Sewer cleaning explained
Municipal sewer cleaning is an important way to keep communities hygienic. Here’s how it works. Communities depends on sanitary conditions to maintain health and safety. An everyday part of keeping a hygienic environment is the sewage system. In some locations, the sewer system combines with the stormwater drainage system. Nevertheless municipal sewer cleaning is a must no matter what system is used. Sewer systems keep toxic wastewater and excess water runoff off the streets and safely underground on their way to treatment. Like every man-made structure, sewer systems also need regular maintenance, which includes inspection and cleaning. This preventative maintenance ensures that the worst won’t happen. There are three main methods to clean a sewer system: Chemical, Mechanical, or manual also known as Hydraulic.
Chemical cleaning method
Several chemical methods are available to kill and retard the re-growth of roots. Examples of chemical application include foaming, dusting and liquid application. All three chemical application methods require special equipment. When the problem is with roots alone then chemical treatment is the most cost-effective method of cleaning. Chemicals can be used to clean grease from sewers as well. Various chemicals are available, such as enzymes, hydroxides, caustics, biocides, and neutralizers, for removing and controlling grease buildups. Some systems use these biological products containing microorganisms and enzymes to digest fats, oils, and other waste naturally. These effectively and safely break down blockages, without introducing pollutants to the system. High-grease areas near restaurants is an example of where this method is the most effective. Standards vary for when and how chemical solutions are used. Chemical cleaning is an expensive method of treatment if applied regularly on an ongoing basis.
There should be thorough evaluation and planning for chemical dosing program. The municipality should consider the following points:
- This method cannot clear stoppages or blockages in sanitary sewer lines.
- It is an expensive method. The EPA states “because of the extreme safety requirements and cost of the chemicals, traditional hydraulic and mechanical cleaning methods are more cost-effective for most situations.”
- Chemicals may be hazardous to employees, and environment
Mechanical cleaning method
Rodding:
Rodding is used to break up grease deposits, cutting roots and loosening debris. Therefore emergency removal of blockages to create way for CCTV inspection equipment in the pipeline use this method. This equipment is available in two ways either power rodding machine or hand rods. Power rodding equipment cleans while being pushed through the pipeline. Firstly a steel rod is placed in the pipe with a cleaning device attached to the lead end of the rod. Secondly the cleaning head rotates at the end of the rod and is push down pipe cleaning as it goes. Routine preventive maintenance uses this method most commonly.
Balling:
This equipment consists of sewer balls to fit different diameters of pipes, a tag line, winch, cable, reels, water source and a dump pick up. In this case high pressure water is forced through the sewer when using the balling method. This high pressure water is what cleans the pipe. Balling is effective in removing heavy concentrations of sand, grit, rock, and grease from the sewers.
Power Bucket:
Power bucket machines are another type of mechanical cleaning device used to remove debris, roots, grease, or sediment from main line sewers. A bucket machine uses a set of specialized winches that pull a special bucket through a pipe to collect debris. The power bucket physically removes the captured materials from the pipe. These machines are very powerful and offer the best output with the least opportunity for operator error that could affect the results. Operating bucket machines is a very labor-intensive process. In particular power buckets are best for removing large amounts of debris from larger sewers.
Hydraulic Cleaning Methods
Flushing:
Flushing is the oldest pipe cleaning technique. It helps to remove disinfectant residual, expel harmful bacteria, remove suspended sediment, and clear up other problems of water discoloration or bad taste and odor. It also helps to clean pipes by lifting loose sediments, reduce chlorine demand, and mitigate water quality risks. However this technique cannot clean away tuberculation and other hard scales. It is not effective in cleaning sediments and bio films from large pipes. There are two techniques when flushing which are conventional flushing and unidirectional flushing.
- Conventional flushing
Opening one or more fire hydrants and allowing the water to run in to the sewers is conventional flushing. This water flow removes sediments, bio films and improves poor-quality water.
- Unidirectional flushing
A technique in which valves are closed and fire hydrants are opened in a systematic way. Initially, the water travels towards hydrant in a single direction. Water in single direction produces high velocities in the main, which makes the cleaning more effective. The water is then flushed in a sequence such that the water is being flushed comes from pipes that have been previously cleaned. Unidirectional uses less water compared to conventional flushing and can be used to locate hydrants in need of repair.
Jetting:
Hydro jetting is the process of using water under high pressure to scour the pipe walls. It cleans grease, debris deposits, roots, sand, or dirt and flushes it all away downstream. High-pressure jet cleaning has gain popularity in recent years. However, it is a challenge for workers to work in the high-pressure environment. Comparing with mechanical cleaning and chemical cleaning method high pressure water jet cleaning has many advantages such as high cleaning efficiency, low cleaning cost, and easy mechanization, convenient operation, safe and reliable. In this operation the pressure should range between 10,000 psi to 22,000 psi. For example the equipment need consists of a truck mounted with high velocity water machine, maintenance hole hose guide, debris traps and a dump pick up or debris trailer.
Scooter:
This method is also a hydraulic method for cleaning of a sewer line. This is effective to remove heavy debris in large diameter sewers. These are also suitable for storm drains of large diameters. In this case this equipment consists of a scooter assembly, dump pick-up truck, power winch, water tank truck, and a tag line. A steel framework on small rubber rimmed wheels with a round metal shield at one end make up the scooter. The shield makes up the upper half of the scooter. A spring system controls the shield. The shield acts as a plug to build up a pressure head. As the pressure increases the shield pushes the scooter frame along the downstream to clean the pipe.
Kites, Bags and Tires:
This method is similar to the balling technique. However this method is more suitable for cleaning large sanitary sewers. Rigid rims on bags and kites induces scouring action. The kite’s shape creates a forward jet of water that scours the pipe wall. It is very effective in moving accumulations of decayed debris and grease downstream.
Poly Pigs:
This is a fast, simple, and economical way to clean water mains pressure pipes. The pig works like a hydraulic ram to remove deposits and tuberculation. They can be launched in a line through an existing fire hydrant or by removing a section of the main. Since poly Pigs are available in many styles they can tackle even the toughest pipe cleaning jobs. These are effective in moving accumulated decayed debris and grease. The other types of pigs available are Turbo Pigs and Steel Mandrel Pigs . Turbo pigs are made out of polyurethane elastomer. This especially strong material gives longer wear and abrasion resistance. Steel Mandrel Pigs are made out of polyurethane attached with split-ring steel wire brushes.
Silt Traps:
This method has been successfully used to collect sewer sediments at convenient locations within the system. As long as silt traps are emptied on a regular basis as part of the maintenance program the pipe will remain clear. Information on design procedures and methodology for silt traps is scarce.
The benefits of pipe cleaning
The type of pipe cleaning used depends on the type of the pipe, nature of the problem, type of the equipment and the cost. For most problems, flushing is usually the first choice of action. This is an inexpensive and easily implemented method which requires less equipment. Whereas bucketing and pigging can be effective in removing large deposits of silt, sand, gravel, and some types of solid waste. Pigging is also effective in removing accumulations of sedimentation, hard scale, bio film and grease whereas scooters can effectively remove heavy debris and grease. Cleaning with chemicals and water jetting can effectively clear the pipeline but sometimes creates new problems. High pressure water jetting can remove roots in the pipeline. A cutting tool can help with jetting in case of large roots.
Overall the benefits of pipe cleaning include higher operating efficiency, lower maintenance cost, and less internal corrosion. Pipe cleaning plays a major role in maintaining and extending the service life of the pipe
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