Effect of metal salt coagulants on treatment of activated sludge effluent in sulfite mill pulp and paper plant

Pulp and paper effluents are considered as serious environmental hazards and their treatment, because of multiplicity of impurities and complexity of their chemical structures, is one of the most difficult and inconvenient industrial processes. As the most pulp and paper mill work on kraft process, there are few studies in literature on the treatment of neutral sulfite semi chemical (NSSC) process effluents. Sulfate lignin (SL) is the main concern of kraft process while lignosulphanates (LS) are primary concern for NSSC process. The high charge density of LS in the wide range of pH makes it more stable than SL. This experimental study examined the effect of metal salt coagulants (Alum, poly aluminum chloride, aluminum chloride and ferric chloride) on the treatment of activated sludge effluent in NSSC process used in Mazandaran pulp and paper industry. These coagulants were able to remove colour turbidity and COD of the waste water up to 90, 95 and 70%, respectively. Results show that ferric chloride has the best performance among coagulants studied here. This feature of ferric chloride supports the idea that the Fe is more amenable to hydrolysis than Al.