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.

Keywords: Industrial wastewater; Organic contamination; Physicochemical processes; Removal efficiency; Sedimentation; Sludge.