below 197 mg/L. In fed-batch fermentation, a biomass of 14.8 g/L was obtained, and the maintenance of aerobic conditions was critical to improving the production of single cell protein. The sterilized and non-sterilized biogas slurry can be used as an effective pH regulator. The obtained single cell protein was a nutritious, safe, and reliable protein source. This study provides novel insights into nitrogen recovery via C. utilis as a single cell protein from biogas slurry.

Economic optimization of hollow fiber membrane contactors for ammonia nitrogen recovery from anaerobic digestion effluents

This study presents the optimization and economic analysis of the membrane contactors to recover ammonia nitrogen from anaerobic effluents. The effects of ammonia nitrogen concentrations and alkalinity of the anaerobic effluents on the operating cost and total recovery cost were investigated, and the optimization of wastewater flowrate and pH was carried out.The sensitivity analysis revealed that the wastewater pH was the dominant parameter of the operating cost, followed by the percentage Am-n recovery and wastewater flowrate. The increase of anaerobic effluent’s alkalinity reduced the optimized wastewater pH and flow rate. The total operating recovery cost, including the production cost of solid ammonium sulfate, was found to be in the range of 0.16–0.31 USD/ kg·ammonium sulfate for the Am-n and alkalinity concentrations of 100–700 mg/L and 400–2800 mg/L as CaCO3, respectively, which are much lower than those of the conventional vacuum thermal stripping/acid absorption technique. The total costs, considering the capital investment of the membrane contactor’s unit, were also determined, and found to be 0.242–0.741 USD/kg·ammonium sulfate in the investigated range of anaerobic effluents

Application of Bipolar Membrane Electrodialysis in Environmental Protection and Resource Recovery: A Review.

Bipolar membrane electrodialysis (BMED) is a new membrane separation technology composed of electrodialysis (ED) through a bipolar membrane (BPM). Under the action of an electric field, H2O can be dissociated to H+ and OH−, and the anions and cations in the solution can be recovered as acids and bases, respectively, without adding chemical reagents, which reduces the application cost and carbon footprint, and leads to simple operation and high efficiency. Its application is becoming more widespread and promising, and it has become a research hotspot. This review mainly introduces the application of BMED to recovering salts in the form of acids and bases, CO2 capture, ammonia nitrogen recovery, and ion removal and recovery from wastewater. Finally, BMED is summarized, and future prospects are discussed.

Simultaneous nutrient-energy recovery from source-separated urine based on bioelectrically enhanced bipolar membrane-driven in-situ alkali production coupling with gas-permeable membrane system

• Simultaneous nutrient-energy recovery from human urine was based on the reactor. • Bipolar membrane produced alkali in-situ without additional chemicals. • Gas-permeable membrane recovered nitrogen with less energy and higher efficiency. • Nitrogen recovery of 90.39% and H 2 production rate of 0.46 m 3 m −3 d −1 were obtained. Source-separated urine has attracted widespread attention recently because it was rich in nutrients and can be recycled for reuse. In this work, the bioelectrically enhanced bipolar membrane-driven in-situ alkali production coupling with gas-permeable membrane system (BBGS) was innovatively proposed to treat urine for organic matter removal, ammonia nitrogen (AN), and value-added product hydrogen recovery, which provided a novel way for nutrient-energy recovery from urine. Urea was hydrolyzed quickly by microorganisms, and ions were migrated and enriched under the driving action of an electric field. In-situ alkali production by the bipolar membrane (BPM) created a high pH environment for the absorption of AN and promoted the formation of gaseous ammonia. Meanwhile, the AN was absorbed by the acid through the gas-permeable membrane (GPM) and thus recovered. Urea with a concentration of 1717 mg L −1 can be 100% removed, while a high AN of 202.94 ± 11.23 mg L −1 is obtained with an AN recovery of 90.39 ± 5.00% in the absorption bottle. With initial COD of 880 ± 10 mg L −1 in influent, the effluent COD was 110.50 ± 10.56 mg L −1 with COD removal of 87.36 ± 1.32%. In addition, the average nitrogen recovery rate was 0.56 ± 0.03 mg h −1 , the average hydrogen production rate was 0.46 ± 0.01 m 3 m −3 d −1 , and the average coulombic efficiency (CE) was 69.53 ± 3.04%. The active recovery of nutrients from urine was beneficial for reducing the high energy consumption in the terminal wastewater treatment plant, solving the sanitary storage problem of urine, and effectively utilizing high-quality nutrition sources for recycling and reuse. The BBGS was of great significance for the treatment and resource utilization of urine.

Performance evaluation of a solar evaporation system for liquid digestate concentration

The safe and efficient treatment and resource recovery of the large amount of liquid digestate (LD) produced by biogas plants has become an important factor limiting the development of the biogas industry. In this study, a solar evaporation system was developed based on low cost, high efficiency, and high nutrient recovery of LD concentration. The effects of different parameters, including solar radiation, LD flowrate, and daily treatment capacity, on the concentration efficiency, nutrient recovery, and thermal efficiency were investigated. Economic and enviroeconomic analyses were conducted to comprehensively assess the feasibility and environmental benefits of the system for large-scale biogas plants. The results showed that the higher the solar radiation, the higher the air temperature and its saturation vapor pressure, which led to an increase in the concentration efficiency of LD. The LD concentration efficiency can reach up to 43.33% when the average daily solar radiation was 773.08 W/m2. High solar radiation also contributed to high LD temperature, leading to an increase in the percentage of free ammonia (NH3) in the LD, which was not conducive to the recovery of ammonia nitrogen (NH3N). By increasing the LD flow rate, the heat and mass exchange between air and LD in the spray chamber was enhanced, resulting in higher concentration efficiency. The variation of LD flow rate and daily treatment capacity had little effect on nutrient recovery. The recovery of NH3N and soluble salts in the concentrated phase could be as high as 78.39% and 84.19%, respectively, when the initial pH of LD was 5, the air flow rate was 0.03 m3/s, and the LD flow rate was 6 L/min. In addition, the economic analysis indicated that the concentration cost of the system in treating a daily LD production of 100 tons was 1.08 USD/ton. The solar evaporation system can reduce CO2 emissions by 2.40 × 105 tons and earn carbon credits of 3.48 × 106 USD over its lifetime. This study provides a new direction and reference for LD concentration.

Application of RSM to optimize the recovery of ammonia nitrogen from high chromium effluent produced in vanadium industry using struvite precipitation

It is difficult to achieve resource separation and recovery from hazardous vanadium-extracted effluent containing high ammonia nitrogen and hexavalent chromium. Multi-objective optimization by response surface methodology (RSM) based on the Box-Behnken design (BBD) was applied to maximize ammonia nitrogen recovery percent (R(N), %) and minimize the Cr loadings (L(Cr), %) during struvite precipitation to realize Cr(VI) separation and resources recovery from vanadium-extracted effluent. The response variables were correctly predicted by two second-order polynomial models, and R(N) of 98.87% and L(Cr) of 0.118% were achieved under optimal conditions (pH of 9.16, Mg/N of 1.3, and P/N of 1.165). Besides, the morphology of the precipitation sample under the optimal condition was confirmed as struvite crystals by XRD and SEM, and the Cr content of the recovered struvite meets the requirements of fertilizer. This paper demonstrated the reliability and validity of direct recover ammonia nitrogen by struvite precipitation from the vanadium-extracted effluent. Moreover, it provided practical support for an effective way on Cr(VI) separation and resources recovery from high hexavalent chromium and ammonia nitrogen complicated effluent like hazardous vanadium-extracted effluent.