Abstract:
This research aimed to develop a technique for producing high efficiency silica-immobilized bacteria and to develop a biofiltration system containing the immobilized bacteria for treatment of phenolic compounds contaminated wastewater as well as for enhancing biomethanation of wastewater after phenolic compounds removal. The inoculum used in this study was a co-culture of Methylobacterium sp. NP3 and Acinetobacter sp. PK1, which is known to degrade high concentrations of phenol. The optimum bacterial immobilization process was to use 3.0 OD578 inoculum and to prepare the immobilized silica in square shape with 0.5x0.5x0.5 cm3 dimension, which led to the initial concentration of immobilized cells at 108 CFU/g silica. The immobilized bacteria could degrade m-cresol, o-cresol, caffeic acid, ferulic acid, 4-hydroxybenzoic acid, catechol and 3-methylcatechol. In addition, the immobilized bacteria could be stored at 4°C for 30 days. The study later developed a small biofiltration unit consisted of an Internal loop Airlift Bioreactor with 25 g/L silica-immobilized bacteria at Hydraulic Retention Time (HRT) of 2.5 h. The immobilized bacteria in biofiltration unit could degrade 100% of 5 – 300 mg/L other phenolic compounds in synthetic wastewater. This biofiltration could be applied continuously for at least 3 months. The following experiment investigated the efficiency of biofiltration system for the treatment of phenol phenolic compounds in wastewater from the final satabilization ponds of 3 factories in Songkhla (plant A), Satun provinces (plant B), and Surattani province (plant C) at HRT of 5.0 h. The biofiltration system could degrade 67-100% of phenolic compounds in wastewater from 3 factories and the biofiltration also partially reduced COD and color without further addition of nutrients. The study later used the biofiltration system for treatment of palm oil mill effluent (POME), which is normally used as substrate of biomethanation. It has been known that phenolic compounds cause harmful effects to methane-producing bacteria and inhibit methane production. This study compared biomethanation between untreated and dephenolized POME. Biochemical Methane Potentials (BMP) in systems with the undiluted untreated POME, untreated dephenolized POME, 4-folds diluted untreated POME, and 4-diluted dephenolized POME were 21, 302-534, 131, and 347-508 mLCH4/gCOD, respectively. Therefore, the developed biofiltration system could be applied to increase methane yield in palm oil mills. In addition, LmPH genes, which involved in phenol degradation of both bacteria were found in the biofiltration system throughout the operation. The results confirmed that the immobilized cells were responsible for the treatment of phenolic compounds in wastewater.