Comparative study of changes in reaction profile and microbial community structure in two anaerobic repeated-batch reactors started up with different seed sludges

Celebrating 50 years of microbial granulation technologies: From canonical wastewater management to bio-product recovery

Microbial granulation technologies (MGT) in wastewater management are widely practised for more than fifty years. MGT can be considered a fine example of human innovativeness-driven nature wherein the manmade forces applied during operational controls in the biological process of wastewater treatment drive the microbial communities to modify their biofilms into granules. Mankind, over the past half a century, has been refining the knowledge of triggering biofilm into granules with some definite success. This review captures the journey of MGT from inception to maturation providing meaningful insights into the process development of MGT-based wastewater management. The full-scale application of MGT-based wastewater management is discussed with an understanding of functional microbial interactions within the granule. The molecular mechanism of granulation through the secretion of extracellular polymeric substances (EPS) and signal molecules is also highlighted in detail. The recent research interest in the recovery of useful bioproducts from the granular EPS is also emphasized.

Potential treatment of aged cow manure using spare capacity in anaerobic digesters treating a mixture of food waste and pig manure

With the increasing production of cow manure (CM) and the continuing decrease in the demand for manure compost, CM management has become an urgent and challenging task in Korea. In most cattle farms in Korea, CM mixed with bedding materials is left in pens exposed to the open air for several months before treatment, which makes CM an unsuitable feedstock for anaerobic digestion. This study examined the co-digestion of aged CM with a mixture of food waste and pig manure as the base substrate to assess the possibility of treating and valorizing CM using spare capacity in existing anaerobic digesters dealing with other wastes. The duplicate digesters initially fed with the base substrate were subjected to the addition of increasing amounts of CM (3-10% in the feed, w/v) over nine months. Co-feeding CM up to 5% in the feed (w/v) did not compromise the methanogenic degradation of the substrates, but adding more CM led to a significant performance deterioration likely related to the buildup of inhibitory free ammonia and H₂S. Adding CM substantially influenced the digester microbial communities, especially methanogenic communities, and induced a dominance shift from aceticlastic Methanothrix to hydrogenotrophic methanogens as the CM fraction increased. The overall results suggest that the CM fraction should not exceed 5% in the feed (w/v) for its stable treatment with the base substrate in the experimental digesters. Although further studies are needed, anaerobic treatment using spare capacity in existing digesters can be a useful strategy for the management of aged CM.

Long-term monitoring of a thermal hydrolysis-anaerobic co-digestion plant treating high-strength organic wastes: Process performance and microbial community dynamics

Two parallel anaerobic digesters (8500 m³ capacity each), combined with thermal hydrolysis (TH) pretreatment, co-digesting dewatered sewage sludge, dewatered human feces, and food wastewater were monitored over a 12-month period from start-up to explore the feasibility of field application of the combined process. The waste mixtures before and after pretreatment and the feed and digestate of each digester were taken semimonthly (i.e., 48 samples in total) for analysis of the feed characteristics, process parameters, and digester microbial community structure. The TH pretreatment proved effective in improving the bioavailability of the waste mixture. The solubilization efficiency tended to increase with the particulate organic fraction in the raw mixture. Although fluctuations in the feed characteristics and loading significantly influenced the process and microbial behaviors, the digesters maintained stable performance during the study period. Our results demonstrate that the TH-anaerobic digestion process can achieve an effective and robust treatment of the waste mixture.

Interfacial Biocatalytic Performance of Nanofiber-Supported β-Galactosidase for Production of Galacto-Oligosaccharides

Molecular distribution, structural conformation and catalytic activity at the interface between enzyme and its immobilising support are vital in the enzymatic reactions for producing bioproducts. In this study, a nanobiocatalyst assembly, β-galactosidase immobilized on chemically modified electrospun polystyrene nanofibers (PSNF), was synthesized for converting lactose into galacto-oligosaccharides (GOS). Characterization results using scanning electron microscopy (SEM) and fluorescence analysis of fluorescein isothiocyanat (FITC) labelled β-galactosidase revealed homogenous enzyme immobilization, thin layer structural conformation and biochemical functionalities of the nanobiocatalyst assembly. The β-galactosidase/PSNF assembly displayed enhanced enzyme catalytic performance at a residence time of around 1 min in a disc-stacked column reactor. A GOS yield of 41% and a lactose conversion of 88% was achieved at the initial lactose concentration of 300 g/L at this residence time. This system provided a controllable contact time of products and substrates on the nanofiber surface and could be used for products which are sensitive to the duration of nanobiocatalysis.

Microbial community structure in full scale anaerobic mono-and co-digesters treating food waste and animal waste

Five mesophilic full-scale anaerobic digesters treating food waste (FW-digester), animal waste (AW-digester), and co-substrate of food waste and animal waste (CO-digesters) were monitored identify bacterial and archaeal communities and to quantify the effect of substrate characteristics on them, and to identify 'core' microorganism. The substrate characteristics and microbial communities of the FW-digester, AW-digester, and CO-digesters were statistically different. Organic concentration and [Na⁺] were identified as major variations that effect microbial community. Methanogen community was more diverse in AW-digester than in FW-digester. Methanogen community in CO-digester was as diverse as in AW-digester, and the most dominant species was Methanoculleus bourgensis same as in FW-digester. Twenty-one bacterial genera and four methanogen species were found in all digesters as a consequence of their metabolic versatility to degrade organic and inhibitor compounds. The results implied that these core microorganisms may contribute to maintaining a stable microbial ecosystem.

Biomethanation of Harmful Macroalgal Biomass in Leach-Bed Reactor Coupled to Anaerobic Filter: Effect of Water Regime and Filter Media

Ulva is a marine macroalgal genus which causes serious green tides in coastal areas worldwide. This study investigated anaerobic digestion as a way to manage Ulva waste in a leach-bed reactor coupled to an anaerobic filter (LBR-AF). Two LBR-AF systems with different filter media, blast furnace slag grains for R1, and polyvinyl chloride rings for R2, were run at increasing water replacement rates (WRRs). Both achieved efficient volatile solids reduction (68.4–87.1%) and methane yield (148–309 mL/g VS fed) at all WRRs, with the optimal WRR for maximum methane production being 100 mL/d. R1 maintained more stable methanation performance than R2, possibly due to the different surface properties (i.e., biomass retention capacity) of the filter media. Such an effect was also noted in the different behaviors of the LBR and AF between R1 and R2. The molecular analysis results revealed that the development of the microbial community structure in the reactors was primarily determined by the fermentation type, i.e., dry (LBR) or wet (AF).

Biogas

Biogas production represents a fascinating process for the recovery of nutrients and renewable energy from various organic waste streams. The process is of interest for the production of value-added chemicals by mixed cultures and can also be applied in combined bioenergy production systems. Strategies and opportunities for optimization of biogas quality and quantity are presented.

A long-term study on the effect of magnetite supplementation in continuous anaerobic digestion of dairy effluent - Enhancement in process performance and stability

Interspecies electron transfer (IET) between microbial populations with different functions is critical to stable anaerobic digestion. This study, in an attempt to facilitate IET, investigated the effect of magnetite supplementation on the biomethanation of dairy effluent in continuous mode. The magnetite-added reactor (RM) was significantly more resistant and resilient to process imbalance than the reactor run without magnetite addition (RC). RC showed unstable performance with repeated process upsets, but its performance improved to be comparable to that of RM after applying magnetite supplementation. Magnetite was particularly effective in stabilizing a build-up of propionic acid and therefore improving the process robustness and reliability. The enhanced biomethanation in terms of productivity and stability was attributed to the facilitated direct IET (DIET) between exoelectrogens and methanogens via magnetite particles. Methanosaeta was the predominant methanogen group in the experimental reactors and likely played a key role in both DIET-mediated carbon dioxide-reducing and aceticlastic methanogenesis.

Intergenomic evolution and metabolic cross-talk between rumen and thermophilic autotrophic methanogenic archaea

Methanobrevibacter ruminantium M1 (MRU) is a rumen methanogenic archaean that can be able to utilize formate and CO₂/H₂ as growth substrates. Extensive analysis on the evolutionary genomic contexts considered herein to unravel its intergenomic relationship and metabolic adjustment acquired from the genomic content of Methanothermobacter thermautotrophicus ΔH. We demonstrated its intergenomic distance, genome function, synteny homologs and gene families, origin of replication, and methanogenesis to reveal the evolutionary relationships between Methanobrevibacter and Methanothermobacter. Comparison of the phylogenetic and metabolic markers was suggested for its archaeal metabolic core lineage that might have evolved from Methanothermobacter. Orthologous genes involved in its hydrogenotrophic methanogenesis might be acquired from intergenomic ancestry of Methanothermobacter via Methanobacterium formicicum. Formate dehydrogenase (fdhAB) coding gene cluster and carbon monoxide dehydrogenase (cooF) coding gene might have evolved from duplication events within Methanobrevibacter-Methanothermobacter lineage, and fdhCD gene cluster acquired from bacterial origins. Genome-wide metabolic survey found the existence of four novel pathways viz. l-tyrosine catabolism, mevalonate pathway II, acyl-carrier protein metabolism II and glutathione redox reactions II in MRU. Finding of these pathways suggested that MRU has shown a metabolic potential to tolerate molecular oxygen, antimicrobial metabolite biosynthesis and atypical lipid composition in cell wall, which was acquainted by metabolic cross-talk with mammalian bacterial origins. We conclude that coevolution of genomic contents between Methanobrevibacter and Methanothermobacter provides a clue to understand the metabolic adaptation of MRU in the rumen at different environmental niches.

Denitrification of groundwater using PHBV blends in packed bed reactors and the microbial diversity

In the present study, three kinds of biopolymers, PHBV, PHBV/starch and PHBV/bamboo powder (BP) blends were used as carbon source and biofilm carriers for denitrification in packed bed reactors to remove nitrate from groundwater. Results showed that a fast start-up was obtained in bioreactors filled with both PHBV/Starch and PHBV/BP blends without external inocula and it took more than 3 month for PHBV reactor to reach the same loading rate. The PHBV/BP packed reactor exhibited a better nitrate removal efficiency (87.4 ± 7.0%) and less adverse effects in nitrite accumulation and DOC release (below 0.5 mg NO2N L(-1) and 10.5 mg DOC L(-1) in the effluent) during stable operation. Pyrosequencing analysis demonstrated that bacteria belonging to genus Clostridium in phylum Firmicus, which play the primary role in degrading the biopolymers, are the most dominant (33-15% of the sequences). The predominant species in all samples is related to Clostridium crotonatovorans. All the identified 11 genera of denitrifying bacteria affiliated with phylum Proteobacteria and constituted 30-55% in the representative sequences. The PHBV/BP blend is economically attractive carbon source with good denitrification performance.

Response of a continuous anaerobic digester to temperature transitions: A critical range for restructuring the microbial community structure and function

Temperature is a crucial factor that significantly influences the microbial activity and so the methanation performance of an anaerobic digestion (AD) process. Therefore, how to control the operating temperature for optimal activity of the microbes involved is a key to stable AD. This study examined the response of a continuous anaerobic reactor to a series of temperature shifts over a wide range of 35-65 °C using a dairy-processing byproduct as model wastewater. During the long-term experiment for approximately 16 months, the reactor was subjected to stepwise temperature increases by 5 °C at a fixed HRT of 15 days. The reactor showed stable performance within the temperature range of 35-45 °C, with the methane production rate and yield being maximum at 45 °C (18% and 26% greater, respectively, than at 35 °C). However, the subsequent increase to 50 °C induced a sudden performance deterioration with a complete cessation of methane recovery, indicating that the temperature range between 45 °C and 50 °C had a critical impact on the transition of the reactor's methanogenic activity from mesophilic to thermophilic. This serious process perturbation was associated with a severe restructuring of the reactor microbial community structure, particularly of methanogens, quantitatively as well as qualitatively. Once restored by interrupted feeding for about two months, the reactor maintained fairly stable performance under thermophilic conditions until it was upset again at 65 °C. Interestingly, in contrast to most previous reports, hydrogenotrophs largely dominated the methanogen community at mesophilic temperatures while acetotrophs emerged as a major group at thermophilic temperature. This implies that the primary methanogenesis route of the reactor shifted from hydrogen- to acetate-utilizing pathways with the temperature shifts from mesophilic to thermophilic temperatures. Our observations suggest that a mesophilic digester may not need to be cooled at up to 45 °C in case of undesired temperature rise, for example, by excessive self-heating, which offers a possibility to reduce operating costs.

Anaerobic treatment of rice winery wastewater in an upflow filter packed with steel slag under different hydraulic loading conditions

Rice-washing drainage (RWD), a strong organic wastewater, was anaerobically treated using an upflow filter filled with blast-furnace slag. The continuous performance of the reactor was examined at varying hydraulic retention times (HRTs). The reactor achieved 91.7% chemical oxygen demand removal (CODr) for a 10-day HRT (0.6 g COD/Ld organic loading rate) and maintained fairly stable performance until the HRT was shortened to 2.2 days (CODr > 84%). Further decreases in HRT caused process deterioration (CODr < 50% and pH < 5.5 for a 0.7-day HRT). The methane production rate increased with decreasing HRT to reach the peak level for a 1.3-day HRT, whereas the yield was significantly greater for 3.4-day or longer HRTs. The substrate removal and methane production kinetics were successfully evaluated, and the generated kinetic models produced good performance predictions. The methanogenic activity of the reactor likely relies on the filter biofilm, with Methanosaeta being the main driver.

Response of a continuous biomethanation process to transient organic shock loads under controlled and uncontrolled pH conditions

The organic loading rate (OLR) is a critical factor that controls the treatment efficiency and biogas production in anaerobic digestion (AD). Therefore, organic shock loads may cause significant process imbalances accompanied by a drop in pH and acid accumulation or even failure. This study investigated the response of a continuous mesophilic anaerobic bioreactor to a series of transient organic shock loads of the substrate whey permeate, a high-strength organic wastewater from cheese making. The reactor was subjected to organic shock loads of increasing magnitude (a one-day pulse of elevated feed organic concentration) under controlled (near 7) and uncontrolled pH conditions at a fixed HRT of 10 days. The reactor was resilient to up to a shock load of up to 8.0 g SCOD/L·d under controlled pH conditions but failed to recover from the serious imbalance caused by a 3.0-g SCOD/L·d shock load, thus indicating the critical effect of pH on system resilience. The acidified reactor was not restored by interrupted feeding under the acidic conditions that were formed (pH ≤ 4.5) but was successfully restored after pH adjustment to 7. The reactor subsequently reverted to continuous mode without pH control and showed a performance comparable to the stable performance at the design OLR of 1.0 g SCOD/L·d. The bacterial community structure shifted dynamically in association with disturbances in the reactor conditions, whereas the archaeal community structure remained simple and less variable during the shock loading experiments. The structural shifts of the bacterial community were well correlated with the process performance changes, and performance recovery was generally accompanied by recovery of the bacterial community structure. The overall results suggest that the reactor pH, rather than simply acting as an accumulation of organic acids, had a crucial effect on the resilience and robustness of the microbial community and thus on the reactor performance under organic shock loads.

Performance of and methanogenic communities involved in an innovative anaerobic process for the treatment of food wastewater in a pilot plant

In this study, dual-cylindrical anaerobic digesters were designed and built on the pilot plant scale for the improvement of anaerobic digestion efficiency. The removal efficiency of organics, biogas productivity, yield, and microbial communities was evaluated as performance parameters of the digester. During the stable operational period in the continuous mode, the removal efficiencies of chemical oxygen demand and total solids were 74.1 and 65.1%, respectively. Biogas productivities of 63.9 m(3)/m(3)-FWW and 1.3 m(3)/kg-VSremoved were measured. The hydrogenotrophic methanogen orders, Methanomicrobiales and Methanobacteriales, were predominant over the aceticlastic methanogen order, Methanosarcinaceae, probably due to the tolerance of the hydrogenotrophs to environmental perturbation in the field and their faster growth rate compared with that of the aceticlastics.

A review: factors affecting excess sludge anaerobic digestion for volatile fatty acids production

This paper presents a review of methods that improve the production of volatile fatty acids (VFA) from excess sludge during the anaerobic digestion process. These methods are mainly divided into two approaches. The first approach is located in the pre-treatment methods, which change the properties of the substrates, such as thermal pre-treatment, alkaline pre-treatment, microwave pre-treatment and ultrasonic pre-treatment. The other approach is found in the fermentation process control methods, which influence the environment of anaerobic digestion for the production of VFA, such as pH, temperature, mixing, additives and solids retention time control. In the text recent research studies of each method are listed and analyzed in detail. Comparably, microwave and ultrasonic pre-treatment methods are considered emerging and promising technologies due to their efficiency and environmentally friendly characteristics. However, the microwave pre-treatment has high electricity demand, which might make the process economically unfeasible. In order to calculate optimal operation, further studies still need to be done.

Rapid fingerprinting of methanogenic communities by high-resolution melting analysis

Characterizing microbial community structure using molecular techniques is becoming a popular approach in studies of waste/wastewater treatment processes. A rapid and robust tool to analyze microbial communities is required for efficient process monitoring and control. In this study, a new community fingerprinting method based on high-resolution melting (HRM) analysis was developed and applied to compare methanogenic community structures of five different anaerobic digesters. The new method produced robust community clustering and ordination results comparable to the results from the commonly used denaturing gradient gel electrophoresis (DGGE) performed in parallel. This method transforms melting peak plots (MPs) of community DNA samples generated by HRM analysis to molecular fingerprints and estimates the relationships between the communities based on the fingerprints. The MP-based fingerprinting would provide a good alternative to monitor variations in microbial community structure especially when handling large sample numbers due to its high-throughput capacity and short analysis time.

Shifts in bacterial and archaeal community structures during the batch biomethanation of Ulva biomass under mesophilic conditions

Mesophilic biomethanation of Ulva biomass was performed in a batch bioreactor, and a high organic removal of 77% was obtained on the basis of chemical oxygen demand (COD) after a month of operation. The estimated methane yield was 0.43 ± 0.02 L CH4/g COD(removed) which is close to the theoretical methane potential. Transitions of bacterial and archaeal community structures, associated with process performance data, were investigated using a combination of molecular fingerprinting and biostatistical tools. During the operation, archaeal community structure had no significant changes while bacterial community structure shifted continuously and dynamically. The reactor completely stabilized volatile fatty acids (primarily acetate and propionate) accumulated from the acidogenesis phase, with Methanosaeta- and Methanolinea-related microbes respectively being the main aceticlastic and hydrogenotrophic methanogens. Methanolinea- and Syntrophobacter-related populations were likely the key members to form a syntrophic propionate-degrading consortium. A Methanolinea-related population was likely the dominant methane producer in the experimental reactor.

Methane production and microbial community structure for alkaline pretreated waste activated sludge

Alkaline pretreatment was studied to analyze the influence on waste activated sludge (WAS) reduction, methane production and microbial community structure during anaerobic digestion. Methane production from alkaline pretreated sludge (A-WAS) (pH = 12) increased from 251.2 mL/Ld to 362.2 mL/Ld with the methane content of 68.7% compared to raw sludge (R-WAS). Sludge reduction had been improved, and volatile suspended solids (VSS) removal rate and protein reduction had increased by ∼ 10% and ∼ 35%, respectively. The bacterial and methanogenic communities were analyzed using 454 pyrosequencing and clone libraries of 16S rRNA gene. Remarkable shifts were observed in microbial community structures after alkaline pretreatment, especially for Archaea. The dominant methanogenic population changed from Methanosaeta for R-WAS to Methanosarcina for A-WAS. In addition to the enhancement of solubilization and hydrolysis of anaerobic digestion of WAS, alkaline pretreatment showed significant impacts on the enrichment and syntrophic interactions between microbial communities.

Influence of ferric oxyhydroxide addition on biomethanation of waste activated sludge in a continuous reactor

This study investigated the potential of enhancing the activity of iron-reducing bacteria (IRBs) to increase the biomethanation rate of waste activate sludge (WAS). The effects of biostimulation by ferric oxyhydroxide (Phase 2) and bioaugmentation with an enriched IRB consortium (Phase 3) were examined in a continuous anaerobic reactor treating WAS. Compared to the control operation (Phase 1), significant rises in methane yield (10.8-59.4%) and production rate (24.5-52.9%) were demonstrated by the biostimulation and bioaugmentation treatments. Visible structural changes were observed in bacterial community with the phases while not in archaeal community. Acinetobacter- and Spirochaetales-related populations were likely the major players driving anaerobic iron respiration and thus leading to enhanced biomethanation performance, in Phases 2 and 3, respectively. Our results suggest an interesting new potential for enhancing biomethanation of WAS.

Volatile fatty acids (VFAs) accumulation and microbial community structure of excess sludge (ES) at different pHs

This study aimed at exploring the potential of volatile fatty acids (VFAs) produced from excess sludge (ES) as a new cost-effective internal carbon source in wastewater treatment processes. The optimal condition for VFA accumulation and the bacterial community structure in the bio-production of VFAs from ES were investigated at different pH conditions. Denaturing gradient gel electrophoresis (DGGE) was performed to characterize the bacterial community structure of ES. The results showed that the optimal pH was 10.0 for VFA production, and acetic and propionic acids were the dominant acid species. Pseudomonas sp. was identified as the major bacteria capable of utilizing organic carbon at all pHs. Uncultured bacterium (AB658278) adapted well at high pH. Uncultured bacteria (KC633537 and JN596370) were mainly responsible for anaerobic degradation of ES. The study demonstrated the variation of bacterial community structures at pHs and the close correlation with the VFA accumulation.

Distribution and abundance of Spirochaetes in full-scale anaerobic digesters

To investigate the distribution and abundance of spirochaetal communities within anaerobic digesters, pyrosequencing of the 16S rRNA gene was conducted. Phylogenetic analysis identified a cluster which included the majority of core spirochaetal operational taxonomic units (OTUs) and environmental clones but no pure-culture strains. Distribution of the core OTUs demonstrated an importance of local factors in shaping the structure of Spirochaetes. Spirochaetal to bacterial 16S rRNA gene copy numbers varied from 1.3% to 30.0% depending on digester samples. Environmental variables were found to influence the relative abundance of Spirochaetes. In a batch anaerobic digestion experiment testing the response to different substrates, acetate most stimulated the activity of Spirochaetes, suggesting possible acetate oxidation by syntrophic acetate oxidation process. Taken together, the results obtained in this study provides an insight into the ecology of Spirochaetes in anaerobic digesters and a basis for future studies examining ecological function of these bacteria.

Comparison of methanogenic community structure and anaerobic process performance treating swine wastewater between pilot and optimized lab scale bioreactors

To investigate methanogenic community structure and process performance of anaerobic digestion treating swine wastewater at different scale, a pilot plant with 20 m(3) of effective working volume and lab scale methanogenic digester with 6L working volume were operated for 71 days and 6 turnover periods, respectively. During the steady state of anaerobic digestion, COD and VS removal efficiency in pilot plant were 65.3±3.2, 51.6±4.3%, respectively, which was similar to those in lab scale. However, calculated VFAs removal efficiency and methane yield were lower in pilot plant than in lab scale digester. Also, organics removal efficiencies, which consist of total carbohydrates, proteins, and lipids, were different between pilot and lab scale. These results were thought to be due to the ratio of carbohydrates to proteins in the raw swine wastewater. As a result of qualitative microbial analysis, Methanoculleus receptaculii, and Methanoculleus bourgensis, were commonly concerned with methane production.

Thermo-alkaline pretreatment of waste activated sludge at low-temperatures: effects on sludge disintegration, methane production, and methanogen community structure

Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0-0.2 M NaOH and 60-90°C, for the effects of NaOH concentration and temperature on sludge degradability in anaerobic digestion (AD). Significant disintegration of sludge solids (up to 75.6%) and an increase in methane production (up to 70.6%) were observed in the pretreatment trials. Two quadratic models were successfully generated by response surface analysis (R(2)>0.9, p<0.05) to approximate how the degree of sludge disintegration (SD) and methane production (MP) respond to changes in the pretreatment conditions. The maximum responses of SD (77.8%) and MP (73.9% increase over the control) were shown at [0.16 M NaOH, 90°C] and [0.10 M NaOH, 73.7°C], respectively. NaOH addition showed a significant influence on the evolution of methanogen community structure during AD, whereas temperature did not. Aceticlastic Methanosaeta and Methanosarcina speceies were likely the major methanogens.