Start-up of UASB reactors treating municipal wastewater and effect of temperature/sludge age and hydraulic retention time (HRT) on its performance

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Abstract
The upflow anaerobic sludge blanket reactors seeded with cow dung manure (UASBCD) and activated sludge of a dairy wastewater treatment plant (UASBASDIT) were used to treat raw domestic wastewater of medium strength. The UASBCD reactor required a period of 120days to start up. In case of UASBASDIT reactor, sludge bed was stabilized in a period of 80days. The performance of both reactors to treat wastewater was enhanced with an increase in the sludge age and temperature. Under psychrophilic temperature (17°C) and at early sludge age (60days), chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal by the reactors were in the range of 57–62% and 61–66%, respectively. However, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal efficiency of the reactors elevated to the range of 79–81% and 77–83%, respectively at sludge age of 150days and temperature of 30°C. In short, overall performance of both reactors was optimum at sludge age ranging from 120 to 150days and temperature varying between 25 and 30°C. At hydraulic retention time (HRT) of 9h the chemical oxygen demand (COD), total suspended solids (TSS) and sulfate removal efficiency of UASBCD reactor reached 81%, 75% and 76%, respectively and 77%, 74% and 69%, respectively for UASBASDIT. The rate of removal of these parameters however, gradually declined with increasing hydraulic retention time. The UASB technology provides a low-cost system for the direct treatment of municipal wastewater and can be applied in small communities

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