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Wei N.,Tsinghua University | Shi Y.,Tsinghua University | Wu G.,Tsinghua University | Hu H.,Tsinghua University | And 2 more authors.
Water (Switzerland) | Year: 2014

Tertiary denitrification of the secondary effluent in wastewater treatment plants is necessary to control the eutrophication of receiving water bodies. Two denitrifying biofilters (DNBF), one packed with quart sand with sizes of 2-4 mm (DNBFS) and the other of 4-6 mm (DNBFL), were operated for tertiary denitrification under empty bed retention times (EBRTs) of 30 min, 15 min and 7.5 min, respectively. Under EBRTs of 30 min, 15 min and 7.5 min, the NO3--N removal percentages were 93%, 82% and 83% in DNBFS, and were 92%, 68% and 36% in DNBFL, respectively. The nitrogen removal loading rates increased with decreasing EBRTs, and at the EBRT of 7.5 min, the rate was 2.15 kg/(m3·d) in DNBFS and 1.08 kg/(m3·d) in DNBFL. The half-order denitrification coefficient of DNBFS increased from 0.42 (mg/L)1/2/min at the EBRT of 30 min to 0.70 (mg/L)1/2/min at the EBRT of 7.5 min, while did not vary much in DNBFL with values from 0.22 to 0.25 (mg/L)1/2/min. The performance of both DNBFs was stable within each backwashing cycle, with the NO3 --N removal percentage variation within 5%. Better denitrification was achieved in DNBFS but with a slightly high decreased flow rate during the operation. © 2014 by the authors. Source

Li B.,Tsinghua University | Wu G.,Tsinghua University | Hu H.,Tsinghua University | Wu Y.,Kunming Dianchi Water Group Co. | And 2 more authors.
Chinese Journal of Environmental Engineering | Year: 2014

The performance of seven wastewater treatments with four different treatment processes types (oxidation ditch, ICEASE, 3AMBR and A2O) in Kunming was evaluated with indicators including technical performance, economic cost, and environmental impact (global warming and eutrophication). The results showed that all wastewater treatment plants had good performance in the removal of BOD, SS, and NH4 +-N with the removal percentage above 91%, the removal percentage of COD was over 86%, the removal percentage of TP was in the range of 86%~96%, and the removal percentage of TN was in the range of 56%~76%.Economic costs were mainly contributed from energy consumption and were closely related to the treatment process and water quality of both influent and effluent; the operation cost of 3AMBR was much higher than that of other treatment processes. Greenhouse gases emission was mainly from energy consumption and nitrous oxide emission from the effluent, and 3AMBR had the highest greenhouse gases emission among all treatment processes. The eutrophication effect of the effluent was mainly contributed by nitrate and was highly affected by treatment processes. Combined with the pollutant removal performance and comprehensive cost, ICEAS had the best comprehensive performance while 3AMBR had the relatively worse comprehensive performance. Source

Wei N.,Tsinghua University | Shi Y.,Tsinghua University | Wu G.,Tsinghua University | Hu H.,Tsinghua University | And 3 more authors.
Water Science and Technology | Year: 2016

Effective control of nitrogen and phosphorus in secondary effluent can reduce or avoid the eutrophication of receiving water bodies. Two denitrifying biofilters (DNBFs) packed with different sizes of quartz sands combined with micro-coagulation were operated for simultaneous removal of nitrogen and phosphorus from the secondary effluent. The quartz sand size in one DNBF was 2-4 mm (DNBFS), and in the other was 4-6 mm (DNBFL). In both DNBFs, methanol was used as the electron donor and different organic carbon to nitrogen (C/N) ratios were applied. Under C/N ratios of 1.5, 1.25, and 0.75 g/g, the nitrate nitrogen (NO3-N) removal percentages were 73%, 77%, and 50% in DNBFS, and 43%, 25%, and 21% in DNBFL; the effluent total phosphorus concentrations were 0.15, 0.14, and 0.18 mg/L in DNBFS, and 0.29, 0.35, and 0.24 mg/L in DNBFL. The performance of both biofilters was quite stable within a backwashing cycle. The NO3-N reduction rates were 1.31, 1.10, and 0.48 mg/(Ĺmin) in DNBFS, and 0.97, 0.27, and 0.10 mg/(Ĺmin) in DNBFL. For biomass detached from both biofilters, their denitrifying activities were similar. Biofilm biomass in DNBFS was higher than that in DNBFL, inducing a high denitrification efficiency in DNBFS. © IWA Publishing 2016. Source

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