Slaughterhouse wastewater is one of the main sources of environmental pollutants, containing a high amount of organic matter (chemical oxygen demand (COD), biochemical oxygen demand (BOD)), total nitrogen (TN), total suspended solids (TSS), total phosphorus (TP), grease, and oil. The main aim of the present research is optimizing the coagulation-flocculation process and examining the effects of experimental factors with each other, for example, pH, the concentration of two different coagulants (FeCl 3 and alum), rapid mixing rate, and settling time. Therefore, it is aimed to treat slaughterhouse wastewater using the coagulation-flocculation process with the optimization of the response surface methodology (RSM). COD, turbidity, and suspended solids (SS) of the treated wastewater are chosen as the response variables. Furthermore, the optimal conditions for three responses are acquired by employing the desirability function approach. When the experimental results of two coagulants are compared, it is observed that the alum coagulant gave better results for the three responses. The alum coagulant utilized in the present research is able to increase COD, SS, and turbidity removal efficiency by 75.25%, 90.16%, and 91.18%, respectively. It is possible to optimize coagulation-flocculation by utilizing the RSM analysis, which proves that coagulation can pre-treat slaughterhouse wastewater.

BACKGROUND: In the present study, the performance of the membrane process, one of the advanced treatment methods that can enable the reuse of slaughterhouse wastewater, was evaluated. The wastewater was treated using ultrafiltration (UF) (10, 50 kDa), nanofiltration (NF) (150-300 DA) and reverse osmosis (RO) (500 kDa) membranes alone, and UF + NF, UF + RO membrane combinations at different pressures. In addition to rejection and permeate flux considerations, it was attempted to select the most effective membrane by performing scanning electron microscopy, Fourier transform infrared, contact angle, and atomic force microscopy analyses of the membranes used.RESULTS: As a result of the experiments, the highest flux was observed at 5 bar for the 50 kDa UF membrane. When the performances of the sequential application of 10 and 50 kDa UF membranes followed by NF and RO membranes were evaluated, the highest flux was obtained for the sequential application of the 50 kDa UF membrane with the NF membrane as 19.68 and 9.05 L m −2 h, respectively. CONCLUSION: The highest chemical oxygen demand (COD) removal was obtained for the RO membrane at 20 bar as 88.67%, and for the 50 kDa UF + RO sequential application, the COD removal was increased from 70% to 88.67%.