Chemical oxygen demand reduction of pineapple industry wastewater by locally isolated microbes in column system

摘要

Wastewater from pineapple canning industry contributes to high levels of Chemical Oxygen Demand (COD), colors and suspended solids when discharged into water environments. Currently, there are many methods that have been used to remove organic pollutants in industrial wastewater such as ozonation, chemical coagulation and electrochemical oxidation. However, these methods involve high operational costs and are energy extensive, besides producing large amounts of sludge. A biological approach may be a good alternative since the operational cost is usually lower and it is environmentally friendly compared to the physico-chemical methods. In this study, the effectiveness of locally isolated microbial agents in reducing COD level in pineapple industry wastewater was investigated. Two bacterial strains identified as Kurthia gibsonii and Klebsiella pneumoniae and a fungal strain (Candida tropicalis) were tested using continuous systems. Rubber wood husk, solid pineapple waste and sugarcane bagasse were utilized as support materials in single packed-bed columns. Parallel packed-bed columns containing sugarcane bagasse were used to enhance the performance of COD reduction. The COD reduction was monitored for five days and analyzed using a Hach DR/5000 spectrophotometer. Growth on microbial biofilms on sugarcane bagasse surface in both systems was analyzed using FESEM. In addition, the ability of an integrated biological system consisting of parallel packed-bed columns containing Kurthia gibsonii immobilized onto sugarcane bagasse to reduce COD level and Cr(VI) concentration in ChromeBacTM effluent was also explored. The results obtained showed that at 50% (v/v) initial COD concentration, the presence of single microbial cultures resulted in reduction of COD by 93-95% whereas at 100% (v/v) initial COD concentration, reduction of 64-84% were observed. The mixed microbial culture resulted in 71% reduction in both cases while in the columns without bacteria, COD reduction of 49% and 37% were observed, respectively. Analysis by FESEM showed the presence of abundant EPS surrounding the cells in the bioreactor. The integrated biological system showed complete removal of Cr(VI) for both synthetic and real electroplating wastewater. The percentage of COD reduction in five batches was observed between 92-96% for synthetic Cr(VI) containing wastewater. The COD reductions for real electroplating wastewater were between 92-95%.