Give sound clarification on desludging of septic tanks

I wish to refer to IWK's advertisement published in most newspapers on 31, December 1996. The advertisement gives a notice to IWK's customers on billings, charges and some information on IWK's services in the privatisation of national sewerage services. However, an important aspect of the advertisement on septic tank has been found to be not only inaccurate but also misleading.

To begin with, it is important to know that a septic tank consists of two major components i.e. a sedimentation tank and a filter bed or a soakaway ( see sketch below extracted from "Guidelines For Developers On The Design & Installation Of Sewerage Systems" published by the Director General, Sewerage Services Department, Ministry Of Housing And Local Government, Malaysia, Jan. 1995).

Domestic sewage is drained first into the sedimentation tank where it undergoes anaerobic decomposition and the partially treated effluent is then conveyed to the filter bed where further biological decomposition takes place before the final effluent is discharged into roadside drains. It must also be noted that the treatment of sewage in a septic tank (including in the filter) will not be complete and the effluent it produces will not fully comply with the Environmental Quality (Sewerage and Industrial Effluents) Regulation, 1979.

Diagram A

Diagram C

Diagram D

In IWK's advertisement, diagrams A, C and D clearly omit the presence of the filter bed and the effluent from the tank is shown to be discharging directly into the drains. IWK should be fully aware of this omission as the issue has been highlighted in this column, e.g. (NST Sept. 26- Desludging interval of two years an "estimate") and the full details of a complete septic tank are given in the guidelines set by the Department of Sewerage Services and also in the Malaysian Standard, M. S. 1228. One wonders why IWK chooses to blatantly ignore the filter bed and the importance it plays in the treatment of domestic sewage and of its maintenance.

In my letter (NST Sept. 26 1996) I have established that a septic tank, if designed to the requirements of M S 1228, could have a sludge storage capacity of about half of the total capacity of the tank. However, the advertisement by IWK mentions that the maximum sludge storage capacity is about 1/3 of its total capacity. Can IWK justify this technically?

The consumers have been told previously by IWK and the Department of Sewerage Services that it is a design criterion to have a the septic desludged once in every two years. Now, IWK contents that it should be desludged REGULARLY. Can IWK be more specific and advise the consumers how frequently a septic tank would be required to be desludged? My letter (NST Sept. 26 1996) concludes that a desludging frequency of once in two years is at best an "guestimate".

In view of the doubts now surrounding this issue, it is important that the technical experts of IWK and the Department of Sewerage Services come out with a technically sound justification of the optimum frequency of desludging a septic tank.

. It is reported that there are over 1.2 million septic tanks in existence which serve over 6 million persons or approximately 1/3 of the total population in Malaysia. It could be a significant battle won if IWK and the Department of Sewerage Services can give satisfactory clarification, with sound technical backing, to the consumers on issues pertaining to the operation and maintenance of a septic tank.

In view of the inherent shortfall of septic tanks as a domestic sewage treatment facility, it is imperative they must be gradually replaced by more efficient central sewerage treatment systems. Are programs of replacement of septic tanks included in the national sewerage services privatisation? This privatisation exercise would be doomed to failure if IWK and the Department of Sewerage Services do not make a clean breast of it vis-à-vis the controversies surrounding the issues of septic tanks.

(This article was published in NST on Jan 8, 1997) 2008