Study On Disinfection Of Excessive Sludge From MBR Treating Hospital Wastewater

Membrane bioreactor (MBR) has good performance in hosipital wastewater treatment, including physical disinfection effect simultaneously. The pathogenic microorganism can be intercepted in the reactor by the high-performance separation of the microfiltration membrane, so it is important to study the disinfection of sludge discharged from MBR. The objetctive of this study is to evaluate the characteristics of excessive sludge from MBR and the disinfection effect using peracetic acid as disinfectant.The results showed that the removal effect of microoranisms by the MBR was good. But large quantities of microoranisms accumulated in the sludge, and the number of microorganism in the sludge was much higer than that in wastewater. In order to determine the total bacteria account in the sludge, a kind of surface active agent to extract the bacteria from sludge into the supernatant was used. After 5 tests, the results showed that the everage recovery ratio was higher than 80% (the highest was 97%). So in this study, this method was chosen to determine the total bacteria account in sludge.The dose and reaction time on the disnfection effect of peracetic acid were investigated. The result showed that the bacteria in the disinfected sludge behaved"conditions of tailing"obviously. When the dose was 400 mg/L and reaction time was 1 h, the total bacteria account was 112 CFU/mL, the total coliform was 91 MPN/100mL, and the fecal coliform was 12 MPN/100mL (81.4 MPN/g), the fecal coliform met the requirement of"Discharge Standard of Water Pollutants for the Medical Organization"(GB18466-2005). The removal ratio increased with the reaction time if the dose is the same. When the dose was 400 mg/L and reaction time was 3 h, the fecal coliform was completely inactivated. When the dose was 600 mg/L and reaction time was 3 h, the total bacteria account and the fecal coliform were both completely inactivated. Their kinetics fit accord with the Collins-selleck model. Besides, pH and H2O2 both contributed to the effect of disinfection of the sludge.The cost of PAA is higher than that of chlorine. In order to reduce the costs in engineering application, the disinfection effect on sludge which was setteled after 30 min was also investigated. The results showed that, when the everage of SV30 is about 37%, the volume of the sludge to be disinfected would be a 63% reduction. If the dose was 400 mg/L and the reaction time was 1 h, the fecal coliform of the settled sludge was 69 MPN/g. It also met the requirement of"Discharge Standard of Water Pollutants for the Medical Organization"(GB18466-2005). When the sludge discharged from MBR, it was settled first. Then the supernatant recycled to the reactor, and the settled sludge can be treated alone. This will not only saves the cost of PAA, but also minishes the volume of disinfection tank and reduce the construction costs.