Potential use of sludge ash as construction material

Abstract

Sludge from wastewater treatment plants creates problems of disposal, which may account for half the total cost of wastewater treatment. Most of the sludge is disposed of either by spreading on land or burial. Some cities solve their problems by incinerating after drying. Other cities, near coasts, convey the sludge out to the sea in pipes or barges, but this practice is now being seriously questioned. In general, land disposal is the cheapest way of disposing of the sludge, particularly if it enables crops to be grown on poor land. The problem of sludge disposal will be intensified as the quantity of sludge to be disposed of increases and availability of suitable landfill sites will be a major problem. Recently, research has been carried out to use dried sludge as a brick-making material or for fuel production. Singapore is an Island-City-State with a total land area of about 620 km/sup 2/. The Island is served by six sewage plants with a combined design capacity of 8 x 10/sup 5/ m/sup 3//d. Sludge from the treatment plants is digested and dewatered and used as a soil conditioner for plants and trees, or disposed of by landfilling. Since land is limited on the Island, alternative means of disposing of the sludge is desirable. Based on heat balance studies, Jarnis and Vickridge stated that sludge dewatered by a filter press was autothermal during combustion at 550 C, which indicates favourable conditions for incineration. Incineration might be a viable alternative for sludge disposal on the Island. However, a substantial amount of ash would be produced for disposal. This communication reports on the feasibility of using sludge ash as a building and construction material. 3 figs., 3 tabs., 16 refs.