Use of Statistically-Based Design of Experiment to Study Olive-Oil Mill Wastewater Biodegradation by Ralstonia Eutropha

Abstract

The biodegradation capacity of Ralstonia eutropha PTCC 1615 for olive-oil mill wastewater (OMW) was evaluated using a central composite design (CCD) technique. An empirical model was developed to mathematically describe the bacterial performance under the influence of the mutual interactions between the independent variables. The selected test parameters include the initial pH of the OMW as a substrate (x1), the inoculum size (x2, InocS), and the substrate dilution ratio (x3, SDR= OMW:H2O). The biodegradation ability of R. eutropha was evaluated based on the removal capability of total phenolics (TP) and chemical oxygen demand (COD). Predicted values for the responses agreed well with experimental values; R 2 values for TP and COD removal were 0.9984 and 0.9963, respectively. The pH and the substrate dilution ratio were both found to significantly impact TP and COD removal, while the significance of the inoculum size was less than that for the other two test variables. The capacity of the adapted R. eutropha for OMW degradation varied with SDR with the following ranking: undiluted > twofold-diluted > fourfold-diluted OMW. Within the design space, the optimum conditions for the biodegradation of OMW in terms of TP and COD removal were established and include pH of 7.9 to 8.4, InocS of 5%, and SDR of 1:0.. This study has demonstrated that it is possible to use the adapted R. eutropha for OMW bioremediation without pretreatment. Commercialization of this type of bio-treatment is promising.