| Summary: | 碩士 === 嘉南藥理科技大學 === 環境工程與科學系碩士班 === 93 === In this study, the performances of a membrane bioreactor for anoxic/aerobic treatment of continuous-flow ABS resin manufacturing wastewater were evaluated by laboratory-scale experiments with no sludge withdrawn for 174 days. This system consists of two reactors, the first reactor is a biological treatment tank (2.3 L) and the second one is a membrane bioreactor (3.5 L). The removal efficiencies of carbon and nitrogen were examined in terms of BOD, COD, TOC, Org-N, NH4+-N, NO2--N and NO3--N. Furthermore, the mixed liquid suspended solids (MLSS), mixed liquid volatile suspended solids (MLVSS), food to microorganism ratios (F/M) and volumetric loadings were measured in this study. Finally, the permeate quantity and fouling of membrane according to different experimental conditions were estimated by flux and SEM images.
Tree stages include different hydraulic retention time (HRT) and operation modes were carried out in this study as follows.
Stage 1: The total HRT of this system was 18 hours. The biological treatment tank was continuous aerobic, the membrane bioreactor was operated at the anoxic/aerobic cycle for 1/1.5 hours. Total aerobic time of this system was 13.6 hours and the anoxic time was 4.4 hours for each HRT.
Stage 2: The total HRT of this system was 22.4 hours. The biological treatment tank was continuous aerobic, the membrane bioreactor was operated at the anoxic/aerobic cycle for 1/2.1 hours. Total aerobic time of this system was 18 hours and the anoxic time was 4.4 hours for each HRT.
Stage 3: The total HRT of this system was 22.4 hours. The biological treatment tank was operated at the anoxic/aerobic cycle for 1/1 hour. The membrane bioreactor was continuous aerobic. Total aerobic time of this system was 18 hours and the anoxic time was 4.4 hours for each HRT.
The results indicated that the HRT seems significantly to affect the concentration of MLSS. The HRT of 18 hours gave the higher biomass concentration than HRT of 22.4 hours. However, the MLSS concentration of the first stage in biological treatment tank was in a range of 8000 to 23300 mg/L. Consequently, decreased and maintained at a range from 3000 to 5000 mg/L for stage 3. A similar MLSS concentration variation was observed in membrane tank. However, the MLSS concentrations of membrane tank were higher than that of biological treatment tank expect for stage 3. The MLVSS/MLSS ratios were also calculated for both the biological and membrane tanks. In generally, the MLVSS/MLSS ratios are in a range of 0.4 to 0.8, but most of the values were below 0.5.
Generally, the effluent concentrations of BOD were remarkably stable and with a highest removal efficiency of 99.2%. COD and TOC removal was 88.8% and 83.6%, respectively. The BOD volumetric loadings of biological treatment tank were in the range of 3.03~5.42kg BOD5/m3 day and in the range of 0.02~0.06kg BOD5/m3 day for membrane tank. The BOD F/M of biological treatment tank was in the range of 0.9~2.3 kg BOD5/kg MLVSS-day and in the range of 0.01~0.02 kg BOD5/kg MLVSS-day for membrane tank. The COD volumetric loadings of biological treatment tank were in the range of 6.7~10.8kg COD/m3 day and in the range of 0.28~0.68kg COD/m3 day for membrane tank. The COD F/M of biological treatment tank was in the range of 3~4kg COD/m3 day and in the range of 0.1~0.37 kg COD/kg MLVSS-day for membrane tank. Compared to the data obtained from conventional aerobic processes, those data obtained from this study were very high.
The removal efficiency of TKN for stage 1 was 42±13.9%, for stage 2 and stage 3 was 48.9±13.7% and 54.4±13.7%, respectively. However, the results showed that low nitrite and nitrate concentrations in the effluent and only 40% to 50% TKN removed. It implied that denitrification can be accomplished and nitrification of the nitritation (NH4+ → NO2-) is inhibited but the nitratation (NO2-→ NO3-) is significant.
In the first 78 days, tree times of chemical cleanings were carried out. It was 24, 56 and 78 day, respectively. On days 99, the flux can be not recovered even the chemical cleaning. A new hollow fiber membrane module with the same material and pore size replace the fouled one and no more chemical cleaning after days 99. However, the water cleaning was more frequent from once a week to once two days after the membrane changed. Images of the new, fouled and cleaned membrane using SEM provide a means for qualitative description of fouling in this study.
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