Method for remediating solids in waste lifting stations

Abstract

A process removes or eliminates altogether accumulations of solid and semi-solid, water immiscible materials adhering to walls, and equipment, particularly near the high liquid mark, in tanks of waste liquid lift stations. Compressed gas is used to generate large bubble masses of six inches to several feet in diameter within the waste liquid. As these large bubble masses rise through the liquid in the tank, convection currents generated by the rising bubbles agitate and loosen pieces of accumulations adhering to the tank and lift station equipment, resulting in a slurry of waste liquid and immiscible materials which can then be pumped from the tank by lift station equipment for further processing. In some embodiments, continuous or frequent periodic generation of the large bubble masses prevents the accumulation of such materials altogether. In some embodiments, wastewater aeration is also provided, which, in combination with biological augmentation, further enhances the effectiveness of accumulated material removal.

Description

BACKGROUND[0001]1. Field of the Invention[0002]This invention relates to methods for mixing liquid waste in lifting stations. More specifically, this invention relates to methods for breaking up grease and other solid and semi-solid accumulations in liquid waste lifting stations.[0003]2. Description of the Related Art[0004]Wastewater systems typically use gravity to transport liquid waste from homes and businesses to provide wastewater treatment at a central facility. For cities that have many changes in elevation, lift stations are used to pump liquid waste, such as storm water and sewage, from low-lying areas to areas of higher elevation for further transport and treatment.[0005]A wastewater lift station typically comprises a concrete well that is fitted with several pumps, often of submersible design. Lift station design further includes level-sensing probes, valves and pressure sensors, and may also include a stand-by generator. In operation, the lift station serves as a tempora...

AI Technical Summary

Benefits of technology

[0011]The present invention provides a means for removing or eliminating altogether accumulations of semi-solid, water immiscible materials adhering to walls, and equipment, particularly near the high liquid mark, in tanks of waste liquid lift stations. Compressed gas is used to generate large bubble masses of six inches to several feet in diameter within the waste liquid toward the bottom of the lift station tank. As these bubble masses rise through the liquid in the tank, convection currents generated by the rising bubbles agitate and loosen pieces of accumulations adhering to the tank and lift station equipment, resulting in a slurry of waste liquid and immiscible materials which can then be pumped from the tank by lift station equipment for further processing. In some embodiments of the invention, continuous or frequent periodic generation of the large bubble masses prevents the accumulation of such materials altogether. In some embodiments of the invention, wastewater aeration is also provided, which, in combination with biological augmentation, further enhances the effectiveness of accumulated solid removal.

Problems solved by technology

Accumulations of insoluble material within the lift station can restrain the floats below the surface of the waste water, leading to improper operation of the lift station and, in extreme cases, lift station overflow when the float is unable to detect that the liquid waste in the well has reached and exceeded its pre-determined operational high level.

Furthermore, over time, the amount of such accumulated insoluble material can actually reduce the holding capacity of the lift station and, because large pieces of such material can break off and become lodged in lift station equipment such as valves and pumps, the presence of such large accumulations may adversely affect lift station operation and damage lift station equipment.

Drawbacks in such approaches include the fact that the station must remain inoperative during the time it is emptied and cleaned.

Other drawbacks simply follow from aesthetic and hygienic challenges of placing personnel inside wells that have held raw sewage.

This approach has the drawback that pumps providing sufficiently strong currents for such purposes consume considerable energy.

Furthermore, the pumps, being electromechanical devices, are inevitably subject to significant maintenance and repair costs.

Because the microorganisms used for biological augmentation are aerobic, the availability of oxygen in the wastewater can be a limiting factor on the effectiveness of the process.

Biological remediation is subject to several additional limitations.

Use of too high a concentration of bacteria in the lift station wastewater, while leading to fairly rapid grease deposit break-up, can result in large quantities of small pieces of undigested grease transferred to the downstream wastewater system, leading to downstream clogging and excessive foaming at the wastewater treatment plant.

While use of lower concentrations of bacteria may actually result in more complete digestion of accumulated grease with fewer downstream problems, effective remediation by lower bacterial concentrations takes much longer, potentially leaving the lift station partially or fully inoperative for a longer period of time.

Further, even when such biological augmentation is optimized, light plastic immiscibles deposited in the lift station, such as condoms, plastic wrap and the like remain unaffected.

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