Treatment of slaughterhouse wastewater by acid precipitation (H2SO4, HCl and HNO3) and oxidation (Ca(ClO)₂, H2O2 and CaO₂)

Abstract

The treatment of slaughterhouse wastewater was investigated by both acid precipitations and by oxidation processes. Precipitation tests were developed using three acids (H2SO4, HCl and HNO3) at different operating pH (1–6). A decrease of the precipitation pH led to an increase of the conductivity values of the supernatant. Precipitation processes allowed the removal of chemical oxygen demand (COD) (41–97%), turbidity (56–99%) and total phosphorus (27–56%). Total phenols were removed (15–96%) from pH ≥ 2, depending on the precipitation process. Generally, precipitation processes decreased the hydroxide and bicarbonates species. Additionally, three different oxidation processes were tested at different concentrations (1–15 g L−1): Ca(ClO)₂, H2O2 and CaO₂. When Ca(ClO)₂ and CaO₂ were applied, an increase of the supernatant conductivity was achieved. COD removal ≥71% and turbidity elimination in the range of 85–100% were achieved by using oxidation processes. CaO₂ was very effective to remove total phosphorus (81–96%). The increase of the oxidant concentration in H2O2 and Ca(ClO)₂ oxidation processes led to a decrease in the removal of total phenols and bicarbonates species. Optical density of the microorganism cultures was efficiently eliminated (up to 100%) by oxidation processes. In addition, acid precipitation and oxidation allowed to remove total solids (TS), total volatile solids (TVS), total suspended solids (TSS), ammonia nitrogen, nitrates and biochemical oxygen demand (BOD5). Acid precipitation and oxidation produced sludge rich in organic matter and nutrients (Ca, Mg, P, Cl, Na and K). Despite the high removal efficiencies, a post-treatment following the precipitation and oxidation processes can be required.