Sewers: The Untapped Renewable Energy Source

Beneath everyone's homes lies a hidden treasure, which has been totally ignored until now. Many people wonder what this hidden treasure could possibly be. It is none other than the heat in wastewater. How many people take cold showers or wash their dishes in cold water? Very few people do. Where is all this heat that people are throwing out? The answer to that it is in our sewers. Day in and day out, we are throwing all this excess heat out. In addition, wastewater contains organic waste, which is subjected to biodecay in the sewers, contributing to even further heat generation. Even if people do not have any wastewater, they could tap into the sewer pipes, which sit below the frost line to get free heat of about 10˚C. The heat contained in our sewers is renewable and using it does not release any carbon dioxide gas.

Purpose

The purpose of this experiment is to determine how much heat there is in a septic tank, as well as in a storm sewer in the city. Using a heat exchanger, this heat will be recovered to see if it can be utilized to heat an external area.

Hypothesis

I hypothesize that septic tanks and sewers contain a lot of heat that can be recovered to provide heating for buildings, houses, pavements and road surfaces. I believe this can be done using a heat exchanger.

Procedures

1. In the first part of the experiment, temperature readings were taken of the water in the toilet bowl, coming from a tap, normal shower temperature, bath temperature, dishwasher water temperature, and washing machine temperature. Temperature readings were taken of the well water entering the house.
2. The temperature inside the septic tank was measured after removing the riser and placing the temperature probe one foot below the top of the riser. After 5 minutes, the temperature was allowed to stabilize and this reading was recorded. Temperature recordings were taken every one-foot distance.
3. The temperature at the bottom of the tank was determined by attaching a small weight to the end of the probe and dropping it into the septic tank. The probe had a cord length of 10'. The depth of the tank was known to be 9'. The temperature reading was taken after 10 minutes to allow the temperature reading to stabilize. Three trials were performed.
4. A room air conditioner was dismantled and the heat exchanger was removed. The heat exchanger was placed inside the septic tank, just above the scum layer. The two ends of the heat exchanger were connected with clear plastic hoses and hose clamps to a fountain pump and a bucket. Inside the bucket, four liters of antifreeze were poured. The temperature of the antifreeze was measured prior to starting the pump.
5. The unit was allowed to operate for two and a half hours and the temperature readings inside the bucket were recorded over 5 minute intervals for the first hour, and then every half hour for the next hour and a half
6. The temperature inside the sanitary storm sewers of two areas were measured using the temperature probe. The temperature probe was lowered down to its maximum length of 10 feet and the temperature readings were taken. The temperature readings were taken in Richmond Hill in the middle of a townhouse complex and in the town of Kleinburg.

Observations/Results

While observations were being taken, the outside temperature was -5˚C. With the windchill, it was -10˚C.

Temperature of Septic Tank at Different Levels

Temperature of the Antifreeze in the Bucket

After taking temperature measures of different household water sources, it was apparent that the water in the bowl of a toilet was about 12˚C. Washing machines discharge wastewater at an average temperature of 27˚C, assuming half the laundry is done with hot water and half is done with cold water. Shower water is generally about 32˚C and bath water is 30˚C. Normal cold water from the faucet is 13˚C and water used inside a dishwasher is 34˚C. The hottest water from a faucet is 38˚C. The temperature of well water entering a house is 12˚C.