Industrial Utility Efficiency

# Atlas Copco Screw Blowers Save Small Town Big Energy

The wastewater treatment plant in the Town of Hurlock, Maryland provides service to approximately 2,100 residences. However, the majority of the water treated comes from a nearby poultry processing plant, giving the plant influent a high organic content. That is why the Town of Hurlock replaced its two million-gallon-per-day (MGD) lagoon plant with a 1.65 MGD four-stage activated sludge facility ten years ago. After construction was completed, operating costs of the new plant were significantly higher than before. This meant the town had to get creative in order to keep costs down for their ratepayers.

The activated sludge process was developed in the United Kingdom in the early 1900s and is currently utilized in medium- to large-scale wastewater treatment plants. The activated sludge process separates the flocculants (suspended solids) from the wastewater through sedimentation. Effluent enters the aeration tank or lane, and low pressure air is introduced through a grid of diffusers. Water usually passes through the process in a few hours, while the sludge retention rates vary from a few days in warmer climates, to a few weeks in colder weather.

Although similar to the activated sludge process, lagoon aeration is typically used in rural areas with small- to large-sized plants. A series of shallow earthen basins (lagoons) act as the aeration basins and holding tanks. Although lagoons are often equipped with surface aerators, there are several diffuser systems available specifically for these applications.

### Conclusion

The Town of Hurlock seems to be fully committed to sustainability. They have 5 acres of land housing 3,420 solar panels on 114 fixed-array tables. “We buy electricity from VW Energy, and it saves 10 to 12 percent on our electric bill,” says Barnhart. “After 20 years, we’ll save about \$500,000 and the system will belong to us.” The wastewater treatment plant will soon switch to all LED lighting, something that has already been done at the water treatment plant and town office building. With all of these plans in place, the town wants to handle the upgrades economically, says Barnhart. “Over the next three years, we’ll phase out the other three blowers and replace them with the Atlas Copco models.”