The overlay interaction plots of two variables: chemical oxygen demand (COD) and initial pH (a), COD and fermented pineapple extract (FPE) (b), initial pH and FPE (c) on oxidation–reduction potential (ORP) value and stimulating purple nonsulfur bacteria (PNSB) growth in non-sterile rubber sheet wastewater (RAW) under microaerobic light conditions over 2 d incubation.