Influence of Sludge Production and Processing on Power Demand of Wastewater Treatment

The sludge produced from wastewater treatment and the subsequent biosolids generated through further processing contain inherent energy which can be extracted. As we have seen in the first part of this article Influence of wastewater treatment on sludge production and processing which appeared in the May-June issue of Asian Water, the configuration of wastewater treatment plants fundamentally influences type and quantity of sludge produced, and consequently the energy available for extraction. Previous work has used COD (Chemical Oxygen Demand) as a surrogate for the energy in wastewater and sludge, however analysis of energy content and COD shows no correlation. Energy content is generally measured by bomb calorimetry, but may also be theoretically determined from an understanding of molecular composition. Using information presented in the previous article, the calorific value (energy content) of primary and secondary sludge is approximately 19,300 and 16,300 kJ/ kg dry matter. The greater carbon content, primarily from lipids, in primary sludge results in it having approximately 20% more intrinsic energy than sludge formed during biological treatment. This article looks at how much of this energy can be captured by both anaerobic digestion and thermal oxidation, and how that influences wider site-energy demands. 

Download the full article here.