Biomedical subjects

Moonil Kim

Publications and source records attributed to Moonil Kim.

21 records · Page 2Linked to original sources

PubMed2002

Aerobic waste activated sludge (WAS) for start-up seed of mesophilic and thermophilic anaerobic digestion.

Since there are very limited numbers of thermophilic anaerobic digesters being operated, it is often difficult to start up a new one using sludge from an existing reactor as a seed. However, for obvious reasons it seems few attempts have been made to compare the start-up performance of thermophilic anaerobic digestion using different sources of seed sludges. The purpose of this study was to evaluate the start-up performance of anaerobic digestion using aerobic waste activated sludge (WAS) from a plant which has no anaerobic digesters and mesophilic anaerobic digested sludge (ADS) as the seed source at both mesophilic (35 degrees C) and thermophilic (55 degrees C) temperatures. In this study, two experiments were conducted. First, thermophilic anaerobic reactors were seeded with WAS (VSS = 4400 mg/L) and ADS (VSS = 14,500 mg/L) to investigate start-up performance with a feed of acetate as well as propionate. The results show that WAS started to produce CH4 soon after acetate feeding without a lag time, while ADS had a lag time of 10 days. When the feed was changed to propionate, WAS removed propionate down to below the detection limit of 10 mg/L, while ADS removed little propionate and produced little CH4. Second, in order to further compare the methanogenic activity of WAS and ADS, both mesophilic and thermophilic reactors were operated. WAS acclimated to anaerobic conditions shortly (< 5 days at both mesophilic and thermophilic) and after acclimating it produced more CH4 per unit amount of seeded VSS than ADS. WAS at mesophilic temperature biodegraded acetate at the same rate as for thermophilic. However WAS at mesophilic temperature biodegraded propionate at a much faster rate than at thermophilic. WAS as the seed source of anaerobic digestion resulted in much better performance than ADS at both mesophilic and thermophilic temperatures for both acetate and propionate metabolism.

Bacteria, Anaerobic↗

PubMed2002

Comparative process stability and efficiency of anaerobic digestion; mesophilic vs. thermophilic.

The comparative process stability and efficiency of mesophilic (35 degrees C) and thermophilic anaerobic digestion (55 degrees C) has been evaluated for four different reactor configurations, which are: daily batch-fed single-stage continuously stirred tank reactor (CSTR), continuously fed single-stage CSTR, daily batch-fed two-phase CSTR, and daily batch-fed non-mixed single-stage reactor. The results are discussed for three periods: (1) start-up, (2) steady state, and (3) organic loading rate (OLR) increase until reactor failure (pH below 5.5). During the start-up, the single-stage CSTRs at both temperatures showed the least stability, while the non-mixed single-stage reactors reached steady state in the shortest time with relatively stable pH and low volatile fatty acid (VFA). In the case of the thermophilic non-mixed reactor, efficient removal of propionate occurred but supplementation of nutrients (Ca, Fe, Ni, and Co) was required when VFA increased. The results imply the importance of inorganic nutrients bioavailability. The comparative results of the reactor performance at steady state clearly showed the superior performance of the thermophilic non-mixed reactor with respect to lower VFA, higher gas production and volatile solids removal implying that microbial consortia proximity can alleviate the problem of poor effluent quality in thermophilic system. During the OLR increase until reactor failure, all thermophilic reactors except the thermophilic non-mixed reactor showed increases in propionate concentrations as the OLR increased, while all mesophilic reactors except the mesophilic two-phase system showed little increase in VFA concentrations. When all reactors had the same conditions with OLR increase, the continuously fed reactors showed the lowest gas production, while the non-mixed reactors showed the highest gas production at both temperatures. It is hypothesized that the non-mixing reactor configuration has closer microbial consortia proximity than others. Therefore, the results in this study indicated the importance of microbial consortia proximity. A proposed model for the effect of the distance between two syntrophic bacteria reasonably matched the data in this study.

Acetates↗

PubMed2002

The role of pH in mesophilic anaerobic sludge solubilization.

The effect of pH on anaerobic solubilization of synthetic sludge (dog food) and domestic primary sludge was investigated and compared. Anaerobic solubilization was carried out in Continuously Stirred Anaerobic Reactors at mesophilic temperature (35 degrees C) and pH was fixed at 6.5 (pH-controlled). The aim of pH control in the reactors consisting of synthetic and primary sludge, was the evaluation of retardation in hydrolysis/acidogenesis at low pH values. Since synthetic and primary sludge have different biodegradation characteristics, the results were compared. In both sludges, acetic acid was the main Volatile Fatty Acids (VFAs) produced. Volatile Suspended Solid (VSS) reduction was found as 67% in about 20 days in the anaerobic digestion of synthetic sludge. whereas for the same interval VSS reduction could only be achieved by 32% in primary sludge at 35 degrees C in the pH-controlled reactors. When both types of sludges were used as substrates, the reactors removed VSS with a corresponding production of VFAs and Soluble Chemical Oxygen Demand (SCOD). However, in the pH-controlled reactors production of VFAs and SCOD was ceased after 5 days in primary sludge whereas VFAs and SCOD production continued after 5 days in synthetic sludge which indicated that hydrolysis and fermentation in the anaerobic solubilization reactors were not complete and continued longer. On the other hand, in the pH-controlled reactor of primary sludge, methanogenic phase could operate after 5 days of operation as hydrolysis/acidogenesis stopped.

Bacteria, Anaerobic↗