AVOIDING THE PROBLEMS OF SEPTIC SEWAGE

Septic sewage develops in a sewerage system when aeration of sewage in gravity sewers is inadequate or when sewage is pumped up a rising-mai n sewer and sulphides are formed. Many variables affect the rate at wh ich septicity develops. Equations have been produced which describe th e relation between the variables and septicity. Such equations can be applied to individual sewers or rising mains. To predict, prevent and control septicity of an entire sewerage system will be complex; preven tative measures taken upstream will affect the formation of septicity downstream. This paper describes the development of a computer program me, consisting of a series of linked algorithms. The programme enables the sewerage system to be mathematically modelled in order to predict the formation of sulphides in the sewage at identified locations. It also enables the effects of applying a range of preventative measures to be assessed in order to optimise a strategy for prevention and cont rol. The results are described and discussed for application of the mo del to an extensive sewerage system, serving a population of 665,000. In some circumstances, prevention of septicity may nor be practical or it may be expensive. To remove odours from ventilated air, which incl udes hydrogen sulphide, a novel, reliable, low-cost and effective cata lytic filter has been developed. This filter is described, together wi th performance data obtained during recent full-scale operation. (C) 1 998 IAWQ. Published by Elsevier Science Ltd.