Hydrolysis of excess sludge by bioaugmentation and nutrient removal from supernatant with low cost

More stringent legislations controlling discharges of wastewater lead to more wastewater treatment plants (WWTPs) constructed, which result in considerably sludge production nowadays. Being an important biological method to reduce sludge, the low rate of hydrolysis limited its efficiency and the released nutrient elements in the supernatant often became a new source of pollutant. In this study, hydrolysis of excess sludge by bioaugmentation and removal of nutrient with a method of low cost were studied. The excess sludge originated from No. 3 Wastewater Treatment Plant of Xi´an city was used and a yeast like was adopted for bioaugmentation. Two reactors with volume of 3.5 liters were operated in parallel for hydrolysis under 35±1°C and investigations on nutrient removal were carried out with jar tests. The results showed that it was an effective method to hydrolyze excess sludge by bioaugmentation, which made the reduction ratio of VSS in sludge increase to 47.9% as compare to the control one. At the same time, the multiples of SCOD, NH₄⁺-N, PO₄^3--P in the supernatant of bioaugmentation reactor were respectively 4.47, 3.79 and 3.25 of that in the control one. The experiment of nutrient removal displayed the concentration of phosphorus in supernatant liquor could decrease to 4.36mg PO₄^3--P.L^- and the percentage of NH₄⁺-N removal was above 43% only by static settling for 42h followed with stirring for 30min under pH value of 9.5. To sum up, hydrolysis of excess sludge by bioaugmentation was potent and removal of nutrient from supernatant without magnesium addition was a potential method to save cost. However more research is required to clarify the mechanisms in the processes mentioned above detailedly later.