Plants installed to treat any intended discharges overboard. The central elements of these plants – the one which removes suspended solids and bacteria – uses either a biological or non- biological process. Biological processes rely on natural bugs to treat the waste. Non-biological process utilizes an electro-mechanical oxidation procedure to treat wastewater streams. All the systems, biological and non-biological, claim to be capable of dealing with grey water, black water or mixed streams and of producing effluent for discharge that meets IMO Marpol 73/78 requirements. See also Sewage treatment.