Sewage sludge conditioning method for fertiliser production

摘要

A method for reducing the heavy metal content in dried sewage sludge and also improving dewatering of the sludge involves stirring the sludge either with iron (III) chloride and lime water or with iron (III) hydroxide. The novel feature is that magnesium sulphate is added to the sludge in an amount given by the following equation: M - ((X/Y)-1). M = amount of magnesium sulphate added in kg per kg dry solids; X = measured heavy metal content in mg per kg dry solids; Y = maximum limit for heavy metal content in mg per kg dry solids.