Abstract
A comparative analysis of the efficiency of activated carbon produced from fermented cassava peels (CPB), unfermented cassava peels (CPA) and commercial grade activated carbon (CAC) in the treatment of refinery wastewater was carried out. CPB was found to be 8% and 18% more efficient when compared to CPA and CAC in the removal of COD, and 14% and 3% better than CAC and CPA respectively in the removal of BOD5. The removal efficiency of Pb 2+ by CPB was 100% compared to 95% and 57% by CPA and CAC while 96% of phenol was removed by CPB against 93% and 83% by CPA and CAC respectively. This better performance of CPB over CPA and CAC is not unconnected with its higher pH resulting from the removal of cyanide from the peels during the fermentation process. However, despite the high phenol removal efficiency by CPB, the concentration of phenol in the treated effluent does not meet the environmental guidelines for disposal. It is therefore, recommended that a two-stage CPB adsorption column arranged in series is necessary to treat refinery wastewater efficiently if it is desired to totally remove phenol from the effluent or reduce the concentration to 0.005 mg/l allowed by the Federal environmental protection agency (FEPA). The equilibrium adsorption test conducted showed that the Freundlich isotherm is a better fit for the adsorption of phenol by the three activated carbons with correlation coefficients (R2) of 0.9364, 0.9383 and 0.9541 for CAC, CPA and CPB respectively. CPB was found to be a better adsorbent as it has the highest adsorptive capacity as evidenced from its better Freundlich exponent. Keyword: Cassava peels, activated carbon, adsorption, refinery wastewater, environment, pollutant. Received: 2016.01.18 Accepted: 2016.03.04 Published: 2016.04.01 before being discharged into the environment or recycled back into the plant depending on water economics [Nekoo and Shoreh, 2013; Hariz and Monser, 2014]. Since refinery wastewater pollutants is made up of both organic and inorganic sources, the treatment of such wastewater will involve chemical, physical, biological or a combination of these processes [Adeyinka and RimiRukeh, 1999; Fetter et al., 1982]. To measure the organic content of wastewater, the biological oxygen demand (BOD) and chemical oxygen demand (COD) as well as the total organic matter
Highlights
Refinery wastewater most often contains hydrocarbons, spent catalyst and acid as well as soluble bases used as raw materials and treatment reagents
Some of the materials used for the experiments were fresh peelings of bitter cassava variety obtained from a cassava farm in Ughelli, Delta State of Nigeria, wastewater collected from the downstream of the dry air flotation (DAF) unit of the wastewater treatment plant of the Warri refinery and petrochemical company (WRPC) in Warri, Delta state of Nigeria, commercial grade activated carbon (CAC) obtained from Pyrex chemical/laboratory equipment in Benin city, citric acid, distilled water, muffle furnace, crucibles, measuring cylinders, filter papers, beakers, weighing balance, mortar and pestle as well as Perkin Elmer HGA 900 spectrophotometer
It was established from the results of this study that activated carbon produced from agricultural waste such as cassava peels hold a great promise in the treatment of wastewater containing organic materials and trace heavy metals
Summary
Refinery wastewater most often contains hydrocarbons, spent catalyst and acid as well as soluble bases used as raw materials and treatment reagents. Cassava peels activated carbon was reported to adsorb 80% of Pb2+ and 77% Cu2+ from water collected from a stagnant pond where various waste is indiscriminately dumped by villagers [Ilaboya et al, 2013]. In all these documented studies, little or no attention is paid to the cyanide content of the cassava peels. Cyanogenic glycoside may not be toxic and harmful as a compound but it hydrolyses to form toxic and harmful hydrocyanic acid [Olayinka, 2013; Oti, 2002] This may possibly happen when the cassava peels activated carbon is contacted with the wastewater during the adsorption process. The adsorption parameters, efficiency and adsorption isotherms for commercial grade activated carbon is compared with activated carbon produced from cyanide laden and cyanide free cassava peels in the treatment of refinery wastewater
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