| Due to the increasingly stringent regulations of drinking water quality and deteriorating water sources,the traditional water treatment processes can no longer satisfy the strict drinking water requirement.Therefore,hybrid membrane techniques, presenting as relatively new processes with special advantages,have attracted a worldwide research interest.In this thesis,a hybrid membrane process,coagulation-submerged hollow fiber microfiltration(CSHFM)process,was applied in a water plant in Tianjin to conduct a pilot-scale study of producing tap water at 300 m3 per day.The operating parameters of the hybrid system were optimized based on the experimental data.The results of this study can provide knowledge and technique for future large-scale(5000m3/d) industrial applications.The CSHFM process introduced an operating mode of continuous air bubbling and intermittent permeation which produced reliable product water quality and achieved good removal of turbidity and organisms.The feed water containing a turbidity of 0.69-7.69NTU and CODMnof 2.87-5.45mg/L was treated to reach 0.08NTU(averaged,87.7%was below 0.1NTU)and 2.18mg/L(averaged)in the effluent water,respectively.In addition,the averaged UV254of the product water was 0.040cm-1,the total bacteria was maintained below 1CFU/mL and no Escherichia coli was detected.At the first stage of the operation,the membrane permeability declined gradually due to membrane fouling.Therefore,the system was chemically cleaned and flushed at the 241stday to restore the membrane permeability to 57.8%of the initial value.Compared to traditional techniques,the CSHFM system requires lower dosage of the chemicals,higher product water quality and higher production rate(as high as 98.4%).The product water quality successfully satisfied the requirement by Sanitary Standard for Domestic Drinking Water(GB 5749-2006).Data from experiments for operating parameters optimization indicated that the addition of sodium hypochlorite had little influence on the removal of the total organic compounds but benefited the removal of organic compounds with special characteristic peaks or with excellent absorption at a wavelength of 254nm.Moreover, the CODMnremoval was evidently enhanced with the increase of the coagulant addition from 1.5 to 4.6mg/L at a condition of low temperature and low turbidity, however,no regular trend was observed at the condition of normal temperature and turbidity.On the other side,changing the sludge discharging mode from 1/d to 2/d had no obvious effect on the membrane permeability.Increasing the different intermittent permeation ratios(on/off:8min/2 min,13 min/2 min,18 min/2 min, 28 min /2 min)had no influence on the product water quality but aggravated membrane fouling.Further,comparative test of different air bubbling intensities (83.1m3/h·m2,71.2m3/h·m2,59.4m3/h·m2,47.5m3/h·m2)showed that the product water quality and membrane fouling were not obviously affected.Finally,the fouled membrane modules were chemically cleaned by using HCl,NaOH and NaClO solutions and the results indicated that the choice of different cleaning procedures had little effect on the cleaning result.The cleaned membrane permeability was restored to 55.5%-61.3%of the initial value,successfully.
|
PDF Full Text Request