Design And Study Of Pilot-scale Sludge Lysis/Hydrolysis And Acidification/CAS Process For Sludge Reduction

Reduction of excess sludge is one of the significant challenges in biological wastewater treatment processes. The sludge reduction method based on the sludge lysis-cryptic growth is one of the promising approaches. The key of this method is the techniques of sludge lysis. In this study, alkali and ultrasonic pretreatment/hydrolysis and acidification/CAS process were employed for sludge reduction. The effects of different sludge lysis techniques on hydrolysis and acidification were examined. Pilot-scale sludge reduced technics was designed based on the results of lab-scale experiment.Experimental results of the hydrolysis and acidification of excess sludge show that the group with the 20 percent of inoculate sludge produces the largest quantity of the soluble chemical oxygen demand (SCOD) and total fatty acids (VFAs) after the 72 h reaction. The reaction is enhanced by using the sludge which is concentrated for 12 h. The combination of alkali and ultrasonic has the best effect on hydrolysis and acidification compared with the methods of alkali, alkali and heat, alkali and tween-80.Excess sludge reduction process based on the lysis growth can be realized by recycling the acidified sludge back to the aeration tank. In the lab-scale experiment 79% of excess sludge could be reduced after 30 d stably running. Based on the lab-scale experiment results, pilot-scale process of alkali and ultrasonic/hydrolysis and acidification/CAS was designed, and its economic cost was analysised. The capacity of the sewage treatment tank is 400 m /d, and the moisture content of excess sludge was concentrated to 97.5 %. After adding 2.14 g/L NaOH into the concentrated sludge, it would overflow into the ultrasonic tank. The volume of filling in the ultrasonic tank is 0.5 L. The ultrasonic time is 5.66 s. The rate of sludge lysis is 0.25 after these treatments. The lysis sludge need to be put into a tank for about 10 h. It will take advantage of the lytic effect of alkali and be good for hydrolysis and acidification. Before back into aeration tank, the sludge begins to hydrolysis and acidification. The aim of design is that the quality of effluent fulfills the discharge standards. Sludge reduction efficiency is 66.8%, and the cost of this technics is less than the traditional sludge disposal. The technics achieved different concentration of sludge. A thin sludge film was realized by putting the ultrasonic equipment on a iron shelf with an angle. It is convenient to change the sludge retention time (SRT) of hydrolysis and acidification. The sludge is heated in a self-made container by water boiler which power is 2000 W. According to the characteristics of the sludge flow in the tank of hydrolysis and acidification, the impeller with four blades which lean a angle of 45 degree is designed. The critical stirring rate is calculated by Yong T empirical formula. The power of impeller under the result of speed is calculated too.