Abstract: There is provided a process of reducing concentration of contaminants in a contaminated wastewater stream, such as contaminated wastewater output from a refinery, such as an oil-refinery; the process comprising: first, passing the contaminated wastewater stream into an electrocoagulation reactor for coagulating dispersed particles, filtering the wastewater stream after electrocoagulation for removing the coagulated dispersed particles, and providing a first stream of treated wastewater after the first filtration; second, passing the first stream of treated wastewater into a Spouted Bed Bio-Reactor (SBBR) containing a micro-organism or bacterium immobilized in polyvinyl alcohol (PVA) gel, filtering the first stream after treatment by the SBBR and providing a second stream of treated wastewater after the second filtration; and third, passing the second stream of treated wastewater into an adsorption column containing granular activated carbon (GAC) and providing a third stream of treated wastewater.