Ammonia Removal Process Research Articles

Comammox rather than AOB dominated the efficient autotrophic nitrification-denitrification process in an extremely oxygen-limited environment

The discovery of complete ammonia oxidizer (comammox) has challenged the traditional understanding of the two-step nitrification process. However, their functions in the oxygen-limited autotrophic nitrification-denitrification (OLAND) process remain unclear. In this study, OLAND was achieved using comammox-dominated nitrifying bacteria in an extremely oxygen-limited environment with a dissolved oxygen concentrations of 0.05 mg/L. The ammonia removal efficiency exceeded 97 %, and the total nitrogen removal efficiency reached 71 % when sodium bicarbonate was used as the carbon source. The pseudo-first- and second-order models were found to best fit the ammonia removal processes under low and high loads, respectively, suggesting distinct ammonia removal pathways. Full-length 16S rRNA gene sequencing and metagenomic results revealed that comammox-dominated under different oxygen levels, in conjunction with anammox and heterotrophic denitrifiers. The abundance of enzymes involved in energy metabolism indicates the coexistence of anammox and autotrophic nitrification-heterotrophic denitrification pathways. The binning results showed that comammox bacteria engaged in horizontal gene transfer with nitrifiers, anammox bacteria, and denitrifiers to adapt to an obligate environments. Therefore, this study demonstrated that comammox, anammox, and heterotrophic denitrifiers play important roles in the OLAND process and provide a reference for further reducing aeration energy in the autotrophic nitrogen removal process.

Fish production, water quality, and the role of nitrification as an ammonia removal process in intensively aerated hybrid catfish ponds

AbstractSix 0.1‐ha earthen ponds with 45 kW/ha of aeration capacity were stocked with hybrid catfish (Ictalurus punctatus x I. furcatus) ranging from 15,000 to 90,000 fish ha−1 in 15,000 fish ha−1 increments to analyze the effect of nitrogen loading on ammonia accumulation and fish production. Minimum dissolved oxygen (DO) concentration was maintained above 3.0 mg O2 L−1 to prevent hypoxia‐induced appetite reduction. Stocking density did not impact survival but decreased average fish harvest weight and increased food conversion ratio (FCR). Gross production increased with stocking density and ranged from 7249 to 35,674 kg ha−1. Average total (TAN) and un‐ionized ammonia (NH3) were not different among stocking densities despite greater nitrogen inputs in ponds with higher feeding rates. Nitrite () and nitrate () concentrations were significantly higher in ponds with higher stocking densities, suggesting that nitrification increased with nitrogen loading. Phytoplankton assimilation of ammonia is the primary ammonia removal process in traditional catfish ponds with modest fish densities and feeding rates. However, in intensively aerated ponds with high feeding rates, nitrification can become an important process for ammonia removal. These data indicate that small earthen hybrid catfish ponds with high aeration capacities can increase catfish production without ammonia accumulating.

The Importance of Ammonia Removal Process in Aquaculture Systems — Towards Improving Malaysian Aquaculture Production

The Importance of Ammonia Removal Process in Aquaculture Systems — Towards Improving Malaysian Aquaculture Production

Electrochemical oxidation of ammonia in water by Pt/NbC membrane-based catalytic nanofluid reactor

Electrochemical oxidation has garnered increasing attention for its potential in treating ammonia in wastewater. However, achieving both high conversion and high nitrogen selectivity simultaneously, while maintaining a short hydraulic retention time (HRT), remains a significant challenge. In this study, we constructed an efficient niobium carbide (NbC) nanoporous membrane reactor by incorporating metal platinum as a catalyst for the electrochemical oxidation of ammonia. The electrocatalytic oxidation process occurred within the nanochannels of the membrane. This design allowed for enhanced single-pass removal of ammonia due to the short diffusion distance on the nanometer scale, which subsequently increased the mass transfer efficiency. Remarkably, we achieved highly controllable pore sizes in the NbC membrane, ranging from 200 to 8.3 nm by dip-coating method. Without the addition of any oxidants, the single-pass removal of ammonia reached 100 % when the applied potential was set at 4 V vs. SCE on a membrane with a pore size of 8.3 nm, and an HRT of 249 s. The primary product obtained from this process was nitrogen, displaying a selectivity of 88.09 %, with a small percentage of nitrate production (selectivity of 11.91 %). By decreasing the applied potential or increasing the pore size, the selectivity of nitrogen can be further improved, reaching 100 %. However, this adjustment may lead to a decrease in the conversion of ammonia. DFT results have revealed that the production of nitrogen on the Pt (111) surface occurs through the NH4+→NH3 → NH2 → N → N2 pathway. This finding contributes to the understanding of the electrochemical process for ammonia removal in water, and provides a viable option for the design of efficient nanomembrane reactors.

CO2 utilization for ammonia removal in skim latex: Processing and rubber properties

An innovative CO2 utilization approach for skim rubber production was developed in this research. Traditionally, skim rubber is produced using a substantial amount of concentrated sulfuric acid to coagulate the rubber particles. Before acid addition, ammonia removal process is required to reduce the volume of acid used. This process, however, involves large operating area, long processing time, environmental issues, and health hazards. To minimize those drawbacks, as a process intensification technique in this study, CO2 microbubbles were applied as a feedstock to reduce the ammonia and hence the volume of acid addition. The properties and microstructure of skim rubbers produced via CO2 microbubbles (MBSL) were investigated in comparison with those produced by traditional processes. The MBSL exhibited smooth surface texture with enhanced tensile strength and thermal stability. Utilization of CO2 as a sustainable feedstock to coagulate skim latex has a potential for not only diminishing the limitations caused by traditional processes but also highlighting an environmental-friendly and cost-effective process with improved product properties.

Influence of Temperature on the Removal Efficiency of Organic Matter and Ammonia from Micro-Polluted Source Water

Temperature is an important factor influencing the treatment effect of biological aerated filters (BAFs). In this study, BAFs incorporating biological manganese oxides (BMOs) were used to treat micro-polluted source water containing organic masses and ammonia, and the influence of temperature on the removal efficiency of the pollutants was investigated. The results showed that after the formation of biogenic manganese oxides (BMOs) in the filter layer, the removal efficiency of CODMn significantly improved. When the water temperature was approximately 24 °C, 16 °C, and 6~8 °C, the removal rates of CODMn, ammonia, and manganese were 60.64, 42.55, and 20.48; 98.40, 95.58, and 85.04; and 98.70, 97.63, and 96.38%, respectively. The influence of water temperature on the removal efficiency of the pollutants was hierarchically structured as follows: CODMn > ammonia > manganese. Analysis of the removal efficiencies of the pollutants along the filter layer showed that CODMn had been eliminated in every filtration layer, and ammonia and manganese were mainly removed in the 0~0.4 m and 0~0.8 m regions of the filter layer, respectively. With a decreasing water temperature, the concentrations of CODMn, ammonia, and manganese along the filter layer increased. The biological CODMn, manganese, and ammonia removal processes were all first-order kinetic reactions. With a decreasing water temperature, the kinetic constant k gradually decreased, and the reaction half-life (t1/2) gradually increased.

Pilot-scale study on acid absorption process for ammonia removal from exhaust gas of denitrification catalyst

This paper presented the results of a study which aimed to removal ammonia from exhaust gas by sulfuric acid liquid. The results of the experiments indicated that absorption processes were efficient for removing ammonia from exhaust gas. pH 3.1 was high enough to removal ammonia from exhaust gas, and decreasing temperature of exhaust gas enhanced the removal efficiencies of NH3. In the case of pH＜3.0, the removal efficiency of NH3 exceeds 95% over all conditions of reaction time.

Study of Ammonia Removal Efficiency and Process Regulation Strategy of Biological Aerated Filter in Treating Low-Temperature Micropolluted Urban Landscape Water

To explore the treatment performance of a biological aerated filter (BAF) for exogenous pollutants in low-temperature landscape water, a laboratory and pilot system were constructed in urban rivers in the alpine region of northern China, and the key influencing factors such as pH, hydraulic load, air–water ratio, and temperature were studied. The results showed that the operation parameters of the BAF need to be controlled to achieve good nitrogen removal effect. Based on the hazard identification of ammonia nitrogen in landscape water effluent, the critical control points of the BAF process were determined, and corresponding control strategies were formulated. By adjusting operation parameters and other measures, hazards can be identified and overcome with reasonable accuracy. Therefore, the effluent ammonia nitrogen and concentration can be kept within the limits of the law. Double-layer aerated organisms can operate stably at normal temperature, in a transition period, and at low temperature period. The average removal rate of ammonia nitrogen in the three periods can reach 83.29%, 68.53%, and 56.55%, respectively, and the effluent quality can meet the requirements of landscape water during operation.

Modeling of an integrated H2S/NH3 scrubber and regeneration columns for coke oven gas purification

A model of an industrial coke oven gas absorption/stripping process for hydrogen sulfide and ammonia removal is developed. Three scrubbing liquids, weak and strong ammoniacal water produced by the strippers and sodium hydroxide solution, are used in the scrubber. Rate-based modeling is used for both the scrubber and the strippers. The model can accurately predict hydrogen sulfide and ammonia concentration in vapor sampled from multiple locations in the scrubber. The effects of the scrubbing liquid flow rates on the scrubbing efficiency is studied with a sensitivity analysis. It is found that increasing the flow rate of strong ammoniacal water can improve the hydrogen sulfide scrubbing efficiency. Increasing the flow rate of weak ammoniacal water can enhance both hydrogen sulfide and ammonia scrubbing efficiency. However, the pH of the wastewater produced by the process also increases, which may adversely affect the wastewater treatment process. Using more sodium hydroxide solution can effectively enhance hydrogen sulfide scrubbing efficiency, but its effect on the pH of the wastewater is profound. These results can provide guidance for improved operation of this process and similar processes.

Membrane degassing with the combination of sweep gas and vacuum pressure for ammonia removal

Schematics of hybrid type membrane degassing process for ammonia removal.

Ammonia Removal from Simulated Wastewater Using Ti3C2T x Mxene in Flow Electrode Capacitive Deionization

The energy-water nexus poses an integrated research challenge with crucial global implications. The nexus highlights the need to adopt a proactive approach by focusing on the conservation and management of both resources. As global freshwater supply continues to deplete, a larger number of people in the world will need to rely on recycled water. One of the ways to address this concern is by focusing efforts on the development and deployment of energy efficient water remediation technologies. Ammonia is one of the most common contaminants found in domestic and industrial wastewater. Concurrently, it is also one of the most liberally produced chemicals because of its widespread use in the agricultural and textile industries. In 2020, approximately 144 million metric tons of ammonia were produced globally (1). Despite that, biological nitrification remains the most widespread method for treating ammonia wastewater (2). Aside from being cumbersome and slow, it also fails to recover ammonia, which is otherwise a valuable product. In pursuit of sustainability, product conservation directly translates to energy conservation and there remains a need for a water purification and ammonia recovery technology that is energy, water, and resource efficient. Capacitive deionization (CDI) is a separation technology that removes ions from water by applying a small voltage below the dissociation potential of water (1.23 V). The ions are temporarily stored in the electrodes and later released to a separate concentrated stream upon voltage removal or reversal. Flowing electrode CDI systems (FE-CDI) have proven advantageous because of their ability to prevent cross contamination, and to run in uninterrupted cycles ad infinitum . The performance of FE-CDI systems relies on the selection of suitable electrode materials with desired properties of high electrical conductivity, high surface area, colloidal stability, and surface sensitivity (3). MXenes are an emerging class of two-dimensional (2D) materials that are highly conductive, hydrophilic, tunable, and possess attractive charge storage and ion transport properties (4,5). In this work, we developed a flowing electrode capacitive deionization (FE-CDI) system using Ti3C2T x MXene suspension electrodes for the removal and recovery of ammonia from synthetic wastewater. A custom-built FE-CDI unit using titanium current collectors with an effective transfer area of 10 cm2 was used to test system efficiency. The electrode performance was evaluated by operating the CDI system with a feed solution of 500 mg/L NH4Cl running in batch mode at a constant voltage of 1.2 and -1.2 V in charging and discharging stages respectively. Despite low loading (1 mg/ml), Ti3C2T x flow electrodes showed a markedly improved performance by achieving 60% ion removal efficiency (Fig. 1a) in a short saturation time of 115 minutes, and an unprecedented ion adsorption capacity of 460 mg/g (Fig. 1b). This is ~ 7× higher than the currently reported value using Ti3C2 in a conventional CDI system targeted at sodium chloride (NaCl) desalination (6). Post-mortem characterization of the suspension electrodes by X-ray diffraction revealed that Ti3C2T x MXene sequestered high amounts of pollutants due to its ability to intercalate ions between its 2D layers. The electrodes possessed favorable electrochemical properties with a high specific capacitance of 148 F/g. The system proved to be a green technology by exhibiting satisfactory charge efficiency of 58-70% while operating at a relatively low energy consumption of 0.45 kWh/kg (Fig. 1c), which is about an order of magnitude lower than the 4.6 kWh/kg used by commercial wastewater treatment plants (7). The results demonstrate that the Ti3C2T x MXene electrodes have the potential to improve the FE-CDI process for energy-efficient removal and recovery of ammonia. IEA, Ammonia Technology Roadmap, International Energy Agency, Paris, (2021).F. Jaramillo, M. Orchard, C. Muñoz, M. Zamorano, and C. Antileo, J. Environ. Manage., 218, 154–164 (2018).Y. Oren, Desalination, 228, 10–29 (2008).Y. Gogotsi and B. Anasori, ACS Nano, 13, 8491–8494 (2019).P. Singh et al., J. Power Sources, 506 (2021).J. Ma, Y. Cheng, L. Wang, X. Dai, and F. Yu, Chem. Eng. J., 384 (2020).M. Ekman, B. Björlenius, and M. Andersson, Water Res., 40, 1668–1676 (2006). Figure 1

Ammonia recovery from anaerobic digestate: State of the art, challenges and prospects

Nitrogen-containing wastewater and organic wastes are inevitably produced during human activities. To reduce nitrogen pollution, much energy has been used to convert ammonia nitrogen into nitrogen gas through biological nitrogen removal method. However, it needs to consume high energy again during industrial nitrogen fixation, which give rise to massive greenhouse gas (GHG) emissions. Therefore, ammonia recovery from organic wastes has attracted much attention in recent years. In this review, the advantages and disadvantages of ammonia stripping, membrane separation and struvite precipitation are discussed firstly. The ammonia stripping mechanisms, influencing factors, mass transfer process, and the latest innovative ammonia stripping techniques from the anaerobic digestate of organic wastes are critically reviewed. Additionally, a comprehensive economic analysis of different ammonia removal or recovery processes is carried out. The challenges and prospects of ammonia recovery are suggested. Ammonia recovery is of great significance for promoting nitrogen cycle, energy saving and GHG emission reduction.

MABR process development downstream of a carbon redirection unit: opportunities and challenges in nitrogen removal processes

ABSTRACT Carbon redirection has become the desired option for sustainable and energy-efficient wastewater treatment due to its contribution to a circular economy. However, its impact on downstream processes such as nitrification and denitrification requires further investigation. This research characterizes the nitrogen removal performance, footprint, aeration mode, and microbial composition of a flow-through membrane aerated biofilm reactor (MABR) downstream of a chemically enhanced primary treatment (CEPT) carbon redirection unit. The batch and long-term studies demonstrated relatively higher nitrification rates than those reported using conventional primary treated wastewaters. The results indicated that reducing carbon in the liquid train positively impacted nitrification by achieving 87 ± 12% (1.4 ± 0.4 g/m2.d) ammonia removal with an effluent 2.5 ± 2.8 mg/L ammonia concentration at a short hydraulic retention time (HRT) of 2.5 h. Despite the lower (1.9 ± 1) soluble COD:N, up to 75 ± 25% (0.6 ± 0.4 g/m2.d) total nitrogen removal was achieved at 4 h HRT by implementing intermittent aeration. The batch tests using the developed biofilms showed nitrification (denitrification) capacity up to 11 ± 1.7 gNH4-N/m2.d (8.5 ± 0.5 gNO3-N/m2.d) and 2.7 ± 0.6 gNH4-N/m2.d (2 ± 0.3 gNO3-N/m2.d) corresponding to ammonia and nitrate concentrations ranging from 10–30 mg/L and 2–10 mg/L, respectively. Microbial analysis indicated that the nitrifiers such as Nitrosomonas and Nitrospira were the dominant species. The ammonia-oxidizing, nitrite-oxidizing, and denitrifying bacteria relative abundances were 10.3 ± 1.5%, 20.7 ± 1.7%, and 20.0 ± 2.8% under continuous aeration and 1.3 ± 0.07%, 1.8 ± 0.09%, and 40.5 ± 3.1% under intermittent aeration, supporting the observed ammonia and total nitrogen removal processes, respectively. Overall, the results demonstrated that MABR downstream of the CEPT behave differently; thus, design guides should be updated accordingly.

Removal and recovery of ammonia from simulated wastewater using Ti3C2Tx MXene in flow electrode capacitive deionization

Flowing electrode capacitive deionization systems (FE-CDI) have recently garnered attention because of their ability to prevent cross contamination and operate in uninterrupted cycles ad infinitum. Typically, FE-CDI electrodes suffer from low conductivity, reducing deionization performance. Utilization of higher mass loadings to combat this leads to poor rheological properties. Herein, Ti3C2Tx MXene was introduced as 1 mg mL−1 slurry electrodes in an FE-CDI system for the removal and recovery of ammonia from simulated agricultural wastewater. The electrode performance was evaluated by operating the FE-CDI system with a feed solution of 500 mg L−1 NH4Cl running in batch mode at a constant voltage of 1.20 and −1.20 V in charging and discharging modes, respectively. Despite the low loading, Ti3C2Tx flowing electrodes showed markedly improved performance, achieving 60% ion removal efficiency in a saturation time of 115 min with an adsorption capacity of 460 mg g−1. To understand the high adsorption performance of the electrodes, physiochemical and structural analysis was done via a variety of characterization techniques such as SEM, TEM, XRD, DLS, and Raman spectroscopy. Cyclic voltammetry and galvanostatic charge/discharge profiles were obtained to evaluate the electrochemical properties of the electrodes. The system proved to be an energy-saving technology by exhibiting a charge efficiency of 58–70% while operating at an energy consumption of 0.45 kWh kg−1. A 92% regeneration efficiency showed that the electrodes were stable and suitable for long term and scalable usage. The results demonstrate that MXenes have the potential to improve the FE-CDI process for energy-efficient removal and recovery of ammonia.

Nanobubble Technology Enhanced Ozonation Process for Ammonia Removal

Ozone (O3) has been widely used for water and wastewater treatment due to its strong oxidation ability, however, the utilization efficiency of O3 is constrained by its low solubility and short half-life during the treatment process. Thereby, an integrated approach using novel nanobubble technology and ozone oxidation method was studied in order to enhance the ozonization of ammonia. Artificial wastewater (AW) with an initial concentration of 1600 mg/L ammonia was used in this study. In the ozone-nanobubble treatment group, the concentration of nano-sized bubbles was 2.2 × 107 particles/mL, and the bubbles with <200 nm diameter were 14 times higher than those in the ozone-macrobubble treatment control group. Ozone aeration was operated for 5 min in both nanobubble treatment and control groups, however, the sampling and measurement were conducted for 30 min to compare the utilization of O3 for ammonia oxidation. H+ was the by-product of the ammonia ozonation process, thus the pH decreased from 8 to 7 and 7.5 in nanobubble treatment and control groups, respectively, after 30 min of operation. The fast removal of ammonia was observed in both systems in the first 10 min, where the concentration of ammonia decreased from 1600 mg/L to 835 and 1110 mg/L in nanobubble treatment and control groups, respectively. In the nanobubble treatment group, ammonia concentrations kept the fast-decreasing trend and reached the final removal performance of 82.5% at the end of the experiment, which was significantly higher than that (44.2%) in the control group. Moreover, the first-order kinetic model could be used to describe the removal processes and revealed a significantly higher kinetic rate constant (0.064 min−1) compared with that (0.017 min−1) in the control group. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of a high level of ammonia in contaminated water.

Removal of ammonia nitrogen from residual ammonium leaching solution by heterotrophic nitrification-aerobic denitrification process

ABSTRACT The aftermath of mining weathered crust elution-deposited rare earth ore produces a large amount of residual ammonium leaching solution, which causes ammonia and nitrogen pollution to the mine site. Recently, denitrification by heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria has attracted much attention. However, limited studies exist regarding the denitrification process of HN-AD bacteria. In this study, we combined four strains of HN-AD bacteria, Pseudomonas fulva K3, Pseudomonas mosselii K17, Klebsiella oxytoca A12, and Enterobacter hormaechei A16, obtained from rare earth element leaching sites, to select the best microbial consortium for ammonia nitrogen removal. We designed an ammonia removal process applicable to HN-AD bacteria to directly remove ammonia nitrogen from acidic leaching solutions. The experimental results demonstrated that the most efficient microbial consortium for ammonia nitrogen removal to be K3 + K17 + A16, with a removal efficiency of 89.68% for 8 h. In this process, considering the influencing factors of the ammonia removal process, the larger the influent flow rate and influent ammonia nitrogen concentration, the greater the ammonia nitrogen accumulation and pH decrease in the reactor. In consecutive multi-batch experiments, the ammonia removal process was used to remove ammonia nitrogen, at concentrations of 100–600 mg/L, from the simulated leaching solution at pH 4–7, whereby the effluent ammonia nitrogen concentration was lower than 15 mg/L. The results demonstrate that the ammonia removal process is highly feasible and stable. These findings will provide new ideas for the application of HN-AD bacteria and new methods for the removal of ammonia nitrogen from acidic leaching solutions.

Intensifying anoxic ammonium removal by manganese ores and granular active carbon fillings in constructed wetland-microbial fuel cells: Metagenomics reveals functional genes and microbial mechanisms

The conventional biological ammonium removal process is challenged for lack of electron acceptors. A lab-scale integrated constructed wetland coupled with microbial fuel cells (CW-MFC) filling manganese ores (MO) and granular active charcoal (GAC) has been developed, named CW-CM. It enhanced the nitrogen removal two times over the control. A metagenomic-based study illustrated the functional genes and taxonomic groups related to N transformations, explored metabolic mechanisms of nitrogen and carbon sources, and then revealed some characteristics of the extracellular electron transfer (EET). Many nitrifying bacteria and autotrophic and heterotrophic denitrifiers were enriched in CW-CM. Furthermore, most nitrification and denitrification reactions except for the conversion of ammonium to hydroxylamine were significantly enhanced in CW-CM. Glycolysis and the TCA cycle were also improved. Overall, a novel anoxic ammonia removal process was achieved in the experimental group with no need of anammox functional bacteria and anammox key genes.

Development and calibration of a new mathematical model for the description of an ion-exchange process for ammonia removal in the presence of competing ions

Ammonia ion removal and recovery via an ion-exchange process using zeolites is a promising alternative to traditional biological treatments. The analysis of its efficiency is not straightforward as it depends on various factors, such as the cation exchange capacity of the zeolite, amount of zeolite available, initial ammonia concentration, contact time, ammonia speciation depending on pH or the presence of competing ions. Mathematical modelling and simulation tools are very useful to analyse the effect of different operational conditions on the efficiency and optimal operation of the process. This paper experimentally analyses the effect that the presence of competing ions has on the efficiency of ammonia removal. This experimental work has shown a reduction of around 21% of ammonia removal efficiency in the presence of competing ions. The main contribution of this paper is the development new mathematical model able to describe the ion-exchange process in the presence of competing ions. The mathematical model developed is able to analyse the performance of the IEX process under different empty bed contact times, influent loads, pH and concentrations of competing ions. The capability of the model to reproduce real data has been proven comparing the experimental and simulation results. Finally, an exploration by simulation has been undertaken to show the potential of the mathematical model developed.

Anaerobic digestion of chicken manure coupled with ammonia recovery by vacuum-assisted gas-permeable membrane process

To overcome the ammonia inhibition problem during anaerobic digestion of chicken manure, this study used a novel vacuum-assisted gas-permeable membrane (V-GPM) process for ammonia removal from liquid digestate prior to the liquid digestate backflow to the digester. Compared with the typical gas stripping process for ammonia removal, the V-GPM process could avoid several process problems, such as pH and dissolved oxygen increase, which harmed the anaerobic digestion process. Results show that more than 80% of the ammonia can be removed from the liquid digestate within 6 h under the conditions of 70 °C and 30 kPa. The low-ammonia-contained liquid digestate can be recycled to dilute the anaerobic feedstock. During the anaerobic digestion treatment of chicken manure, 75% of the feed solution can be replaced by this low-ammonia-contained liquid digestate. Compared with the case of liquid digestate recycling without ammonia removal, a higher biogas yield is obtained for the ammonia removal case, in which the specific methane production increases from 1.0 L/g-VS to 2.4 L/g-VS. Finally, the economic evaluation indicates that the ammonia recovery process could bring an extra benefit of $ 0.51/kg-N.

Coupling of cathodic aluminum dissolution and anodic oxidation process for simultaneous removal of phosphate and ammonia in wastewaters

Removal of excessive nutrients (N and P) is one of the most concerned issues for wastewater treatment. This study presents a paired electrolytic system consisting of Al cathode and RuO2/Ti anode for the simultaneous removal of phosphate and ammonia in wastewaters. The comparative study on the dissolving behaviors of Al cathode and Al anode showed that Al cathode could achieve a continuous and stable dissolution of aluminum, thereby forming flocs and small amounts of water soluble aluminum species for decontamination. The electrogenerated OH– in the vicinity of cathode raised the local alkalinity and caused the chemical dissolution of aluminum. According to the experiment of non-electrolytic dissolution of aluminum in alkaline solution, the local pH resulting in the cathodic dissolution of Al was estimated. The paired electrolytic system showed the capability to simultaneously remove ammonia and phosphate in simulated wastewater, and the pH neutralizing effect in association with the formation of Al species could promote the electrochemical oxidation of ammonia. When the paired electrolytic system was applied to the treatment of landfill leachate, 96.9% of ammonia nitrogen, 87.4% of total phosphorous and 89.9% of COD could be eliminated after three hours of electrolysis at 80 mA/cm2. The results shown in study reveal that the dissolution process of Al cathode enables a convenient control on the dissolving-out amounts of aluminum via regulating the applied current density, and the paired electrolytic system can be developed as an energy-efficient electrochemical wastewater treating method.