Analysing wastewater temperature development in a sewer system as a basis for the evaluation of wastewater heat recovery potentials

Regardless of the potential of recovering heat from wastewater in a sewer system which serves as a source of renewable energy, wastewater temperature change involved in this process needs to be considered as it may have a negative effect on the downstream wastewater treatment process. Hence, a research on the proper wastewater temperature development in view of gratifying the wishes of energy supply and effective performance of wastewater treatment needs to be taken into consideration.

Researchers from University of Natural Resources and Life Sciences, Vienna in Austria published an article in the journal, Energy and Buildings with the provisions of a methodological framework to identify a suitable way of finding potential heat recovery sites in a sewer system while considering both wastewater treatment and energy supply.

The authors used a four-step approach which includes; preselection of a potential heat recovery site, data processing of wastewater flow and temperature, assessment of the potential heat recovery site with the use of the processed data and finally, a decision making task which compares the present heat demand and the available potential heat supply on view of their impact on the related wastewater treatment plant.

They provided four criteria for site preselection of a potential heat recovery site in a selected sewer system. For instance, they concluded that the location of the potential heat recovery site in a sewer system should be placed near areas of the major lateral inflows specifically in urban areas. They also ascertained reasons why they should be placed in a downstream region, rather than in upstream regions of densely build areas especially in rural areas.

The authors presented the relationship between wastewater flow and the potential amount of heat available which can be applied at any site in the selected sewer system. This makes the site assessment and decision making in perspective of energy supply easier.

An estimation of expectable wastewater temperature reduction in the inflow of a wastewater treatment plant as a function of heat recovery and flow rates was also provided. The authors similarly supplied four planning principles to back this estimation and thus to support wastewater related decision making which would be relevant to water authorities.

Besides introducing a methodological approach including different criteria and planning principles for evaluating the suitability of in-sewer wastewater heat recovery sites in view of satisfying the objectives of energy supply and effective wastewater treatment this research provides a relevant understanding of wastewater temperature development processes in a sewer system.