Thermal / electrochemical processing of slaughterhouse wastewater

The paper presents slaughterhouse wastewater treatment implemented as a combination of thermal pre-treatment and main electrochemical treatment, with a simultaneous ozonation. The efficiency of the characteristic indicator removal and the quantity of generated sludge according to electrode types (stainless steel, iron and aluminium), treatment time (5-30 minutes) and amperage (50-100 A) was tested. The wastewater is characterized by a very unpleasant odour, high colouring value (17400 CoPt), turbidity (4230 NTU), total suspended solids (1730 mg dm(-3)), chemical oxygen demand (3720 mg dm(-3)) and biochemical oxygen demand (1870 mg dm(-3)) as well as increased values of ammonium (128 mg dm(-3)) and phosphates (93 mg dm(-3)). Thermal pre-treatment removed 98.23% turbidity, 89.94% colour, 75.14% total suspended solids (TSS), 49.73% BOD5 and 36.29% COD. A stainless steel electrode set proved to be the most efficient in the removal of organic indicators and ammonium and the lowest sludge volume, whereas aluminium electrodes were the most efficient in colour removal, although with the highest sludge production. The best results were achieved by a combination of all three electrode types, with a simultaneous ozonation of 20-minute contact time, amperage of 70 A and voltage of 10 V. Following the electrocoagulation / electrooxidation by stainless steel electrodes, electrocoagulation / ozonation by iron electrodes and electrocoagulation / ozonation with aluminium electrodes and the final ozonation, 100% colour, turbidity and TSS were removed as well as 99.77% COD and 99.25% BOD5, 99.98% phosphates, 99.80% ammonium and 43.86% total dissolved solids. All measured indicators complied with the conditions for discharge into the environment.