| There is a shortage of water resources in China. Domestic wastewater as a stable and reliable, renewable water resources, their recycling is an important and effective means of conserving water resources. In this work, a sequencing batch membrane bioreactor (SMBR) which designed and manufactured by the writer had been operated using synthetic domestic wastewater as feed in an anaerobic/aerobic process. There were several contents, including defining the optimal operating parameters, characteristics of pollutants removal, formation and control of membrane fouling, which were investigated to obtain stable and efficient system performance and the effluent can reach the standard of recycling while slowed membrane fouling simultaneously. The main results of study were as follows:Sludge acclimation were used the method of continuous and intermittent cultivating for 24 days. The activated sludge bred quickly in sludge acclimation. Mixed liquor suspended solids (MLSS) concentration was from 2000 mg/L to 6200mg/L. The sludge yield rate was 0.37 kg(MLSS)/kg(COD). Nitrate bacteria's growth was slow. In the later of sludge acclimation, by reducing the CODCr concentration of raw water to slow down the growth of heterotrophic bacteria and provide a better growth environment for nitrate bacteria.The optimal operating parameters of this SMBR were:period time was 6 hours which contained 1 hour anoxic,5 hours aerobic; volume exchange ratio was 0.3, that means each period yielded effluent 9L; MLSS concentration was 8000mg/L; aeration rate was 0.3 m3/h, DO maintained at 2mg/L or so. In this condition, SMBR both can maintain high pollutants removal rates and save energy.SMBR ran for 40 days under the optimal operating condition. The experimental results showed that:when raw water pH values were among 7-9, SMBR had a higher pollutants removal rate. The average removal efficiency of CODCr, NH4+-N, TN and TP were 98.01%,96.51%,77.38% and 73.21% respectively. Turbidity and chromaticity average removal rate were 99.56% and 92.2%. SMBR had a stronger resistance of load capability. Effluent quality can reach the standard of urban miscellaneous water quality (GB/T 18920-2002).When raw water pH value declined to 6, CODCr average removal rate could still reach 95%. NH4+-N, TN and TP average removal rates declined to 75.34%,61.42% and 62.87% respectively. Turbidity and chromaticity average removal rate was almost not affected. The results indicated that low-water pH is not conducive to biological nutrient removal.Critical fluxes were measured at five different MLSS concentrations and three different aeration intensities at each MLSS concentration. The result showed that increased the aeration intensity can increase the critical flux when MLSS concentration were in a certain range (<10000mg/L). When MLSS concentration was small than 4000mg/L, aeration intensity had a critical value. Critical flux will not further increase with the increased of aeration intensity which greater than the value. When MLSS concentration was large than 10000mg/L, the role of aeration intensity in order to delay membrane fouling had become insignificant.Kept the reactor operated with influent/effluent and aeration intermittently under the conditions of MLSS concentration at 8000mg/L, aeration intensity at 0.3m3/h and effluent flux at 15L/(m2·h). The membrane fouling increased slowly and constantly at the rate of 0.126KPa/d. The phenomenon of TMP rose rapidly was not observed. That means the process can control membrane fouling effectively. Dosed powdered activated carbon (PAC) can optimize the characteristic of MLSS and slow down membrane fouling further. PAC dosage was 1.5g/L when MLSS was 8000mg/L. After dosed the PAC into mixed liquor at the later of the experiment, the TMP decreased slightly and its increasing rate declined to 0.04KPa/d. |
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