The development of a pilot plant study into the effects of flow and load balancing on sewage treatment

The traditional concept of sewage treatment works having to be designed to accept the maximum instantaneous load imposed during the diurnal cycle is being challenged by modern technologies. The advent of reliable methods for on-line monitoring of sewage strength have made it possible to automatically calculate the mass of organic load entering a works. It is postulated that by balancing the load, the retention times of the treatment processes may be reduced not only by removing the extra capacity needed for the peak loads, but also by making the treatment processes more efficient. A pilot scale activated sludge sewage treatment plant of 2 m3 /h dry weather flow was constructed to a conventional design with variable aeration capacity and a balance tank. The settled sewage strength was continuously monitored as total organic carbon by a TOCsin Mkll analyser. The plant could be operated in zero, flow or load balanced modes by the use of pneumatic control instrumentation. The plant and methods of operational control were commissioned and shown to be feasible. The plant variables were monitored in all three modes of operation at conventional loading, and the kinetics of the activated sludge studied in a laboratory batch treatment system. A mathematical model, based upon the observed treatment kinetics, was formulated. The mathematical output was compared with the plant output, and was also used to forecast the plant performance at higher rates of lr -ding in the three operational modes.