The Technology Behind CLSD

Technology

in 1972, during a time when America's lakes, rivers, and streams were being polluted with domestic and industrial waste, the United States Congress saw the need for and passed the Clean Water Act, which began the regulation of the wastewater industry and a road to a better environment.

Not only have major advances in wastewater technology improved water quality in lakes, rivers, and streams, but it has done so to the degree that we are now able to reuse this water for the cooling water needs of an electric generating plant, lawn watering and other outdoor needs. The following are just a few of the components that have assisted this industry to have such a positive impact on our environment.

Programmable Logic Controller

The Programmable Logic Controller (PLC) is a duty-specific, industrial compact personal computer. Although the PLC was not invented for the wastewater industry, it is now being used to operate treatment processes like the one employed by the Clear Lake Sanitary District. Utilizing the PLC in the wastewater treatment process allows environmental engineers to design "high-tech" treatment facilities identical to the AquaSBR^® system that treats not only organic waste, but also reduces nitrogen and phosphorous compounds that are harmful to our environment. The PLC and other featured SBR equipment also provide a built-in, energy saving, environment-friendly mechanism.

Supervisory, Control, and Acquisition Data Analysis

Supervisory, Control, and Acquisition Data Analysis (SCADA) systems are the "watch-dogs" and remote "arms" for electrical components and controls that allow personnel to monitor and operate equipment from a standard PC. These systems can save a company an enormous amount of labor cost. Instead of multiple personnel having to make rounds periodically or continuously "baby-sit" equipment around the clock to ensure proper operation, the SCADA system allows a single person to monitor and even control all electrical components from a remote site. For instance, a SCADA system for your house would allow you to monitor the status of each light in your house or turn it on or off, garage down (up/down), appliances (on/off/temperature), thermostat setting in each room or even the wind speed and direction and outdoor temperature. Granted, you would need to have a weather station installed, but as you can see, the capabilities are endless.

A SCADA system will also detect an alarm from a PLC that has resulted from equipment failure and be programmed to initiate an automatic dialer system during periods when the treatment plant is closed so that personnel are aware of the problem and can respond before disaster strikes. Even further, personnel can dial-up the treatment plant fro their home through PC-to-PC contact and review the actual SCADA system and make corrections on-line rather than having to travel to the treatment plant site. This in itself saves the sanitary district overtime.

The SCADA system not only monitors and controls plant treatment equipment, but pump station equipment, as well. Information from each of the seven off-site pump stations is transferred back to the plant SCADA system via FM radio frequency. Not only can operators monitor and control off-site pumping or backup generator operation from the plant's PC, but also from their home PCs, as well.

In essence, what the above technology provides to the Clear Lake Sanitary District is an assurance that wastewater conveyance, treatment, and alarm identification/correction is accomplished efficiently and effectively at any hour of the day.

Cured-in-Place Liners.

Cured-in-place liners allow defective sewage collection system pipes to be rehabilitated to a state of new condition through manhole openings without having to dig, i.e. trenchless technology. Although potentially expensive, the cost is offset by the cost that would have been incurred if streets and/or houses had to be removed and replaced because of their proximity to the sewer pipe location.

The Clear Lake Sanitary District employed this technology on two separate systems. The first system was a gravity sewer pipe lying an average of twenty-five feet underneath a five-year-old concrete street in very wet soil conditions. The cost to replace the street and to dig to a depth of twenty-five feet in wet conditions was no comparison to the cured-in-place pipe fix. Although hard to determine, a cost should also be fixed to the inconvenience that the public would have had to endure during the digging.

The second system renovated with the cured-in-place liner was a sewer main pressure pipe installed in the 1950's on the bottom of Clear Lake that extends from near the Harbor Inn restaurant pump station across the lake and into Ventura Heights. Although it was not leaking at the time, authorities believed that is was better to be proactive that reactive and proceeded with the upgrades to that pipe section. The only alternative to cured-in-place was to replace the pipe all together, but a very expensive choice.

Jack Boring

Jack boring technology allows contractors to bore pipes underneath roads and other accessed areas without interruption to traffic, wildlife, or aquatic life. The alternative to jack boring is to "open cut" the terrain, which can leave scars and seasonal bumps on roadways. It has been and continues to be a technology that will be specifies and used on Clear Lake Sanitary District projects.

Horizontal Directional Drilling

One of the most interesting technologies utilized during the Clear Lake Sanitary District's recent upgrade was the horizontal directional drilling process that installed a new sewer pressure pipe system under and across Clear Lake. Sure, this process is used every day by cable television, telephone, and even gas companies, but the Clear Lake Sanitary District's project included a world-record distance of 6,024 feet and eighteen-inch diameter pipe. Not only was the 29-day project a world record, but it was one of four finalists out of fifteen entries selected as the 1999 Project of the Year award issued by Trenchless Technology magazine.

Capacities

The pump capacity to the treatment plant is approximately 18 million gallons per day with an additional pumping capacity to the 3.0 million-gallon storm retention basin of 8 million-gallons per day. The gravity fill rate capacity of the 5 million-gallon storm retention basin is 5.0 million-gallons per day.

The capacity of the treatment system is 5.7 million gallons per day during dry-weather conditions and approximately 11 million gallons per day during wet weather conditions. Why the difference? The aeration system that provides oxygen for the aerobic bacteria is based on a typical design sewage concentration at 5.7 million gallons per day. During wet weather conditions the total amount of sewage is the same, but more dilute, i.e. the excess is water only and does not require more aeration.

Current dry weather flow is approximately 2.1 million gallons per day. The maximum wet weather flow received in one day since improvements have been made is over 10 million gallons. During this day the flow rate to the plant reached an all-time record high of 18 million gallons per day for a period of two hours.

The combined 8 million-gallon storm basin storage capacity, which allows diversion of the flow from the treatment plant, protects the treatment system from being hydraulically overloaded and provides a total process capacity of 19 million gallons per day.

What would have happened if we did not have the storm basin capacity? The excess untreated diluted sewage would be pumped to the treatment plant and then diverted/bypassed into Buffalo Creek, which eventually flows into the Iowa River. We have never, since completion of the renovations, exceeded the pumping capacity of each pump station and it is hard to believe that we could ever experience a storm event that could make that happen.

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