Papers by Author: Sung Hoon Park

Abstract: Anaerobically digested sludge was seeded in a mesophilic UASB reactor and the sludge was monitored for seven months to better understand the start-up process of the reactor. The reactor was fed with synthetic wastewater containing glucose. As the COD loading rate increased stepwise (from 1 to 4 g COD l-1 d-1), the methane production rate increased. COD removal efficiency was maintained to be greater than 90% after day 36. Maximum value of the methane production rate (6.0-6.5 l d-1) was achieved from day 152 and remained stable afterward. Although the reactor showed steady performance in terms of COD removal efficiency and methane production under constant hydraulic retention time (HRT) or COD loading rates, physicochemical and microbial properties of UASB sludge kept changing during the initial 5 months of operation. Specific methanogenic activity was initially negligible but increased until day 150, and then remained constant (0.72 + 0.11 g CH4-COD g-1 VSS d-1) afterward. Sludge volume index showed that the settling ability of UASB sludge gradually improved until it reached a plateau in day 120. Improved settling-ability could provide a basis for keeping bed height constant despite shortened HRT. The mean diameter of the UASB sludge gradually increased until approximately day 150 and maintained a maximum value (0.48 mm) afterward. Confocal laser scanning microscopy revealed F420-based autofluorescence of physical and optical sections of UASB sludge, suggesting the locations of autofluorescent methanogens in the UASB sludge during the start-up period. During the initial operation of the reactor, autofluorescence showed random and uneven distribution inside the sludge. However, autofluorescence appeared as an inner layer near the edge of the sludge with time, suggesting more abundant or active methanogens in this layer. The highest autofluorescence was observed in the range of 20 to 28 µm depth from the surface of granule as determined by optical slicing of UASB sludge. The results obtained in this study provide insight into UASB sludge development that involves dynamic changes in physicochemical and microbial aspects during the start-up period.

Abstract: A new type of biofilter, the rotating drum biotrickling filter (RDBF) system, was developed and operated to remove styrene from waste gas stream. Porous polyurethane foam sheets were used as a packing material for the RDBF and a pure culture of the Gram-positive bacterium Brevibacillus sp. SP1 was as an inoculum. The reactor showed a short start-up period of 18 days. Once uniform biofilms were developed on the packing, a high and stable removal of styrene over 95 % was observed at an incoming concentration of 200 ppmv and a retention time of 0.5 min. The maximum elimination capacity was estimated to be 125 g/m3/hr. The outstanding performance was attributed to an efficient gas-liquid mass transfer and proper supply of nutrient solution to the packing during the rotation of the drum. However, this performance of the RDBF was not maintained longer than 7 days because of the clogging of the open pores in the polyurethane foam due to an excessive growth of the biofilms. This result indicates that the RDBF has great potential as a gas purification system if a proper method to control the biofilm growth is developed.

Abstract: The luminometry assay using the wild-type Vibrio harveyi BB120 was evaluated as a possible detection method for quorum sensing inhibitors. The effects of the concentration of the quorum sensing signal molecule (AHL) as well as the cell density of the reporter strain and the different AHL analogues on luminescence expressed as relative light units (RLU) were examined. Inhibition of V. harveyi luminescence was observed in a dose dependent manner for all five AHL analogues. The RLU values exhibited linearity within the range of 2.9 x 102 ~ 3.2 x 105. Detection up to 102nM was possible for dodecanoyl-homoserine lactone and AHLs with alkyl chain lengths of C-8~C-14 were more active than the shorter chain-lengthed hexanoyl-homoserine lactones. Lipophilicity of the AHL seems to affect the sensitivity of the assay.