The Energy Potential in Wastewater

The Essentials of Wastewater Heat Recovery

Wastewater systems carry a remarkable amount of energy. A typical municipal treatment plant can harness enough energy to significantly contribute to local heating and cooling demands. The specific energy content varies, influenced by factors like wastewater flow and temperature. Wastewater Heat Recovery (WWHR) stands out as a particularly transformative technology because most of the infrastructure we need to make it work is already in place. 

What is Wastewater Heat Recovery?

A Potent Solution in the Sustainable Energy Landscape 

In a typical municipal wastewater treatment plant, there is a lot of heat energy. Such a facility might handle tens of millions of gallons of wastewater daily. The temperature of this wastewater generally ranges from 10°C to 30°C (50°F to 86°F), which is significantly higher than the ambient temperature, especially in cooler climates and is cooler than the rejected heat of air conditioning.

The energy potential can be roughly estimated by considering the heat capacity of water. For instance, the heat capacity of water is about 4.18 joules per gram per degree Celsius. If a sewage thermal energy unit removed 5°C from one million gallons of sewage, this would represent almost 80,000 megajoules of heat energy. In other words, the heat value of sewage is 80,000 megajoules per million gallons. A 10 MGD plant would be equivalent to a 9-megawatt thermal energy plant.

Qualitatively, the energy in wastewater is reliable and constant, unlike many renewable sources like solar or wind energy. It's also relatively low-grade heat, meaning it's not at a high temperature, but it's ample for applications like space heating, space cooling and water heating. This consistent, low-grade thermal energy is particularly useful in district heating systems, where it can provide a steady supply of heat to multiple buildings or facilities.

Moreover, the energy in wastewater is inherently sustainable and eco-friendly. By harnessing this energy, we are essentially recycling a waste product, reducing the need for fossil fuels and decreasing greenhouse gas emissions.

The Energy Content in Wastewater Is Influenced by Various Factors:

• Wastewater Volume:  Larger volumes of wastewater contain more thermal energy. Hence, big cities with more significant wastewater outputs have higher energy recovery potential.
• Temperature:  The temperature of the wastewater depends on several factors, including geographic location, season, and the source of the wastewater (industrial, residential, etc.). Warmer wastewater carries more thermal energy for heating.
• Efficiency of Heat Recovery Systems:  The technology used for heat recovery also plays a crucial role. More advanced systems can extract a higher percentage of the available thermal energy.
  

Contemporary WWHR Techniques

Modern WWHR systems employ two methods for heat capture from sewage. The choice between these methods depends on project-specific requirements and environmental guidelines. It is important to note that sewage itself if never used in the building heating or cooling process. Neither of these methods uses sewage directly in a building. Heat is removed from the sewage, nothing more. 

1. In situ Heat Exchange:  Utilizes a heat exchanger installed within the sewer to facilitate heat transfer between wastewater and a separate clean water circuit. This method is preferred for its lower operating cost, and reduced maintenance, once it is installed it works. 
2. Direct Heat Exchange:  Involves the transfer of sewage from sewer to the heat exchange, from there it is returned to the sewer. It is more efficient but necessitates screening to reject contamination that would foul the heat exchangers. 
   

Transforming Waste into A Valuable Resource

Of all the sustainable energy solutions available today, Wastewater Heat Recovery (WWHR) is a potent solution in the sustainable energy landscape. As engineers and professionals in related fields, it's crucial to continue exploring and promoting such innovative technologies. There is enough heat capacity available to power highly efficient electric heat pump systems to heat and cool many large buildings. Allowing them to quickly transition from fossil fuels and make a real meaningful decarbonization difference very quickly.

No Need to Wait - Start Recycling This Heat Energy Now!

Do you want to do more to help the world utilize clean energy, but don't know where to begin STEN is all about professional planners who understand the potential of heat recapture. We are eager to hear your thoughts, concerns and hopes for this promising approach to making our energy systems more sustainable. So don't wait another moment - the time is now. Take the leap and unlock the potential. We invite you to send a message to begin a conversation that will give you the answers you need…