Shift in microbial community structure of anaerobic side-stream reactor in response to changes to anaerobic solid retention time and sludge interchange ratio

In-Situ Sludge Reduction Performance and Mechanism in Sulfidogenic Anoxic-Oxic-Anoxic Membrane Bioreactors

The excess sludge generated from the activated sludge process remains a big issue. Sustainable approaches that achieve in situ sludge reduction with satisfactory effluent quality deserve attention. This study explored the sludge reduction performance of sulfidogenic anoxic-oxic-anoxic (AOA) membrane bioreactors. The dynamics of the microbial community and metabolic pathways were further analyzed to elucidate the internal mechanism of sludge reduction. Compared with the conventional anoxic-oxic-oxic membrane bioreactor (MBR_control), AOA_S150 (150 mg/L SO₄^2- in the membrane tank) and AOA_S300 (300 mg/L SO₄^2- in the membrane tank) reduced biomass production by 40.39% and 47.45%, respectively. The sulfide reduced from sulfate could enhance the sludge decay rate and decrease sludge production. Extracellular polymeric substances (EPSs) destruction and aerobic lysis contributed to sludge reduction in AOA bioreactors. The relative abundance of Bacteroidetes (phylum), sulfate-reducing bacteria (SRB, genus), and Ignavibacterium (genus) increased in AOA bioreactors compared with MBR_control. Our metagenomic analysis indicated that the total enzyme-encoding genes involved in glycolysis, denitrification, and sulfate-reduction processes decreased over time in AOA_S300 and were lower in AOA_S300 than AOA_S150 at the final stage of operation. The excess accumulation of sulfide in AOA_S300 may inactive the functional bacteria, and sulfide inhibition induced sludge reduction.

In-Situ Sludge Reduction in Membrane-Controlled Anoxic-Oxic-Anoxic Bioreactor: Performance and Mechanism

Conventional and advanced biological wastewater treatment systems generate excess sludge, which causes socio-economic and environmental issues. This study investigated the performance of membrane-controlled anoxic-oxic-anoxic (AOA) bioreactors for in-situ sludge reduction compared to the conventional anoxic-oxic-oxic membrane bioreactor (MBR_control). The membrane units in the AOA bioreactors were operated as anoxic reactors at lower sludge recirculation rates to achieve hydrolysis of extracellular polymeric substances (EPS) and extensive endogenous respiration. Compared to MBR_control, the AOA bioreactors operated with 90%, and 80% recirculation rates reduced the sludge growth up to 19% and 30%, respectively. Protein-like components were enriched in AOA bioreactors while fulvic-like components were dominant in MBR_control. The growth of Dechloromonas and Zoogloea genra was promoted in AOA bioreactors and thus sludge reduction was facilitated. Metagenomics analysis uncovered that AOA bioreactors exhibited higher proportions of key genes encoding enzymes involved in the glycolysis and denitrification processes, which contributed to the utilization of carbon sources and nitrogen consumption and thus sludge reduction.

Responses of microbial structures, functions and metabolic pathways for nitrogen removal to different hydraulic retention times in anaerobic side-stream reactor coupled membrane bioreactors

Synchronous sludge reduction and nitrogen removal have attracted increasing attention, while the underlying mechanisms of diverse nitrogen metabolism within the complicated processes remain unclear. Four anoxic/oxic membrane bioreactors, three of which were upgraded by anaerobic side-stream reactors (ASSR) and carriers (APSSR-MBRs), were operated to determine effects of hydraulic retention time of ASSRs. APSSR-MBRs achieved more significant nitrogen removal and higher nitrate uptake rate because of more denitrifying bacteria and the supernumerary release of secondary substrates. Ammonia uptake rate showed the diverse Nitrospira preceded over anaerobic decay and sulfide inhibition in the ASSR, and made the reactor exhibit higher nitrification capacity. Metagenomic analysis indicated that APSSR-MBRs showed higher abundances of genes related to nitrogen consumption processes, and higher abundances on the carriers, confirming their pivotal roles in nitrogen metabolism. This study provided novel perspectives to build a bridge between process model and nitrogen metabolism in the sludge reduction system..

Bacterial and Microfauna Mechanisms for Sludge Reduction in Carrier-Enhanced Anaerobic Side-Stream Reactors Revealed by Metagenomic Sequencing Analysis

Packing carriers into the anaerobic side-stream reactor (ASSR) can enhance sludge reduction and save footprint by investigating ASSR-coupled membrane bioreactors (AP-MBRs) under different hydraulic residence times of the ASSR (HRT_SR). Three AP-MBRs and an anoxic-aerobic MBR (AO-MBR) showed efficient chemical oxygen demand (>94.2%) and ammonium nitrogen removal (>99.3%). AP-MBRs have higher (p < 0.05) total nitrogen (61.4-67.7%) and total phosphorus (57.5-63.8%) removal than AO-MBRs (47.8 and 47.7%). AP-MBRs achieved sludge reduction efficiencies of 11.8, 31.8, and 36.2% at HRT_SR values of 2.5, 5.0, and 6.7 h. Packing carriers greatly improved sludge reduction under low HRT_SR and is promising for accelerating sludge reduction in compact space. Metagenomic sequencing analysis showed that genes responsible for metabolism were enriched in AO-MBRs, while genes related to cellular motility and cell signaling were more abundant in the AP-MBRs. A longevity-regulating pathway showed that long lifespan provided more opportunities for worms to prey bacteria. Microscopic examination revealed that some specific protozoa (Arcella, Clathrulina, Aspidisca, Litonotus, Chiloclonella, and Vorticella) and metazoa (Rotaria and Aeolosoma hemprichi) were enriched in ASSRs. Aeolosoma hemprichi was only detected in ASSRs, and unique Cylops appeared on carriers. These results contribute to growing understanding of micrometabolic mechanisms including functional genes and microfauna-driving sludge reduction.

Identifying the mechanisms of sludge reduction in the sulfidogenic oxic-settling anaerobic (SOSA) process: Side-stream sulfidogenesis-intensified sludge decay and mainstream extended aeration

An energy-/cost-efficient and environment-friendly in-situ sludge reduction process, called the sulfidogenic oxic-settling anaerobic (SOSA) was developed recently. However, the underpinning mechanism of sludge reduction by the SOSA process remains elusive. This paper investigated the possible mechanisms of sludge reduction through biomass cultivation in three lab-scale experimental systems: one anoxic-oxic CAS process with a long sludge retention time (SRT) and extended aeration (EAO) process, and two EAO-based in-situ sludge reduction processes, i.e., the conventional oxic-settling anaerobic (COSA) process and the new SOSA process. These three comparative biosystems were operated with identical influent and reactor configurations as well as the same biomass concentrations and SRTs (approximately 5 g/L and 46 days, respectively), and the sludge interchange ratios (between the CAS and side-stream reactors) in COSA and SOSA were both 10% per day. Three systems all achieved high organic (>93%) and total nitrogen (TN) (>74%) removal efficiencies. SOSA produced 29% and 20% less sludge than EAO and COSA, respectively, simultaneously consumed 14% and 8% more oxygen than EAO and COSA, indicating that the sludge reduction in SOSA was not only caused by EAO-based aerobic digestion in the mainstream and conventional anaerobic reactions in the side-stream, but more importantly due to the bioaugmentation of sulfidogenesis. The roles of sulfidogenesis were further studied in batch tests, and the key findings were as follows: i) the SOSA biomass had a faster endogenous decay rate (0.097 d^-1) than that of the COSA biomass (0.045 d^-1), and ii) sulfidogenesis accelerated anaerobic solubilization, hydrolysis, acidogenesis and acetogenesis by 2.3 - 3.1 times, 6 - 22 %, 22 - 60% and 6 - 22%, respectively. Overall, the mechanisms of sludge reduction in SOSA were unraveled in this study which will help promote its full-scale application in future.

Understanding mechanisms of sludge in situ reduction in anaerobic side-stream reactor coupled membrane bioreactors packed with carriers at different filling fractions

An anoxic/oxic membrane bioreactor (AO) and three pilot-scale anaerobic side stream reactors (ASSR) coupled MBRs (ASSR-MBRs), packed with 0%, 25% and 50% carriers in ASSRs, were continuously operated to study the mechanisms for sludge reduction. Four systems showed efficient COD and NH₄⁺-N removal, while packing carriers significantly enhanced nitrogen removal. 25% filling fraction (AP₂₅) achieved the highest sludge reduction efficiency of 50.5% compared to 0% (21.7%) and 50% (39.7%). Compared to ASSR-MBR, carriers enhanced the release of dissolved organic matters, and accelerated the secretion of enzyme for cell lysis and hydrolysis. In AP₂₅, the presence of carriers prompted the formation of environment propitious to sludge reduction in bulk sludge. AP₂₅ tended to enrich hydrolytic, fermentative and denitrifying bacteria to accelerate hydrolysis process, while excessive carriers had negative effect on biomass stability and movement of carriers.

Effects of bioporous carriers on the performance and microbial community structure in side-stream anaerobic membrane bioreactors

The aim of this study was to investigate the effects of a volcanic rock porous carrier (VRPC) on sludge reduction, pollutant removal, and microbial community structure in an anaerobic side-stream reactor (ASSR). Three lab-scale membrane bioreactors (MBRs), including an anoxic-oxic MBR, which served as the control (C-MBR), an ASSR-coupled MBR (A-MBR), and an A-MBR filled with VRPC (FA-MBR) were stably and simultaneously operated for 120 days. The effect of the three reactors on the removal of chemical oxygen demand (COD) was almost negligible (all greater than 95%), but the average removal efficiency of ammonium nitrogen, total nitrogen, and total phosphorus was significantly improved by the insertion of an ASSR, especially when the ASSR was filled with VRPC. Finally, A-MBR and FA-MBR achieved 16.2% and 26.4% sludge reduction rates, with observed sludge yields of 0.124 and 0.109 g mixed liquid suspended solids/g COD, respectively. Illumina MiSeq sequencing revealed that microbial diversity and richness were highest in the VRPC, indicating that a large number of microorganisms formed on the carrier surface in the form of a biofilm. Abundant denitrifying bacteria (Azospira, Comamonadaceae_unclassified, and Flavobacterium) were immobilized on the carrier biofilm, which contributed to increased nitrogen removal. The addition of a VRPC to the ASSR successfully immobilized abundant hydrolytic, fermentative, and slow-growing microorganisms, which all contributed to reductions in sludge yield.

Sludge reduction based on microbial metabolism for sustainable wastewater treatment

Sludge reduction via microbial metabolism does not require extra energy and resource inputs and thus merits attention as an alternative approach for sustainable wastewater treatment. This review presents a summary and analysis of the existing literatures on sludge reduction based on microbial metabolism, as well as interprets these sludge reduction mechanisms using bacterial thermodynamics and stoichiometry. Future efforts should be directed toward using advanced analytical techniques to further reveal sludge reduction mechanisms. The feasibility of coupling sludge reduction and nutrient removal by microorganism metabolism needs to be further evaluated to minimize the effect of sludge reduction on nutrient removal. A comprehensive life cycle assessment of sludge reduction strategies is recommended to effectively confirm their sustainability. Full-scale research is needed to verify the results obtained from bench- and pilot-scale experiments. This review presents the future opportunities and challenges for sludge reduction based on microbial metabolism in the excess sludge disposal.

Biological nutrient removal in the anaerobic side-stream reactor coupled membrane bioreactors for sludge reduction

An anoxic-aerobic membrane bioreactor (AO-MBR), an anaerobic side-stream reactor (ASSR) coupled MBR (A-MBR), and an MBR with ASSR packed with carriers (AP-MBR) were operated parallelly to investigate biological nutrient removal, microbial community structure and mass balance of nutrients in sludge reduction systems. Compared to AO-MBR, A-MBR and AP-MBR were both efficient in COD and NH₄⁺-N removal, had significantly higher nitrogen removal, reduced sludge production by 35.0% and 45.9%, but deteriorated biological phosphorus removal. Nitrosomonadaceae and Nitrospira were major bacteria responsible for ammonium and nitrite oxidation in the three systems. Inserting ASSR and packing carriers both favored denitrifying bacteria enrichment and organic substances release, and thus resulted in higher nitrate uptake rate (NUR) in the anoxic tank. Higher endogenous NUR in ASSR than in anoxic tank also indicated that ASSR and carriers both accelerated sludge decay. Denitrification and sludge reduction occurred in ASSR played important roles in biological nutrient removal.

Nutrient removal and microbial community structure variation in the two-sludge system treating low carbon/nitrogen domestic wastewater

A two-sludge system with separated phosphorus removal unit and nitrification unit was used to treat the actual municipal sewage deficient in organic carbon sources, with the carbon/nitrogen (C/N) ratio of 4.39. The system was first operated as anaerobic/oxic-nitrification (A/O-N) mode for 60 days (phase I), and then transformed into anaerobic/anoxic/oxic-nitrification (A/A/O-N) mode for the next following 80 days (phase II). Noteworthy, oxygen and nitrate acted as electronic acceptors for phosphorus removal in chronological order. Results indicated that deep phosphorus removal and complete nitrification were achieved at both phase I and phase II, and the system exhibited a higher microbial diversity. Microbial community abundance on genus level analysis indicated that Dechloromonas and Accumulibacter were respectively accumulated with 11.6 and 2.42% abundance (A/A/O sludge); and 9.31 and 1.29% Nitrospira and Nitrosomonas occupied the biofilm, and they performed denitrifying phosphorus removal (DNPR) and nitrification, respectively.

Effects of Olive and Pomegranate By-Products on Human Microbiota: A Study Using the SHIME® in Vitro Simulator

Two by-products containing phenols and polysaccharides, a “pâté” (OP) from the extra virgin olive oil milling process and a decoction of pomegranate mesocarp (PM), were investigated for their effects on human microbiota using the SHIME^® system. The ability of these products to modulate the microbial community was studied simulating a daily intake for nine days. Microbial functionality, investigated in terms of short chain fatty acids (SCFA) and NH₄⁺, was stable during the treatment. A significant increase in Lactobacillaceae and Bifidobacteriaceae at nine days was induced by OP mainly in the proximal tract. Polyphenol metabolism indicated the formation of tyrosol from OP mainly in the distal tract, while urolithins C and A were produced from PM, identifying the human donor as a metabotype A. The results confirm the SHIME^® system as a suitable in vitro tool to preliminarily investigate interactions between complex botanicals and human microbiota before undertaking more challenging human studies.

Application of real-time nitrogen measurement for intermittent aeration implementation in a biological nitrogen removal system: performances and efficiencies

Several automatic strategies for aeration control have been investigated so far to favor a significant decrement of energy consumptions in biological processes in wastewater treatment plants (WWTPs). Above all, the intermittent aeration process has demonstrated to have several advantages. This work reports the results of a case study made in a small municipal WWTP where an intermittent aeration control strategy based on the online measurement of real-time nitrogen forms has been implemented to optimize the nitrogen removal and the energy consumption in an activated process. High organic removal efficiency was achieved during the whole experimental period. Results indicated that nitrogen removal efficiency has been improved, especially during winter months, by the control strategy adopted that helped to determine the perfect length for the nitrification and denitrification phases. The intermittent aeration process increased the activity of the biomass, further selecting phosphate-accumulating bacteria and improving the growth of bacteria able to internally store carbon source. Excellent effects were achieved on energy and chemical consumption, with a reduction of about 15% and 23%, respectively. Finally, a 12% reduction of sludge production was also detected.

Determination and evaluation of kinetic parameters of activated sludge biomass from a sludge reduction system treating real sewage by respirometry testing

Oxic-settling-anoxic (OSA) process is one of the promising variants that produces lower amounts of sludge and has been applied to aerobic and nutrient removal systems. The only consequence on this modification is that supplementary research is advisable to fully understand the mechanism, which eventually leads to the development of a more realistic model. This study evaluated the characteristics of an OSA process as a sludge reduction system by calibration of kinetic coefficients of ASM1 model with some modifications. A series of respirometric tests were designed for the assessment of microbial kinetics and for further clarification of sludge reduction mechanism. The calibration results depicted that the decay rate is the most variable kinetic parameter depending on the system configuration. It was determined that this kinetic coefficient increased significantly after the system was modified into OSA configuration while other model parameters were almost kept constant. This may be referred to a change either in the microbial population or in the metabolism of the community. The active biomass ratio in the CAS reactor was found to be around 75%, while it was almost 2 times lower in the side-stream reactor. All results led to a conclusion that OSA process is encouraging endogenous decay and consequently lowers biomass viability in the reactor and achieves excess sludge reduction in the system. All experimental results confirmed that side-stream reactor accelerates decay rate of the community and causes the introduction of sludge with low viability to the main reactor.

Microbial community shifts in the oxic-settling-anoxic process in response to changes to sludge interchange ratio

This particular study set out to demonstrate alterations on the microbial community of the oxic-settling-anaerobic/anoxic (OSA) process treating real domestic wastewater by changing interchange ratios (IRs). The sludge yield of systems operated at different IRs (1/13, 1/17 and 1/20) to assess sludge reduction was used to analyze microbial community composition variations. The highest IR (1/13) resulted in the highest sludge reduction (52.1%), while the OSA systems with IR of 1/17 and 1/20 reduced sludge production by 37.4% and 35.5%, respectively, in comparison to conventional systems. 16S rRNA gene amplicon sequencing analysis showed that the bacterial communities were composed of similar phylogenetic groups, Proteobacteria, Acidobacteria, and Bacteroidetes being dominant. The relative abundances differed due to the applied IRs. The highest abundance of Actinobacteria was determined at the highest IR (1/13) and increasing of the HRT to 1/20 caused a significant reduction in Actinobacteria species and the lowest abundance (6%) was determined in the OSA systems. The abundant of Thiothrix species that are boosted in the OSA trials may have a vital role in OSA systems, where its abundance was below the detection limits in the seed sludge sample. Therefore, they could be used as bioindicators in the OSA system.

Progress toward full scale application of the anaerobic side-stream reactor (ASSR) process

In order to reduce the investment costs of the anaerobic side-stream reactor (ASSR) process coupled with an activated sludge system and promote the full scale application, the impact of 1 d anaerobic solid retention time (SRT_ASSR) and 100% interchange ratio (IR) has been investigated on sludge reduction, carbon and nutrient removal efficiency and microbial community, in a sequencing batch reactor (SBR)-ASSR system. The SBR-ASSR achieved good removal efficiencies in COD (91.5 ± 3.4%), ammonium nitrogen (98.8 ± 0.5%), total nitrogen (87.9 ± 4.9%) and phosphate (92.8 ± 6.7). The sludge yield of the system was 0.1648 g TSS g^-1COD; 54% lower compared to a conventional activated sludge (CAS) system. Real time quantitative polymerase chain reaction (q-PCR) showed an abundance of hydrolyzing and fermentative bacteria. Comparison at class and genus level confirmed an abundance of anaerobic hydrolyzing and fermentative bacteria, denitrifying bacteria able to simultaneous perform nitrogen and phosphate removal and phosphate accumulating organisms.

Sludge reduction and microbial structures of aerobic, micro-aerobic and anaerobic side-stream reactor coupled membrane bioreactors

An anoxic/oxic membrane bioreactor (MBR) and three side-stream reactor (SSR) coupled membrane bioreactors were operated in parallel to investigate effects of dissolved oxygen (DO) level in SSR on sludge reduction and microbial community structure of SSR-MBRs. The four MBRs were equally efficient in COD and ammonium nitrogen removal. The anaerobic and micro-aerobic SSR favored nitrogen removal through denitrification, simultaneous nitrification and denitrification and autochthonous substrate release as carbon source. The micro-aerobic SSR achieved greatly higher sludge reduction efficiency (61.1%) than anaerobic (37.3%) and aerobic SSR (7.9%). Micro-aerobic SSR obtained the highest endogenous decay constant (0.035 d^-1) compared to anaerobic (0.023 d^-1) and aerobic SSR (0.015 d^-1). High-throughput sequencing results revealed that anaerobic SSR enriched hydrolytic and fermentative bacteria, aerobic environment favored the growth of slow-growing bacteria, and micro-aerobic SSR stimulated biological activities of both anaerobic and aerobic bacteria.

Anode potential selection for sulfide removal in contaminated marine sediments

Sulfate reducing microorganisms are typically involved in hydrocarbon biodegradation in the sea sediment, with their metabolism resulting in the by-production of toxic sulfide. In this context, it is of utmost importance identifying the optimal value for anodic potential which ensures efficient toxic sulfide removal. Along this line, in this study the (bio)electrochemical removal of sulfide was tested at anodic potentials of -205 mV, +195 mV and +300 mV (vs Ag/AgCl), also in the presence of a pure culture of the sulfur-oxidizing bacterium Desulfobulbus propionicus. Current production, sulfide concentration and sulfate concentration were monitored over time. At the end of the experiment sulfur deposition on the electrodes and the microbial communities were characterized by SEM-EDS and by next generation sequencing of the 16S rRNA gene respectively. Results confirmed that current production was linked to sulfide removal and D. propionicus promoted back oxidation of deposited sulfur to sulfate. The highest electron recovery was observed at +195 mV vs Ag/AgCl, and the lowest sulfur deposition was obtained at -205 mV vs Ag/AgCl anode polarization.

Correlation of microbial community structure with pollutants removal, sludge reduction and sludge characteristics in micro-aerobic side-stream reactor coupled membrane bioreactors under different hydraulic retention times

A micro-aerobic side-stream reactor (MSSR) was inserted in returned sludge line of a membrane bioreactor (MBR) for sludge reduction. Three MSSR coupled MBRs (M-MBRs) and an anoxic/oxic MBR (AO-MBR) were operated in parallel to investigate effects of micro-aerobic condition and hydraulic retention time (HRT) of MSSR (HRT_M) on process performance. M-MBRs and AO-MBR were equally effective in COD and NH₄-N removal. Rising HRT_M from 3.3 to 6.7 h increased sludge reduction from 10.8% to 47.5%, and promoted dissolved organic matters release and utilization by enriching hydrolytic, fermentative and predatory bacteria. M-MBR at HRT_M of 3.3 h obtained the highest nitrogen removal, and enriched denitrifiers (Thauera and Hyphomicrobium) in the MSSR. The highest relative abundance of polyphosphate-accumulating organisms was observed in M-MBR at HRT_M of 5.0 h, which achieved the highest phosphorus removal. Prolonging HRT_M to 6.7 h improved sludge dewaterability by enriching floc-formation bacteria (Nannocystis) and inhibiting filamentous bacteria (Candidatus_Alysiosphaera).

The role of microbial diversity and composition in minimizing sludge production in the oxic-settling-anoxic process

The oxic-settling-anoxic (OSA) process, which involves an aerobic tank attached to oxygen- and substrate-deficient external anoxic reactors, minimizes sludge production in biological wastewater treatment. In this study, the microbial community structure of OSA was determined. Principal coordinate analysis showed that among the three operational factors, i.e., (i) redox condition, (ii) external reactor sludge retention time (SRT_ext), and (iii) sludge interchange between aerobic and anoxic reactors, redox condition had the greatest impact on microbial diversity. Generally, reactors with lower oxidation-reduction potential had higher microbial diversity. The main aerobic sequencing batch reactor of OSA (SBR_OSA) that interchanged sludge with an external anoxic reactor had greater microbial diversity than SBR_control which did not have sludge interchange. SBR_OSA sustained high abundance of the slow-growing nitrifying bacteria (e.g., Nitrospirales and Nitrosomondales) and consequently exhibited reduced sludge yield. Specific groups of bacteria facilitated sludge autolysis in the external reactors. Hydrolyzing (e.g., Bacteroidetes and Chloroflexi) and fermentative (e.g., Firmicutes) bacteria, which can break down cellular matter, proliferated in both the external aerobic/anoxic and anoxic reactors. Sludge autolysis in the anoxic reactor was enhanced with the increase of predatory bacteria (e.g., order Myxobacteriales and genus Bdellovibrio) that can contribute to biomass decay. Furthermore, β- and γ-Proteobacteria were identified as the bacterial phyla that primarily underwent decay in the external reactors.

Effects of carbon source on methanogenic activities and pathways incorporating metagenomic analysis of microbial community

In this study, the effects of four types of organic compounds (tryptone, acetate/propionate, glucose and ethanol) on methanogenesis, electron transfer processes and microbial community structure were examined. When tryptone and acetate/propionate were used, the dominant methanogenic pathway was aceticlastic methanogenesis and Methanosarcina was the most abundant methanogen. When glucose or ethanol were provided as the external carbon source, the aceticlastic and hydrogenotrophic pathways were utilised simultaneously, and Methanosarcina and Methanobacterium were enriched. However, the reactor fed with glucose was prone to acidification because volatile fatty acids accumulated in the medium, which inhibited methane synthesis. Geobacter was dominant in the reactor fed with ethanol and 45% of genes encoding pili synthesis were attributable to Geobacter, indicating that direct interspecies electron transfer may be a possible mechanism during syntrophic methanogenesis.

Unraveling the Microbial Interactions and Metabolic Potentials in Pre- and Post-treated Sludge from a Wastewater Treatment Plant Using Metagenomic Studies

Sewage waste represents an ecosystem of complex and interactive microbial consortia which proliferate with different kinetics according to their individual genetic as well as metabolic potential. We performed metagenomic shotgun sequencing on Ion-Torrent platform, to explore the microbial community structure, their biological interactions and associated functional capacity of pre-treated/raw sludge (RS) and post-treated/dried sludge (DS) of wastewater treatment plant. Bacterial phylotypes belonging to Epsilonproteobacteria (∼45.80%) dominated the RS with relatively few Archaea (∼1.94%) whereas DS has the dominance of beta- (30.23%) and delta- (13.38%) classes of Proteobacteria with relatively greater abundance of Archaea (∼7.18%). In particular, Epsilonproteobacteria appears as a primary energy source in RS and sulfur-reducing bacteria with methanogens seems to be in the potential syntrophic association in DS. These interactions could be ultimately responsible for carrying out amino-acid degradation, aromatic compound degradation and degradation of propionate and butyrate in DS. Our data also reveal the presence of key genes in the sludge microbial community responsible for degradation of polycyclic aromatic hydrocarbons. Potential pathogenic microbes and genes for the virulence factors were found to be relatively abundant in RS which clearly reflect the necessity of treatment of RS. After treatment, potential pathogens load was reduced, indicating the sludge hygienisation in DS. Additionally, the interactions found in this study would reveal the biological and environmental cooperation among microbial communities for domestic wastewater treatment.

The bioelectric well: a novel approach for in situ treatment of hydrocarbon-contaminated groundwater

Groundwater contamination by petroleum hydrocarbons (PHs) is a widespread problem which poses serious environmental and health concerns. Recently, microbial electrochemical technologies (MET) have attracted considerable attention for remediation applications, having the potential to overcome some of the limiting factors of conventional in situ bioremediation systems. So far, field‐scale application of MET has been largely hindered by the limited availability of scalable system configurations. Here, we describe the ‘bioelectric well’ a bioelectrochemical reactor configuration, which can be installed directly within groundwater wells and can be applied for in situ treatment of organic contaminants, such as PHs. A laboratory‐scale prototype of the bioelectric well has been set up and operated in continuous‐flow regime with phenol as the model contaminant. The best performance was obtained when the system was inoculated with refinery sludge and the anode potentiostatically controlled at +0.2 V versus SHE. Under this condition, the influent phenol (25 mg l⁻¹) was nearly completely (99.5 ± 0.4%) removed, with an average degradation rate of 59 ± 3 mg l⁻¹ d and a coulombic efficiency of 104 ± 4%. Microbial community analysis revealed a remarkable enrichment of Geobacter species on the surface of the graphite anode, clearly pointing to a direct involvement of this electro‐active bacterium in the current‐generating and phenol‐oxidizing process.

Effects of side-stream ratio on sludge reduction and microbial structures of anaerobic side-stream reactor coupled membrane bioreactors

An anoxic/oxic membrane bioreactor (AO-MBR) and three anaerobic side-stream reactor (ASSR) coupled MBRs (ASSR-MBR) were operated to investigate effects of side-stream ratio (SR) on sludge reduction and microbial community structure of ASSR-MBRs. The ASSR-MBR achieved efficient COD and ammonium nitrogen removal. SR increased from 0.2 to 1.0 favored nitrogen removal, and increased sludge reduction from 6.0% to 49.7%. The total released COD in the ASSR increased with the rising SR and was inversely proportional to sludge yield of ASSR-MBR. Pyrosequencing analysis showed that phyla Chloroflexi and Armatimonadetes surviving in anaerobic conditions were enriched in the ASSR, while Nitrospirae was dominant in the MBR. Comparison at the genus level revealed that higher SR favored the growth of slow growers, while lower SR enriched hydrolytic and predatory bacteria. The results suggested that SR has a profound effect on nitrogen removal, sludge reduction and microbial community structure in the ASSR-MBR.

Rheology and Microbiology of Sludge from a Thermophilic Aerobic Membrane Reactor

A thermophilic aerobic membrane reactor (TAMR) treating high-strength COD liquid wastes was submitted to an integrated investigation, with the aim of characterizing the biomass and its rheological behaviour. These processes are still scarcely adopted, also because the knowledge of their biology as well as of the physical-chemical properties of the sludge needs to be improved. In this paper, samples of mixed liquor were taken from a TAMR and submitted to fluorescent in situ hybridization for the identification and quantification of main bacterial groups. Measurements were also targeted at flocs features, filamentous bacteria, and microfauna, in order to characterize the sludge. The studied rheological properties were selected as they influence significantly the performances of membrane bioreactors (MBR) and, in particular, of the TAMR systems that operate under thermophilic conditions (i.e., around 50°C) with high MLSS concentrations (up to 200 gTS L−1). The proper description of the rheological behaviour of sludge represents a useful and fundamental aspect that allows characterizing the hydrodynamics of sludge suspension devoted to the optimization of the related processes. Therefore, in this study, the effects on the sludge rheology produced by the biomass concentration, pH, temperature, and aeration were analysed.