Phenols and color removal from palm oil mill wastewater by immobilized bacteria and white rot fungi

Abstract

This study used bacterial co-culture of Methylobactrium sp. NP3 and Acinetobacter sp. PK1 and white rot fungus, Trametes hirsuta AK4 to remove phenols and color from treated palm oil mill effluent (POME). Initially, the quality of effluent from the last stabilization pond of a palm oil mill in Surat Thani province was investigated. The values of pH, phenols and color of these treated POME samples were ranged 8 - 9, 264 - 338 mg/L and 95 -117 color units, respectively. After that, the efficiencies of two immobilized bacteria, i.e. silica- and recycled plastic immobilized co-culture bacteria and two kinds of Trametes hirsuta AK4, i.e. pellets and immobilized on palm pericarp fiber (PF) were compared. The result showed that silica immobilized co-culture bacteria had higher phenols and color removal efficiency than recycled plastic immobilized co-culture bacteria. The immobilized silica removed 38% and 40% of phenols and color from 100% treated POME, respectively while immobilized recycled plastics removed 33% and 1% of phenols and color removal, respectively. For white rot fungal treatment, 250 g/L of Trametes hirsuta AK4 pellets had the highest color removal efficiency. The study with diluted treated POME found that 250 g/L of white rot fungal pellets could remove color up to 82% and 38% in 25% (diluted) and 100% (undiluted) treated POME, respectively. However, white rot fungal pellets were broken after 7 days. Therefore, Trametes hirsuta AK4 was immobilized on palm pericarp fiber (PF) to solve the problem. The immobilized fungus removed color up to 55% within 4 days. Since many researchers reported the toxicity of phenolic compounds to fungi, two-stage treatment was conducted. There were three types of two-stage treatment i.e. the systems with (1) silica immobilized bacteria and fungal pellets, (2) silica immobilized bacteria and PF immobilized fungus and (3) recycled plastic immobilized bacteria and PF immobilized fungi. The result showed that two-stage treatment of silica immobilized bacteria and white rot fungal pellets had the highest phenols and color removal efficiency. In addition, PF immobilized white rot fungus could remove color from wastewater that had not been treated by the bacteria. This is probably due to the protection of fungal cells by palm pericarp fiber.