Wastewater Heat Recovery

By: Adam Stephenson | Mar 03, 2022

Wastewater from domestic, commercial, and industrial facilities contains significant amounts of thermal energy. This thermal energy can be harnessed and reused through a process called wastewater heat recovery. In this article we’ll explore what wastewater heat recovery is, discuss components of heat recovery, and look at benefits and issues with wastewater heat recovery.

What is Wastewater Heat Recovery? 

Wastewater is a renewable heat source. Think about how you use hot water at home, taking showers, cleaning dishes, and washing clothes. This water contains thermal energy that can be reused. Now think about multiplying your dishwasher or washing machine 10-fold or more. This would be an example of a commercial laundromat or kitchen operation supplying loads (pun intended) of thermal energy to the wastewater system. Now think bigger, think factories. Not necessarily the processes in the factory but the cleaning of the processing equipment. Enormous amounts of hot water are used to wash down industrial facilities. Often, this water must be cooled before it can be discharged to the sewer system, talk about wasteful. This wasted thermal energy can be used to benefit the environment and businesses. There are four main locations within the sewer system for energy recovery from wastewater: at the component level, at building level, in the sewer pipe network, and from wastewater treatment plants (WWTPs). 

Typical equipment for wastewater heat recovery is heat exchangers and heat pumps. A heat exchanger is a device that facilitates the transfer of internal thermal energy between two fluids without mixing the fluids. This is a passive technology that does not require any external energy. Think of it as two pipes side by side where one is heating the pipe next to it. A heat pump, on the other hand, is a technology that uses electricity and the reverse refrigeration cycle to transfer heat from one place to another. In some systems, the heat exchanger is used in conjunction with the heat pump.

Benefits 

The major benefits of wastewater heat recovery are a reduction in primary energy used, and in turn, cost savings, for preheating the cold-water supply in a building or space-heating. There is also a reduction in greenhouse gas emissions by reducing the amount of fossil fuels needed to be burned to heat cold water. Recovered wastewater thermal energy can be used in a variety of applications, from heating swimming pools and showers, to drying sludge or heating industrial process liquids.  

Issues 

There are some factors to be aware of when considering a wastewater heat recovery system. Recovering heat from wastewater in sewer systems may lead to a reduction in influent temperature at WWTPs. The reduction in the temperature of influent wastewater can negatively impact the nitrification/denitrification capacity of WWTP, leading to higher ammonia concentrations in the effluent water of WWTP.

Conclusion  

Wastewater heat recovery has both positive and negative factors, especially depending upon where in the wastewater system the heat is recovered. Wastewater can be recovered in multiple places in a wastewater system. There are many applications that can utilize recovered wastewater heat. While this is a new thought process that requires more research and trials, it is exciting to see the potential in recovering energy sources from wastewater.

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