Effect of mean cell residence time on the base hydrolytic assist activated sludge process

Abstract

Treatment of municipal and industrial wastewaters results in the production of wastes in the form of sludge. Since the quantity and characteristics of sludge depend upon the degree of treatment, the upgrading of treatment facilities has had the effect of increasing sludge production. Since the quantity of sludge is a function of the type of treatment provided, any attempt to minimize sludge handling should begin at the source.

The hydrolytic assist activated sludge process provides positive control of the mixed liquor solids and is effective in the disposal of organic sludge created in the wastewater treatment process. In theory, this modification involves the hydrolysis of waste activated sludge by acid addition to a pH of 1.0 or with base addition to a pH of 13.0. Hydrolysis is followed by autoclaving at 15 psi and 121°c for a period of five hours. This treatment will solubilize most of the cellular material which can then be reintroduced to the aeration tank after pH neutralization. No sludge is wasted; it is all recycled as hydrolyzed sludge.

The main objective of this research was to operate laboratory activated sludge units over a range of Qc values to determine effects and differences in process performance and operation for the hydrolytic assist mode.

Results obtained during this study indicate that COD removal efficiency for the hydrolytic assist is compatible with the conventional process. In addition, the hydrolytic assist process proved to be an effective disposal method for sludge produced in the activated sludge process.