| Many traditional secondary wastewater treatment plants face such problems, namely high construction cost, expensive operating cost and low phosphorous removal. The chemical-biological flocculation & suspended medium bioreactor process was used in this study to treat low concentration wastewater in Shanghai, in which the chemical-biological flocculation was studied emphatically and was compared with the chemically enhanced primary treatment in pilot scale. The flocculation capability of the recycled sludge in the chemical-biological flocculation process was analyzed in jar tests, and the flocculation mechanism of this process was discussed by applying particle size distribution, molecular weight distribution and molecular biological method. The chemical-biological flocculation process was compared with primary tank, chemically enhanced primary treatment process and secondary conventional activated sludge process.The startup phase was analyzed and a series of experiments were conducted to determine optimal operation parameters of the chemical-biological flocculation & suspended medium bioreactor process. The results are as follows: (1) It took about 5 days to finish the startup phase for the chemical-biological flocculation with properly inoculating activated sludge and 25 days for biofilm maturation in the suspended medium bioreactor under the water temperature of higher than 20℃. (2) Optimal operation parameters of the chemical-biological flocculation are determined as follows: HRT 35min, PAFC 70mg/L, sludge return ratio 33% and aeration rate 6.0 m3/h, 3.5 m3/h and 0.8 m3/h in each channel(the ratio of air to water 3.0,1.8, 0.4);the suspended medium bioreactor HRT 2.7h, the carrier filling ratio 50% and air/water ratio 2.0:1. Under above conditions, the removal rates of CODCr, TP and SS are 61.6%, 70.9% and 76.3% with volume loading rate 3.85kg/m3.d, 0.097kg/m3.d and 2.50kg/m3.d respectively in the chemical-biological flocculation stage. The suspended medium reactor achieved good nitrification results with ammonia volume loading rate kg NH4+/m3.d and the removal rates of CODcR, TP and NH4+ are 42.1%,31.4% and 49.7% respectively. The effluent meets I-class A criteria specified in Integrated Wastewater Discharge Standard. (3) PAM was cancelled in the chemical-biological flocculation because of the biological flocculation, which can reduce the dosage expenditure by 30%. Under the same PAFC dosage, the chemical-biological flocculation was superior to the chemically enhanced treatment process and its surplus sludge was less than the latter by 10-15%. ? A satisfactory results can be achieved with chemical-biological flocculation & suspended medium bioreactor process even under low temperature condition. (§) Compared with the traditional secondary wastewater treatment process, the chemical-biological flocculation & suspended medium bioreactor process shows the characteristic of short HRT, low construction cost, good phosphorous removal and little energy consumption.Studies on the flocculation capability of the recycled sludge show that: (D The sludge from the chemically enhanced primary treatment is not as efficient as those from the chemical-biological flocculation. That is an evident that the latter process is a closely chemical-biological-ingrated wastewater treatment process. (2) Chemical dosage can lead to the change of the microbial community which are suitable the environment of chemical-biological flocculation. (3) Extracellular polymeric substances(EPS) concentration is 145.89mg/gVSS and microorganism is more active in the chemical-biological flocculation.The results of the particle size distributions and removal show that: (D Compared with the chemically enhanced primary treatment, small particles are easier to aggregate into bigger ones and those disrupted floes could properly flocculate again in the chemical-biological flocculation. (D Particles in influent, the primary tank effluent, the chemically enhanced primary treatment effluent, the secondary biological treatment effluent and the chemical-biological flocculation effluent are distributed in 0.4-340um, 0.4-3.Oum, 0.4-112.6um and 0.4-260um with the mean size at 29.96um, 25.14um, 12.19um, 10.38um and 0.819um respectively, which indicate that the best particle removal efficiencies are achieved in the chemical-biological flocculation. (3) The removal rates of Cr, Cu, Sn, Ag, Pb, Zn and Ba are 99.4%, 98.6%, 84.0%, 97.8%, 88.5%, 85.1%, and 75.1%, respectively, in thechemical-biological flocculation, and its capability of high and non-selective heavy metal removal might be closely related to its. strong ability to eliminate small particles.The results of the molecular weight distribution analysis and removal of the dissolved organic matter show that: (D The dissolved organic matter average removal rate is 45.9% through chemical dosage and biological adsorption in the chemical-biological flocculation, which is superior to the chemically enhanced primary treatment because of biological flocculation. (2) Because of short HRT and poor1 biological degradation, microorganism is less efficient in dissolved organic matter <2ku removal in the chemical-biological flocculation.
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