Low-temperature (10°C) anaerobic digestion of dilute dairy wastewater in an EGSB bioreactor: microbial community structure, population dynamics, and kinetics of methanogenic populations

Full-scale study on high-rate low-temperature anaerobic digestion of agro-food wastewater: process performances and microbial community

The fast-growing global population has led to a substantial increase in food production, which generates large volumes of wastewater during the process. Despite most industrial wastewater being discharged at lower ambient temperatures (<20 °C), majority of the high-rate anaerobic reactors are operated at mesophilic temperatures (>30 °C). High-rate low-temperature anaerobic digestion (LtAD) has proven successful in treating industrial wastewater both at laboratory and pilot scales, boasting efficient organic removal and biogas production. In this study, we demonstrated the feasibility of two full-scale high-rate LtAD bioreactors treating meat processing and dairy wastewater, and the microbial communities in both reactors were examined. Both reactors exhibited rapid start-up, achieving considerable chemical oxygen demand (COD) removal efficiencies (total COD removal >80%) and generating high-quality biogas (CH4% in biogas >75%). Long-term operations (6-12 months) underscored the robustness of LtAD bioreactors even during winter periods (average temperature <12 °C), as evidenced by sustained high COD removal rates (total COD removal >80%). The stable performance was underpinned by a resilient microbial community comprising active acetoclastic methanogens, hydrolytic, and fermentative bacteria. These findings underscore the feasibility of high-rate low-temperature anaerobic wastewater treatment, offering promising solutions to the zero-emission wastewater treatment challenge.

Integrated bioprocess for carbon dioxide sequestration and methanol production

Carbon dioxide (CO2) poses a significant threat, contributing to global warming and climate change. This study focused on isolating efficient CO2-reducing methanogens and methanotrophs for converting methane into methanol. Samples from diverse regions in India were collected and processed, yielding 82 methanogenic and 48 methylotrophic isolates. Methanogenic isolate M11 produced a higher amount of methane, reaching 2.9 mol L-1 on the sixth day of incubation at 35 °C, pH 7.0, and CO2:H2 (80:20) as feeding rates. Under optimized conditions, isolate M11 effectively converted 8.3 mol CO2 to 7.9 mol methane in 24 h. Methylotrophic isolate M31 demonstrated significant soluble methane monooxygenase activity (450 nmol/ml) and produced 0.4 mol methanol in 24 h. 16S rRNA analysis identified Methanobacterium sp. and Methyloceanibacter sp. among the isolates, elucidating their taxonomic diversity. This study offers valuable insights into methanogens' potential in CO2 sequestration and methane conversion to methanol through methanotrophism, a promising sustainable biofuel production.

Unlocking the potential of sugarcane leaf waste for sustainable methane production: Insights from microbial pre-hydrolysis and reactor optimization

Sugarcane leaf waste, a byproduct of the growing global sugar industry, challenges agricultural waste management. This study explores its potential for methane production via anaerobic digestion. A microbial pre-hydrolysis, using lignocellulose-degrading bacteria, enhanced soluble chemical oxygen demand at an optimal initial substrate concentration of 40 g-volatile solid/L. Comparative analysis with untreated and bioaugmented leaves revealed the pre-hydrolyzed leaves achieved the highest methane production rate (MPR) at 14.0 ± 0.5 mL-CH4/L·d, surpassing others by 1.47 and 1.67 times. Two continuous stirred tank reactors were employed to assess the optimal hydraulic retention time (HRT). Results showed a stable methane production with an HRT of 25 days, yielding high MPRs: 88.70 ± 0.63 mL-CH4/L·d from pre-hydrolyzed sugarcane leaves and 82.57 ± 1.22 mL-CH4/L·d from microbial consortium-augmented leaves. A 25-day HRT fosters high microbial diversity with Bacteroidota, Firmicutes, Chloroflexi, and Verrucomicrobiota dominance, indicating favorable conditions. Conversely, a 20-day HRT results in lower diversity due to unfavorable factors like low pH during organic overloading, leading to increased concentrations of volatile fatty acids and lactic acid, with Firmicutes as the predominant phylum. This study highlights sugarcane leaf waste's potential as a valuable resource for sustainable methane production.

Psychrophilic and mesophilic anaerobic treatment of synthetic dairy wastewater with long chain fatty acids: Process performances and microbial community dynamics

Facilitating the anaerobic degradation of long chain fatty acids (LCFA) is the key to unlock the energy potential of lipids-rich wastewater. In this study, the feasibility of psychrophilic anaerobic treatment of LCFA-containing dairy wastewater was assessed and compared to mesophilic anaerobic treatment. The results showed that psychrophilic treatment at 15 ℃ was feasible for LCFA-containing dairy wastewater, with high removal rates of soluble COD (>90%) and LCFA (∼100%). However, efficient long-term treatment required prior acclimation of the biomass to psychrophilic temperatures. The microbial community analysis revealed that putative syntrophic fatty acid bacteria and Methanocorpusculum played a crucial role in LCFA degradation during both mesophilic and psychrophilic treatments. Additionally, a fungal-bacterial biofilm was found to be important during the psychrophilic treatment. Overall, these findings demonstrate the potential of psychrophilic anaerobic treatment for industrial wastewaters and highlight the importance of understanding the microbial communities involved in the process.

Quantification of hydrolysis activity in a biological wastewater treatment context

This paper reviews currently available methods for hydrolysis activity monitoring of the most commonly encountered enzyme categories in biological wastewater treatment. While highlighting the relevant methods for protein, lipid, carbohydrate, organic phosphate, and ester hydrolysis, the discussion of their pros and cons is predominantly aimed at revealing the relevance of the to-be-hydrolyzed substrates that are used in the methods. These "substrates" should mimic the proteins, lipids, or other polymers that are present in the wastewater and are in the reviewed methods (i) real substrates (i.e., naturally present in the wastewater), (ii) chromogenic substrates, or (iii) fluorogenic substrates. We conclude that exploiting relevant substrates such as casein or starch, containing fluorophores, has the highest potential for meaningful high throughput hydrolysis quantification and that lipase activity monitoring is still cumbersome. Monitoring the hydrolysis activity in biological wastewater treatment systems is an underdeveloped area. With this review, which aims at providing a condensed and practice-oriented overview, we hope to facilitate the start or continuation of such monitoring. This monitoring will only grow in importance, given the transition from wastewater treatment plants towards water resource recovery facilities. KEY POINTS: • Colorimetric-based methods are vulnerable to sludge matrix interference. • Bonds in p-nitrophenol-based methods are not representative for the targeted substrates. • Direct methods with relevant/real substrates are preferred. • Fluorophore-containing (real) substrates enable high throughput screening.

Stimulating Effect of Trichococcus flocculiformis on a Coculture of Syntrophomonas wolfei and Methanospirillum hungatei

Syntrophic anaerobic consortia comprised of fatty acid-degrading bacteria and hydrogen/formate-scavenging methanogenic archaea are of central importance for balanced and resilient natural and manufactured ecosystems: anoxic sediments, soils, and wastewater treatment bioreactors. Previously published studies investigated interaction between the syntrophic bi-cultures, but little information is available on the influence of fermentative bacteria on syntrophic fatty acid oxidation, even though fermentative organisms are always present together with syntrophic partners in the above-mentioned ecosystems. Here, we present experimental observations of stimulated butyrate oxidation and methane generation by a coculture of Syntrophomonas wolfei with any of the following methanogens: Methanospirillum hungatei, Methanobrevibacter arboriphilus, or Methanobacterium formicicum due to the addition of a fermentative Trichococcus flocculiformis strain ES5. The addition of T. flocculiformis ES5 to the syntrophic cocultures led to an increase in the rates of butyrate consumption (120%) and volumetric methane production (150%). Scanning electron microscopy of the most positively affected coculture (S. wolfei, M. hungatei, and T. flocculiformis ES5) revealed a tendency of T. flocculiformis ES5 to aggregate with the syntrophic partners. Analysis of coculture’s proteome with or without addition of the fermentative bacterium points to a potential link with signal transducing systems of M. hungatei, as well as activation of additional butyryl coenzyme A dehydrogenase and an electron transfer flavoprotein in S. wolfei.

IMPORTANCE Results from the present study open doors to fascinating research on complex microbial cultures in anaerobic environments (of biotechnological and ecological relevance). Such studies of defined mixed populations are critical to understanding the highly intertwined natural and engineered microbial systems and to developing more reliable and trustable metabolic models. By investigating the existing cultured microbial consortia, like the ones described here, we can acquire knowledge on microbial interactions that go beyond “who feeds whom” relations but yet benefit the parties involved. Transfer of signaling compounds and stimulation of gene expression are examples of indirect influence that members of mixed communities can exert on each other. Understanding such microbial relationships will enable development of new sustainable biotechnologies with mixed microbial cocultures and contribute to the general understanding of the complex natural microbial interactions.

Principles, Advances, and Perspectives of Anaerobic Digestion of Lipids

Several problems associated with the presence of lipids in wastewater treatment plants are usually overcome by removing them ahead of the biological treatment. However, because of their high energy content, waste lipids are interesting yet challenging pollutants in anaerobic wastewater treatment and codigestion processes. The maximal amount of waste lipids that can be sustainably accommodated, and effectively converted to methane in anaerobic reactors, is limited by several problems including adsorption, sludge flotation, washout, and inhibition. These difficulties can be circumvented by appropriate feeding, mixing, and solids separation strategies, provided by suitable reactor technology and operation. In recent years, membrane bioreactors and flotation-based bioreactors have been developed to treat lipid-rich wastewater. In parallel, the increasing knowledge on the diversity of complex microbial communities in anaerobic sludge, and on interspecies microbial interactions, contributed to extend the knowledge and to understand more precisely the limits and constraints influencing the anaerobic biodegradation of lipids in anaerobic reactors. This critical review discusses the most important principles underpinning the degradation process and recent key discoveries and outlines the current knowledge coupling fundamental and applied aspects. A critical assessment of knowledge gaps in the field is also presented by integrating sectorial perspectives of academic researchers and of prominent developers of anaerobic technology.

Effect of static magnetic field on microbial community during anaerobic digestion

Dairy wastewater is characterized by high concentration of organic compounds and is commonly used for energy production. Methods for enhancement of biogas production include application of magnetizers on the digester to induce static magnetic field (SMF). The study aimed at investigation of Bacteria and Archaea communities during anaerobic digestion of model dairy wastewater exposed to SMF. Magnetic field caused a significant increase in methane production to 373.2 mL/g VS compared to 200.2 mL/g VS in a control reactor and methane content to 56.8% compared to 49.1% in a control reactor. In both reactors, the biomass was dominated by Trichococcus sp. The relative abundance of lactic acid bacteria was of about 10% higher in the reactor exposed to SMF. This higher number of Lactobacillales resulted from a higher acetate production, which additionally caused enhanced growth of Methanosarcinacaea in the reactor exposed to SMF. SMF also stimulated the growth of hydrogenotrophic methanogens.

Integrated ABR and UASB system for dairy wastewater treatment: Engineering design and practice

This work designed and assessed the engineering performance of dairy wastewater treatment by an integrated system consisting of an anaerobic baffled reactor (ABR) and an upflow anaerobic sludge blanket (UASB). With fats adsorbed and decomposed, proteins were first denatured coagulated into solids in the ABR treatment process, and this process created suitable conditions for sludge retention in the sludge bed of the UASB. As a result, the combined system achieved a substantial reduction in excess sludge from 3 to 5 t/d to 3 t/m, notable biogas generation, and 98% COD removal, while the other pollutants in the effluent met relevant standards. In addition, the system attained an excellent performance in terms of the energy consumption and water treatment agent amount. Two active plants achieved operation costs lower than 0.5 kW h/t, while stable operations under ambient temperature conditions lasted longer than three years. Engineering practices both technically and economically affirmed the potential of the proposed system for dairy wastewater treatment.

Microbial Community Redundancy and Resilience Underpins High-Rate Anaerobic Treatment of Dairy-Processing Wastewater at Ambient Temperatures

High-rate anaerobic digestion (AD) is a reliable, efficient process to treat wastewaters and is often operated at temperatures exceeding 30°C, involving energy consumption of biogas in temperate regions, where wastewaters are often discharged at variable temperatures generally below 20°C. High-rate ambient temperature AD, without temperature control, is an economically attractive alternative that has been proven to be feasible at laboratory-scale. In this study, an ambient temperature pilot scale anaerobic reactor (2 m³) was employed to treat real dairy wastewater in situ at a milk processing plant, at organic loading rates of 1.3 ± 0.6 to 10.6 ± 3.7 kg COD/m³/day and hydraulic retention times (HRT) ranging from 36 to 6 h. Consistent high levels of COD removal efficiencies, ranging from 50 to 70% for total COD removal and 70 to 84% for soluble COD removal, were achieved during the trial. Within the reactor biomass, stable active archaeal populations were observed, consisting mainly of Methanothrix (previously Methanosaeta) species, which represented up to 47% of the relative abundant active species in the reactor. The decrease in HRT, combined with increases in the loading rate had a clear effect on shaping the structure and composition of the bacterial fraction of the microbial community, however, without affecting reactor performance. On the other hand, perturbances in influent pH had a strong impact, especially when pH went higher than 8.5, inducing shifts in the microbial community composition and, in some cases, affecting negatively the performance of the reactor in terms of COD removal and biogas methane content. For example, the main pH shock led to a drop in the methane content to 15%, COD removals decreased to 0%, while the archaeal population decreased to ~11% both at DNA and cDNA levels. Functional redundancy in the microbial community underpinned stable reactor performance and rapid reactor recovery after perturbations.

Anaerobic treatment of LCFA-containing synthetic dairy wastewater at 20 °C: Process performance and microbial community dynamics

Facilitating anaerobic degradation of long-chain fatty acids (LCFA) is key for tapping the high methane production potential of the fats, oil and grease (FOG) content of dairy wastewaters. In this study, the feasibility of using high-rate granular sludge reactors for the treatment of mixed LCFA-containing synthetic dairy wastewater (SDW) was assessed at 20 °C. The effects of the LCFA concentration (33-45% of COD) and organic loading rates (2-3 gCOD/L·d) were determined using three parallel expanded granular sludge bed reactors. For the first time, long term anaerobic treatment of LCFA-containing feed at 20 °C was shown to be feasible and was linked to the microbial community dynamics in high-rate reactors. During a two-month operation, a soluble COD removal of 84-91% and COD to methane conversion of 44-51% was obtained. However, granular sludge flotation and washout occurred after two months in all reactors without volatile fatty acids (VFA) accumulation, emphasizing the need for sludge retention for long-term granular sludge reactor operation with LCFA-containing feed at low ambient temperatures. The temporal shifts in microbial community structure were studied in the high-rate treatment of SDW, and the process disturbances (elevated LCFA loading, LCFA accumulation, and batch operation) were found to decrease the microbial community diversity. The relative abundance of Methanosaeta increased with higher LCFA accumulation in the settled and flotation layer granules in the three reactors, therefore, acetoclastic methanogenesis was found to be crucial for the high-rate treatment of SDW at 20 °C. This study provides an initial understanding of the continuous anaerobic treatment of LCFA-containing industrial wastewaters at low ambient temperatures.

Anaerobic digestion of agricultural manure and biomass - Critical indicators of risk and knowledge gaps

Anaerobic digestion (AD) has been identified as a potential green technology to treat food and municipal waste, agricultural residues, including farmyard manure and slurry (FYM&S), to produce biogas. FYM&S and digestate can act as soil conditioners and provide valuable nutrients to plants; however, it may also contain harmful pathogens. This study looks at the critical indicators in determining the microbial inactivation potential of AD and the possible implications for human and environmental health of spreading the resulting digestate on agricultural land. In addition, available strategies for risk assessment in the context of EU and Irish legislation are assessed. Storage time and process parameters (including temperature, pH, organic loading rate, hydraulic retention time), feedstock recipe (carbon-nitrogen ratio) to the AD plant (both mesophilic and thermophilic) were all assessed to significantly influence pathogen inactivation. However, complete inactivation of all pathogens is unlikely. There are limited studies evaluating risks from FYM&S as a feedstock in AD and the spreading of resulting digestate. The lack of process standardisation and varying feedstocks between AD farms means risk must be evaluated on a case by case basis and calls for a more unified risk assessment methodology. In addition, there is a need for the enhancement of AD farm-based modelling techniques and datasets to help in advancing knowledge in this area.

Cold adaptation and replicable microbial community development during long-term low-temperature anaerobic digestion treatment of synthetic sewage

The development and activity of a cold-adapting microbial community was monitored during low-temperature anaerobic digestion (LtAD) treatment of wastewater. Two replicate hybrid anaerobic sludge bed-fixed-film reactors treated a synthetic sewage wastewater at 12°C, at organic loading rates of 0.25-1.0 kg chemical oxygen demand (COD) m-3 d-1, over 889 days. The inoculum was obtained from a full-scale anaerobic digestion reactor, which was operated at 37°C. Both LtAD reactors readily degraded the influent with COD removal efficiencies regularly exceeding 78% for both the total and soluble COD fractions. The biomass from both reactors was sampled temporally and tested for activity against hydrolytic and methanogenic substrates at 12°C and 37°C. Data indicated that significantly enhanced low-temperature hydrolytic and methanogenic activity developed in both systems. For example, the hydrolysis rate constant (k) at 12°C had increased 20-30-fold by comparison to the inoculum by day 500. Substrate affinity also increased for hydrolytic substrates at low temperature. Next generation sequencing demonstrated that a shift in a community structure occurred over the trial, involving a 1-log-fold change in 25 SEQS (OTU-free approach) from the inoculum. Microbial community structure changes and process performance were replicable in the LtAD reactors.

The Advanced Anaerobic Expanded Granular Sludge Bed (AnaEG) Possessed Temporally and Spatially Stable Treatment Performance and Microbial Community in Treating Starch Processing Wastewater

This study implements temporal and spatial appraisals on the operational performance and corresponding microbial community structure of a full-scale advanced anaerobic expanded granular sludge bed (AnaEG) which was used to treat low organic loading starch processing wastewater. Results showed stable treatment efficiency could be maintained with long-term erratic influent quality, and a major reaction zone located at the bottom of the AnaEG, where the main pollutant removal rate was greater than 90%. Remarkably, high-throughput sequencing of 16S rRNA gene amplicons displayed that the predominant members constructed the major part of the overall microbial community and showed highly temporal stability. They were affiliated to Chloroflexi (16.4%), Proteobacteria (14.01%), Firmicutes (8.76%), Bacteroidetes (7.85%), Cloacimonetes (3.21%), Ignavibacteriae (1.80%), Synergistetes (1.11%), Thermotogae (0.98%), and Euryarchaeota (3.18%). This part of microorganism implemented the long-term stable treatment efficiency of the reactor. Simultaneously, an extraordinary spatial homogeneity in the granule physic properties and microbial community structure along the vertical direction was observed within the AnaEG. In conclusion, the microbial community structure and the bioreactor’s performance showed notable spatial and temporal consistency, and the predominant populations guaranteed a long-term favorable treatment performance of the AnaEG. It provides us with a better understanding of the mechanism of this recently proposed anaerobic reactor which was used in low organic loading wastewater treatment.

Characterization of Trichococcus paludicola sp. nov. and Trichococcus alkaliphilus sp. nov., isolated from a high-elevation wetland, by phenotypic and genomic analyses

Two psychrotolerant facultative anaerobes, strains B7-2^T and B5^T, were isolated from the Zoige Wetland on the Qinghai-Tibetan Plateau. The 16S rRNA gene sequences of strains B7-2^T and B5^T shared high similarity (>99 %) with those of the type strains of the genus Trichococcus, while their digital DNA-DNA hybridization values with each other (49 %) and with the reference type strains (48-23 %) were lower than 70 %, which suggest that they represent two novel species of the genus Trichococcus. Cells of strains B7-2^T and B5^T were immotile cocci, grew in the temperature range of 4-37 °C (optimum 25 °C) and were alkaliphilic with optimum growth at pH 9.0. The major components of the cellular fatty acids were C16 : 0, anteiso-C17 : 0 and C18 : 0 for strain B7-2^T, and C16 : 0, anteiso-C17 : 0, C18 : 1ω9c and C18 : 0 for strain B5^T. The genomic DNA G+C contents were 46.0 and 46.7 mol% for strains B7-2^T and B5^T, respectively. Based on physiological and genomic characteristics, it is suggested that strains B7-2^T and B5^T represent two novel species within the genus Trichococcus, for which the names Trichococcus paludicola sp. nov. and Trichococcus alkaliphilus sp. nov. are proposed. The type strains are B7-2^T (=DSM 104691^T=KCTC 33886^T) and B5^T (=DSM 104692^T=KCTC 33885^T), respectively.

Comparative Analysis of Methanogenic Communities in Different Laboratory-Scale Anaerobic Digesters

Comparative analysis of methanogenic archaea compositions and dynamics in 11 laboratory-scale continuous stirred tank reactors fed with different agricultural materials (chicken manure, cattle manure, maize straw, maize silage, distillers grains, and Jatropha press cake) was carried out by analysis of the methyl coenzyme-M reductase α-subunit (mcrA) gene. Various taxa within Methanomicrobiales, Methanobacteriaceae, Methanosarcinaceae, Methanosaetaceae, and Methanomassiliicoccales were detected in the biogas reactors but in different proportions depending on the substrate type utilized as well as various process parameters. Improved coverage and higher taxonomic resolution of methanogens were obtained compared to a previous 16S rRNA gene based study of the same reactors. Some members of the genus Methanoculleus positively correlated with the relative methane content, whereas opposite correlations were found for Methanobacterium. Specific biogas production was found to be significantly correlating with Methanosarcinaceae. Statistical analysis also disclosed that some members of the genus Methanoculleus positively correlated with the ammonia level, whereas the prevalence of Methanocorpusculum, Methanobacterium, and Methanosaeta was negatively correlated with this parameter. These results suggest that the application of methanogenic archaea adapted to specific feedstock might enhance the anaerobic digestion of such waste materials in full-scale biogas reactors.

Genomic composition and dynamics among Methanomicrobiales predict adaptation to contrasting environments

Members of the order Methanomicrobiales are abundant, and sometimes dominant, hydrogenotrophic (H₂-CO₂ utilizing) methanoarchaea in a broad range of anoxic habitats. Despite their key roles in greenhouse gas emissions and waste conversion to methane, little is known about the physiological and genomic bases for their widespread distribution and abundance. In this study, we compared the genomes of nine diverse Methanomicrobiales strains, examined their pangenomes, reconstructed gene flow and identified genes putatively mediating their success across different habitats. Most strains slowly increased gene content whereas one, Methanocorpusculum labreanum, evidenced genome downsizing. Peat-dwelling Methanomicrobiales showed adaptations centered on improved transport of scarce inorganic nutrients and likely use H⁺ rather than Na⁺ transmembrane chemiosmotic gradients during energy conservation. In contrast, other Methanomicrobiales show the potential to concurrently use Na⁺ and H⁺ chemiosmotic gradients. Analyses also revealed that the Methanomicrobiales lack a canonical electron bifurcation system (MvhABGD) known to produce low potential electrons in other orders of hydrogenotrophic methanogens. Additional putative differences in anabolic metabolism suggest that the dynamics of interspecies electron transfer from Methanomicrobiales syntrophic partners can also differ considerably. Altogether, these findings suggest profound differences in electron trafficking in the Methanomicrobiales compared with other hydrogenotrophs, and warrant further functional evaluations.

Biological Phosphorus Removal During High-Rate, Low-Temperature, Anaerobic Digestion of Wastewater

We report, for the first time, extensive biologically mediated phosphate removal from wastewater during high-rate anaerobic digestion (AD). A hybrid sludge bed/fixed-film (packed pumice stone) reactor was employed for low-temperature (12°C) anaerobic treatment of synthetic sewage wastewater. Successful phosphate removal from the wastewater (up to 78% of influent phosphate) was observed, mediated by biofilms in the reactor. Scanning electron microscopy and energy dispersive X-ray analysis revealed the accumulation of elemental phosphorus (∼2%) within the sludge bed and fixed-film biofilms. 4′, 6-diamidino-2-phenylindole (DAPI) staining indicated phosphorus accumulation was biological in nature and mediated through the formation of intracellular inorganic polyphosphate (polyP) granules within these biofilms. DAPI staining further indicated that polyP accumulation was rarely associated with free cells. Efficient and consistent chemical oxygen demand (COD) removal was recorded, throughout the 732-day trial, at applied organic loading rates between 0.4 and 1.5 kg COD m^-3 d^-1 and hydraulic retention times of 8–24 h, while phosphate removal efficiency ranged from 28 to 78% on average per phase. Analysis of protein hydrolysis kinetics and the methanogenic activity profiles of the biomass revealed the development, at 12°C, of active hydrolytic and methanogenic populations. Temporal microbial changes were monitored using Illumina MiSeq analysis of bacterial and archaeal 16S rRNA gene sequences. The dominant bacterial phyla present in the biomass at the conclusion of the trial were the Proteobacteria and Firmicutes and the dominant archaeal genus was Methanosaeta. Trichococcus and Flavobacterium populations, previously associated with low temperature protein degradation, developed in the reactor biomass. The presence of previously characterized polyphosphate accumulating organisms (PAOs) such as Rhodocyclus, Chromatiales, Actinobacter, and Acinetobacter was recorded at low numbers. However, it is unknown as yet if these were responsible for the luxury polyP uptake observed in this system. The possibility of efficient phosphate removal and recovery from wastewater during AD would represent a major advance in the scope for widespread application of anaerobic wastewater treatment technologies.

Influence of organic loading rate on integrated bioreactor treating hypersaline mustard wastewater

Mustard tuber wastewater is characterized by high salinity and high organic content that is potentially detrimental to the biological treatment system and affects the treatment efficiency accordingly. The experiment used the integrated bioreactor to reduce much of the organics in mustard tuber wastewater, and found the influence of organic loading rate on effluent chemical oxygen demand (COD) and phosphate (PO4 (3-) -P). Results showed that under the condition of 10-15 °C, 6 mg/L of dissolved oxygen, the reduction value of COD removal rate in anaerobic and aerobic area was 14.5% and 31.7% when the organic loading rate increased from 2.0 to 4.0 kg COD/m(3) /day. Therefore, an integrated bioreactor should take 2.0 kg COD/m(3) /day organic loading rate in mustard wastewater treatment if the effluent is expected to meet the third level of "Integrated Wastewater Discharge Standard" (GB 8978-1996).

Characteristics, process parameters, and inner components of anaerobic bioreactors

The anaerobic bioreactor applies the principles of biotechnology and microbiology, and nowadays it has been used widely in the wastewater treatment plants due to their high efficiency, low energy use, and green energy generation. Advantages and disadvantages of anaerobic process were shown, and three main characteristics of anaerobic bioreactor (AB), namely, inhomogeneous system, time instability, and space instability were also discussed in this work. For high efficiency of wastewater treatment, the process parameters of anaerobic digestion, such as temperature, pH, Hydraulic retention time (HRT), Organic Loading Rate (OLR), and sludge retention time (SRT) were introduced to take into account the optimum conditions for living, growth, and multiplication of bacteria. The inner components, which can improve SRT, and even enhance mass transfer, were also explained and have been divided into transverse inner components, longitudinal inner components, and biofilm-packing material. At last, the newly developed special inner components were discussed and found more efficient and productive.