Optimization of atmospheric carbonation in the integrated treatment immediate one-step lime precipitation and atmospheric carbonation. The case study of slaughterhouse effluents

Abstract

Long carbonation time has been a common feature in the integrated process composed by immediate one-step lime precipitation and atmospheric carbonation. This work aims to understand how carbonation time can be influenced by reaction pH, as well as how reactor area/volume ratio affects carbonation time and ammonia removal, using slaughterhouse wastewater due to its variable characteristics. In the integrated immediate one-step lime precipitation and atmospheric carbonation process, the immediate one-step lime precipitation results showed that the reaction pH and the type of slaughterhouse wastewater influenced the removal, however, removals were the highest at reaction pH 12. In atmospheric carbonation process, the carbonation time required to reach pH 8 was independent of the reaction pH used. Additionally, at reaction pH 12, the reactor area/volume ratios applied (from 0 to 155.4 m2/m3) showed that higher reactor area/volume ratios caused lower carbonation time, but ammonia removal was not affected. For reactor area/volume ratios of 5 and 155.4 m2/m3, 15 and 1 days were spent to reduce the pH from 11.9 to 8.2, with removals of 71 and 82.6% for NH4+ and 10 and 79.1% for calcium, respectively. High removals of total Kjeldahl nitrogen (≥71%), biological oxygen demand (≥80%), ammonium nitrogen (≥52%), total phosphorus (98%), total suspended solids (≥52%), turbidity (≥62%), absorbance at 254 nm (≥87%), absorbance at 410 nm (≥83%) and oils & fats (≥47%) were obtained using immediate one-step lime precipitation and atmospheric carbonation integrated process to treatment slaughterhouse wastewater, indicating that the these process is an efficient pretreatment for slaughterhouse wastewaters.