Bio-electrochemical COD removal for energy-efficient, maximum and robust nitrogen recovery from urine through membrane aerated nitrification

Bioinspired High-Magnesium Calcite for Efficiently Reducing Chemical Oxygen Demand in Lake Water

Organic matter accumulation in water can cause serious problems such as oxygen depletion and quality deterioration of waters. While calcium carbonate has been used as green and low-cost adsorbent for water treatment, its efficiency in reducing the chemical oxygen demand (COD) of water, which is a measure of organic pollution, is restrained by the limited specific surface area and chemical activity. Herein, inspired by the high-magnesium calcite (HMC) found in biological materials, a feasible method to synthesize fluffy dumbbell-like HMC with large specific surface area is reported. The magnesium inserting increases the chemical activity of the HMC moderately but without lowering its stability too much. Therefore, the crystalline HMC can retain its phase and morphology in aqueous environment for hours, which allows the establishment of adsorption equilibrium between the solution and the adsorbent that retains its initial large specific surface area and improved chemical activity. Consequently, the HMC exhibits notably enhanced capability in reducing the COD of lake water polluted by organics. This work provides a synergistic strategy to rationally design high-performance adsorbents by simultaneously optimizing the surface area and steering the chemical activity.

Bioelectrochemically-assisted ammonia recovery from dairy manure

The sustainability of direct land application of dairy manure is challenged by significant nutrient losses. Bioelectrochemical systems for ammonia recovery offer a manure management strategy that can recover both ammoniacal and organic nitrogen as a stable ammonia fertilizer. In this research, a microbial fuel cell (MFC) was used to treat two types of dairy manure under a variety of imposed anode compartment conditions. The system achieved a maximum coulombic efficiency of 20 ± 18 % and exhibited both COD and total nitrogen removals of approximately 60 %. Furthermore, the MFC showed a maximum organic nitrogen removal of 73.8 ± 12.1 %, and no differences in organic nitrogen (orgN) removal were detected among different conditions tested. Decreasing concentrations of anolyte ammonia nitrogen coupled with the observed orgN removal from the anolyte indicate that the MFC is effective at recovering orgN in dairy manure as ammoniacal nitrogen in the catholyte. Additionally, ion competition between NH4+ and other relevant cations (Na+, K+, and Mg2+) for transport across the CEM was investigated, with only K+ showing minor competitive effects. Based on the results of this research, we propose three key processes and two sub-processes that contribute to the successful operation of the MFC for nitrogen recovery from dairy manure. Bioelectrochemical systems for nitrogen recovery from dairy manure offer a novel, robust technology for producing a valuable ammonia nitrogen fertilizer, a thus far untapped resource in dairy manure streams.

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.

Overcoming hydrogen loss in single-chamber microbial electrolysis cells by urine amendment

The effective hydrogen production in single-chamber microbial electrolysis cells (MECs) has been seriously challenged by various hydrogen consumers resulting in substantial hydrogen loss. In previous studies, the total ammonia nitrogen (TAN) has been used to inhibit certain hydrogen-consuming microorganisms to enhance hydrogen production in fermentation. In this study, we explored the feasibility of using source-separated urine to overcome hydrogen loss in the MEC, with the primary component responsible being TAN generated via urea hydrolysis. Experimental results revealed that the optimal TAN concentration ranged from 1.17 g N/L to 1.75 g N/L. Within this range, the hydrogen production rate substantially improved from less than 100 L/(m3·d) up to 520 L/(m3·d), and cathode recovery efficiency and energy recovery efficiency were greatly enhanced, with the hydrogen percentage achieved over 95 % of the total gas volume, while maintaining uninterrupted electroactivity in the anode. Compared to using chemically added TAN, using source separated urine as the source of ammonia also showed the effect of overcoming hydrogen loss but with lower Coulombic efficiency due to the complex organic components. Pre-adaptation of the reactor with urea enhanced hydrogen production by nearly 60 %. This study demonstrated the effectiveness of TAN and urine in suppressing hydrogen loss, and the results are highly relevant to MECs treating real wastewater with high TAN concentrations, particularly human fecal and urine wastewater.

A new quantitative insight: Interaction of polyethylene microplastics with soil - microbiome - crop

In this study, the interaction between primary/secondary PE MPs and soil - microbiome - crop complex system and PE MPs enrichment behavior in crops were studied by using the self-developed quantitative characterization method of Eu-MPs and in situ zymography. The results demonstrated for the first time the enrichment effect of micron-sized PE (> 10 µm) in crops, manifested as roots>leaves>stems. Primary PE MPs significantly increased soil TN, TC, SOM and β-glu activity and inhibited Phos activity. Age-PE MPs significantly reduced soil TN, TP, β-glu and Phos activities and also have significant inhibitory effects on plant height, stem diameter, and leaf dry weight of maize. Age-PE MPs significantly affected soil microbial diversity, mainly caused by bacterial genera such as UTCFX1, Sphingomonas, Subgroup-6 and Gemmatimonas. Age-PE MPs also affected some metabolism related to microbial community composition and maize growth, including Glycerolipid, Citrate cycle (TCA cycle), C5-Branched dibasic acid, Arginine and proline, Tyrosine metabolism, pentose phosphate pathway, Valine, leucine and isoleucine biosynthesis. These research results indicated that the PE MPs, which are widely present in farmland soils, can affect crop growth, soil microbial community and metabolic function after aging, thus affecting agroecosystems and terrestrial biodiversity.

Enhanced 4-bromophenol anaerobic biodegradation in electricity-stimulated anaerobic system: The key role of humic acid in reshaping microbial eco-interrelations and functions

Electricity-stimulated anaerobic system (ESAS) has shown great potential for halogenated organic pollutants removal. Exogenous redox mediators can improve electron transfer efficiency to enhance pollutants removal in ESAS. In this study, humic acid (HA), a low-cost electron mediator, was added into ESAS to enhance the simultaneous reductive debromination and mineralization of 4-bromophenol (4-BP). Results showed that the highest 4-BP removal efficiency at 48 h was 95.43 % with HA dosage of 30 mg/L at - 700 mV, which was 34.67 % higher than that without HA. The addition of HA decreased the requirement for electron donors and enriched Petrimonas and Rhodococcus for humus respiratory. HA addition regulated microbial interactions, and enhanced species cooperation between Petrimonas and dehalogenation species (Thauera and Desulfovibrio), phenol degradation-related species (Rhodococcus) as well as fermentative species (Desulfobulbus). Functional genes related to 4-BP degradation (dhaA/hemE/xylC/chnB/dmpN) and electron transfer (etfB/nuoA/qor/ccoN/coxA) were increased in abundance by HA addition. The enhanced microbial functions, as well as species cooperation and facilitation, all contributed to the improved 4-BP biodegradation in HA-added ESAS. This study provided a deep insight into microbial mechanism driven by HA and offered a promising strategy for improving halogenated organic pollutants removal from wastewater.

Ammonia recovery from organic nitrogen in synthetic dairy manure with a microbial fuel cell

Increasing pressures on the animal and cropland agriculture sectors have led to the realization of problems with animal waste management and ammonia-based fertilizer supply. Bioelectrochemical systems (BES) are a new-age technology that offer a way to address these problems. Microbial fuel cells (MFCs), one type of BES, are traditionally used for electricity generation from microbial degradation of organic matters, but can also be used to recover nutrients from wastes simultaneous with treatment. This research investigated an MFC for ammonia recovery from the organic nitrogen (orgN) fraction of synthetic dairy manure, using the simple amino acid glycine as the orgN source. We used five different synthetic manure compositions to determine their effects on MFC performance, and found minimal sacrifices in performance under orgN conditions when compared to the base condition without orgN. The MFC achieved greater than 90% COD removal in all orgN conditions. Nitrogen (N) removal efficiencies of between 40% and 60% were achieved in orgN conditions, indicating that organic nitrogen can be used as the substrate for ammonia mineralization and further recovery as fertilizer. In addition, we found the MFC was largely populated by electrogenic organisms from the phyla Bacteroidota, Firmicutes, Proteobacteria, and Halobacterota, with organisms in both Bacteroidota and Firmicutes capable of N mineralization present. Lastly, we found that in conditions where orgN is scarce and the only N source provided, microbes preferentially degraded organic matter from other dead organisms, especially as an N source. This increases the concentration of N in the MFC system and introduces important operational constraints for MFCs operated for ammonia recovery from orgN.

A novel approach for enhancing nitrogen and hydrogen recovery from urine in microbial electrochemical gas-permeable membrane system

Source-separated urine is a readily accessible nutrients dense waste stream that can be used to recover nitrogen and hydrogen. In the research, the microbial electrochemical gas-permeable membrane system (MEGS) is creatively introduced for urine treatment in removing organics, recovering the total ammonia nitrogen and high-value product of hydrogen (H₂) as well as ammonium sulfate ((NH₄)₂SO₄). MEGS can simultaneously realize the functions of H₂ recovery, in-situ efficient alkali production at the cathode, and the efficient absorption capacity of the gas-permeable membrane (GPM). Under the action of the urease enzyme, urea is hydrolyzed into large amounts of carbonic acid and ammonium, causing the pH (7.87 ± 0.13) and conductivity (5.44 ± 0.21 mS cm^-1) of the anode to increase extremely rapidly. A large amount of NH₄⁺ was transported to the cathode chamber under the strengthening effect of the electric field, enriched, and then absorbed to produce the high-quality (NH₄)₂SO₄ to be recovered. The findings reveal that MEGS can achieve 100 % of urea removal, 88.52 ± 0.40 % of COD removal, 94.22 ± 2.57 % of nitrogen recovery, 0.58 ± 0.03 m³ m^-3 d^-1 of hydrogen yield, and 3.78 kg m^-3 of (NH₄)₂SO₄ production with 78.03 ± 3.51 % of coulombic efficiency during a 30-h cycle. A benefit of $18.29 can be achieved with the recovery of (NH₄)₂SO₄ and H₂ from 1 m³ of urine. The study presents a promising idea for the efficient nutrient-energy recovery and utilization of urine.

Performance of pilot-scale membrane aerated biofilm reactors integrated with anoxic nano-biotechnological reactor for domestic wastewater treatment

Membrane-aerated biofilm reactors (MABRs) have aroused increasing attention due to their excellent performance in treating wastewater, where the membranes behave as bio-carriers for microorganisms and bubbleless air diffusers. The MABR technology has not been fully commercialized due to reactor design and low total nitrogen (TN) removal efficiency at short hydraulic retention times (HRT). In this study, a hybrid system of MABR 1 integrated with an anoxic nano-biotechnological reactor filled with Granulated Nanoscale Oxyhydroxides of Fe (GNOF) media was evaluated to assess the improvement in nitrogen removal performance at 12, 10, and 4 h of HRTs. At the same time, another MABR (MABR 2) was operated individually at 12, 10, 8, 6, 4, and 2 h of HRTs to assess the influence of HRT on nitrogen removal performance. An enhancement in removal performance was reported in the hybrid MABR-GNOF, achieving the highest removal efficiencies of 74.3 ± 3.1% for ammonium nitrogen (NH₄⁺-N), 69.8 ± 2.1% for total nitrogen (TN), and 90.9 ± 1.7% for chemical oxygen demand (COD), at 12 h HRT. The hybrid MABR-GNOF system attained 18% higher nitrogen removal than the MABR-only system at 12 h of HRT. A simultaneous anoxic nitrification-denitrification and COD oxidation might be developed for the removal of COD, NH₄⁺-N, and TN from domestic wastewater by using GNOF as an electron acceptor in the hybrid MABR-GNOF unit. The findings in this study confirmed the possibility of integration of GNOF and MABR on a pilot scale and are promising for the application of this hybrid system on a full scale.

Electricity-Driven Microbial Metabolism of Carbon and Nitrogen: A Waste-to-Resource Solution

Electricity-driven microbial metabolism relies on the extracellular electron transfer (EET) process between microbes and electrodes and provides promise for resource recovery from wastewater and industrial discharges. Over the past decades, tremendous efforts have been dedicated to designing electrocatalysts and microbes, as well as hybrid systems to push this approach toward industrial adoption. This paper summarizes these advances in order to facilitate a better understanding of electricity-driven microbial metabolism as a sustainable waste-to-resource solution. Quantitative comparisons of microbial electrosynthesis and abiotic electrosynthesis are made, and the strategy of electrocatalyst-assisted microbial electrosynthesis is critically discussed. Nitrogen recovery processes including microbial electrochemical N₂ fixation, electrocatalytic N₂ reduction, dissimilatory nitrate reduction to ammonium (DNRA), and abiotic electrochemical nitrate reduction to ammonia (Abio-NRA) are systematically reviewed. Furthermore, the synchronous metabolism of carbon and nitrogen using hybrid inorganic-biological systems is discussed, including advanced physicochemical, microbial, and electrochemical characterizations involved in this field. Finally, perspectives for future trends are presented. The paper provides valuable insights on the potential contribution of electricity-driven microbial valorization of waste carbon and nitrogen toward a green and sustainable society.

Long-term stability of reactor microbiome through bioaugmentation with Alcaligenes aquatilis AS1 promotes nitrogen removal of piggery wastewater

Bioaugmentation is considered as an attractive method for nitrogen removal in water treatment, but its effectiveness in actual high-strength piggery wastewater has not been adequately verified and the mechanism of bioaugmentation in actual wastewater treatment system is not very clear especially from the perspectives of microbial communities and functional genes. This study investigated the mechanisms of a heterotrophic nitrifying-aerobic denitrifying strain Alcaligenes aquatilis AS1 in the bioaugmentation of continuous biological nitrogen removal of actual piggery wastewater at laboratory scale. The addition of strain AS1 significantly improved the nitrogen removal efficiency (more than 95% of NH₄⁺-N and 75% of TN were removed) and raised the activated sludge resistance to shock loading. AS1 addition also significantly shifted the microbiota structure and interactions among microbial networks were enhanced to obtain the stable bacterial communities. Moreover, strain AS1 achieved effective proliferation and long-term colonization in activated sludge with a relative abundance of genus Alcaligenes more than 70% during the whole operation process and played a dominant role in biological nitrogen removal, while different genera were respectively enriched and involved in pollutants removal at different stages in the control group. In addition, the abundances of most functional genes involved in carbon (C) degradation, carbon fixation and nitrogen (N), phosphorus (P), sulfur (S) cycling in activated sludge were significantly increased in reactor AS1, indicating that strain AS1 not only relied on its unique C and N metabolic activities, but also recruited microorganisms with diverse functions to jointly remove pollutants in wastewater, which could be a common bioaugmentation mechanism in open reactors. This study proves the promising application prospect of strain AS1 in the treatment of high-strength piggery wastewater and shows great importance for guiding bioaugmentation application of functional strains in practical wastewater treatment systems.

Mechanism insights into enhanced treatment of wasted activated sludge by hydrogen-mediated anaerobic digestion

In the current study, different forms of added gas including H₂, CO₂, and mixed gas (V_H2:V_CO2 = 4:1), as well as different hydrogen partial pressures (0.10, 0.30, and 0.50 atm) were investigated for the influence on anaerobic performance in waste activated sludge (WAS) treatment. The mixed gas significantly improved methane production by over 20%, which positively correlated with the hydrogen partial pressure. However, pure H₂ (0.5 atm) heavily inhibited methane production by 76.5%. Combined with the microbial metabolic activity study, H₂ accelerated the hydrolysis process. Afterward, mixing with CO₂ accelerated H₂ and organic consumption, thus promoting WAS degradation and methane production. Based on the most extra release of organics, the mixed group exerted the superior performance with hydrogen partial pressure at 0.3 atm. The microbial community analysis evidenced that mixed gas enriched proteolytic and homoacetogenic bacteria and hybrid-trophic methanogens. By metagenomics study, hydrolysis, acetogenic, and methanogenesis pathways were all enhanced via the exogenous addition of H₂ and CO₂, sustainably transforming WAS towards CH₄. This study discovered the mechanism of the enhanced conversion from WAS to CH₄ by exogenous H₂ and provided a promising approach for WAS reduction and energy recovery.

Distribution of microbial communities in seasonally frozen soil layers on the Tibetan Plateau and the driving environmental factors

Large stocks of carbon and nitrogen stored in permafrost regions can potentially feed back to global biogeochemical cycles under climate warming. To understand the response of microbial communities to environmental changes, this study investigated the spatial distribution of bacterial communities in the upper layers (0-10, 10-20, and 20-30 cm) of seasonally frozen soil on the Tibetan Plateau and their relationships with the environmental factors. A total of 135 soil samples were collected from the soils at depths of 0-10, 10-20, and 20-30 cm in the Lhasa River and Nyang River basins, and the diversity and composition of bacterial communities in them were identified by high-throughput 16S rRNA gene sequencing. Bacterial diversity changed significantly with soil depth in the Nyang River basin (p < 0.001), while no obvious change was found in the Lhasa River basin. The whole bacterial composition exhibited small variations across different soil layers (p > 0.05). The relative abundance of aerobic bacteria, Sphingomonas and Arthrobacter, decreased with soil depth, while that of the other aerobic, facultative anaerobic, and anaerobic bacteria did not exhibit this trend. Soil pH was the key driving edaphic factor of the whole bacterial composition in all three depth layers, while vegetation also had an important influence on bacterial composition. Arthrobacter, Bradyrhizobium, and Bacillus had obvious correlations with soil nutrients or vegetation, while the other species were not significantly correlated with any environmental factors. Structural equation modeling revealed that vegetation and mean annual temperature had a key direct impact on the bacterial diversity and composition, respectively. Climate also indirectly affected bacterial communities, mainly through shaping soil pH and vegetation. These results indicate that the soil depth has a different impact on the bacterial α-diversity, whole bacterial composition, and specific taxa in the 0-30-cm surface layers of seasonally frozen soil, which were mainly determined by various environmental factors.

Research on removal of fluoroquinolones in rural domestic wastewater by vertical flow constructed wetlands under different hydraulic loads

Antibiotics had attracted more and more attention in recent years due to their harmfulness. Fluoroquinolones (FQs), one class of antibiotics widely used in human and veterinary medicine, were found in various water bodies in China. Therefore, in order to found an efficient method for removing FQs in rural domestic wastewater and optimize the process parameters, ceramsite and soil were applied in vertical flow constructed wetlands (VFCWs) to study the effects of different hydraulic loads and different substrates on the removal of FQs and conventional pollutants. The results showed the VFCW-D filled with 45 cm soil layer and 15 cm ceramasite layer had the highest removal efficiency of conventional pollutants and FQs under low hydraulic load. Nevertheless, the removal efficiency of conventional pollutants was significantly declined for the VFCWs which contained soil substrates under high hydraulic load due to the soil pores were clogged by the accumulation of organic matter. Finally, VFCW-A filled with 60 cm ceramasite layer revealed good ability to remove conventional pollutants and FQs under high hydraulic load. Deinococcus played a vital role here due to its excellent removal effect on conventional pollutants. The microbial composition in the substrate changed greatly after adding antibiotics under high hydraulic load. Devosia, Pseudorhodoferax, Cellvibrio, Bosea, Caulobacter, Acinetobacter, Zoogloea, Arcobacter, Dechloromonas, Flavobacterium, Nakamurella, Chloroplast, Clostridium_sensu_stricto_1, Pelosinus, UTCFX1 and Hypnocyclicus became the new dominated genera and were essential to remove pollutants. In summary, VFCW was an effective system to remove fluoroquinolones in rural domestic wastewater.

Modelling the benefits of urine source separation scenarios on wastewater treatment plants within an urban water basin

Stringent discharge regulations are encouraging researchers to create innovative and sustainable wastewater treatment solutions. Urine source separation (USS) is among the potent approaches that may reduce nutrient peak loads in the influent wastewater and improve nutrient recovery. A phenomenological model was used to simulate dynamic influent properties and predict the advantages gained from implementing USS in an urban water basin. Several scenarios were investigated assuming different levels of deployment: at the entire city, or specifically in office buildings for men's urine only, or for both men and women employees. The results confirmed that all scenarios of urine source separation offered benefits at the treatment plant in terms of reducing nitrogen influent load. The economic benefits in terms of reducing energy consumption for nitrification and decreasing methanol addition for denitrification were quantified, and results confirmed environmental advantages gained from different USS scenarios. Despite larger advantages gained from a global USS rate in an entire city, implementation of a specific USS in office buildings would remain more feasible from a logistical perspective. A significant benefit in terms of reducing greenhouse gas emissions is demonstrated and this was especially due to the high level of N₂O emissions avoided in nitrifying biological aerated filter.

High current density with spatial distribution of Geobacter in anodic biofilm of the microbial electrolysis desalination and chemical-production cell with enlarged volumetric anode

The aim of this study was to establish the relationship between spatial distribution of Geobacter and electric intensity in the microbial electrolysis desalination and chemical-production cell (MEDCC) and to investigate the effect of enlarged volumetric anode on the performance of MEDCC. The MEDCC was constructed with nine carbon brush anodes (length × diameter = 11 cm × 3 cm) as enlarged volumetric anode, and operated by feeding with 1 g/L acetate as substrate and 35 g/L NaCl as artificial seawater under the applied voltages of 1.2-4.5 V. Spatial distribution of Geobacter in the anodic biofilm was determined according to the bacterial community analysis on 27 biofilm samples from the top, middle and bottom layers of anodes (i.e., with distance of 4.5, 10, and 15.5 cm to the cathode, respectively). Results showed that the enlarged volumetric anode significantly improved the performance of MEDCC. The maximum desalination rate and current density reached 338.5 ± 21.8 mg/L∙h and 55.7 ± 3.7 A/m² in the MEDCC, respectively. The electric intensity values decreased with the distance from the anode to the cathode and formed an uneven distribution in the anode chamber. The samples in the top layer of anodes had the highest average 16S rRNA gene copy number of Geobacter of 1.55 × 10⁷ copies/μL, which was 18 times higher than that in the bottom layer of anodes. A linear relation was established between the spatial distribution of Geobacter and electric intensity (R² = 0.994-0.999). The electric intensity gradient created the uneven spatial distribution of Geobacter in the biofilms of volumetric anode. Results from this study could be useful to enrich Geobacter in the anodic biofilm thus to improve the performance of MEDCC.

A novel electrochemical sensor based on autotropic and heterotrophic nitrifying biofilm for trichloroacetic acid toxicity monitoring

Trichloroacetic acid (TCA), a toxic substance produced in the disinfection process of wastewater treatment plants, will accumulate in the receiving water. The detection of TCA in the water can achieve the purpose of early warning. However, currently there are few reports on microbial sensors used for TCA detection, and the characteristics of their microbial communities are still unclear. In this work, a toxicity monitoring microbial system (TMMS) with nitrifying biofilm as a sensing element and cathode oxygen reduction as a current signal was successfully constructed for TCA detection. The current and nitrification rate showed a linear relationship with low TCA concentration from 0 to 50 μg/L (R²_current = 0.9892, R²_{nitrification} = 0.9860), and high concentration range from 50 to 5000 μg/L (R²_current = 0.9883, R²_{nitrification} = 0.9721). High-throughput sequencing revealed that the TMMS was composed of autotrophic/heterotrophic nitrifying and denitrifying microorganisms. Further analysis via symbiotic relationship network demonstrated that Arenimonas and Hyphomicrobium were the core nodes for maintaining interaction between autotropic and heterotrophic nitrifying bacteria. Kyoto Encyclopedia of Genes and Genomes analysis showed that after adding TCA to TMMS, the carbon metabolism and the abundance of the tricarboxylic acid cycle pathway were reduced, and the activity of microorganisms was inhibited. TCA stress caused a low abundance of nitrifying and denitrifying functional enzymes, resulting in low oxygen consumption in the nitrification process, but more oxygen supply for cathode oxygen reduction. This work explored a novel sensor combined with electrochemistry and autotrophic/heterotrophic nitrification, which provided a new insight into the development of microbial monitoring of toxic substances.

The third route: A techno-economic evaluation of extreme water and wastewater decentralization

Water systems need to become more locally robust and sustainable in view of increased population demands and supply uncertainties. Decentralized treatment is often assumed to have the potential to improve the technical, environmental, and economic performance of current technologies. The techno-economic feasibility of implementing independent building-scale decentralized systems combining rainwater harvesting, potable water production, and wastewater treatment and recycling was assessed for six main types of buildings ranging from single-family dwellings to high-rise buildings. Five different treatment layouts were evaluated under five different climatic conditions for each type of building. The layouts considered varying levels of source separation (i.e., black, grey, yellow, brown, and combined wastewater) using the corresponding toilet types (vacuum, urine-diverting, and conventional) and the appropriate pipes and pumping requirements. Our results indicate that the proposed layouts could satisfy 100% of the water demand for the three smallest buildings in all but the aridest climate conditions. For the three larger buildings, rainwater would offset annual water needs by approximately 74 to 100%. A comprehensive economic analysis considering CapEx and OpEx indicated that the cost of installing on-site water harvesting and recycling systems would increase the overall construction cost of multi-family buildings by around 6% and single-family dwellings by about 12%, with relatively low space requirements. For buildings or combined water systems with more than 300 people, the estimated total price of on-site water provision (including harvesting, treatment, recycling, and monitoring) ranged from $1.5/m³ to $2.7/m,³ which is considerably less than the typical tariffs collected by utilities in the United States and Western Europe. Where buildings can avoid the need to connect to centralized supplies for potable water and sewage disposal, water costs could be even lower. Urine-diversion has the potential to yield the least expensive solution but is the least well developed and had higher uncertainty in the cost analysis. More mature layouts (e.g., membrane bioreactors) exhibited less cost uncertainty and were economically competitive. Our analysis indicates that existing technologies can be used to create economically viable systems that greatly reduce demands on centralized utilities and, under some conditions, eliminate the need for centralized water supply or sewage collection.

Integrated self-forming dynamic membrane (SFDM) and membrane-aerated biofilm reactor (MABR) system enhanced single-stage autotrophic nitrogen removal

The membrane aerated biofilm reactor (MABR) is a novel bioreactor technology, facilitating single-stage autotrophic nitrogen removal. Two laboratory-scale MABRs equipped with non-woven fabrics were operated simultaneously without and with a self-forming dynamic membrane (SFDM) filtration module. After 87 days of operation (system start-up), the reactor incorporated with SFDM filtration showed better performance in terms of total nitrogen removal (>80%) and effluent suspended solid (less than1 mg/L) than the MABR in the up flow anaerobic sludge blanket (UASB) configuration (i.e., without SFDM). The incorporation of SFDM has the ability to retain more slow growing biomass (anammox) inside the reactor. Microbial characterization by 16S rRNA-based amplicon sequencing shows that the abundance and composition of microbial communities in two MABR systems were different, i.e., the genusRhodanobacterwas abundant in UASB-MABR, while Calorithrixwas dominant in SFDM-MABR. PCA-based statistical analysis demonstrated a positive association between reactor performance, membrane characteristics and microbial communities.

Aerobic biocathodes with potential regulation for ammonia oxidation with concomitant cathodic oxygen reduction and their microbial communities

Aerobic biocathodes are effective construct for the simultaneous nitrification and denitrification, but the disturbance of cathodic oxygen reduction on ammonia oxidation and denitrification remains unclear. In this study, we revealed the oxygen reduction peak at -0.4 V (versus silver/silver chloride) by cyclic voltammetry analysis at a cathode without a biofilm. The reduction peak, however, showed a right shift from -0.4 to -0.3 V for the biocathode, indicating that the aerobic biocathode could simultaneously perform traditional nitrification and cathode oxygen reduction. Therefore, different electrode potentials ranging from -0.5 to -0.1 V were designed for regulating the ammonia oxidation rate, and the results showed that the highest oxidation rate reached 3.08 mg/h/L at a potential of -0.2 V under a low-aeration rate of 5 mL/min. High-throughput sequencing showed that Nitrosomonas and Rhodococcus were the dominant nitrogen removal genera in the biocathode, and the abundance of Devosia was related to the interactions between the aeration rate and the electrode potential. Furthermore, the amoC and hao genes responded to aeration and electrode potential regulation, and -0.2 V was more suitable for promoting the denitrification process under low-aeration conditions. Therefore, these findings provided new insights on cathodic potential control for ammonia oxidation and nitrogen removal as well as for the regulation of microbial communities.

Response of extracellular polymeric substances and microbial community structures on resistance genes expression in wastewater treatment containing copper oxide nanoparticles and humic acid

The extracellular polymeric substances (EPS) and microbial community structures were investigated in wastewater treatment containing copper oxide nanoparticles (CuO NPs) (reactor R1) and CuO NPs and humic acid (HA) (reactor R2) using both sequencing batch bioreactors (SBRs), and their response on resistance genes expression was analyzed. The removal of influent chemical oxygen demands (COD) and NH₄⁺-N was moderately influenced under CuO NPs (5 mg/L) stress, while the function of HA (10 mg/L) was not reflected. However, the EPS production and microbial community were affected by the HA addition. The expression of different antibiotic resistance genes (ARGs), metal-resistance genes (MRGs), and intI1 was related to the primary compositions of polysaccharides and proteins in EPS and different microbial communities at the genus level. Furthermore, the expression of resistance genes was not stimulated under CuO NPs stress, and supplying HA was suggested to reduce their expression in wastewater treatment.

Recent progress using membrane aerated biofilm reactors for wastewater treatment

The membrane biofilm reactor (MBfR), which is based on the counter diffusion of the electron donors and acceptors into the biofilm, represents a novel technology for wastewater treatment. When process air or oxygen is supplied, the MBfR is known as the membrane aerated biofilm reactor (MABR), which has high oxygen transfer rate and efficiency, promoting microbial growth and activity within the biofilm. Over the past few decades, laboratory-scale studies have helped researchers and practitioners understand the relevance of influencing factors and biological transformations in MABRs. In recent years, pilot- to full-scale installations are increasing along with process modeling. The resulting accumulated knowledge has greatly improved understanding of the counter-diffusional biological process, with new challenges and opportunities arising. Therefore, it is crucial to provide new insights by conducting this review. This paper reviews wastewater treatment advancements using MABR technology, including design and operational considerations, microbial community ecology, and process modeling. Treatment performance of pilot- to full-scale MABRs for process intensification in existing facilities is assessed. This paper also reviews other emerging applications of MABRs, including sulfur recovery, industrial wastewater, and xenobiotics bioremediation, space-based wastewater treatment, and autotrophic nitrogen removal. In conclusion, commercial applications demonstrate that MABR technology is beneficial for pollutants (COD, N, P, xenobiotics) removal, resource recovery (e.g., sulfur), and N₂O mitigation. Further research is needed to increase packing density while retaining efficient external mass transfer, understand the microbial interactions occurring, address existing assumptions to improve process modeling and control, and optimize the operational conditions with site-specific considerations.

Development of Nitrogen Recycling Strategies for Bioregenerative Life Support Systems in Space

To enable long-distance space travel, the development of a highly efficient and robust system to recover nutrients from waste streams is imperative. The inability of the current physicochemical-based environmental control and life support system (ECLSS) on the ISS to produce food in situ and to recover water and oxygen at high enough efficiencies results in the need for frequent resupply missions from Earth. Therefore, alternative strategies like biologically-based technologies called bioregenerative life support systems (BLSSs) are in development. These systems aim to combine biological and physicochemical processes, which enable in situ water, oxygen, and food production (through the highly efficient recovery of minerals from waste streams). Hence, minimalizing the need for external consumables. One of the BLSS initiatives is the European Space Agency's (ESA) Micro-Ecological Life Support System Alternative (MELiSSA). It has been designed as a five-compartment bioengineered system able to produce fresh food and oxygen and to recycle water. As such, it could sustain the needs of a human crew for long-term space exploration missions. A prerequisite for the self-sufficient nature of MELiSSA is the highly efficient recovery of valuable minerals from waste streams. The produced nutrients can be used as a fertilizer for food production. In this review, we discuss the need to shift from the ECLSS to a BLSS, provide a summary of past and current BLSS programs and their unique approaches to nitrogen recovery and processing of urine waste streams. In addition, compartment III of the MELiSSA loop, which is responsible for nitrogen recovery, is reviewed in-depth. Finally, past, current, and future related ground and space demonstration and the space-related challenges for this technology are considered.

Biologically-Based and Physiochemical Life Support and In Situ Resource Utilization for Exploration of the Solar System-Reviewing the Current State and Defining Future Development Needs

The future of long-duration spaceflight missions will place our vehicles and crew outside of the comfort of low-Earth orbit. Luxuries of quick resupply and frequent crew changes will not be available. Future missions will have to be adapted to low resource environments and be suited to use resources at their destinations to complete the latter parts of the mission. This includes the production of food, oxygen, and return fuel for human flight. In this chapter, we performed a review of the current literature, and offer a vision for the implementation of cyanobacteria-based bio-regenerative life support systems and in situ resource utilization during long duration expeditions, using the Moon and Mars for examples. Much work has been done to understand the nutritional benefits of cyanobacteria and their ability to survive in extreme environments like what is expected on other celestial objects. Fuel production is still in its infancy, but cyanobacterial production of methane is a promising front. In this chapter, we put forth a vision of a three-stage reactor system for regolith processing, nutritional and atmospheric production, and biofuel production as well as diving into what that system will look like during flight and a discussion on containment considerations.

Dynamics of dissolved organic matter and dissolved organic nitrogen during anaerobic/anoxic/oxic treatment processes

With Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and fluorescence spectroscopy, this study investigated the transformation of dissolved organic matter (DOM) and nitrogen (DON) during the widely-applied anaerobic/anoxic/oxic (A²O) processes to provide molecular insights into the removal, generation, and reduction of DOM/DON species in different biological treatment units. Results indicated that the anaerobic process decomposed the macromolecules of influent DOM/DON and decreased their mass. The anoxic process denitrified DON and generated DOM, as indicated by the decreased molecule number of CHON and CHONS and the increased CHO and CHOS species, as well as the increased overall DOM intensities. DOM mineralization and ammonia nitrogen-DON conversion occurred in the oxic process. Aromaticity and unsaturation degree increased slightly after the A²O processes, which was correlated with the relative abundance of Proteobacteria (positively) and Bacteroidetes (negatively). The results have strong implications to the understanding of DOM/DON dynamics in wastewater treatment plants.

Oxygen-reducing bidirectional microbial electrodes designed in real domestic wastewater

Microbial electrodes were designed in domestic wastewaters to catalyse the oxidation of organic matter (anode) and the reduction of oxygen (cathode) alternately. The successive aeration phases (cathode) enhanced the anodic efficiency, resulting in current densities of up to 6.4 Am^-2 without the addition of any substrate. Using nitrogen during the anodic phases affected the microbial populations and the electrodes showed a lower ability to subsequently turn to O₂ reduction than the microbial anodes formed in open-to-air conditions did. No strong difference was observed between internal and external biofilm, both of which showed a very large variety of taxa in terms of abundance as well as variance. They comprised a mix of aerobic and anaerobic species, many of which have already been identified separately in bioelectrochemical systems. Such a large diversity, which had not been observed in aerobic bidirectional bioelectrodes so far, can explain the efficiency and robustness observed here.

Urine nitrification robustness for application in space: Effect of high salinity and the response to extreme free ammonia concentrations

Urine nitrification is one of the possibilities for the future recovery of water and elements for soilless crop production in space systems. The start-up of artificial urine nitrification was conducted for over 85 days in a sequencing batch reactor (SBR). Two free ammonia (FA) incidents occurred, which gave the opportunity to demonstrate the impressive ability of nitrifiers to resist temporary inhibition by FA without long lasting adverse effects. The failures led to very high FA concentrations of 280 and 84 gN-NH₃/m³, respectively. Sludge was exposed to FA for 19 and 27 h. It was possible to restore nitrification with simple remedy actions (dilution and pH restoration). No inhibitory effects on the nitrification rate were seen after implementation of the remedy actions and the nitrification rate increased considerably (up to 300% of the pre-failure value) due to decrease in salinity. After a few days of normal operation and salt concentration, the nitrification rate returned to the pre-failure values in both cases.

Biogas Upgrading and Ammonia Recovery from Livestock Manure Digestates in a Combined Electromethanogenic Biocathode—Hydrophobic Membrane System

Anaerobic digestion process can be improved in combination with bioelectrochemical systems in order to recover energy and resources from digestates. An electromethanogenic microbial electrolysis cell (MEC) coupled to an ammonia recovery system based on hydrophobic membranes (ARS-HM) has been developed in order to recover ammonia, reduce organic matter content and upgrade biogas from digested pig slurry. A lab-scale dual-chamber MEC was equipped with a cation exchange membrane (CEM) and ARS with a hydrophobic membrane in the catholyte recirculation loop, to promote ammonia migration and absorption in an acidic solution. On the other hand, an electromethanogenic biofilm was developed in the biocathode to promote the transformation of CO2 into methane. The average nitrogen transference through the CEM was of 0.36 gN m−2 h−1 with a removal efficiency of 31%, with the ARS-HM in the catholyte recirculation loop. The removal of ammonia from the cathode compartment helped to maintain a lower pH value for the electromethanogenic biomass (7.69 with the ARS-HM, against 8.88 without ARS-HM) and boosted methane production from 50 L m−3 d−1 to 73 L m−3 d−1. Results have shown that the integration of an electromethanogenic MEC with an ARS-HM allows for the concomitant recovery of energy and ammonia from high strength wastewater digestates.

Urine Treatment on the International Space Station: Current Practice and Novel Approaches

A reliable, robust, and resilient water recovery system is of paramount importance on board the International Space Station (ISS). Such a system must be able to treat all sources of water, thereby reducing resupply costs and allowing for longer-term space missions. As such, technologies able to dewater urine in microgravity have been investigated by different space agencies. However, despite over 50 years of research and advancements on water extraction from human urine, the Urine Processing Assembly (UPA) and the Water Processor Assembly (WPA) now operating on the ISS still achieve suboptimal water recovery rates and require periodic consumables resupply. Additionally, urine brine from the treatment is collected for disposal and not yet reused. These factors, combined with the need for a life support system capable of tolerating even dormant periods of up to one year, make the research in this field ever more critical. As such, in the last decade, extensive research was conducted on the adaptation of existing or emerging technologies for the ISS context. In virtue of having a strong chemical resistance, small footprint, tuneable selectivity and versatility, novel membrane-based processes have been in focus for treating human urine. Their hybridisation with thermal and biological processes as well as the combination with new nanomaterials have been particularly investigated. This article critically reviews the UPA and WPA processes currently in operation on the ISS, summarising the research directions and needs, highlighted by major space agencies, necessary for allowing life support for missions outside the Low Earth Orbit (LEO). Additionally, it reviews the technologies recently proposed to improve the performance of the system as well as new concepts to allow for the valorisation of the nutrients in urine or the brine after urine dewatering.