Electrochemical oxidation of palm oil mill effluent using platinum as anode: Optimization using response surface methodology by Rakhmania, Rakhmania, Kamyab, Hesam, Yuzir, Muhammad Ali, Riyadi, Fatimah Azizah, Ostadrahimi, Alireza, Khademi, Tayebeh, Ghfar, Ayman A., Kirpichnikova, Irina