Removal of Toxic Metals from Petroleum Refinery Wastewater Using a Simultaneous Mixture of Local Materials

Abstract Petroleum refinery processes are a major source of industrial wastewater characterised by high levels of hydrocarbon pollutants and heavy metals. This wastewater, when discharged into the ecosystem, can cause serious environmental degradation and endanger public health and safety. In this study, the use of three local materials (rice husk, snail shell, and maize stalk) as bioadsorbents for the treatment and removal of heavy metals was investigated. The three agricultural wastes were ground, dried, and sieved into particle sizes of 150 and 300 microns, treated, and oven-dried. The snail shell was treated with warm water, and the rice husk and maize were treated with calcium hydroxide and hydrochloric acid, respectively. The obtained bioadsorbents were used simultaneously to treat the wastewater using an equal amount of each adsorbent in a batch adsorption experiment. Filtrate was collected at intervals of 1 hour for a 5-hour period and analysed using the atomic absorption spectrometer (AAS) for the following heavy metals (Cd, Ni, Cu, Co, and As). The results obtained established a substantial decrease in the concentration of the heavy metals under investigation, with percentage reductions of 98%, 76%, 97%, 100%, and 90% for Cd, Ni, Cu, Co, and As, respectively, for the particle size of 150 microns. Similarly, for the particle size of 300 microns, reductions of 67%, 76%, 96%, 77%, and 100% were obtained for Cd, Ni, Cu, Co, and As, respectively. The results exhibited that the smaller particles had better adsorption capacity. Kinetic investigations were conducted to examine the impact of factors like temperature, adsorbent dose, and pH. The analysis showed that a pseudo-second-order kinetic model governed the adsorption rate and best described correlated experimental data.