Immobilization of phosphorus in sewage sludge using inorganic amendments

Sewage sludge contains large amount of water-soluble phosphorus, which is prone to runoff loss when sewage sludge is land applied. Phosphorus export from sewage sludge is an important cause for water eutrophication. Immobilization of phosphorus before sewage sludge land application seems necessary. In this study, three amendments including red mud (RM), lime and mixture of RM and lime were employed to immobilize phosphorus in fresh sewage sludge. It was found that phosphorus was effectively controlled by RM, lime and mixture of RM and lime. Sequential chemical extraction results indicate that the RM amendment transformed H2O-P in the sewage sludge into the NaOH-P, while the lime amendment transformed H2O-P in the sewage sludge into the HCl-P. Such transformations in phosphorus fractions would have little influence on phosphorus availability but would retard and reduce potential phosphorus loss following sewage sludge was land applied.