Application of hybrid ultrasonic cavitation/adsorption and coagulation for treatment of palm oil mill effluent

Ultrasound cavitation (US), coagulation treatment (natural coagulant chitosan and synthetic coagulant ferric chloride (FeCl₃)) and activated carbon as adsorbent were applied for treatment of raw palm oil mill effluent (POME). The findings showed that for US alone, increasing pH >11 COD removal increased due to more hydroxyl radical (OH·) present in alkali solution phase. The COD, colour and TSS removal at pH 11 were 26.3%, 52.7% and 58.2%, respectively after 60 min. Application of coagulants (Chitosan and FeCl₃) required acidic medium for coagulation (i.e. between pH 4.5 and 5) to be effective. A dosage of 100 mg/L chitosan at pH 4.5 removed 15.4% COD, 85.8% colour and 97% TSS from POME. A dosage of 450 mg/L FeCl₃ at pH 5 removed 38.54% COD, 88.6% colour and 91.5% TSS. It was observed that FeCl₃ removed COD better than chitosan. Adsorption studies indicated that 800 mg/L of activated carbon removed 64.3% COD, 99.16% colour and 99.5% TSS. The dosage needed for adsorption was much higher compared to chitosan and FeCl₃ coagulants required. However, activated carbon could be recycled and reused. The hybrid treatment of ultrasound cavitation and coagulation (US-FeCl₃) removed 56.3% COD, 92.4% colour and 96% TSS. The US-Chitosan removed 35.1% COD, 86.8% colour and TSS 89.2%. The eventual hybrid treatment of ultrasound cavitation, FeCl₃ coagulation and activated carbon adsorption in series removed BOD₅ 89.7%, COD 88.1%, colour 99.9% and TSS 99.5% cumulatively. The final effluent concentration of the treated POME was in the accepted range set by Department of Environment (DOE) Malaysia. The study showed that a combination of ultrasound cavitation, adsorption and coagulation (Chitosan and FeCl₃) treatments were effective for removal of BOD₅, COD, colour and TSS in POME wastewater. In addition, the efficiency of the treatment will further improve when these treatment technologies are combined.