A new process for wastewater treatment has been developed by using the combination of CSTR and PBR.
The system consisted of a circular tank (14 cm ID, 25 cm height) with a draft (8.8 cm ID, 20 cm height) concentrically mounted inside for the first stage and a packed column (8.8 cm ID, 41 cm height) for the second stage. As a support media for the formation of biomass layer, polypropylene Rashing rings (12.7 mm OD, 9.7 mm ID, 12.7 mm long) were used in PBR.
The process was tested over a range of hydraulic and organic loadings typical of industrial scale operation. The process was operated various combinations of four retention times (4, 7, 10, 15 hour) and three organic concentrations (292,675,1300 mg/l COD) with synthetic sewage. Return-sludge of a local activated sludge plants (Chung Gye Chun) was employed as seeds for the process start up.
It was found that the process was capable of function under organic loadings 1.6 to 1.9 kg COD/㎥/d and appeared similar or superior in performance to other biological wastewater treatment processes. Under the above mentioned loadings, the sludge yield was 0.12 to 0.31 g sludge/g COD removed and SVI of waste sludge was 26.2 to 36.6. Effluent COD was reduced to 29 (90.1% removal efficiency), 25 (96.3%), and 33 mg/l (97.5%) for organic loadings of 1.8, 1.6, 1.9 kg COD/㎥/d, respectively. Experimental results for polishing in PBR showed that approximately 60% of the SS and 70% of the COD were removed.
A new critical equation relating the overall biochemical reaction rate in activated sludge process on activated sludge load was used for modeling. The concept used here was shown to be valid for conventional activated sludge loading range.
The PBR, the second stage in the system, was modeled with the series of stirred tanks. Simple plug flow model could not adequately fit the experimental results. The axial mixing length was about 41 cm when the air flow rate was 13.15 cm/min and the liquid flow rate was 0.11 to 0.41 cm/m.
새로이 제안된 "2단식 복합 생물산화 처리법"에 의한 유기오염물질의 제거상태와 효율적인 조업조건에 대해 조사하였다.
충진탑의 기능과 다단식 처리의 효율을 고려하여 개발한 "2단식 복합 생물산화 장치"는, 첫째 단으로는 4.16ℓ 용량의 원통형 폭기조 (내경 14cm, 높이 25cm) 를 사용했고, 둘째 단은 충진탑 (내경 8.8cm, 높이 41cm) 인데, 미생물막이 형성되는 충진재는 폴리프로필렌 Raschig ring (내경 9.7 mm, 외경 12.7 mm, 길이 12.7 mm) 을 사용했다.
네가지 체류시간 (4,7,10,15시간) 과 세 가지 유기물의 농도 (292, 675, 1300 mg/ℓ COD) 에 대해 각각 실험했으며, 처음에는 청계천 하수처리장 (활성오니법) 의 반송오니를 seed로 사용했다.
실험결과에서, 본 장치는 유기물 부하 1.6~1.9kg COD/d/㎥ 하에서 좋은 처리상태 (처리 효율 90% 이상) 를 보여주었고, 다른 공정에 비해 우수했다. 즉, 위의 COD 부하에서, 오니 발생율은 0.21~0.31g sludg/g COD removed이며, SVI는 26.2~36.6 이었다. 처리수의 COD는 유기물 부하 1.8, 1.6, 1.9 kg COD/d/㎥에 대해 29 mg/ℓ (처리 효율 90.1%), 25mg/ℓ (처리 효율 96.3%), 33 mg/ℓ (처리 효율 97.5%)로 각각 나타났다. 둘째 단 (충진탑) 에서 현탁물질과 COD 제거율은 대략 60%와 70%로 각각 나타났다.
활성오니법에서의 반응속도에 영향을 미치는 인자로서, 활성오니부하를 도입했으며, 실험에서 그 타당성을 알 수 있었다.
충진탑의 수력학적 모델을 일련의 교반조로서 나타내 보았는 바, 단순한 플러그 흐름 모델을 사용하는 것보다 타당함을 알 수 있었다. 공기의 유속이 13.15 cm/min, 액체의 유속이 0.11~0.41 cm/min 일 때 축 방향으로 완전히 혼합되는 길이는 약 41 cm 였다.
