Wastewater Infrastructure handles both sewage and runoff. Wastewater infrastructure components consist of pipes, manholes, pumping stations, storm overflows, receiving drains and screening chambers. Two of the main types of wastewater systems are sanitary and gravity sewers. Sanitary systems include effluent sewers and vacuum sewers. Gravity sewers include simple sewers, combined sewer, and storm drains. Both types of sewer systems need to have an effective maintenance program to keep the infrastructure working as it should. When an effective maintenance program is not in place the potential for system failures skyrocks. A poorly maintained system may be overrun with inflow/infiltration (I/I), overflows and stoppages. When these failures happen a maintenance plan must be initiated. A successful maintenance program includes inspection, assessment, cleaning, and repair.
Maintenance crews use pipeline inspection equipment to perform routine assessments of sewer systems. They look for pipe defects such as obstructions, excessive deposits, offset joints, and damage such as cracks or collapse. They will make a note of the location of the defect in the pipe. An inspection is necessary to identify the cause of a stoppage. A second inspection is necessary after removing the stoppage to check if the obstruction has been removed and the condition of the pipe. Systems may require specialized equipment to inspect them, depending on the size and nature of the components.
Municipalities commonly require video inspection of new sewer lines prior to final approval. Inspection occurs after the pipes have been installed for at least 30 days. This inspection should take place after completing specialized tests like those for air, pipe deflection, joints, and general visual inspections. The final inspection ensures the lines have been installed according to specifications and are free of any defects. These inspections establish a baseline of the sewer system. Inspectors can use this base line for comparison with future inspection.
A software system should be used to store the data that crew members collect during the cleaning and inspection phase of wastewater infrastructure maintenance. This data will be used to evaluate the overall condition of a sewer system’s infrastructure, especially pipes and manholes. Crews can also use the data to enhance and adjust cleaning and inspection schedules. Assessment data can be used to identifying needed repairs and rehabilitation. Visual inspections provide the basis of assessment for above ground facilities and manholes, but they can also indicate where video inspection may be needed. Most assessment data for sewer lines comes from video inspections since operators cannot visually inspect these components. Supervisors will use the information gained on pipe conditions to direct maintenance for both the long and short term. The maintenance needed could include cleaning, replacement, and rehabilitation.
Cleaning wastewater infrastructure requires forcing pressurized water through pipelines. This is commonly known as hydro-jetting. This process removes accumulated solid debris, typically grease (FOG), roots and scale. Roots require additional methods of cleaning including mechanical and chemical treatment to prevent future growth. The combination of these methods is extremely effective in reducing stoppages caused by roots. This should be done on a consistent basis for best results. Maintenance crews will note the dates that each component was cleaned for their records. They will also note any pipe defects in the systems at this time for repair.
Wastewater infrastructure degrade more rapidly than other types of infrastructure due to their harsh operating conditions. Physical damage such as cracks, joint displacement and root intrusion can all lead to significant leakage of sewage. This results in a substantial risk to public health. Hydrogen sulfide (H2S) is a major component of sewer gas. This gas is a corrosive elemet to sewer components. The application of a cementitious material or a pipelining also known as cured-in-place pipelining (CIPP) are two of the most common types of sewer repairs.
The methods of applying a cement material onto a substrate can be classified into low-pressure wet spray and high-pressure dry spray. Low-pressure wet spray is the most common. Low pressure wet spray loses the smallest amount of material in the pipe. High-pressure dry sprays can rehabilitate concrete structures quicker and apply thicker layers of material with each pass. High-pressure dry spray does waste a large percent of material.
The method of applying a CIPP lining starts with cleaning the pipe with mechanical cutters. This cleaning step allows the liner to adhere to the pipe. Once the pipe is cleaned the technicians saturate a felt liner with a two-part epoxy. They score the outside of the liner to get the best adhesion to the inside of the pipe. No water will be able to get in between the liner and the inside of the pipe once cured. The liner is then pulled through the pipe with a rubber bladder inside. Once placed into the pipe the rubber bladder is expanded to allow the epoxy liner to cure and adhere to its host pipe. Once the CIPP liner hardens to the pipe, the rubber bladder is deflated and removed. Leaving behind a better than new pipe within the existing system.