In this research, the comprehensive characteristics of anaerobic granular sludges and the scale-up effect of UASB reactor were studied. The morphological and microbial characteristics of both acidogenic and methanogenic granules cultivated on distillery wastewater were investigated, and the preservation and re-activation characteristics of granules formed on synthetic glucose wastewater were quantified in terms of storing period and temperature. And the scale-up effect of UASB reactor was examined by using a pilot-scale reactor of 3.3 m height.
The acidogenic granular sludge, formed in the acidogenic UASB reactor treating raw distillery wastewater for 90 days of operation, consisted of long chains of large rods, short plump rods, and cocci of various sizes, which have different shapes and cytoplasmic appearances from common methanogenic bacteria. In the methanogenic granule, which cultivated in the methanogenic reactor treating acidified distillery wastewater for 120th day, long multicellular filaments of Methanothrix spp. with diverse entrapped bacteria were prevalent. It is expected that extensive microscopic studies on acidogenic granular sludges should help in understanding the granulation process.
During 10 months of storage without feeding, specific acidogenic activity(SAA) reduced to about 30% of an initial value regardless of the storage condition, however the extent of the decrease in specific methanogenic activity(SMA) was quite different. In case in the room condition, SMA decreased to 60%, whereas 80% of SMA was decreased at 4℃. Room temperature seemed more beneficial than 4℃ in maintaining the methanogenic activity. In the microscopic study of granular sludges, although some debris formed on the surface of granular sludges and dead cells were observed by transmission electron micrography, no remarkable change in the overall configuration of granular sludges was observed in 8-month storage. In spite of 10 months storage without feeding, anaerobic granular sludges showed outstanding re-activation characteristics. It took only 12 days to increase the organic loading rate up to 11.2 kg COD/㎥.day. And granular sludge stored at room temperature had better re-activation characteristic than those at 4℃. Results from this study indicate that as the anaerobic granular sludge has very outstanding preservation and reactivation characteristics, and that UASB system can be effectively applied to the industries operating seasonally or intermittently.
Results on the role of acidogenic bacteria in anaerobic bioassay indicated that although unacclimated acidogenic bacteria could not degrade phenol for itself, it might play a certain role in the degradation. When treating corn starch wastewater with solid concentration of 420 - 855 mg TSS/l and TCOD of 2,500 - 3,000 mg/l, using a UASB reactor, COD removal efficiencies were maintained over 70% up to the loading rate of 3.2 kg COD/㎥.day and the maximum gas production rate was about 55 l/day, equivalent to 3.5 l/day per liter of reactor volume, at the organic loading rate of 8.4 kg COD/㎥.day.
A pilot-scale UASB reactor of 3.3 m height was successfully operated up to a loading rate of 9.7 kg COD/㎥.day, with an average COD removal efficiency of 85% and methane yield of about 0.26 l $CH_4/g$ $COD_re$. A distinct layer of the sludge bed was formed from the initial stage, and the VSS concentration of the blanket zone increased slightly with VLR. The sludge hold-up efficiency of Inner Tube(IT)-type GSS device was gradually increased as superficial gas production rate increased. The great part of the influent organic materials was removed when passing through the sludge bed. During 100 days of operation, SMA measured at 30cm height from the bottom of reactor increased by 3.6 times from 0.22 to 0.79 g $COD-CH_4/g$ VSS.day. However, in case of SMA measured at 60cm height, it increased more than 5 times from 0.17 to 1.01g $COD-CH_4/g$ VSS.day. When the superficial gas velocity was 0.26 m/hr, it was concluded that the part of reactor excluding the settler could not be described as an ideal mixer. The fluid flow pattern of the settler was a plug flow. In case that the superficial gas velocity was 0.67 m/hr, the overall fluid flow pattern was close to completly stirred tank reactor(CSTR) rather than non-ideal plug flow. The reason for these differences between two superficial gas velocities are due to the increased superficial gas velocity, caused by increased VLR. However, there was no significant difference in flow pattern of the settler.
본 논문은 최근에 활발히 실용화되고 있는 UASB 공법의 핵심기술인 입상슬러지의 제반 특성과 UASB 반응조의 scale-up 영향조사를 연구목표로 한다. 이를 위하여, 주정폐수를 처리한 이상(two-phase) UASB 시스템에서 형성된 산형성 및 메탄형성 입상슬러지의 형태학적 특성과 포도당 인공폐수로부터 형성된 입상슬러지의 보존 및 재활성특성을 조사하였으며, 높이 3.3m의 pilot-scale 반응조를 운전하여 scale-up 영향을 조사하였다.
산형성 입상슬러지는 메탄형성균과 형태학적 특성이 다른 다양한 산형성균으로 구성되었으며, 메탄형성 입상슬러지는 Methanothrix spp.가 주종을 이루는 network 내에 다양한 형태의 박테리아가 포획되어 있는 구조를 보였다.
기질을 공급하지 않은 상태로 10개월간 입상슬러지를 보관하였을 때, 산형성균의 비활성도(SAA)는 약 30% 감소하였다. 그러나, 메탄형성균의 비활성도(SMA)는 상온보관의 경우 60%, 냉장보관한 경우 80% 감소하였다. 따라서 입상슬러지는 상온에서 보관하는 것이 메탄형성균의 활성도 유지에 효과적이다. 장기간 보관하는 경우에도 입상슬러지는 형태학적으로 크게 변하지 않으며, 매우 우수한 재활성특성을 갖는 것으로 밝혀졌다. 결론적으로 입상슬러지를 미생물 보유수단으로 이용하는 UASB 시스템은 간헐적으로 발생하는 폐수처리에 효과적인 것으로 기대된다.
비록 적응되지 않은 산형균에 의해 페놀은 전혀 분해되지 않았지만, 산형성균의 작용을 받은 경우에 페놀은 더 빨리 분해되었다. 420 - 855 mg/l의 TSS와 2,500 -3,000 mg/1의 TCOD를 갖는 옥수수 전분폐수를 UASB 반응조로 처리한 결과, 체적 부하 3.2 kg COD/㎥.day에서 COD 제거율은 70% 이상이었으며, 최대 가스발생량은 부하 8.4 kg COD/㎥.day에서 반응조 단위 체적당 3.5 l/day 이었다.
높이 3.3m의 pilot-scale UASB 반응조는 체적부하 9.7 kg COD/㎥.day까지 약 85%의 평균 COD 제거율과 약 0.26 l $CH_4/g$ $COD_re$의 메탄회수율을 보였다. 체적부하가 증가함에 따라 sludge blanket 지역의 VSS 농도가 증가하는 경향을 보였으며, IT-형 GSS 장치의 슬러지 보유능도 증가하였다. 유입폐수 내의 유기물은 대부분 베드(bed) 층에서 제거되었다. 운전 100일이 경과하는 동안, 베드층에서 30m 높이에 위치한 슬러지의 SMA는 0.22에서 0.79g COD-$CH_4/g$ VSS.day로 3.6배 증가한 반면에, 60cm 높이에 위치한 슬러지의 SMA는 5배 이상 증가하였다. 반응조의 표면가스부하(superficial gas velocity)가 0.26 m/hr 일때, 반응조의 흐름특성은 축방향 혼합이 있는 압출형 흐름으로서 약 20%의 사영역(dead space)이 존재하였으며, 침전부는 이상적인 압출형 흐름특성을 보였다. 표면가스부하가 0.67 m/hr로 증가하였을때 반응조의 흐름특성은 증가된 가스발생량으로 인해 완전혼합에 가까웠으나, 침전부는 여전히 압출형 흐름특성을 갖는 것으로 밝혀졌다.
