New progress of ammonia recovery during ammonia nitrogen removal from various wastewaters

Investigation of microbial induced calcium carbonate and struvite co-precipitation on cementitious material surfaces

Microbial-induced carbonate precipitation (MICP) has garnered increasing attention in the realm of building materials. Among them, urease microorganisms have been extensively investigated due to their favorable attributes, including facile reaction control, heightened mineralization efficiency, and straightforward microorganism cultivation. Nevertheless, the presence of ammonia byproducts throughout the reaction process significantly restricted its extensive utilization. This work employed the application of microbial-induced carbonate precipitation (MICP) technology to modify the surface of cement-based materials in a solution environment. Simultaneously, the generation of struvite (MgNH4PO4•6H2O) was induced to eliminate ammonia byproducts and improve the cementitious ability of the film layer. The potential synergistic impact between calcium carbonate (CaCO3) and struvite was observed, resulting in the production of a composite film with enhanced performance. Furthermore, the elimination efficacy of ammonia byproducts was found to exceed 90% after a treatment duration of 96 h.

Recent advances in low-temperature nitrogen oxide reduction: effects of electric field application

This article presents a review of catalytic processes used at low temperatures to reduce emissions of nitrogen oxides (NOx) and nitrous oxide (N2O), which are exceedingly important in terms of their environmental impacts on the Earth. With conventional purification technologies, it has been difficult to remove these compounds under low-temperature conditions. By applying a catalytic process in an electric field for the three reactions of three-way catalysts (TWC), NOx storage reduction catalysts (NSR), and direct decomposition of N2O, we have achieved high catalytic activity even at low temperatures. By promoting ion migration on the catalyst surface, we have filled in the gaps in conventional catalytic technology and have opened the way to more efficient conversion of NOx and N2O.

Effective denitrification from landfill leachate using magnetic PVA/CMC/DE carrier immobilized microorganisms

Ammonia nitrogen (NH4+-N) discharge has caused eutrophication of water bodies and harm to humans and organisms. In this work, polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), diatomite (DE), and Fe3O4 were used to prepare magnetic immobilized carriers by encapsulating microorganisms for the treatment of NH4+-N wastewater. The response surface methodology was used to explore the optimal ratio of the immobilized carriers. The obtained optimal raw material ratio was 99.10 %. The obtained carriers are spherical (4-5 mm in diameter) with a rich honeycombed pore structure. The magnetic carrier improves the ammonia oxidation activity, and the carrier achieved 99.0 % of NH4+-N and 86.7 % of total nitrogen (TN) removal rates from the simulated wastewater (NH4+-N concentration: 300 mg/L) through nitrification and denitrification under aerobic conditions. Upon applied for a 60 days' treatment of landfill leachate (NH4+-N concentration of 300 mg/L), the daily removal rates for NH4+-N and TN reached 93.7 % and 78.3 %, respectively. The analysis of the microbial community showed that the abundances of heterotrophic nitrifying-aerobic denitrifying bacteria including Enterobacter, Pseudomonas, and Bacillus increased with prolonging treatment days, which accelerated nitrification and denitrification, consequently promoting the nitrogen removal effect.

Application of artificial intelligence for nutrient estimation in surface water bodies of basins with intensive agriculture

Eutrophication is one of the most relevant concerns due to the risk to water supply and food security. Nitrogen and phosphorus chemical species concentrations determined the risk and magnitude of eutrophication. These analyses are even more relevant in basins with intensive agriculture due to agrochemical discharges. However, analyzing these nutrients is labor intensive, as sampling to intercalibration in the laboratory requires considerable financial and human resources. Currently, artificial intelligence allows the modeling of phenomena and variables in various fields. This research focuses on the exploration of other machine learning methods, including multilayer perceptron (MLP), k-nearest neighbor (KNN), convolutional neural network (CNN), and random forest (RF) for the estimation of nutrients in surface waters of Sinaloa, Mexico (11 model basins), the states with the highest exports of agricultural products. Nutrients were considered in all possible chemical forms, such as total nitrogen, Kjeldahl nitrogen, ammonia nitrogen, total phosphorus, and orthophosphate. For estimation, the selected input parameters are characterized by pH, dissolved oxygen, conductivity, water temperature, and total suspended solids, which do not require chemical reagents and can be measured in real time. The parameter information was obtained from the National Network for Water Quality Monitoring database (6,200 data recorded since 2012). Finally, hyperparameter normalization and optimization (HPO) methods were implemented to maximize the best-performing model. Each model obtained different coefficient of determination values (R2): MLP between 0.64 and 0.77, CNN from 0.65 to 0.76, KNN from 0.64 to 0.79, and RF from 0.79 to 0.85. The latter is considered the best performer, with values of 0.95 in training and 0.94 in validation after applying HPO. Notably, the models are valid for any surface water body and in any climatic season in the state of Sinaloa, México. Therefore decision-makers can use them for science-based environmental regulation of land use and pesticide application.

Electrodegradation of nitrogenous pollutants in sewage: from reaction fundamentals to energy valorization applications

The excessive accumulation of nitrogen pollutants (mainly nitrate, nitrite, ammonia nitrogen, hydrazine, and urea) in water bodies seriously disrupts the natural nitrogen cycle and poses a significant threat to human life and health. Electrolysis is considered a promising method to degrade these nitrogenous pollutants in sewage, with the advantages of high efficiency, wide generality, easy operability, retrievability, and environmental friendliness. For particular energy devices, including metal-nitrate batteries, direct fuel cells, and hybrid water electrolyzers, the realization of energy valorization from sewage purification processes (e.g., valuable chemical generation, electricity output, and hydrogen production) becomes feasible. Despite the progress in the research on pollutant electrodegradation, the development of electrocatalysts with high activity, stability, and selectivity for pollutant removal, coupled with corresponding energy devices, remains a challenge. This review comprehensively provides advanced insights into the electrodegradation processes of nitrogenous pollutants and relevant energy valorization strategies, focusing on the reaction mechanisms, activity descriptors, electrocatalyst design, and actuated electrodes and operation parameters of tailored energy conversion devices. A feasibility analysis of electrodegradation on real wastewater samples from the perspective of pollutant concentration, pollutant accumulation, and electrolyte effects is provided. Challenges and prospects for the future development of electrodegradation systems are also discussed in detail to bridge the gap between experimental trials and commercial applications.

Effects of potassium-mediated electrical communication inhibition on nitrogen removal in microbial fuel cells

Potassium ion signaling mediates microbial communication in electroactive biofilms within microbial fuel cells (MFCs), but its role in nitrogen removal remains unclear. This study investigated the impact of inhibiting potassium signaling on nitrogen removal in MFCs using tetraethylammonium chloride (TEA) as an inhibitor. Results demonstrated that 5 mM and 10 mM TEA reduced the maximum power generation of MFCs from 77.95 mW/cm2 to 57.18 mW/cm2 and 48.23 mW/cm2, respectively. Correspondingly, total nitrogen (TN) removal efficiency was decreased from 46.57 ± 1.01% to 35.93 ± 0.63% and 38.97 ± 0.74%, respectively. This decline was attributed to inhibited potassium ion signaling, which compromised the electrochemical performance of the MFC and hindered the nitrogen removal process. The relative abundance of exoelectrogen Geobactor decreased from 15.37% to 5.17% and 8.05%, while the relative abundance of cathodic nitrifying bacteria Nitrosomonas decreased from 17.87% to 4.92% and 3.63% under 5 mM and 10 mM TEA. These findings underscore the crucial role of potassium ion signaling in enhancing the bioelectrochemical nitrogen removal process in MFCs.

A holistic valorization of treasured waste activated sludge for directional high-valued products recovery: Routes, key technologies and challenges

Global energy shortages and environmental crises underscore the imperative for a circular economy to tackle resource scarcity and waste management. The circular economy model encourages the recovery and reuse of valuable materials, reducing reliance on finite natural resources and lessening the environmental impact of waste disposal. Among urban organic solid wastes, waste activated sludge (WAS) emerges as a potent reservoir of untapped resources (including various inorganic and organic ones) offering significant potential for recovery. This review delves into a comprehensive analysis of directional valorization of WAS to recover high-valued products, including the inorganic matters (i.e. phosphorus, ammonia nitrogen, and heavy metals), organic resources (i.e. extracellular polymers like alginate and protein, volatile fatty acid, methane, hydrogen, and plant growth hormones) and reutilization of WAS residues for the preparation of adsorbent materials - the biochar. Moreover, the main recovery methodologies associated influencing parameters, product application, and attendant challenges for those diverse recovered resources are unveiled. Future research are encouraged to prioritize the development of integrated multi-resource recovery approaches, the establishment of regulatory frameworks to support resource recovery and product utilization, and the systematic evaluation of disposal strategies to foster a more sustainable and resource-efficient future. This work illuminates avenues for sustainable WAS management with high-valued resource recovery towards circular economy.

Development of an ion exchange process for ammonium removal and recovery from municipal wastewater using a metakaolin K-based geopolymer

Ion exchange represents a promising process for ammonium removal from municipal wastewater (MWW), in order to recover it for fertilizer production. Previous studies on ammonium ion exchange neglected the assessment of process robustness and the optimization the desorption/recovery step. This study aimed at developing a continuous-flow process of ammonium removal/recovery based on a metakaolin K-based geopolymer, named G13. Process robustness was assessed by operating 7 adsorption/desorption cycles with two types of MWW. These tests resulted in satisfactory and constant performances: operating capacity at 40 mgN L-1 in the inlet = 12 mgN gdry sorbent-1, bed volumes of treated MWW at the selected breakpoint = 199-226, ammonium adsorption yield = 88-91%. Empty bed contact time (EBCT) was decreased from 10 to 5 min without any reduction in performances. The NH4+ adsorption process was effectively simulated by the Thomas model, allowing a model-based assessment of the effect of EBCT reductions on process performances. An innovative desorption procedure led to high ammonium recovery yields (86-100%) and to a desorbed product composed primarily of KNO3 (54%w) and NH4NO3 (39%w), two salts largely used in commercial fertilizers. The energy consumption of ammonium removal/recovery with G13 resulted 0.027 kWh m-3treated WW, with a relevant reduction in comparison to traditional nitrification/denitrification, whereas the operational cost resulted equal to 60-110% of the cost of the benchmark process. These results show that G13 is a promising material to recover ammonium in a circular economy approach.

Simultaneous deammoniation and denitrification under vacuum ultraviolet irradiation

The oxidative nitrate (NO3-) and reductive ammonium (NH4+) constitute the common nitrogen pollution in water. However, the high energy barrier of the comproportionation reaction makes it challenging for the deammoniation and denitrification reactions to occur simultaneously. This study evaluated the performance of simultaneous deammoniation and denitrification under vacuum ultraviolet (VUV) irradiation. The results demonstrate that the reduction reaction of NO3- and the oxidation reaction of NH4+ conform to the pseudo-first-order reaction kinetics, with respective kinetic constants of 0.012 min-1 and 0.002 min-1. The presence of Cl- and SO42- inhibits the reduction of NO3-, while HCO3- and CO32- promote NO3- reduction and NH4+ oxidation. The reaction mechanism of simultaneous NO3- and NH4+ removal was proven through free radical capture and electron spin resonance (ESR) experiments. It was determined that NO3- was reduced to NO2-, NH4+, and N2 by hydrated electrons (eaq-) in turn. While the free hydroxyl radical (·OH) produced by direct photolysis of water by VUV was identified as the key to the oxidation of NH4+. When NO3- and NH4+ coexist, they can capture eaq- and ·OH, respectively, thus avoiding the quenching of the two highly active species. Thus, energy waste is avoided and nitrogen removal efficiency is improved. The process study shows that the adjustment of the NO3- and NH4+ ratio and the control of process conditions are essential for the synchronous conversion of nitrate and ammonium.

Photocatalysis coupled electro-Fenton process for treatment of acrylamide wastewater: an optimised study

Electro-Fenton is a commonly used approach for pollutant removal from different wastewater that requires high energy consumption. Coupling electro-Fenton with solar energy could potentially overcome high power consumption. Thus, this study combined photocatalysis with three-dimensional electro-Fenton to treat acrylamide (AM) wastewater. The removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), and total organic carbon (TOC) in photocatalysis-coupled electro-Fenton were studied. The effects of current density, iron powder dosage, plate spacing, and photocatalyst dosage on COD and NH3-N removal were also optimised using response surface methodology (RSM). The photocatalysis coupled three-dimensional electro-Fenton reduced energy consumption compared to single photocatalysis or electro-Fenton technology. The COD and NH3-N removal rates were 82.444% and 92.810%, respectively, at the current density of 16.000 mA/cm2, iron powder dosage of 1.330 g, plate spacing of 16.643 mm, photocatalyst dosage of 0.2 g. This study demonstrated that organic pollutants can be degraded efficiently at a low concentration of catalysts coupled with the electro-Fenton process, offering a low-energy consumption treatment of wastewater.

Ammonia recovery via direct contact membrane distillation: Modeling and performance optimization

Ammonia recovery from wastewater has positive environmental benefits, avoiding eutrophication and reducing production energy consumption, which is one of the most effective ways to manage nutrients in wastewater. Specifically, ammonia recovery by membrane distillation has been gradually adopted due to its excellent separation properties for volatile substances. However, the global optimization of direct contact membrane distillation (DCMD) operating parameters to maximize ammonia recovery efficiency (ARE) has not been attempted. In this work, three key operating factors affecting ammonia recovery, i.e., feed ammonia concentration, feed pH, and DCMD running time, were identified from eight factors, by a two-level Plackett-Burman Design (PBD). Subsequently, Box-Behnken design (BBD) under the response surface methodology (RSM) was used to model and optimize the significant operating parameters affecting the recovery of ammonia though DCMD identified by PBD and statistically verified by analysis of variance (ANOVA). Results showed that the model had a high coefficient of determination value (R2 = 0.99), and the interaction between NH4Cl concentration and feed pH had a significant effect on ARE. The optimal operating parameters of DCMD as follows: NH4Cl concentration of 0.46 g/L, feed pH of 10.6, DCMD running time of 11.3 h, and the maximum value of ARE was 98.46%. Under the optimized conditions, ARE reached up to 98.72%, which matched the predicted value and verified the validity and reliability of the model for the optimization of ammonia recovery by DCMD process.

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.

Treatment appraisal and fate of HMs in up-flow anaerobic sludge blanket and trickling filter-based sewage treatment process: The case of a kaliti Centralized Wastewater Treatment Plant, Addis Ababa, Ethiopia

Heavy metals (HMs) in wastewater could pose a significant challenge to biological treatment systems such as in an Up-flow Anaerobic Sludge Blanket Reactor (UASBr) as well as Trickling Filter (TF) performances. These HMs are associated with retention and accumulation of solid precipitates, limitting solid-liquid separation, disrupting biochemical processes, which ultimately brings environmental risks, such as soil contamination and public health issues, dominantly due to the inhibited activities of degrading microorganisms. A cross-sectional study was applied to investigate the levels of HMs in sewage using composite and grab sampling taken from Kaliti Wastewater Treatment Plant and the samples were analyzed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The HMs concentrations in mean±(SD) were, Ag ranges from below detection level (BDL) to 63.5 (13.5) mg/kg; Ba 60 (4.47) μg/l to 1291(58.5) mg/kg; Al, BDL to 2358.5(662.5) mg/kg; Cd 0 μg/l to 0.35(0.15) mg/kg; Cr 0 μg/l to 10.5(0.7) mg/kg; Cu 0 μg/l to 23.9(1.2) mg/kg; Zn 5.45 (12.3) to 165(5.4) mg/kg, and Mn 165 (49.5) μg/l to 92.5(3.8) mg/kg. Results indicated that Kaliti Wastewater Treatment Plant was effective in removing pollutants and thereby meeting local and international discharge limits. The plant was also found to be effective in removing Al, Cd, Cu, and Cr, but not in removing Ba and Zn. However, a real time data collection and monitoring of seasonal physicochemical parameters and HM levels in the wastewater treatment plant is suggested useful.

Electro-oxidation of ammonia nitrogen using W, Ti-doped IrO2 DSA as a treatment method for mariculture and livestock wastewater

Animal farming wastewater is one of the most important sources of ammonia nitrogen (NH4+-N) emissions. Electro-oxidation can be a viable solution for removing NH4+-N in wastewater. Compared with other treatment methods, electro-oxidation has the advantages of i) high removal efficiency, ii) smaller size of treatment facilities, and iii) complete removal of contaminant. In this study, a previously prepared DSA (W, Ti-doped IrO2) was used for electro-oxidation of synthetic mariculture and livestock wastewater. The DSA was tested for chlorine evolution reaction (CER) activity, and the reaction kinetics was investigated. CER current efficiency reaches 60-80% in mariculture wastewater and less than 20% in livestock wastewater. In the absence of NH4+-N, the generation of active chlorine follows zero-order kinetics and its consumption follows first-order kinetics, with cathodic reduction being its main consumption pathway, rather than escape or conversion to ClO3-. Cyclic voltammetry experiments show that NH4+-N in the form of NH3 can be oxidized directly on the anode surface. In addition, the generated active chlorine combines with NH4+-N at a fast rate near the anode, rather than in the bulk solution. In electrolysis experiments, the NH4+-N removal rate in synthetic mariculture wastewater (30-40 mg/L NH4+-N) and livestock wastewater (~ 450 mg/L NH4+-N) is 112.9 g NH4+-N/(m2·d) and 186.5 g NH4+-N/(m2·d), respectively, which is much more efficient than biological treatment. The specific energy consumption (SEC) in synthetic mariculture wastewater is 31.5 kWh/kg NH4+-N, comparable to other modified electro-catalysts reported in the literature. However, in synthetic livestock wastewater, the SEC is as high as 260 kWh/kg NH4+-N, mainly due to the suppression of active chlorine generation by HCO3- and the generation of NO3- as a by-product. Therefore, we conclude that electro-oxidation is suitable for mariculture wastewater treatment, but is not recommended for livestock wastewater. Electrolysis prior to urea hydrolysis may enhance the treatment efficiency in livestock wastewater.

Stress Responses and Ammonia Nitrogen Removal Efficiency of Oocystis lacustris in Saline Ammonium-Contaminated Wastewater Treatment

The increasing concern over climate change has spurred significant interest in exploring the potential of microalgae for wastewater treatment. Among the various types of industrial wastewaters, high-salinity NH4+-N wastewater stands out as a common challenge. Investigating microalgae's resilience to NH4+-N under high-salinity conditions and their efficacy in NH4+-N utilization is crucial for advancing industrial wastewater microalgae treatment technologies. This study evaluated the effectiveness of employing nitrogen-efficient microalgae, specifically Oocystis lacustris, for NH4+-N removal from saline wastewater. The results revealed Oocystis lacustris's tolerance to a Na2SO4 concentration of 5 g/L. When the Na2SO4 concentration reached 10 g/L, the growth inhibition experienced by Oocystis lacustris began to decrease on the 6th day of cultivation, with significant alleviation observed by the 7th day. Additionally, the toxic mechanism of saline NH4+-N wastewater on Oocystis lacustris was analyzed through various parameters, including chlorophyll-a, soluble protein, oxidative stress indicators, key nitrogen metabolism enzymes, and microscopic observations of algal cells. The results demonstrated that when the Oocystis lacustris was in the stationary growth phase with an initial density of 2 × 107 cells/L, NH4+-N concentrations of 1, 5, and 10 mg/L achieved almost 100% removal of the microalgae on the 1st, 2nd, and 4th days of treatment, respectively. On the other hand, saline NH4+-N wastewater minimally impacted photosynthesis, protein synthesis, and antioxidant systems within algal cells. Additionally, NH4+-N within the cells was assimilated into glutamic acid through glutamate dehydrogenase-mediated pathways besides the conventional pathway involving NH4+-N conversion into glutamine and assimilation amino acids.

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. Molecules 2024;29:2185. [PMID: 38792046 PMCID: PMC11123745 DOI: 10.3390/molecules29102185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

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.

From sustainable feedstocks to microbial foods

Climate change-induced alterations in weather patterns, such as frequent and severe heatwaves, cold waves, droughts, floods, heavy rain and storms, are reducing crop yields and agricultural productivity. At the same time, greenhouse gases arising from food production and supply account for almost 30% of anthropogenic emissions. This vicious circle is producing a global food crisis. Sustainable food resources and production systems are needed now, and microbial foods are one possible solution. In this Perspective, we highlight the most promising technologies, and carbon and energy sources, for microbial food production.

Ammonia removal mitigates white plague type II in the coral Pocillopora damicornis

White Plague Type II (WPL II) is a disease increasingly affecting scleractinian coral species and progresses rapidly. However, the etiological pathogen and remedy remain elusive. In this study, transmission experiments demonstrated that Aureimonas altamirensis and Aurantimonas coralicida, representing the WPL II pathogens, could infect Pocillopora damicorni. The infection produced selected pathological symptoms, including bleaching, tissue loss, and decolorization. Furthermore, ammonia degradation significantly reduced the severity of infection by these pathogens, indicating that ammonia may be a virulence factor for WPL II. Coral microbiome analysis suggested that ammonia degradation mediates the anti-white plague effect by maintaining the density of Symbiodiniaceae and stabilizing the core and symbiotic bacteria. Aureimonas altamirensis and Aurantimonas coralicida have been shown to cause diseases of P. damicornis, with ammonia acting as a virulence factor, and ammoniac degradation may be a promising and innovative approach to mitigate coral mortality suffering from increasing diseases.

Solar photo-Fenton and persulphate-based processes for landfill leachate treatment: A critical review

Landfilling is the most usual solid waste management strategy for solid residues disposal. However, it entails several drawbacks such as the generation of landfill leachate that seriously threaten human life and the environment due to their toxicity and carcinogenic character. Among various technologies, solar photo-Fenton and sulphate-based processes have proven to be suitable for the treatment of these polluted streams. This review critically summarises the last three decades of studies in this field. It is found that the solar homogeneous photo-Fenton process should be preferably used as a pre- and post-treatment of biological technologies and as a standalone treatment for young, medium, and mature leachates, respectively. Studies on heterogeneous solar photo-Fenton process are lacking so that this technology may be scaled-up for industrial applications. Sulphate radicals are attractive for removing both COD and ammonia. However, no study has been reported on solar sulphate activation for landfill leachate treatment. This review discusses the main advances and challenges on treating landfill leachate through solar AOPs, it compares solar photo-Fenton and solar persulphate-based treatments, indicates the future research directions and contributes for a better understanding of these technologies towards sustainable treatment of landfill leachate in sunny and not-so-sunny regions.

Towards a sustainable transformation of municipal wastewater treatment plants into biofactories using advanced NH3-N recovery technologies: A review

Ammonia (NH3), as a prevalent pollutant in municipal wastewater discharges, can impair aquatic life and have a negatively impact on the environment. Proper wastewater treatment and management practices are essential to protect ecosystems and keep human populations healthy. Therefore, using highly effective NH3-N recovery technologies at wastewater treatment plants (WWTPs) is widely acknowledged as a necessity. In order to improve the overall efficiency of NH3 removal/recovery processes, innovative technologies have been generally applied to reduce its concentration when discharged into natural water bodies. This study reviews the current status of the main issues affecting NH3 recovery from municipal/domestic wastewater discharges. The current study investigated the ability to recover valuable resources, e.g., nutrients, regenerated water, and energy in the form of biogas through advanced and innovative methods in tertiary treatment to achieve higher efficiency towards sustainable wastewater and resource recovery facilities (W&RRFs). In addition, the concept of paradigm shifts from WWTP to a large/full scale W&RRF has been studied with several examples of conversion to innovative bio-factories producing materials. On the other hand, the carbon footprint and the high-energy consumption of the WWTPs were also considered to assess the sustainability of these facilities.

In-situ microbial protein production by using nitrogen extracted from multifunctional bio-electrochemical system

Upgrading of waste nitrogen sources is considered as an important approach to promote sustainable development. In this study, a multifunctional bio-electrochemical system with three chambers was established, innovatively achieving 2.02 g/L in-situ microbial protein (MP) production via hydrogen-oxidizing bacteria (HOB) in the protein chamber (middle chamber), along with over 2.9 L CO2/(L·d) consumption rate. Also, 69% chemical oxygen demand was degraded by electrogenic bacteria in the anode chamber, resulting in the 394.67 J/L electricity generation. Focusing on the NH4+-N migration in the system, the current intensity contributed 4%-9% in the anode and protein chamber, whereas, the negative effect of -6.69% on contribution was shown in the cathode chamber. On the view of kinetics, NH4+-N migration in anode and cathode chambers was fitted well with Levenberg-Marquardt equation (R2 > 0.92), along with the well-matched results of HOB growth in the protein chamber based on Gompertz model (R2 > 0.99). Further evaluating MPs produced by HOB, 0.45 g/L essential amino acids was detected, showing the better amino acid profile than fish and soybean. Multifunctional bio-electrochemical system revealed the economic potential of producing 6.69 €/m3 wastewater according to a simplified economic evaluation.

Combined zeolite-based ammonia slow-release and algae-yeast consortia to treat piggery wastewater: Improved nitrogen and carbon migration

Integration of zeolite-based ammonia adsorption and algae-yeast consortia was developed to remediate piggery wastewater (PW) containing high concentrations of total ammonia nitrogen (TAN) and total organic carbon (TOC). After optimizing the conditions of ammonia adsorption in the PW. Zeolite addition mitigated ammonia toxicity, allowing zeolites to gradually release ammonia while effectively attenuating algal oxidative stress caused by high TAN concentration. Coupling zeolite-based adsorption and yeast co-incubation further increased TOC degradation and available C/N ratio, thus improving biomass (4.51 g/L), oil yield (2.11 g/L), and nutrient removal (84.18%-99.14%). The integrated microalgae-based PW treatment exhibited higher carbon migration into biomass (46.14%) and reduced treatment costs than conventional approaches. Simultaneously, the lowest carbon migration to wastewater also meant the smallest carbon emission into water bodies. These findings demonstrate that this novel strategy can remove nutrients in raw PW effectively and produce high oil-rich biomass in a sustainable and environmentally-friendly manner.

Evaluation of volatile fatty acids and ammonia recovery approach from landfill leachate using pilot-scale mechanical vapor recompression

Treatment of landfill leachate is still a current problem due to the high treatment costs in addition to the difficulty of meeting the discharge criteria. However, there is a more important issue that should be underlined; it is also valuable compounds that leachate contains. Conventional methods used for treatment of leachate such as membrane filtration, advanced oxidation processes, biological processes and their combinations have largely focused on treatment. However, the recovery of ammonia and volatile organic acids (VFA) in leachate is a promising approach both to overcome high treatment costs and to sustainably manage leachate. In this study, leachate treatment potential was investigated by mechanical vapor recompression (MVR) process, which offers an operational opportunity to recover high value-added products from leachate while providing an effective treatment for wastewater. Optimum operating conditions for the pilot-scale MVR process have been determined by laboratory-scale studies. VFAs were recovered as organic acid salts from the pilot-scale MVR distillate, while ammonia recovery was accomplished as ammonium sulfate from a highly contaminated concentrate stream. VFA and ammonia recovery rates were 89% and 99%, respectively. The treatment cost of leachate with MVR process was calculated according to the data obtained in pilot scale MVR studies considering the operating cost, chemical cost and economical contribution of value-added products. The results showed that the integrated MVR-crystallization process, all treatment costs are covered, with a net gain of 3.8 USD/m3. Consequently, MVR integrated crystallization process offers an economical and sustainable solution for the treatment of leachate by recovering valuable products.

Poly(vinyl alcohol)/modified porous starch gel beads for microbial preservation and reactivation: preparation, characterization and its wastewater treatment performance

Poly(vinyl alcohol) (PVA)/modified porous starch (MPS) gel beads were prepared through in situ chemical cross-linking by incorporating with MPS, which was obtained by modifying porous starch (PS) with polyethyleneimine (PEI) and glutaraldehyde (GA). Addition of MPS could improve the storage modulus and the effective crosslinking density (ve) of the gel beads, and the mechanical properties were enhanced. The PVA-MPS gel beads were preserved as immobilized microbial carriers for 40 d and reactivated in wastewater. Scanning electron microscope (SEM) observations showed that the beads were highly porous and conducive for microorganism adhesion. The PVA-MPS gel beads were able to remove 97% of ammonia nitrogen and 80% of chemical oxygen demand (COD) after reactivation under all four preservation conditions. The abundance of Hydrogenophaga as denitrifying bacteria on PVA-MPS gel beads increased, with abundance of 8.44%, 5.55%, 8.90% and 9.48%, respectively. It proved that the carrier provided a partial hypoxic environment for microorganisms.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400 °C for 2 h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00 mg L-1 by the DTCA-Na was more than 80% when the contact time was 60 min, pH was 6-10, the dosage of adsorbent was 1.00 g, and the temperature was 25 °C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.

Microalgae and biogas: a boon to energy sector

The global energy generation market immensely depends on fossil fuels which balances our survival on this planet. Energy can be called as the "master element" for our daily needs, starting from household power supply, agricultural purpose, automobile and transportation, industrial workload to economic and research domains. Fuel switching initiatives are being adapted by environmentalist and scientists to bring a novel sustainable source of energy. An environment and renewable alternative to fossil fuels are a must. Over the years, the world has shifted toward generating green fuels immensely. One such potential alternative to fossil fuels are biogases. Being versatile and renewable in nature, it has drawn immense attention globally. Despite having such potentials there exist some major drawbacks which mainly deal with the starting material. One such source for biogases can be microalgae. Microalgae based biogas production can produce huge amount of energy and that has been implemented by many foreign countries and their companies. Despite being in use in many countries, there are issues which needs to be addressed which will overall improve the biogas potential from microalgae even more. This review mainly focuses on generation of biogas from microalgae as a feedstock which are very economical and sustainable in its nature, presenting improvement strategies which can be impended to boost the over biogas sector globally.

Renewable energy driven electroreduction nitrate to ammonia and in-situ ammonia recovery via a flow-through coupled device

Green ammonia production from wastewater via electrochemical nitrate reduction contributes substantially to the realization of carbon neutrality. Nonetheless, the current electrochemical technology is largely limited by the lack of suitable device for efficient and continuous electroreduction nitrate into ammonia and in-situ ammonia recovery. Here, we report a flow-through coupled device composed of a compact electrocatalytic cell for efficient nitrate reduction and a unit to separate the produced ammonia without any pH adjustment and additional energy-input from the circulating nitrate-containing wastewater. Using an efficient and selective Cl-modified Cu foam electrode, nearly 100% NO3- electroreduction efficiency and over 82.5% NH3 Faradaic efficiency was realized for a wide range of nitrate-containing wastewater from 50 to 200 mg NO3--N L-1. Moreover, this flow-through coupled device can continuingly operate at a large current of 800 mA over 100 h with a sustained NH3 yield rate of 420 μg h-1 cm-2 for nitrate-containing wastewater treatment (50 mg NO3--N L-1). When driven by solar energy, the flow-through coupled device can also exhibit exceptional real wastewater treatment performance, delivering great potential for practical application. This work paves a new avenue for clean energy production and environmental sustainability as well as carbon neutrality.

Optimizing total ammonia-nitrogen concentration for enhanced microbial fuel cell performance in landfill leachate treatment: a bibliometric analysis and future directions

Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia-nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011-2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject's ten most productive universities. Most studies found that maintaining TAN concentrations in the 400-800 mg L-1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.

Development of a green fermentation strategy with resource cycle for the docosahexaenoic acid production by Schizochytrium sp

The fermentation production of docosahexaenoic acid (DHA) is an industrial process with huge consumption of freshwater resource and nutrient, such as carbon sources and nitrogen sources. In this study, seawater and fermentation wastewater were introduced into the fermentation production of DHA, which could solve the problem of fermentation industry competing with humans for freshwater. In addition, a green fermentation strategy with pH control using waste ammonia, NaOH and citric acid as well as FW recycling was proposed. It could provide a stable external environment for cell growth and lipid synthesis while alleviating the dependence on organic nitrogen sources of Schizochytrium sp. It was proved that this strategy has good industrialization potential for DHA production, and the biomass, lipid and DHA yield reached to 195.8 g/L, 74.4 g/L and 46.4 g/L in 50 L bioreactor, respectively. This study provides a green and economic bioprocess technology for DHA production by Schizochytrium sp.

Nitrite-resistance mechanisms on wastewater treatment in denitrifying phosphorus removal process revealed by machine learning, co-occurrence, and metagenomics analysis

Nitrite is a key intermediate in nitrogen metabolism that determines microbial transformations of N and P, greenhouse gas (N₂O) emissions, and system nutrient removal efficiency. However, nitrite also exerts toxic effects on microorganisms. A lack of understanding of high nitrite-resistance mechanisms at community- and genome-scale resolutions hinders the optimization for robustness of wastewater treatment systems. Here, we established nitrite-dependent denitrifying and phosphorus removal (DPR) systems under a gradient concentration of nitrite (0, 5, 10, 15, 20, and 25 mg N/L), relying on 16S rRNA gene amplicon and metagenomics to explore high nitrite-resistance mechanism. The results demonstrated that specific taxa were adopted to change the metabolic relationship of the community through phenotypic evolution to resist toxic nitrite contributing to the enhancement of denitrification and inhibition of nitrification and phosphorus removal. The key specific species, Thauera enhanced denitrification, whereas Candidatus Nitrotoga decreased in abundance to maintain partial nitrification. The extinction of Candidatus Nitrotoga induced a simpler restructuring-community, forcing high nitrite-stimulating microbiome to establish a more focused denitrification rather than nitrification or P metabolism in response to nitrite toxicity. Our work provides insights for understanding microbiome adaptation to toxic nitrite and giving theoretical support for operation strategy of nitrite-based wastewater treatment technology.

Electrochemical removal of ammonium nitrogen in high efficiency and N2 selectivity using non-noble single-atomic iron catalyst

Ammonia nitrogen (NH₄⁺-N) is a ubiquitous environmental pollutant, especially in offshore aquaculture systems. Electrochemical oxidation is very promising to remove NH₄⁺-N, but suffers from the use of precious metals anodes. In this work, a robust and cheap electrocatalyst, iron single-atoms distributed in nitrogen-doped carbon (Fe-SAs/N-C), was developed for electrochemical removal of NH₄⁺-N from in wastewater containing chloride. The Fe-SAs/N-C catalyst exhibited superior activity than that of iron nanoparticles loaded carbon (Fe-NPs/N-C), unmodified carbon and conventional Ti/IrO₂-TiO₂-RuO₂ electrodes. And high removal efficiency (> 99%) could be achieved as well as high N₂ selectivity (99.5%) at low current density. Further experiments and density functional theory (DFT) calculations demonstrated the indispensable role of single-atom iron in the promoted generation of chloride derived species for efficient removal of NH₄⁺-N. This study provides promising inexpensive catalysts for NH₄⁺-N removal in aquaculture wastewater.

A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes

Discharging large amounts of domestic and industrial wastewater drastically increases the reactive nitrogen content in aquatic ecosystems, which causes severe ecological stress and biodiversity loss. This paper reviews three common types of denitrification processes, including physical, chemical, and biological processes, and mainly focuses on the membrane technology for nitrogen recovery. The applicable conditions and effects of various treatment methods, as well as the advantages, disadvantages, and influencing factors of membrane technologies, are summarized. Finally, it is proposed that developing effective combinations of different treatment methods and researching new processes with high efficiency, economy, and energy savings, such as microbial fuel cells and anaerobic osmotic membrane bioreactors, are the research and development directions of wastewater treatment processes.

A review on membrane concentrate management from landfill leachate treatment plants: The relevance of resource recovery to close the leachate treatment loop

Membrane filtration processes have been used to treat landfill leachate. On the other hand, closing the leachate treatment loop and finding a final destination for landfill leachate membrane concentrate (LLMC) - residual stream of membrane systems - is challenging for landfill operators. The re-introduction of LLMC into the landfill is typical; however, this approach is critical as concentrate pollutants may accumulate in the leachate treatment facility. From that, leachate concentrate management based on resource recovery rather than conventional treatment and disposal is recommended. This work comprehensively reviews the state-of-the-art of current research on LLMC management from leachate treatment plants towards a resource recovery approach. A general recovery train based on the main LLMC characteristics for implementing the best recovery scheme is presented in this context. LLMCs could be handled by producing clean water and add-value materials. This paper offers critical insights into LLMC management and highlights future research trends.

Ampere-level current density ammonia electrochemical synthesis using CuCo nanosheets simulating nitrite reductase bifunctional nature

The development of electrocatalysts capable of efficient reduction of nitrate (NO₃^-) to ammonia (NH₃) is drawing increasing interest for the sake of low carbon emission and environmental protection. Herein, we present a CuCo bimetallic catalyst able to imitate the bifunctional nature of copper-type nitrite reductase, which could easily remove NO₂^- via the collaboration of two active centers. Indeed, Co acts as an electron/proton donating center, while Cu facilitates NO_x^- adsorption/association. The bio-inspired CuCo nanosheet electrocatalyst delivers a 100 ± 1% Faradaic efficiency at an ampere-level current density of 1035 mA cm^-2 at -0.2 V vs. Reversible Hydrogen Electrode. The NH₃ production rate reaches a high activity of 4.8 mmol cm^-2 h^-1 (960 mmol g_cat^-1 h^-1). A mechanistic study, using electrochemical in situ Fourier transform infrared spectroscopy and shell-isolated nanoparticle enhanced Raman spectroscopy, reveals a strong synergy between Cu and Co, with Co sites promoting the hydrogenation of NO₃^- to NH₃ via adsorbed *H species. The well-modulated coverage of adsorbed *H and *NO₃ led simultaneously to high NH₃ selectivity and yield.

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.

Thermally Modified Palygorskite Usage as Adsorbent in Fixed-Bed Reactor for High Concentration NH4+-N Removal and Further Application as N-Fertilizer in Hydroponic Cultivation

Palygorskite sample (Pal) underwent thermal treatment at 400 °C (T-Pal) to be used as adsorbent for the removal of 200 mg NH₄⁺-N/L from artificial solution. After thermal treatment, the sample was characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). For NH₄⁺-N removal, T-Pal was added as a bed matrix in fixed-bed reactor experiments and the effect of flow rate was determined. It was indicated that with the flow rate increase from 10 mL/min to 50 mL/min, fewer liters of the solution were purified, rendering a longer residual time of interactions, which is optimal for NH₄⁺-N removal from T-Pal. The maximum removed amount was calculated at 978 mg NH₄⁺-N (q_total), suggesting T-Pal is a promising ammonium adsorbent. The data of kinetic experiments were applied to Clark, Yoon-Nelson, and Thomas kinetic models, with Clark having the best fit, highlighting a heterogenous adsorption. At the end of kinetic experiments, T-Pal applied in hydroponic cultivations and presented a sufficient release rate, which was found utilizable for saturated T-Pal usage as N fertilizer that satisfactory results were deemed concerning lettuces characteristics and growth.

Advanced organic recovery from municipal wastewater with an enhanced magnetic separation (EMS) system: Pilot-scale verification

The up-concentration process has been demonstrated as an attractive approach to carbon-neutral wastewater treatment. Innovation in the separation processes can help eliminate the current heavy dependence on gravity, and credible pilot-scale verification is crucial for application promotion. We hereby proposed a pilot-scale enhanced magnetic separation (EMS) system as an up-concentration step to maximize energy recovery from municipal wastewater. The design of EMS was based on the hypothesis that magnetic-driven separation could be a breakthrough in separation speed, and adsorption could further enhance the separation efficiency by capturing soluble substances. Jar tests confirmed the feasibility of activated carbon adsorption, which could also roughen the surface of aggregates. Further, over one-year operation of a 300 m³/d EMS equipment provided optimum operation strategies and evidence of system effectiveness. More than 80% of particulate organics and 60% of soluble organics were removed within 10 min at an energy consumption of only 0.036 kWh/m³. The characteristics of sludge were clarified in terms of organic concentration, extracellular polymeric substances composition, and micro-community analysis. The anaerobic experiments further demonstrated the potential value of the concentrated products. Surprisingly, the developed EMS system exhibited significant advantages in time consumption and space occupation, with competitive operating cost and energy consumption. Overall, the results of this study posed the EMS process for up-concentration as a potential approach to organics recovery from municipal wastewater.

Electrolytic manganese residue disposal based on basic burning raw material: Heavy metals solidification/stabilization and long-term stability

Solidification/stabilization (S/S) is an option for the treatment of electrolytic manganese residue (EMR). Basic burning raw material (BRM) could successfully solidify/stabilize EMR, though heavy metals S/S mechanism and long-term stability remain unclear. Herein, Mn²⁺ and NH₄⁺ S/S behavior, hydrated BRM and S/S EMR characterization, Mn²⁺ long-term leaching behavior, phase and morphology changes for long-term leaching were discussed in detail to clarify these mechanisms. Mn²⁺ and NH₄⁺ leaching concentrations as well as pH value in S/S EMR were respectively 0.02 mg/L, 0.68 mg/L and 8.75, meeting the regulations of Chinese standard GB 8978-1996. Long-term stability of EMR was significantly enhanced after S/S. Mn²⁺ leaching concentration, Mn²⁺ migration, Mn²⁺ cumulative release, Mn²⁺ apparent diffusion coefficient and conductivity of EMR reduced to 0.05 mg/L, 5.5 × 10^-6 mg/(m²·s), ~ 9 mg/m², 6.30 × 10^-15 m²/s and 435 μs/cm. Mechanism studies showed that the hydration of BRM forms OH^-, calcium silicate hydrate gels (C-S-H) and ettringite. Therefore, during S/S process, NH₄⁺ was escaped as NH₃, Mn²⁺ was solidified/stabilized as tephroite (Mn₂SiO₄), johannsenite (CaMnSi₂O₆) and davreuxite (MnAl₆Si₄O₁₇(OH)₂), and Pb²⁺, Cu²⁺, Ni²⁺, Zn²⁺ were solidified/stabilized by C-S-H and ettringite via substitution and encapsulation. This study provides a good choice for EMR long-term stable storage.

Multiple hydrolyses of rice straw by domesticated paddy soil microbes for methane production via liquid anaerobic digestion

The aim of this study was to investigate the hydrolysis of rice straw (RS) using domesticated paddy soil microbes (DPSMs) with swine wastewater (SW) as the nitrogen source and the multiple hydrolyses for CH₄ production via liquid anaerobic digestion (L-AD). Three hydrolyses of RS with a 45% inoculation ratio (IR) under the conditions of a carbon/nitrogen ratio (C/N ratio) of 40, temperature of 37 °C, inoculum/substrate ratio (I/S ratio) of 2:1, and immersion depth of 6.0 cm were optimal, attaining maximum volatile fatty acids (VFAs) after five days, possibly owing to the synergistic effect of aerobic microbes (Firmicutes and Actinomycetes) and anaerobic microbes (Bacteroidetes and Acidobacteria). After three hydrolyses, the degradation rates of hemicellulose, cellulose, and lignin in RS were 88.45%, 83.19% and 70.09%, respectively. The accumulative CH₄ production reached 462.11 mL/g VS after three hydrolyses, and its curve fitted well with the modified Gompertz model (R² > 0.984).

Evaluation of Different Capture Solutions for Ammonia Recovery in Suspended Gas Permeable Membrane Systems

Gas permeable membranes (GPM) are a promising technology for the capture and recovery of ammonia (NH3). The work presented herein assessed the impact of the capture solution and temperature on NH3 recovery for suspended GPM systems, evaluating at a laboratory scale the performance of eight different trapping solutions (water and sulfuric, phosphoric, nitric, carbonic, carbonic, acetic, citric, and maleic acids) at 25 and 2 °C. At 25 °C, the highest NH3 capture efficiency was achieved using strong acids (87% and 77% for sulfuric and nitric acid, respectively), followed by citric and phosphoric acid (65%) and water (62%). However, a remarkable improvement was observed for phosphoric acid (+15%), citric acid (+16%), maleic acid (+22%), and water (+12%) when the capture solution was at 2 °C. The economic analysis showed that water would be the cheapest option at any working temperature, with costs of 2.13 and 2.52 €/g N (vs. 3.33 and 3.43 €/g N for sulfuric acid) in the winter and summer scenarios, respectively. As for phosphoric and citric acid, they could be promising NH3 trapping solutions in the winter months, with associated costs of 3.20 and 3.96 €/g N, respectively. Based on capture performance and economic and environmental considerations, the reported findings support that water, phosphoric acid, and citric acid can be viable alternatives to the strong acids commonly used as NH3 adsorbents in these systems.

The role of single cell protein in cellular agriculture

More food needs to be produced for the growing human population, but the possibilities of expanding the area of arable land are limited. Cellular Agriculture is an emerging field of biotechnology, aimed at finding alternatives to agricultural production of various commodities. As a part of Cellular Agriculture, the use of microbes and microalgae as food and feed with high protein content, so-called single cell protein (SCP), is gaining renewed scientific and commercial interest. In this review, we give an introduction to SCP production by heterotrophic microbial species, phototrophs, methanotrophs and autotrophic hydrogen oxidizers, as well as highlight some challenges and the latest developments in the growing SCP industry.

Optimization and Modeling of Ammonia Nitrogen Removal from High Strength Synthetic Wastewater Using Vacuum Thermal Stripping

Waste streams with high ammonia nitrogen (NH3-N) concentrations are very commonly produced due to human intervention and often end up in waterbodies with effluent discharge. The removal of NH3-N from wastewater is therefore of utmost importance to alleviate water quality issues including eutrophication and fouling. In the present study, vacuum thermal stripping of NH3-N from high strength synthetic wastewater was conducted using a rotary evaporator and the process was optimized and modeled using response surface methodology (RSM) and RSM–artificial neural network (ANN) approaches. RSM was first employed to evaluate the process performance using three independent variables, namely pH, temperature (°C) and stripping time (min), and the optimal conditions for NH3-N removal (response) were determined. Later, the obtained data from the designed experiments of RSM were used to train the ANN for predicting the responses. NH3-N removal was found to be 97.84 ± 1.86% under the optimal conditions (pH: 9.6, temperature: 65.5 °C, and stripping time: 59.6 min) and was in good agreement with the values predicted by RSM and RSM–ANN models. A statistical comparison between the models revealed the better predictability of RSM–ANN than that of the RSM. To the best of our knowledge, this is the first attempt comparing the RSM and RSM–ANN in vacuum thermal stripping of NH3-N from wastewater. The findings of this study can therefore be useful in designing and carrying out the vacuum thermal stripping process for efficient removal of NH3-N from wastewater under different operating conditions.

Toxic Effect of Ammonium Nitrogen on the Nitrification Process and Acclimatisation of Nitrifying Bacteria to High Concentrations of NH4-N in Wastewater

The aim of the conducted research was to assess the effectiveness of the nitrification process, at different concentrations of ammonium nitrogen, in biologically treated wastewater in one of the largest municipal and industrial wastewater treatment plants in Poland. The studies also attempted to acclimate nitrifying bacteria to the limited concentration of ammonium nitrogen and determined the efficiency of nitrification under the influence of acclimated activated sludge in the biological wastewater treatment system. The obtained results indicate that the concentration of ammonium nitrogen above 60.00 mg·dm−3 inhibits nitrification, even after increasing the biomass of nitrifiers. The increase in the efficiency of the nitrification process in the tested system can be obtained by using the activated sludge inoculated with nitrifiers. For this purpose, nitrifiers should be preacclimated, at least for a period of time, allowing them to colonize the activated sludge. The acclimated activated sludge allows reducing the amount of ammonium nitrogen in treated sewage by approx. 35.0%. The process of stable nitrification in the biological treatment system was observed nine days after introducing the acclimated activated sludge into the aeration chamber.

The Sensitivity of a Specific Denitrification Rate under the Dissolved Oxygen Pressure

The biological denitrification process is extensively discussed in scientific literature. The process requires anoxic conditions, but the influence of residual dissolved oxygen (DO) on the efficiency is not yet adequately documented. The present research aims to fill this gap by highlighting the effects of DO on the specific denitrification rate (SDNR) and consequently on the efficiency of the process. SDNR at a temperature of 20 °C (SDNR_20°C) is the parameter normally used for the sizing of the denitrification reactor in biological-activated sludge processes. A sensitivity analysis of SNDR_20°C to DO variations is developed. For this purpose, two of the main empirical models illustrated in the scientific literature are taken into consideration, with the addition of a deterministic third model proposed by the authors and validated by recent experimentations on several full-scale plants. In the first two models, SDNR_20°C is expressed as a function of the only variable food:microrganism ratio in denitrification (F:M_DEN), while in the third one, the dependence on DO is made explicit. The sensitivity analysis highlights all the significant dependence of SDNR_20°C on DO characterized by a logarithmic decrease with a very pronounced gradient in correspondence with low DO concentrations. Moreover, the analysis demonstrates the relatively small influence of F:M_DEN on the SDNR_20°C and on the correlation between SDNR_20°C and DO. The results confirm the great importance of minimizing DO and limiting, as much as possible, the transport of oxygen in the denitrification reactor through the incoming flows and mainly the mixed liquor recycle. Solutions to achieve this result in full-scale plants are reported.