Thermal Energy recovery from Drinking Water Distribution systems
Evaluation of the impacts of cold recovery from drinking water distribution system, in terms of microbiological water quality.
Drinking water distribution systems(DWDS) are used for supplying clean and microbial safe water for human consumption. Meanwhile, drinking water distribution systems are also carrying thermal energy, as surplus of cold and heat are present in the water during distribution. In Amsterdam, the Netherlands, the average temperature within the DWDS is between 4-10oC in winter and between 10-20oC in summer. This thermal energy (cold) in winters can be recovered by direct heat exchange, where water exchanges its cold with a warm carrier medium (e.g. air, water, glycol etc) inside a heat exchanger and slightly heated water flows back into the DWDS. According to a previous study, the theoretical cold recovery potential for the city of Amsterdam is around 338TJ per year.This recovered cold can either be stored in aquifer thermal energy storage (ATES) systems to be used in preceding summers to provide space cooling, or be utilized directly in facilities with intensive cooling requirements (e.g. blood banks and in hospitals). It seems DWDS can become a potential resource to provide thermal energy in the form of cold energy for cooling purpose. However, the effects of increased temperature, result from after cold recovery, on microbial quality of water and biofilm during distribution are not known yet.
Thus, the current research is investigating the microbial quality of water both with and without introducing cold recovery, in pilot distribution systems before its large scale application.
The initial findings showed that cold recovery has minor effects on bulk water, while some significant impacts were observed on the biofilm after cold recovery compared to without cold recovery conditions. But no significant influence was found for the selected microorganisms of human health concern after introducing cold recovery in neither water nor biofilm. Till now, it is evident from our research that the temperature increase caused by cold recovery has minor effects on the bulk water and some significant but not critical effects on biofilm.
The thermal energy recovery (TER) might make the distribution network vulnerable for high growth of some bacterial communities. This is still a working question that either TER will enhance the growth of microbial communities in the system or not. The current study is trying to fill this knowledge gap in the field of drinking water supplies in order to use distribution systems as a renewable thermal energy resource.
Reducing carbon emissions by recovering energy from water and making it a new renewable energy resource is an innovative and challenging idea but provision of clean drinking water to masses of population is also the core responsibility of drinking water utilities. This research is trying to correlate and achieve both goals by evaluation of water quality after cold recovery from DWDS, to come up with the standard operating conditions for cold recovery temperatures after which water quality cannot be compromised.
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