Experiences with the Deep‐shaft Process at Tilbury

Abstract

ABSTRACTThe deep‐shaft activated‐sludge process, which was originally developed for single‐cell protein production by ICI1, has been successfully applied to the treatment of high‐strength domestic and industrial waste water. The process exploits the hydrostatic pressure generated at the bottom of a column of liquid to enhance the transfer of oxygen to a rapidly‐circulating mixed liquor.About forty deep‐shaft plants are in operation worldwide of which four have been built in the UK. The latest of these treats a mixed industrial and domestic waste water at Anglian Water Authority's sewage‐treatment works at Tilbury. At a dry‐weather flow of 30 Ml/d, this is the largest deep‐shaft plant in the world.The paper gives a description of this works and some performance data obtained during a 3‐month monitoring period following plant commissioning. The results show that the BOD and suspended solids loads were extremely variable and exceeded the design capacity of the works by approximately 40% during the month of July. Despite this, the effluent quality remained within consent limits with a 95 percentile BOD of 83 mg/1 (consent limit: 120 mg/1 BOD).The computerized aeration control system was not functional during the trial period; nevertheless, considerable potential energy savings were indicated. During a one‐week period, an average of 41 000 kg BOD were removed daily at a mean oxygenation efficiency of 2.5 kg BOD removed/kWh.