Sludge production in chemical precipitation

Abstract

Ferric chloride as in many other wastewater plants is used as a coagulant in wastewater treatment at Ivar (SNJ) since its multivalence nature has a significant effect on overcoming the stability of particles and consequently results in material precipitation by gravitational sedimentation process that concludes in proper removal of suspended solids as well as colloidal particles. This results in sludge production which should be treated before disposal. Prediction the amount of sludge produced during the chemical treatment is essential to estimate the volume and retention time required for the sludge treatment. Observation at SNJ showed that the sludge production was not proportional with suspended solids removed or ferric chloride added. Laboratory-scale studies were carried out to investigate a corresponding relationship between the actual and expected sludge production during the coagulation and flocculation process. For this purpose, jar tests were conducted and effect of ferric chloride dosage on pH, conductivity, TSS, TSS- removal, alkalinity and calculated and measured sludge production as well as comparison of those two last parameters was investigated. Results achieved in the laboratory showed an acceptable conformity between the measured and calculated sludge productions, particularly in dilute wastewater samples which resulted in lesser amounts of sludge. In addition to laboratory experience, the result of full-scale plant that received from Ivar was reviewed and investigated to express the distinction between both scales.