Treatment of domestic wastewater containing phosphate using water treatment sludge through UASB–clariflocculator integrated system

In the present study, treatment of low-strength synthetic wastewater through upflow anaerobic sludge blanket (UASB)–clariflocculator integrated system was carried out. Synthetic wastewater containing sucrose as a carbon source and phosphate as a nutrient was passed through the UASB reactor followed by clariflocculator. Water treatment sludge (WTS) was used as a coagulant in the clariflocculator. Box–Behnken design methodology with response surface methodology was used for optimizing the parameters including WTS dose, hydraulic retention time (HRT) and pH of UASB reactor. The phosphate removal was considered as a response. The observed values of responses were fitted by using second-order polynomial to compute the model. The suitability of this second-order polynomial model was checked by performing ANOVA test. Fisher’s test was done to analyze the significance of each factor and interactions between each other. With this methodology, the optimum operational condition of integrated system was obtained at 20 g/L as a WTS dose, HRT 7.68 h and pH 9. The UASB–clariflocculator integrated system removed 72.5% of phosphate at this optimum condition, whereas the phosphate removal through UASB reactor alone was obtained in the range of 8–20% only. The results suggested that water treatment sludge can be used as a coagulant to enhance the removal of phosphate from UASB reactor effluent treating low-strength wastewater and integrated system can be considered as a promising alternative of conventional system for the removal of nutrient from the effluent of UASB reactor.