Conserve Energy by Reducing Flow

Efficient energy management through flow measurement and educating the user on practices to conserve water and energy contributes to reducing flow. One way is to reduce the water use in the community. As less water flows, less enters the wastewater treatment plant, less volume is treated and less energy is consumed. Altering the operation of certain processes to off-peak hours, including pump cycles, contribute to conserving energy. An aggressive Infiltration and Inflow program can also reduce flows directed to the wastewater treatment plant.

In addressing flow equalization, an equalization basin allows the plant to even out pumping needs by running pumps during off-peak hours. Reducing infiltration and inflow in the collection system can pay for itself in energy savings. By rehabilitating damaged or deteriorated sewer lines and eliminating improper connections to the system, the overall flow to the wastewater treatment plant is reduced, thus reducing the amount of energy required to treat the flows. This is a beneficial operation that is used to reduce the variability of influent flows, which enhances treatment and allows the treatment system to be sized based on the average daily, rather than the peak day, influent flow. The ability to equalize the flow through the automatic valve at the influent pump station eliminates pump cycling and reduces the electrical demand. This equalization creates a steady state in the extended aeration process, which improves treatment.

For applications involving varying flow requirements, mechanical devices such as valves are often used to control flow. This process uses excessive energy and can create less-than-ideal conditions for the mechanical equipment involved. Variable Frequency Drives (VFD) enable pumps to accommodate fluctuating demand, resulting in operating at lower speeds and conserving energy while still meeting pumping needs. VFDs can eliminate over-pumping and help reduce startup load and energy imbalance. VFDs can also result in significant energy savings; a VFD can reduce a pump’s energy use by as much as 50 percent.

Water conservation practices can be promoted through educating residents about high efficiency appliances, plumbing fixtures and water saving habits. Checking toilet flappers, adding faucet aerators and low-flow showerheads are recommendations to reduce water usage. Informing the community of such measures can reduce peak water demands to avoid the extra costs associated with operating additional pumps. Offering education to manage energy more efficiently can result in eliminating peak operations at several pumping stations and reduced electric cost and pump use. To conserve energy in the treating of wastewater, the reducing of flow to the plant and reducing water use in the community can benefit the overall system performance and prevent occurrences when the system would otherwise be overloaded with inflow and infiltration. Alternative measures to conserve water could be addressed in those cases to prevent the potential for system overuse.

Doing this requires knowing the sewage flow. Wet weather events can affect daily flow and system performance if inflow and infiltration is suspected. Measuring flow should indicate if a hydraulic overload condition exists. Daily flow can exceed the system design capacity, resulting in frequent sewer backups or puddling of sewage onto the ground surface. Sanitary sewer overflows are evident in cases where additional flows can cause potential problems with a sewer collection system.

The use of ice machines, automatic dishwashers, coolers, sinks, and floor drains may increase the flow. Sewage flow includes the discharge of showers, baths, toilet flushes, tooth brushing, dishwashing, laundry, and other indoor uses. Lawn watering and other outdoor uses are also considered as flow but are not introduced as contributing to the daily flow.

Infiltration, inflow, and exfiltration can affect sewage flow, as well. Oftentimes, these conditions are not considered when sizing a septic system or a sewer collection system. When there is a break in the sewer line, or if the sewer clean out cap is missing, this can affect the flow entering a septic tank. Possible leaking from root intrusion or movement of above ground piping can make the joints in the pipe susceptible to leaks due to stress and shifting.

Flow should be able to be measured accurately. Using a device to measure flow provides a more accurate value compared to the estimated value of flow design for the system. Knowing the flow would allow the user to justify alternative methods to reduce water usage or to consider modifying the system to accommodate the true flow entering the system. Being able to meter sewage flow would be a benefit to municipal sewer professionals, septic utility groups and septic tank contractors that service onsite management programs. Flow measurement can benefit the overall management of system performance and contribute to a longer lasting system if monitored.

Story by Albert Royster

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