High-performance internal circulation anaerobic granular sludge reactor for cattle slaughterhouse wastewater treatment and simultaneous biogas production.

This research investigates the efficacy of a high-performance pilot-scale Internal Circulation Anaerobic Reactor inoculated with Granular Sludge (ICAGSR) for treating cattle slaughterhouse wastewater while concurrently generating biogas. The primary objective is to assess the efficiency and performance of ICAGSR in terms of organic pollutant removal and biogas production using granular anaerobic sludge. The research methodology entails operating the ICAGSR system under ambient conditions and systematically varying key parameters, including different Hydraulic Retention Times (HRTs) (24, 12, and 8 h) and Organic Loading Rates (OLRs) (3.3, 6.14, and 12.83 kg COD/m³. d). The study focuses on evaluating pollutants' removal and biogas production rates. Results reveal that the ICAGSR system achieves exceptional removal efficiency for organic pollutants, with Chemical Oxygen Demand (COD) removal exceeding 74%, 67%, and 68% at HRTs of 24, 12, and 8 h, respectively. Furthermore, the system demonstrates stable and sustainable biogas production, maintaining average methane contents of 80%, 76%, and 72% throughout the experimental period. The successful operation of the ICAGSR system underscores its potential as a viable technology for treating cattle slaughterhouse wastewater and generating renewable biogas. In conclusion, this study contributes to wastewater treatment and renewable energy production by providing a comprehensive analysis of the ICAGSR system's hydrodynamic properties. The research enhances our understanding of the system's performance optimization under varying conditions, emphasizing the benefits of utilizing ICAGSR reactors with granular sludge as an effective and sustainable approach. Identifying current gaps, future research directions aim to further refine and broaden the application of ICAGSR technology in wastewater treatment and renewable energy initiatives.

Taxonomic characterization of Sphaerotilus microaerophilus sp. nov., a sheath-forming microaerophilic bacterium of activated sludge origin.

A microaerophilic Gram-stain-negative bacilliform bacterial strain, FB-5 T, was isolated from activated sludge in Yokohama, Japan, that exhibited filamentous growth and formed a microtube (sheath). Cells were motile using a single polar flagellum. The optimum growth temperature and pH were 30 °C and 7.5, respectively. Strain FB-5 T was catalase-negative. Peptides and amino acids were utilized as energy and carbon sources. Sugars and organic acids were not utilized. Vitamin B12 enhanced the growth of strain FB-5 T. Sulfur-dependent lithotrophic growth was possible. Major respiratory quinone was UQ-8. Major fatty acids were C16:1ω7 and C16:0. The genomic DNA G + C content was 69.16%. Phylogenetic analysis of the 16S rRNA gene suggested that strain FB-5 T belongs to the genus Sphaerotilus. The close relatives were S. natans subsup. sulfidivorans and S. natans subsup. natans with 98.0% and 97.8% similarity based on the 16S rRNA gene analysis, respectively. The genome size (6.06 Mbp) was larger than that (4.39-5.07 Mbp) of the Sphaerotilus strains. The AAI values against the related strains ranged from 71.0 to 72.5%. The range of ANI values was 81.7 - 82.5%. In addition to these distinguishable features of the genome, the core genome and dDDH analyses suggested that this strain is a novel member of the genus Sphaerotilus. Based on its physiological properties and genomic features, strain FB-5 T is considered as a novel species of the genus Sphaerotilus, for which the name S. microaerophilus sp. nov. is proposed. The type strain is FB-5 T (= JCM 35424 T = KACC 23146 T).

Magnetic iron oxide nanoparticle enhanced microwave pretreatment for anaerobic digestion of meat industry sludge.

Our study investigates the effects of iron oxide (Fe3O4) nanoparticles combined microwave pretreatment on the anaerobic digestibility and soluble chemical oxygen demand (SCOD) of meat industry sludge. One of our main objectives was to see whether the different microwave-based pretreatment procedures can enhance biogas production by improving the biological availability of organic compounds. Results demonstrated that combining microwave irradiation with magnetic iron oxide nanoparticles considerably increased SCOD (enhancement ratio was above 1.5), the rate of specific biogas production, and the total cumulative specific biogas volume (more than a threefold increment), while having no negative effect on the biomethane content. Furthermore, the assessment of the sludge samples' dielectric properties (dielectric constant and loss factor measured at the frequency of 500 MHz) showed a strong correlation with SCOD changes (r = 0.9942, R2 = 0.99), offering a novel method to evaluate pretreatment efficiency.

Research progress and perspective on sludge anaerobic digestion technology: A bibliometric analysis.

Rational disposal of sludge is an ongoing concern. This work is the first attempt for in-depth statistical analysis of anaerobic digestion (AD) research in recent three decades (1986-2022) using both quantitative and qualitative approaches in bibliometrics to investigate the research progress, trends and hot spots. All publications in the Web of Science Core Collection database from 1986 to April 4, 2022 were analyzed. Results showed that the research on AD started in 1999 and the number of papers significantly increased since 2012. The research about the disposal of sewage sludge mainly focuses on energy recovery (e.g. methane and short chain volatile organic acids) by AD. Besides, different pretreatment technologies were studied in this study to eliminate the negative effects on the disposal of sludge caused by hydrolysis (rate-limiting step of AD), water content (increasing the costs) and heavy metal (toxic to the environment) of sludge. Of those, the treatment technologies related to direct interspecies electron transfer were worth further studied in the future. Towards that end, iron conductive material, iron-based advanced oxidation and biological treatment were concluded as the prospective technologies and worth to further study.

Effects of carbonization temperature and time on the characteristics of carbonized sludge.

To investigate the influence of carbonization process parameters on the characteristics of municipal sludge carbonization products, this study selected carbonization temperatures of 300-700 °C and carbonization times of 0.5-1.5 h to carbonize municipal sludge. The results showed that with an increase in temperature and carbonization time, the sludge was carbonized more completely, and the structure and performance characteristics of the sludge changed significantly. Organic matter was continuously cracked, the amorphous nature of the material was reduced, its morphology was transformed into an increasing number of regular crystalline structures, and the content of carbon continued to decrease, from the initial 52.85 to 38.77%, while the content of inorganic species consisting continued to increase. The conductivity was reduced by 87.8%, and the degree of conversion of salt ions into their residual and insoluble states was significant. Natural water absorption in the sludge decreased from 8.13 to 1.29%, and hydrophobicity increased. The dry-basis higher calorific value decreased from 8,703 to 3,574 kJ/kg. Heavy metals were concentrated by a factor of 2-3, but the content of the available state was very low. The results of this study provide important technological support for the selection of suitable carbonization process conditions and for resource utilization.

Physicochemical parameters affecting the adhesion of ciprofloxacin-resistant Escherichia coli to activated sludge.

To investigate the physicochemical conditions necessary to stably remove antibiotic-resistant bacteria (ARB) via contact with activated sludge (AS), the adhesion of ciprofloxacin (CIP)-resistant and -susceptible Escherichia coli to AS was simulated by contact tests in the laboratory. The CIP-resistant E. coli and susceptible E. coli were removed by a 3 log smaller concentration by a 5 h contact test at maximum. Considering the hydraulic retention time of a reaction tank (∼5 h) and step-feeding operation, we considered the removal rate of E. coli in the current simulated contact test to be in agreement with the actual situation where 1-2 log concentrations of E. coli were reported to be removed from an AS reaction tank. With the increase in the AS concentration and/or dissolved oxygen, the removal rate of E. coli increased. The removal rate of CIP-resistant E. coli was greater than that of susceptible E. coli under all experimental conditions. Although the mechanism by which CIP-resistant E. coli preferably adhered to AS was not clearly understood in detail, finding optimum conditions under which bacteria, including ARB, were efficiently removed by the AS process may be possible.

A dynamic one-dimensional model for simulating unsteady air-water stratified flow in sewer pipes.

Ventilation is paramount in sanitary and stormwater sewer systems to mitigate odor problems and avert pressure surges. Existing numerical models have constraints in practical applications in actual sewer systems due to insufficient airflow modeling or suitability only for steady-state conditions. This research endeavors to formulate a mathematical model capable of accurately simulating various operational conditions of sewer systems under the natural ventilation condition. The dynamic water flow is modeled using a shock-capturing MacCormack scheme. The dynamic airflow model amalgamates energy and momentum equations, circumventing laborious pressure iteration computations. This model utilizes friction coefficients at interfaces to enhance the description of the momentum exchange in the airflow and provide a logical explanation for air pressure. A systematic analysis indicates that this model can be easily adapted to include complex boundary conditions, facilitating its use for modeling airflow in real sewer networks. Furthermore, this research uncovers a direct correlation between the air-to-water flow rate ratio and the filling ratio under natural ventilation conditions, and an empirical formula encapsulating this relationship is derived. This finding offers insights for practical engineering applications.

Microbiome structure and function in parallel full-scale aerobic granular sludge and activated sludge processes.

Aerobic granular sludge (AGS) and conventional activated sludge (CAS) are two different biological wastewater treatment processes. AGS consists of self-immobilised microorganisms that are transformed into spherical biofilms, whereas CAS has floccular sludge of lower density. In this study, we investigated the treatment performance and microbiome dynamics of two full-scale AGS reactors and a parallel CAS system at a municipal WWTP in Sweden. Both systems produced low effluent concentrations, with some fluctuations in phosphate and nitrate mainly due to variations in organic substrate availability. The microbial diversity was slightly higher in the AGS, with different dynamics in the microbiome over time. Seasonal periodicity was observed in both sludge types, with a larger shift in the CAS microbiome compared to the AGS. Groups important for reactor function, such as ammonia-oxidising bacteria (AOB), nitrite-oxidising bacteria (NOB), polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs), followed similar trends in both systems, with higher relative abundances of PAOs and GAOs in the AGS. However, microbial composition and dynamics differed between the two systems at the genus level. For instance, among PAOs, Tetrasphaera was more prevalent in the AGS, while Dechloromonas was more common in the CAS. Among NOB, Ca. Nitrotoga had a higher relative abundance in the AGS, while Nitrospira was the main nitrifier in the CAS. Furthermore, network analysis revealed the clustering of the various genera within the guilds to modules with different temporal patterns, suggesting functional redundancy in both AGS and CAS. KEY POINTS: • Microbial community succession in parallel full-scale aerobic granular sludge (AGS) and conventional activated sludge (CAS) processes. • Higher periodicity in microbial community structure in CAS compared to in AGS. • Similar functional groups between AGS and CAS but different composition and dynamics at genus level.

Wastewater treatment bacteria show differential preference for colonizing natural biopolymers.

Most reduced organic matter entering activated sludge systems is particulate (1-100-µm diameter) or colloidal (0.001-1-µm diameter), yet little is known about colonization of particulate organic matter by activated sludge bacteria. In this study, colonization of biopolymers (chitin, keratin, lignocellulose, lignin, and cellulose) by activated sludge bacteria was compared with colonization of glass beads in the presence and absence of regular nutrient amendment (acetate and ammonia). Scanning electron microscopy and quantitative PCR revealed chitin and cellulose were most readily colonized followed by lignin and lignocellulose, while keratin and glass beads were relatively resistant to colonization. Bacterial community profiles on particles compared to sludge confirmed that specific bacterial phylotypes preferentially colonize different biopolymers. Nitrifying bacteria proved adept at colonizing particles, achieving higher relative abundance on particles compared to bulk sludge. Denitrifying bacteria showed similar or lower relative abundance on particles compared to sludge. KEY POINTS: • Some activated sludge bacteria colonize natural biopolymers more readily than others. • Nitrifying bacteria are overrepresented in natural biopolymer biofilm communities. • Biopolymers in wastewater likely influence activated sludge community composition.

Detection of thermotolerant coliforms and SARS-CoV-2 RNA in sewage and recreational waters in the Ecuadorian coast: A call for improving water quality regulation.

Wastewater surveillance represents an alternative approach to regulating contamination and the early detection of infectious agents and outbreaks of diseases of public health importance. This study evaluated domestic wastewater effects on recreational waters in estuarine and seawater bodies in Guayas and Santa Elena provinces in Ecuador, South America. Fecal indicator bacteria (thermotolerant coliforms) served as key indicators for evaluation. Physical, chemical, and microbiological quality markers following the Ecuadorian environmental quality standard and the discharge of effluents to the water resource were analyzed. Samples were collected from 44 coastal sites and 2 oxidation lagoons during the dry and rainy seasons of 2020 and 2021, respectively. SARS-CoV-2 RNA was detected in samples with higher E. coli concentrations using reverse transcription quantitative PCR to detect the genes N and ORF1ab. All samples analyzed for SARS-CoV-2 showed Ct ˂ 40 for at least one gene. Four samples showed at least 20 genome copies of gene N per reaction. These were at an artisanal fishing port, an estuarine area (Palmar), a recreational bay, and an oxidation lagoon. A moderate correlation was found between SARS-CoV-2 RNA, thermotolerant coliform and E. coli (p-value ≤ 0.0037), and a strong and positive correlation between thermotolerant coliform and E. coli. (p-value ≤ 0.00001), highlighting the utility of these established parameters as a proxy of the virus. Significant differences were found in the concentrations of thermotolerant coliforms between seasons (p-value = 0.016) and sites (p-value = 0.005). The highest levels of coliforms were found in the dry season (63000 MPN/100 mL) in Anconcito and during the rainy season (14000 MPN/100 mL) at Esterillo in Playas County. It is recommended that the decentralized autonomous governments of the surveyed provinces in Ecuador implement urgent corrective actions and establish medium-term mechanisms to minimize a potential contamination route. Additional parameters must be included in the monitoring, such as Enterococcus and intestinal parasites, due to their public health implications. In the oxidation lagoons, maintenance actions must be carried out, including the dissolution of sediments, an increase in water retention times, and in situ treatment of the sludge, to improve the system's performance.

Study on efficiency and mechanism of ultrasonic controlling membrane fouling in ceramic membrane bioreactors.

In recent years, ceramic membranes have been increasingly used in membrane bioreactors (MBRs). However, membrane fouling was still the core issue restricting the large-scale engineering application of ceramic MBRs. As a novel and alternative technology, ultrasonic could be used to control membrane fouling. This research focused on the efficiency and mechanism of ultrasonic controlling membrane fouling in ceramic MBRs. The results showed that ultrasonic reduced the sludge concentration in MBR, and the average particle size of sludge was always in a high range. The sludge activity of the system was stable at 6-9 (mg O2·(g MLSS·h)-1), indicating that ultrasonic did not destroy the activity of microorganisms in the system. The extracellular polymer substance (EPS) of the ultrasonic group was slightly higher than that of the control group, while the soluble microbial product (SMP) content was relatively stable. The ceramic membrane of the ultrasonic group has a partial retention effect on the organic components. The application of ultrasonic slowed down the decrease of the hydrophilicity of the ceramic membrane. The main pollutants on the membrane surface exist in the form of aromatic and heteroaromatic rings, alkynes, and so forth. Ultrasonic removes the amide substances from the membrane surface. Membrane fouling resistance is mainly due to membrane pore blockage, accounting for 75.53%. PRACTITIONER POINTS: Enrich the research on the mechanism of ultrasonic technology in membrane fouling control. The MBR can still operate normally with ultrasonic applied. The time for the ceramic membrane to reach the fouling end point is 2.4 times that without ultrasonic. The main cause of membrane fouling was pore blocking, accounting for 75.53%.

Characterization and efficacy against carbapenem-resistant Acinetobacter baumannii of a novel Friunavirus phage from sewage.

Carbapenem-resistant Acinetobacter baumannii (CRAB) has become a new threat in recent years, owing to its rapidly increasing resistance to antibiotics and new effective therapies are needed to combat this pathogen. Phage therapy is considered to be the most promising alternative for treating CRAB infections. In this study, a novel phage, Ab_WF01, which can lyse clinical CRAB, was isolated and characterized from hospital sewage. The multiplicity of infection, morphology, one-step growth curve, stability, sensitivity, and lytic activity of the phage were also investigated. The genome of phage Ab_WF01 was 41, 317 bp in size with a GC content of 39.12% and encoded 51 open reading frames (ORFs). tRNA, virulence, and antibiotic resistance genes were not detected in the phage genome. Comparative genomic and phylogenetic analyses suggest that phage Ab_WF01 is a novel species of the genus Friunavirus, subfamily Beijerinckvirinae, and family Autographiviridae. The in vivo results showed that phage Ab_WF01 significantly increased the survival rate of CRAB-infected Galleria mellonella (from 0% to 70% at 48 h) and mice (from 0% to 60% for 7 days). Moreover, after day 3 post-infection, phage Ab_WF01 reduced inflammatory response, with strongly ameliorated histological damage and bacterial clearance in infected tissue organs (lungs, liver, and spleen) in mouse CRAB infection model. Taken together, these results show that phage Ab_WF01 holds great promise as a potential alternative agent with excellent stability for against CRAB infections.

Measuring Biomethane Potential of Food Scrap Waste Anaerobically Co-Digested with Waste-Activated Sludge Using Respirometry.

The use of respirometry to study the biokinetics of microbiota treating wastewater or digesting wastewater sludges has become more prevalent over the last few decades. The use of respirometry to examine the biokinetics of anaerobic microbiota co-digesting organic waste streams such as wastewater sludge and food scrap is an area of active research. To date, no visualized protocol has been published on the topic. Accordingly, in this protocol, we configured a respirometer to measure methane production and flow rate over time using three different food-to-microorganism (F:M) ratios and food scrap waste and waste-activated sludge as substrates. The resulting data, coupled with substrate utilization measurements, provides the basis for understanding how different substrate concentrations influence the rate at which anaerobic microbiota produce methane. Additionally, this protocol presents a method to develop biokinetic parameters (e.g., methane production rate constant and yield). Others can use this respirometry protocol to examine organic degradation under anaerobic conditions and develop microbial parameters.

Application of Magnetic Materials Combined with Echo® Mass Spectrometry System in Analysis of Illegal Drugs in Sewage.

The aim of this study is to solve the problems of the complicated pretreatment and high analytical cost in the detection technology of trace drugs and their metabolites in municipal wastewater. A high-performance magnetic sorbent was fsynthesized for the enrichment of trace drugs and their metabolites in wastewater to develop a magnetic solid-phase extraction pretreatment combined with the acoustic ejection mass spectrometry (AEMS) analytical method. The magnetic nanospheres were successfully prepared by magnetic nanoparticles modified with divinylbenzene and vinylpyrrolidone. The results showed that the linear dynamic range of 17 drugs was 1-500 ng/mL, the recovery was 44-100%, the matrix effect was more than 51%, the quantification limit was 1-2 ng/mL, and the MS measurement was fast. It can be seen that the developed magnetic solid-phase extraction (MSPE) method is a good solution to the problems of the complicated pretreatment and analytical cost in the analysis of drugs in wastewater. The developed magnetic material and acoustic excitation pretreatment coupled with mass spectrometry analysis method can realize the low-cost, efficient enrichment, and fast analysis of different kinds of drug molecules in urban sewage.

Pre-exposure of Triclosan compromise tetracycline-derived antibiotic resistance in methanogenic digestion microbiome.

Triclosan (TCS) and tetracycline (TC) are commonly detected antibacterial agents in sewage and environment matrices. Nonetheless, the impact of sequential exposure to TCS and TC on the methanogenic digestion microbiome remains unknown. In this study, TCS was shown to reduce COD removal efficiency to 69.8%, but alleviated the inhibitive effect of consequent TC-amendment on the digestion microbiome. Interestingly, TCS pre-exposure resulted in abundance increase of acetotrophic Methanosaeta to 2.68%, being 2.91 folds higher than that without TCS amendment. Microbial network analyses showed that TCS pre-exposure caused microorganisms to establish a co-ecological relationship against TC disturbance. Further analyses of total antibiotic resistance genes (ARGs) showed the TCS-derived compromise of TC-induced ARGs enrichment in digestion microbiomes, e.g., 238.2% and 152.1% ARGs increase upon TC addition in digestion microbiomes without and with TCS pre-exposure, respectively. This study provides new insights into the impact of antibacterial agents on the methanogenic digestion microbiome.

Absorbing oxygen carriers promotes phosphorus recovery from sludge via the microwave thermal conversion process.

This study aims to apply the Absorbing oxygen carriers (AOCs) to induce the migration and transformation of phosphorus compounds during the microwave thermal conversion of sludge so the hard-to-extract organic phosphorus (OP) can be converted to easy-to-extract inorganic phosphorus (IP) and be enriched onto the sludge char. The AOCs were recycled by screen separation from the IP-rich sludge char, with the latter being a renewable phosphorus source from sludge. The AOCs in this novel process enhanced the conversion efficiency of OP into non-apatite inorganic phosphorus (NAlP), which was further converted to apatite inorganic phosphorus (AP). Most phosphorus in the sludge char is presented in the form of orthophosphate.

Enhanced dewaterability and triclosan removal of waste activated sludge with iron-rich mineral-activated peroxymonosulfate.

High water and pharmaceutical and care products (PPCPs) bounded in sludge flocs limit its utilization and disposal. The advanced oxidation process of perxymonosulfate (PMS) catalyzed by iron salts has been widely used in sludge conditioning. In this study, two iron-rich minerals pyrite and siderite were proposed to enhance sludge dewatering performance and remove the target contaminant of triclosan (TCS). The permanent release of Fe2+ in the activation of PMS made siderite more effective in enhancing sludge dewater with capillary suction time (CST) diminishing by 60.5 %, specific resistance to filtration (SRF) decreasing by 79.2 %, and bound water content (BWC) dropping from 37.1 % to 2.6 % at siderite/PMS dosages of 0.36/0.20 mmol/g-TSS after 20 min of pretreatment. Pyrite/PMS performed slightly inferior under the same conditions and the corresponding CST and SRF decreased by 51.5 % and 71.8 % while the BWC only declined to 17.8 %. Rheological characterization was employed to elucidate the changes in sludge dewatering performance, with siderite/PMS treated sludge showing a 48.3 % reduction in thixotropy, higher than 28.4 % of pyrite/PMS. Oscillation and creep tests further demonstrated the significantly weakened viscoelastic behavior of the sludge by siderite/PMS pretreatment. For TCS mineralization removal, siderite/PMS achieved a high removal efficiency of 43.9 %, in comparison with 39.9 % for pyrite/PMS. The reduction in the sludge solids phase contributed the most to the TCS removal. Free radical quenching assays and EPR spectroscopy showed that both siderite/PMS and pyrite/PMS produced SO4-·  and ·OH, with the latter acting as the major radicals. Besides, the dosage of free radicals generated from siderite/PMS exhibited a lower time-dependence, which also allowed it to outperform in destroying EPS matrix, neutralizing the negative Zeta potential of sludge flocs, and mineralizing macromolecular organic matter.

A new strategy for accelerating recovery of anaerobic granular sludge after low-temperature shock: In situ regulation of quorum sensing microorganisms embedded in polyvinyl alcohol sodium alginate.

Low-temperature could inhibit the performance of anaerobic granular sludge (AnGS). Quorum sensing (QS), as a communication mode between microorganisms, can effectively regulate AnGS. In this study, a kind of embedded particles (PVA/SA@Serratia) based on signal molecule secreting bacteria was prepared by microbial immobilization technology based on polyvinyl alcohol and sodium alginate to accelerate the recovery of AnGS system after low temperature. Low-temperature shock experiment verified the positive effect of PVA/SA@Serratia on restoring the COD removal rate and methanogenesis capacity of AnGS. Further analysis by metagenomics analysis showed that PVA/SA@Serratia stimulated higher QS activity and promoted the secretion of extracellular polymeric substance (EPS) in AnGS. The rapid construction of EPS protective layer effectively accelerated the establishment of a robust microbial community structure. PVA/SA@Serratia also enhanced multiple methanogenic pathways, including direct interspecies electron transfer. In conclusion, this study demonstrated that PVA/SA@Serratia could effectively strengthen AnGS after low-temperature shock.

Optimizing hydraulic retention time of high-rate activated sludge designed for potential integration with partial nitritation/anammox in municipal wastewater treatment.

The integration of high-rate activated sludge (HRAS), an effective carbon redirection technology, with partial nitritation/anammox (PN/A) is a novel AB treatment process for municipal wastewater. In this study, an airlift HRAS reactor was operated in the continuous inflow mode for 200 d at a wastewater treatment plant. The balance between potential PN/A system stability and peak HRAS performance under decreasing hydraulic retention time (HRT) was optimized. Energy consumption and recovery and CO2 emissions were calculated. The results showed that the optimal HRT suitable with the PN/A process was 3 h, achieving 2-3 g/L mixed liquor volatile suspended solid, 67.8 % chemical oxygen demand (COD) recovery, 81 % total COD removal efficiency, 2.27 ± 1.03 g COD/L/d organic loading rate, 62 % aeration reduction, and 0.24 kWh/m3 power recovery potential. Such findings hold practical value and contribute to the development of the optimal AB process capable of achieving energy autonomy and carbon neutrality.

Competitive partitioning of denitrification pathways during arrested methanogenesis: Implications in ammonium recovery, N2O emission, and volatile fatty acid production.

The complex interaction between nitrate (NO3-) reduction and fermentation is poorly understood when high levels of NO3- are introduced into anaerobic systems. This study investigated the competitive distribution between conventional denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA) during simultaneous denitrification and fermentation in arrested methanogenesis. Up to 62% of initial NO3- (200 mg-N/L) was retained as ammonium through DNRA at a chemical oxygen demand (COD)/N ratio of 25. Significant N2O emission occurred (1.7 - 8.0% of the initial NO3-) with limited carbon supply (≤1600 mg COD/L) and sludge concentration (≤3000 mg COD/L). VFA composition shifted predominantly towards acetic acid (>50%) in the presence of nitrate. A novel kinetic model was developed to predict DNRA vs. DEN partitioning and NO2- accumulation. Overall, NO3- input, organic loading, and carbon source characteristics independently and collectively controlled competitive DNRA vs. DEN partitioning.