Lopez et al. was capable of using both coagulation and flotation with the coagulant being alum and anionic polymer as flocculent for treating slaughterhouse wastewater. Removing efficiency was 94% when using 250 mg/L alum, 51 mg/L of polymer, with a pH of 4. This is compared with the biological process using an anaerobic filter (AF) and sequencing batch reactor (SBR) where COD ranged 50–81%, configured with optimum removal was 97% for hydraulic retention time (HRT) 20 h in the AF and 9 h in the SBR [61]. Abreau and Zaiat found that using an upflow anaerobic-aerobic reactor where the anaerobic reactor had an HRT of 10 h and COD reduction from 389 to 137 mg/L. Using a combined, COD removal went from 259 to 93 mg/L with an HRT of 12 h (6 h of anaerobic and 6 h of aerobic [62].