Critical analysis of the current state of knowledge in the field of waste heat recovery in sewage systems

Abstract

The need for efficient use of energy and sustainable energy management and the fact that large quantities of heat are deposited in the discharged sewage have contributed to the development of research on waste heat recovery. Gray water began to be seen not just as waste, but also as an alternative source of energy. Research related to the development, improvement, and finally, the popularization of waste energy recovery devices and systems has evolved rapidly over the last two decades. Initially, technologies for gray water reuse were not widely used, which was due to the low efficiency of the current heat exchangers and the significant investment outlays that would have to be covered by potential users. Research conducted by scientists from around the world has allowed us to eliminate construction flaws, improve efficiency, and also provide information on the selection of optimal waste heat recovery technology, depending on the installation conditions and operating parameters. The ability to correctly select the device allows for effective energy collection from gray water, which improves the investment profitability. This paper reviews the research regarding issues related to waste heat recovery from gray water in sewage installations and systems. A critical analysis of the current state of knowledge was carried out with a special consideration to the technologies intended for the residential buildings.