Comparative goal-oriented assessment of conventional and alternative sewage sludge treatment options

Phosphorous (P) is a limited and non-substitutable resource. Sewage sludge contains significant amounts of P and is therefore a widely applied fertilizer. Due to its organic and inorganic contaminants, sewage sludge is also combusted in industrial facilities as well as in waste incinerators. This study compares five common methods and one novel alternative based on a thermo-chemical process to treat and dispose of sewage sludge with regard to environmental impact, resource recovery, and materials dissipation. The comparison is based on material flow analysis, energy balances, selected LCA impact analysis, and statistical entropy analysis. This work shows that the novel technology combines both advantages of the established practices: organic and inorganic pollutants are either destroyed or removed from the P containing material, and the P returned to the soil exhibits high plant-availability. The novel method also has low emissions. The additional energy requirements should be reduced. However, with regards to sewage sludge P recovery is more important than energy recovery.