| With the rapid development of bamboo industry, the bamboo industry wastewater (BIWW),, causes more and more environmental problems. The BIWW has high organic content (chemical oxygen demand (COD)20000-50000mg/L) coupled with low pH (2.5-5) and comparative color content. AnMBR-Fenton-SBR combimed process was applied for the treatment of BIWW.At the AnMBR process, the set-up stage was kept for160d and the organic load rate (OLR) finally reached4.4kgCOD/m3.d at the hydraulic retention time (HRT) of5d. The final COD removal obtained was91%, and the mixed liquor suspended solids (MLSS) in the anaerobic reactor had increased from8000mg/L to15000mg/L. At the middle of the set-up stage, the membrane was cleaned for reuse. However, the membrane fouling still aggravated until the set-up stage ended, and the membrane resistance increased significantly from4.0×1012m-1to2.3×1013m-1The removal of COD and NH3-N changed slightly from92%to94%and55%to60%, respectively, while the HRT increased from5d to10d. However, as the HRT decreased rapidly to2d, the COD and NH3-N removal significantly declined to82%and40%, respectively. It is worth noting that while the permeating water was pumped slowly and continuasly, the rejection of COD and NH3-N increased dramatically compared with the mode of intermittent and rapid pumping. Through the gel permeation chromatography (GFC) analysis, it is found that the molecular weight in the effluent decreased with the HRT, indicating that the higher HRT can promote the effect of biological degradation and membrane rejection.N2was applied in the membrane cleaning process, and the optimum N2flow rate (40L/h) and cleaning duration (20min) was obtained by a preliminary experiment. Although the N2-cleaning process could slow down the membrane fouling rate at a certain extent, the transmembrane pressure (TMP) reached50kPa at the HRT of2d, which was not suitable for long-time running of membrane. As the scanning electron microscope (SEM) analysis showed, the top part of the membrane encountered the most serious fouling because of the insufficient cleaning of N2. Gas chromatography-mass spectrometer (GC-MS) was applied for the analyses of raw and permeating water. Long-chain alkanes were found to be the main organic matter in the raw wastewater, and benzene derivatives were the dominating by-products in the permeating water. Additonally, a small number of amine and fluoro derivatives were also detected in the effluent.After the AnMBR treatment, the organic matter in the raw BIWW had been significantly degraded. However, the COD of the effluent was still high (1600-1700mg/L), and the biodegradability deacresed sharply with a higher color content. As a solution, Fenton-SBR process was applied for the AnMBR effluent treatment. At the Fenton process, the orthogonality method was used to optimize the Fenton process for partial mineralization (total organic carbon (TOC) removal) and biodegradability (BOD5/COD ratio) enhancement. The optimum dosages at pH4.0were determined to be52.9mM H2O2and7.9mM Fe(II), with a TOC removal of76%and BOD5/COD improvement from0.13to0.50.At the SBR stage, the effect of anoxic-aerobic durations was evaluated. The best resulting operation mode was4h for the anoxic phase and6h for the aerobic phase. During this operation mode, the global removals of COD, NH3-N and color had reached93%,98%and98%, respectively. The effect of HRT on SBR performance was also studied. As a result, the reductions of TOC, COD, NH3-N, TN and color all decreased with the HRT. Generally, effluents with HRTs of more than1.5d met China’s second grade national discharge standard.Major organic compounds were identified with GC-MS. After Fenton-SBR process, most of the alkane derivatives were reduced significantly, and the amine and fluoro derivatives existed in AnMBR effluent were completely removed. By-products as benzene and ester derivatives were generated in different treatment stages, while the by-products in the SBR effluent were much less than those in the Fenton effluent. |
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