In the ‘seventies, sludge was still being used extensively as an agricultural fertiliser. The government sets much more stringent requirements for the open disposal of sludge these days. This is partly due to the presence of environmentally harmful substances such as heavy metals and other contaminants. Sludge has to be processed by specialised companies into granules or some other form of bulk material. The granules are incinerated in purpose-designed installations (cement kilns, or as additional fuel for brown coal burning power plants).