ABSTRACT
The concentrations of contaminants in industrial wastewater are generally so high that some form of pretreatment, such as anaerobic digestion, is necessary. Wastewater from beverage and food processing, pulp and paper mills, petroleum refineries and other industrial enterprises differ in concentration from municipal sewage or stormwater. Each industrial sector presents a different set of treatment challenges. A general measure of biodegradability is the initial wastewater ratio of biological oxygen demand to chemical oxygen demand. Horizontal subsurface flow wetlands are most implemented due to their capacity to tolerate high organic loading, treatment of effluent colour and where anoxic conditions are necessary to degrade contaminants. Vertical subsurface flow wetlands are necessary where aerobic conditions are necessary, such as in the conversion of ammonia to nitrate. Free water surface wetlands are effective for effluent high in suspended solids, oil and grease. Free water surface and horizontal subsurface flow wetlands have been used to provide secondary or tertiary treatment of pulp and paper wastewater.
