Combined water–oxygen pinch analysis for better wastewater treatment management

The aim of this paper was to combine water pinch analysis and oxygen pinch analysis for more cost-effective wastewater treatment. Emphasis was placed on energy and resource saving. The variables that affect the cost of wastewater treatment are the quantity and the quality of the wastewater to be treated. The quantity of the wastewater to be treated was directly proportional to the treatment cost. The quality of the wastewater was inversely proportional to the treatment cost. It was found that the quantity of wastewater treated could be decreased by the application of water pinch analysis. This application also had a negative effect on the quality of the wastewater. The effect of the application of water pinch analysis decreased the quality of the wastewater being treated, hence increasing the treatment cost. This effect was negated by the application of a combined water–oxygen pinch analysis. The quality of the wastewater determined the amount of oxygen required. The oxygen pinch concept addresses this problem and in addition gives even more information about the health of the working micro-organisms. A 22.6% reduction in wastewater quantity was realised applying combination of both pinch concepts. A reduction of 23.44% in the oxygen requirement for the biodegradation of wastewater was achieved. An important feature of the combined water–oxygen pinch analysis is the balance obtained between the quantity of wastewater produced and the quality of this wastewater.