ASSESSING THE POTENTIAL OF ASPERGILLUS FLAVUS AND PENICILLIUM SP IN REMOVING MERCURY, ZINC AND CHROMIUM FROM RAW REFINERY EFFLUENTS
CHAPTER ONE
1.0Â INTRODUCTION
Heavy metal contaminants are common features of effluents generated and released by wide range of modern industries (Singh and Sharma 2013) and refinery effluents bearing heavy metals considered to highly toxic (Ezeonuegbu et al., 2014). Heavy metal contaminated wastewater has been identified as one of the most important sources of pollution. Such waste waters are usually generated from a variety of sources such as crude oil producing and refining, other petrochemical industries, metal processing, lubricant and car washing. These sources serve as the major contributors to the problems of heavy metal pollution especially of soil and water environments (Machido, 2015). The discharge of oily wastewater to the environment has potential to cause significant environmental hazard. This is because it contains toxic substances such as petroleum hydrocarbons, phenols, polyaromatic hydrocarbons which are inhibitory to animal and plant growth and also are mutagenic and carcinogenic to human beings (Musa et al., 2015).
Beddri and Ismail (2007) reported that waste-water effluents from petroleum refinery and petrochemical plants contain a diverse range of pollutants including heavy metals. The effluents also contain oil and grease,and are characterized by high biochemical oxygen demand (BOD) – bearing materials, suspended solids, dissolved solids, phenols and sulfides.
Heavy metals in refinery effluent mainly originate from the feedstock. Others are from corrosion products of the equipment and pipes, processed chemical additives and from materials like catalysts and other chemicals used in processes downstream of the primary distillation. The most common of these metals are Nickel, Vanadium, Copper, Chromium, Lead, Cadmium, Zinc and Selenium. Mercury has also been found to appear as impurity in natural gas and crude oil (Alao et al., 2010).
Heavy metals particularly Zinc, Chromium, Arsenic and Mercury are environmental pollutants threatening the health of human population and natural ecosystem through direct ingestion, inhalation and indirect by consumption of fish, animals or plants in which the metals have accumulated (Alao et al., 2010). Other metals like gold, aluminum, cadmium, silver, lead and mercury are also potentially toxic to living organisms (Kumar et al., 2010, Ezeonuogbu et al 2014). Toxicity of these metals occurs through the displacement of essential metals from their natural binding site or through ligand interactions.
Methods employed for the removal of organic pollutants from refinery effluents are not applicable when heavy metal ions are at issue because, unlike the organic pollutants, they are non- biodegradable and therefore persist in effluent subjected to conventional treatments (Tran et al., 2015).
Over the years, several approaches including chemical precipitation, chemical oxidation, solidification, ultra filtration, flocculation, electrolyte extraction, dilution, sedimentation, evaporation, reverse osmosis, neutralization and membrane separation have been used for removal of metal ions from solution (Viraraghavan and Yan, 2000).
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ASSESSING THE POTENTIAL OF ASPERGILLUS FLAVUS AND PENICILLIUM SP IN REMOVING MERCURY, ZINC AND CHROMIUM FROM RAW REFINERY EFFLUENTS
