Seungyong Lee

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

Microbial community structure and dynamics were examined in two anaerobic reactors run in repeated-batch mode to treat whey permeate. Despite being started up using different seeding sources, the reactors showed generally similar reaction patterns and performances. During the repeated-batch operation for three cycles, the overall reaction rate increased with the increase in the initial population size of both bacteria and methanogens over cycles. Clostridium- and Methanospirillum-related microorganisms were likely the main acidogenic and methanogenic populations, respectively, in both reactors. Bacterial community structure shifted dynamically over cycles, while little change was observed in methanogen community structure throughout the operation. This means that the changes in bacterial community structure changes had little influence on the formation and evolution of methanogen community structure in the reactors. The increased methanogenesis rate with cycles seemed therefore more likely due to the effect of the increase in methanogen abundance rather than the alteration of community structure.

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.

Effect of mild-temperature H 2O 2 oxidation on solubilization and anaerobic digestion of waste activated sludge

Efficient sludge management is among the most challenging issues in wastewater treatment today, and anaerobic digestion is regarded as a viable solution. Mild-temperature H 2O 2 oxidation was examined for enhanced solubilization and biogas production of waste activated sludge (WAS). The effects of pretreatment factors (i.e. temperature and H 2O 2 concentration) on the degree of WAS disintegration (DD) and biogas yield (BY) were assessed by response surface analysis within the design space of 60–90°C and 0–200 mM H 2O 2. Significant sludge disintegration (up to 23.0% DD) and visibly enhanced BY (up to 26.9%) were shown in the pretreatment trials. Two response surface models to describe how DD and BY respond to changes in the pretreatment conditions were successfully constructed (R2>0.95, p<0.05). The models showed totally different response surface shapes, indicating the DD and BY were influenced by pretreatment conditions in very different ways. DD was dominantly affected by temperature and showed higher model responses at the high-temperature region, while the BY response peaked in the low-temperature and mid-level H 2O 2 region. This observation implies that the enhanced solubilization of WAS was not directly translated into an increase in biogas production. Our results showed that WAS can be efficiently disintegrated by H 2O 2 oxidation under mild-temperature conditions for enhanced anaerobic digestibility. Within the explored region of pretreatment conditions, the maximum BY was estimated to be 82.1 mL/gCODadded (32.8% greater than the untreated control) at (60.0°C, 74.2 mM H 2O 2).

Development of biocathode during repeated cycles of bioelectrochemical conversion of carbon dioxide to methane

Functioning biocathodes are essential for electromethanogenesis. This study investigated the development of a biocathode from non-acclimated anaerobic sludge in an electromethanogenesis cell at a cathode potential of -0.7V (vs. standard hydrogen electrode) over four cycles of repeated batch operations. The CO2-to-CH4 conversion rate increased (to 97.7%) while the length of the lag phase decreased as the number of cycles increased, suggesting that a functioning biocathode developed during the repeated subculturing cycles. CO2-resupply test results suggested that the biocathode catalyzed the formation of CH4 via both direct and indirect (H2-mediated) electron transfer mechanisms. The biocathode archaeal community was dominated by the genus Methanobacterium, and most archaeal sequences (>89%) were affiliated with Methanobacterium palustre. The bacterial community was dominated by putative electroactive bacteria, with Arcobacter, which is rarely observed in biocathodes, forming the largest population. These electroactive bacteria were likely involved in electron transfer between the cathode and the methanogens.

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 m3/m3-FWW and 1.3 m3/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. Graphical Abstract Innovative dual-cylindrical anaerobic digester

Anaerobic co-digestion of high-strength organic wastes pretreated by thermal hydrolysis

Thermal hydrolysis (TH) pretreatment was investigated for the anaerobic digestion (AD) of a mixture of high-strength organic wastes (i.e., dewatered human feces, dewatered sewage sludge, and food wastewater) at laboratory scale to simulate a full-scale plant and evaluate its feasibility. The reactors maintained efficient and stable performance at a hydraulic retention time of 20 days, which may be not sufficient for the mesophilic AD of high-suspended-solid wastes, despite the temporal variations in organic load. The addition of FeCl3 was effective in controlling H2S and resulted in significant changes in the microbial community structure, particularly the methanogens. The temporary interruption in feeding or temperature control led to immediate performance deterioration, but it recovered rapidly when normal operations were resumed. The overall results suggest that the AD process coupled with TH pretreatment can provide an efficient, robust, and resilient system to manage high-suspended-solid wastes, supporting the feasibility of its full-scale implementation.