The Wastewater Collection Division is responsible for maintaining the sanitary sewer collection system that collects and delivers wastewater to the Wastewater Treatment Plant for treatment. The collection system infrastructure includes 400 miles of gravity and forced sewer mains, 15,000 manholes and 38 lift stations. The sewer lines are constructed of vitrified clay pipe, PVC truss pipe and SDR pipe. The pipes range in size from eight inches to 48 inches in diameter.
This division is staffed by a field operations superintendent, two operation supervisors, nine collection system operators, an infiltration & inflow technician and a master plan coordinator.
An important program of the Wastewater Collection Division is the Television Inspection Program. The television inspection system eliminates guesswork and estimates by providing positive and reliable answers to what, where, when and how much work needs to be done to correct any problems within a line. The television system consists of a mobile van unit, video, computer and a specially designed camera that can function in eight-inch to 48-inch lines. Up to 1,000 feet of pipe can be televised at one time. The camera is controlled from a van and crawls through the pipe while attached to a video cable. The video picture is sent back to the van and is observed by the operator on two monitors. Pictures can be printed out in real-time or downloaded to the computer. Also, a detailed report is made by the computer of all defects that are found. The television inspection system is used for new sewer inspections, preventative maintenance, and emergency calls.
The division uses the latest technology in pipeline rehabilitation. One example of this technology is the use of cured-in-place liners. A liner is inserted into an existing line, cured in four hours, all service openings are cut out and the line is ready to use after eight hours. All this is done without any excavating and at about one-third the cost of digging and replacing. The division also has a chemical root control program. A contractor will apply a chemical into the sewer main that will foam up like shaving cream. The foam will eliminate tree roots within the pipe and will also prevent new root growth for three years. This is done without any harm to trees or the environment.
Because of the Lawrence terrain, 38 lift stations are used to pump sewage towards the Wastewater Treatment Plant. The Collection Division operates these pump stations through inspection, preventative maintenance, and repairs. These stations are monitored remotely with the use of modems and computers, allowing operators to respond to alarm conditions whenever they occur.
The division inspects the sewer lines through manholes near commercial and industrial locations to detect any hazardous materials infiltrating into the system. Tests include lower explosive levels that test for flammability, hydrogen sulfide, and oxygen.
Do some homework before you call the Utilities Department. Check the trap and drains for water. If you find they are empty, pour water into them as the floor drains tend to dry up. If it still smells foul, call the Municipal Services & Operations Department at 785-832-7800.
Inflow and Infiltration Reduction
Flow monitoring and manhole inspections are performed in an effort to identify leaks in the sewer pipes. Leaks allow extra water into the sewer system, increasing treatment costs. The monitoring and inspection reports are used to select line segments and manholes for rehabilitation.
Why do sewers back up?
Anything that blocks the pipe can cause the sewer to back up. Tree roots, clothing, plastics, diapers, abnormal debris, any cooking grease can all accumulate and block the flow of the sewer. Be wise, make sure what you flush or drain in the sewer does not cause it to block. If you find that your sanitary sewer is backing up, call the Municipal Services & Operations Department at 832-7800.
How clean are the city sewers?
As part of the Preventive Maintenance Program, the Collection Division continues its preventive maintenance schedule to clean city sewer mains. The division uses jet trucks that clean lines by using high-pressure water nozzles and root saws that can clean lines up to 1,000 feet and a vacuum jet truck that not only cleans the lines but can also vacuum debris out of manholes.
The City of Lawrence Wastewater Treatment Plant, located at 1400 East 8th Street, has the capacity to treat approximately 12.5 million gallons of wastewater per day, with peak flows of 25 million gallons per day through the normal process and an additional 40 million gallons through the excess flow system during extreme rain events. City staff members are responsible for the plant’s efficient operation and maintenance.
Wastewater is defined as water that has been used for domestic or industrial purposes. Wastewater treatment is the physical, chemical, and biological processes used to remove pollutants from wastewater before discharging it into a water body. The various treatment stages are described below.
Influent Pump Station:
The influent pump station receives wastewater from the wastewater collection system through sewer lines located 25 to 30 feet underground. At the front of the pumping station, wastewater passes through mechanical bar screens that remove large debris (3/4″ or greater) such as boards, rags, and paper, which would clog pumps and damage equipment. These materials are mechanically raked off and landfilled.
The influent pump station houses four pumps with a pumping capacity of approximately 25 million gallons per day. On an average day, they will pump approximately nine million gallons of wastewater, lifting it 25 feet and delivering it to the grit chamber so that it may continue through most of the plant processes by gravity. Although the collection system is designed to receive only sanitary wastewater, imperfections in the system allow groundwater and rainwater to infiltrate and inflow (I&I) into the system. Peak flows during rain events can exceed the 25 MGD pumping capacity of the influent pump station, which then requires the excess flow to be treated through the excess flow system.
The screened wastewater proceeds to the grit complex where heavy inorganic solids, such as sand or gravel (grit) are allowed to settle while lighter organic solids are kept in suspension. The grit is removed, washed and dewatered by mechanical methods prior to disposal in a sanitary landfill.
The wastewater is divided between two basins, which use gravity to settle the solids to the bottom of the basin where they are removed for treatment. This process uses a detention time of approximately three to four hours to allow for the particulates in the wastewater to settle out. Approximately 65% of the suspended solids are removed in this process with the remainder being dissolved and un-settlable pollutant solids.
Secondary Treatment of Activated Sludge:
Aeration basins are used to accelerate the naturally occurring breakdown of waste that occurs in the environment. The alkalinity, dissolved oxygen, and mixing are adjusted to encourage optimum microbial activity. Diffused air ensures that the contents of the basin are mixed and provides oxygen. The dissolved oxygen is used by the microbes to respire (breathe) as they consume food (wastewater solids). As the microbes consume the food their population increases. The quantity of microbes is adjusted to balance with the volume of waste received.
Final sedimentation basins are used to hold the wastewater for a period of time. Through the process called flocculation, the microbes and remaining waste material form particulates that are heavier than water and settle to the bottom of the basins. Portions of the settled solids are continually removed and sent back to the aeration basins to maintain the microbial population there. The excess solids are periodically removed and sent to the anaerobic digesters.
The wastewater (or called effluent at this point) proceeds to disinfection where liquid chlorine is added to kill most of the remaining pathogens (disease-causing organisms).
Due to the potentially toxic effects of chlorine on aquatic life, sodium bisulfite is then added to remove any residual chlorine prior to discharge into the Kansas River.
Excess Flow System:
Due to imperfections in the collections system, flow to the wastewater treatment plant can increase significantly during substantial rain events. Due to the need to treat this excess water (mostly dilute), a system, named Actiflo, was developed to be used during these periods of high flow. The excess flows to the wastewater treatment plant greater than 25 million gallons per day are pumped from the head of the plant, bypassing normal treatment and moving through fine screens to screen out any objects over the size of a pencil eraser. After screening, the flow proceeds to the Actiflo basins. There, ferric chloride, polymer, and micro sand are mixed with the wastewater to form ballasted floc, which settles quickly and is removed from the flow. The clear effluent from Actiflo flows to a chlorine contact basin that is dedicated to this flow, where liquid chlorine is added for disinfection and sodium bisulfite is added to remove the residual chlorine (as takes place under normal treatment). The effluent from this process is combined with the normal plant effluent and discharged to the Kansas River. Small rain events may be diverted through the fine screens to the excess flow storage basin until flow subsides and it can be returned to the head of the plant. Although this system has been widely used in drinking water treatment, this was the first system to be installed and operational in the United States for use in wastewater treatment.
The solids that are removed from the primary and secondary treatment processes are stabilized by anaerobic digestion. This process is maintained at 98o° F. In a controlled environment, a complex population of bacteria work in the absence of oxygen, in a process called anaerobic respiration, to reduce and stabilize biodegradable waste products prior to removal. End products of this process include a stabilized organic material, carbon dioxide and methane. The boilers used to maintain the digester temperature use the methane from this process as their fuel source. The stabilization process takes anywhere from 14 to 30 days. The digested solids (now called biosolids) are removed from digester for dewatering.
Two two-meter belt filter presses are used to remove excess water from the digested solids. The water is removed using gravity to drain excess water away and applied pressure between two perforated belts that squeeze as they move over rollers. The biosolids enter the presses at approximately 2% solids and leave the presses at approximately 20% solids. The biosolids are transported to storage bays via a series of conveyors. The excess water removed from the biosolids (called filtrate) is returned to the headworks of the plant for treatment through the normal process.
Storage exists for approximately 4,000 cubic yards of biosolids. These bays are designed for 120 days of storage in the year 2020. It is divided into two cells to allow for removal from one while the other is being used. Each cell has large water-tight gates, which when opened allow for access with a front end loader for easier removal of the material.
Biosolids End Use:
Approximately 95% of the biosolids produced at the Lawrence Wastewater Treatment Plant are beneficially reused as a nutrient source and soil conditioner on privately owned agricultural land. The treated biosolids contain three key crop nutrients – nitrogen, phosphorus, and potassium, as well as other nutrients in trace amounts. Organic matter supplied by the biosolids improves soil structure, increases the soil’s ability to absorb and store water, and increases the availability of the nutrients to the crop.
The City of Lawrence has recycled biosolids in this manner since the mid-1970s on City-owned and privately-owned agricultural fields. With the adoption of the federal regulations (EPA 40 CFR Part 503), which regulate the disposal and reuse practices for biosolids, the City developed its Biosolids Beneficial Reuse Program. Through this program, biosolids are applied to local agricultural land at no cost to the participating farmer or landowner. A private contractor that specializes in the land application of biosolids takes soil samples, compiles reports and performs the application activities with oversight of city staff. The program applies biosolids and its nutrients to approximately 400 acres annually.
The remaining 5% of biosolids production is set aside for residential use by the public. The material is tested extensively and upon meeting compliance with federal regulations is made available for use on residential lawns, gardens, flowers, and other residential uses. The practice of making biosolids available to the public in Lawrence for residential uses has taken place since 1956 when the plant was first constructed.
The biosolids must meet stringent testing and procedural requirements. The City’s reuse activities are in complete compliance with all Environmental Protection Agency regulations and the Kansas Department of Health and Environment guidelines. The City of Lawrence is committed to the safe, economical, and environmentally friendly reuse of this valuable material.
To learn more about wastewater, biosolids, or the City’s EMS for Biosolids, please contact the Utilities Department at 785-832-7800.