Evaluation of chemical sludge production in wastewater treatment processes

Sludge production in the wastewater treatment process is still a critical environmental issue today. The present study evaluates the production of chemical sludge as a result of chemical precipitation for treated wastewater from two different sources, the aerobic (conventional activated sludge) and the anaerobic (UASB reactor) treatment processes. The sludge production was estimated by implementing chemical precipitation processes using iron salts as coagulants (ferric chloride). The results indicated that the chemical sludge production increased linearly with the coagulant dosage, with sludge production values of 0.49–0.82 mg/mg FeCl3 for the aerobic effluent and 0.40–0.64 mg/mg FeCl3 for the anaerobic effluent. These values were expected according to the theoretical stoichiometry of the reactions involving the total precipitation of iron to form metal hydroxide. The increase in metal hydroxide precipitate content in the sludge reduced the volatile solids to total solids ratio up to 0.5 for dosages of coagulant equal to or greater than 80 mg FeCl3/L. For both wastewaters, the total concentration of phosphorus in the liquid phase was less than 1.0 mg/L for coagulant dosages equal to or greater than 80 mg FeCl3/L.