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| Investigation on water quality of the effluent of large-scale swine wastewater treatment plant |
| Received:November 27, 2016 |
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| KeyWord:swine wastewater;biological treatment;water quality;effectiveness;cause analyses |
| Author Name | Affiliation | E-mail | | HAN Wei-cheng | Department of Environmental Engineering, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China | | | YAN Cheng | Nanjing BACT Environmental Solutions Co. Ltd, Nanjing 211505, China | | | ZHOU Li-xiang | Department of Environmental Engineering, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China | lxzhou@njau.edu.cn |
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| Abstract: |
| In this study, we investigated and determined for successive 4 months the water quality indexes (pH, SS, COD, NH3-N, TN and TP) of the effluent at different treatment stages from a large-scale swine wastewater treatment plant located in Changsha, Hunan. The results showed that the effluent achieved by solid-liquid separator still contained high concentration of SS, COD, NH3-N, TN and TP with 3040~4900, 6440~11 290, 652.3~1044, 721.3~1187 mg·L-1 and 55.5~148.1 mg·L-1, respectively. The anaerobic digestion process mainly removed soluble COD instead of the insoluble COD attached to SS, which resulted in high organic loads of anaerobic fermentation slurry into subsequent biological treatment system. Consequently, the effluent from the secondary clarifier still contained 37.9~108.7 mg·L-1 NH3-N, 179.1~203.4 mg·L-1 TN and 20.1~41.6 mg·L-1 TP, which couldn't meet the water quality standard regulated by China. Therefore, additional two CASS tanks had to be constructed to continuously treat the effluent from the secondary clarifier. However, the effluent by CASS process only could achieve low concentration of NH3-N with 0.54~3.2 mg·L-1, but TN and TP could not be removed effectively, implying that nitrification reaction occurred much stronger than denitrification in the CASS tanks. In addition, the effluent from CASS tank was of high chroma. As a result, in the plant, the coagulation and sedimentation processes were needed and used to remove phosphorus and chroma. Unfortunately, this process consumed great amounts of chemicals and produced more chemical sludge needed to be treated, which undoubtedly increased the operation cost to as high as nearly 10 yuan (RMB) ·t-1. Obviously, it was still very difficult for conventional biological treatment technique to treat the large-scale swine slurry to completely meet water quality standard. High concentration of SS and “inert” COD, N and P were found to be responsible for the phenomenon. Therefore, to develop a new technique with completely removal of SS in the first stage followed by conventional secondary biological treatment was expected to enhance the effectiveness of large-scale swine wastewater treatment plant. |
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