Studies on decreasing Chemical Oxygen Demand (COD) on artificial laundry wastewater using anaerobic-aerobic biofilter dipped with bio ball mediaNetti Herlina, Muhammad Turmuzi Lubis, Amir Husin and Ihmawani PutriMATEC Web Conf., 276 (2019) 06015DOI: https://doi.org/10.1051/matecconf/201927606015