Controlling Metal Uptake from Heat-Treated Sludge Applied to Grasslands

A Zimpro heat-treated sewage sludge containing high levels of zinc, nickel, lead and chromium was successfully used to establish high-grade pastures and turf on two different coastal soils in South Africa, using guidelines developed in the United Kingdom to control the rate of application. The properties and composition of the sludge and soils are described and levels of metals in the grass are reported. The rates of application suggested by the guidelines were effective in preventing excessive metal uptake. The results obtained are discussed in relation to tentative guidelines for controlling sewage sludge applications to land in South Africa.