Lightweight aggregates made from sludge

Current EU initiatives towards promoting sustainable development requires, amongst other things, member states to look towards ways of minimising the production of waste and reducing the demands on natural resources. The work described in this paper goes someway towards achieving these aims, in that it uses an innovative rotary kiln to convert a number of waste streams (including sewage sludge) into synthetic aggregates for use in the construction industry. The wastes used were incinerated sewage sludge ash (ISSA), pulverised fuel ash (PFA), activated sewage sludge, granite washings, and a low-grade clay. Different waste combinations were mixed, pelletised and fired in the kiln to produce aggregates. The properties of the aggregates produced were similar, and in some cases better, than those of a commercially available lightweight aggregate (Lytag). The aggregate properties were influenced by the mix proportions used in their manufacture but were influenced very little by the range of firing conditions used.