The use of photocatalytic degradation to improve the quality of crude refinery effluent
Authors:   , Naidoo Dushen Bisetty 
Published: March 2021

Water plays a fundamental role in sustaining life on Earth. Water is largely used by industries to support their processes and utilities. Through growing industrialisation, each year more and more wastewater is generated and the demand for water rises rapidly. The incorrect and unsustainable use of water is placing a great strain on the South African water supply. Much emphasis is now being placed on industries re-using and treating their effluent and wastewater. Of recent, government has placed stringent specifications for industrial effluent quality and industry find it difficult to continuously improve their effluent quality to be within acceptable limits. Crude refineries are major contributors to wastewater, producing effluent comprising largely of Oil, grease and hydrocarbon. Much focus is placed on finding alternate means of wastewater treatment to assist with the removal of oil and hydrocarbon contaminants. More effluent treatment processes need to be explored to ensure industries operate in a sustainable manner and do not place unnecessary strain on the South African water supply. Photocatalytic degradation is a wastewater treatment technique that has drawn a lot of attention in the last decade. This is an Advanced Oxidation Process (AOP) which involves the production of a hydroxyl radical (OH-) which is then used for the degradation of organic contaminants. The degradation converts the organic pollutants into CO2 and H2O. A synthetic crude refinery effluent was developed and underwent the photocatalytic degradation process. The catalyst concentration was varied at 2 g/L, 5 g/L and 8 g/L. The oxidation reaction took place over time intervals of 30, 60 and 90 minutes and aeration to the reaction vessel was supplied at 0.768 L/min, 1.11 L/min and 1.48 L/min. This photodegradation took place under UV light conditions. The degradation process was conducted with the aim of evaluating the degradation of oil and phenol in crude refinery effluent. Sulphates were also monitored to observe if an effect was noticed. Design of Experiment (DOE) involved the development of experimental run matrices for a multilevel factorial design, Central Composite Design (CCD) and Box-Behnken Design (BBD) model. Randomized runs were then conducted as per the design matrix for each model. Model verification and evaluation was then conducted and the best suited degradation models were selected. It was observed that the best fitted model for the degradation of oil in water was the BBD. The best design model for phenol degradation was the CCD. Throughout the photocatalytic degradation process, it was noted that no change took place with the sulphates. The models were then optimised to determine the optimum degradation conditions. This was carried out using Response Surface Methodology (RSM) techniques. The CCD model yielded a combined oil and phenol degradation of 71.5%. This occurred at a catalyst concentration of 2.07g/L, a run time of 90 minutes and an air flow rate of 0.768L/min. The BBD model produced a combined oil and phenol degradation of 68%. This took place at a catalyst concentration of 2 g/L, a run time of 30 minutes and an air flow rate of 1.04 L/min. pH were monitored throughput the degradation process and both these models yielded output products within the stipulated pH band. The testing of a local crude refinery effluent was conducted using the CCD and BBD optimum conditions. When using the CCD optimum conditions degradation of 76.98% and 84.21% was observed for both oil and phenol respectively. The BBD optimum conditions yielded a degradation of 83.33% for oil and 78.95% for phenol. This indicated that the photocatalytic process can be considered for degrading crude refinery effluent as its products met the specifications of municipal industrial waste water. The above results clearly indicate a positive outcome for the treatment method of photocatalytic degradation on the synthetic crude refinery effluent. This technique can therefore be further explored when considering crude effluent treatment and the treatment advantages should be used by all industries to improve effluent quality and allow for more sustainable and environmentally friendly operations.