Sewer cleaning

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The term sewer cleaning describes measures for cleaning sewers and sewers and manholes.

Depending on the pipe diameter, cleaning can be carried out by machine or by hand. Manual cleaning is used for safely accessible canals. In large canals (> 2 meters), balloons, walls or so-called ships or boats are propelled forward. Sewers up to 2 meters in diameter are usually cleaned by machine.

Solids are also discharged into the sewer system with the wastewater. The sewage flow rate is usually too slow to flush or push these solids forward in the sewer. If these deposits are not removed, blockages or flooding can result. Gases and a deposit develop in the sewer which can attack the pipes and shorten their service life.

When cleaning sewers using high pressure, the sewer skin on the pipe wall is largely or completely removed.

Intervals

Wastewater pipes should be cleaned at regular intervals in order to protect them from premature "aging". In many places, construction-related defects, subsidence, deposits and incorrect slopes are the cause of blockages. Regular cleaning will prevent such blockages.

species

Surge flushing: surge door with drive rod in the Mannheim sewer system

Differentiation according to the method of implementation

There are three common ways to clean a duct :

  • High-pressure flushing: flushing water (e.g. from a water tank) is sprayed onto the sewer wall through a cleaning nozzle using a high-pressure pump and high-pressure hose.
  • Surge flushing (the oldest process): It is carried out using built-in shut-off elements. The shut-off elements accumulate the water and after suddenly opening a flood of rinsing occurs, which washes away the deposits.
  • Backwashing: The energy from the accumulated wastewater is also used for cleaning. For the flushing effect, the pent-up wastewater is directed to the front via a built-in pipe to a nozzle shape for swirling . Like the surge rinse, it is not suitable for stubborn dirt.

Differentiation according to the size of the duct to be cleaned

A distinction is made according to the size of the sewer to be cleaned

  • Property sewer cleaning - cleaning the sewer of a property (single or multi-family house)
  • Cleaning of medium-sized sewers: In every household, several hundred liters of water mixed with urine , faeces and toilet paper (" dirty water ") flow through the sewers every day . Incorrectly disposed of waste produces solids . Sand , gravel , stones, etc. are also washed in. Since the flow rate of the wastewater is not sufficient to wash away all solids, these must be removed mechanically.
  • Large sewer cleaning: Other equipment is used for large sewer cleaning, e.g. B. Plows and balloons.

By fermentation occurs at the pipe wall a slippery coating that acts aggressively to the pipe wall. It promotes the "decomposition" of z. B. concrete pipes u. Ä. They then appear washed out, or have a rough surface or become thinner-walled.

Industrial high-pressure cleaning of pressure equipment parts in the chemical industry with special protective equipment

High pressure cleaning

Sewer cleaning is always done with water. Due to the high consumption, there is also a form of sewer cleaning using water recycling . By inserting a pressurized nozzle , it is "pulled or pushed" upstream into the channel. When the end of the path to be cleaned is reached, the nozzle is withdrawn. The water exits through precisely calculated nozzle openings in the form of a sharp jet in order to loosen the material to be transported, to throw it backwards and thus to transport it out of the channel in the direction of flow. The actual cleaning of a channel takes place when the nozzle is withdrawn.

Sewer cleaning vehicles

Suction truck in use (sewer cleaning)

This basically includes:

  • Water tank
  • High pressure pump , this generates the necessary pressure with a suitable flow rate
  • Hose , it guides the water from the pump to the nozzle and has to slide well outside
  • Reel and pulleys
  • Nozzle that is / must be matched to the high pressure pump

high pressure pump

The high-pressure pump generates pressure by displacing water, with piston pumps and pressure converter pumps being used.

  • Piston pumps are more suitable for use with clean water. A piston pump can also be used for water recycling in the case of complex cleaning and filtration. In the piston pump, several pistons generate the necessary pressure (similar to how the pistons in the combustion engine compress the air / fuel mixture). The force to be delivered by the transport vehicle is comparatively small.
  • A different method is used for the pressure converter. Here a large piston (diameter about 15-20 cm) is housed in a cylinder housing. There is an oil circuit on one side and the water circuit on the other. The more oil pressure is applied, the more water pressure there is. When the piston hits the "stop" on one side of the stroke, the hydraulic system releases the other hydraulic circuit and the piston moves to the other side.

The more oil pressure you allow, the more water pressure you get. The pressure converter is insensitive to dirty water, so it is suitable for use in water recycling. The power to be supplied by the vehicle is comparatively large, mostly or predominantly via NMV (gear-independent power take-off for large power outputs).

Nominal capacities of high pressure pumps vary greatly depending on the type of application. There are pumps up to 300–400 bar and outputs up to 800 liters / min. At maximum pressure (e.g. for demarcation of lane strips or when renovating bridges to remove concrete) up to 4000 bar (at approx. 10 liters / min.) Are used. Compared to pressure converters, piston pumps tend to achieve higher volume flow than pressure, whereby, depending on the type of application, more attention is paid to pressure or liter output, or even both.

tube

The water pressure generated by the high pressure pump is passed on by means of a hose. This hose should be as light and smooth as possible (inside and outside) in order to enable greater distances with little pressure loss, its outer surface should be abrasion-resistant so that it is not damaged in contact with the pipes, edges or manholes. Furthermore, it should allow a tight radius so that it can also be used in curves or arcs. Another criterion is the type of hose:

  • The rubber hose consists of a rubber mixture. Its advantages are the abrasion resistance of the outer shell and the bending radius. The disadvantages are in the weight. Its weight is around 960 g / m (1 "hose) without water. The pressure loss of the rubber hose is significantly higher than that of the plastic hose.
  • The plastic tube in turn consists of one or more plastic layers. Its advantages are its lower weight. At around 630 g / m (1 "hose) without water, it is around a third lighter than the rubber hose, so it is well suited for longer distances. The pressure loss is significantly smaller than with the rubber hose. Its disadvantages are in the area of ​​abrasion, it is sensitive to external influences such as mechanical contacts on rough surfaces (manhole edges etc.). Another disadvantage of the plastic hose is its lack of kink resistance. The plastic hose can be kinked very easily, which leads to small injuries in the jacket Noticeably stiffer in winter, which increases the risk of buckling.

Both types of hose have the same structure. The innermost layer ("core") should be as smooth as possible in order to minimize pressure loss. The pressure loss is caused by the porosity of the " soul " (including the "friction of the water") and the length of the hose. Although the hose is completely smooth on the inside, there is a pressure loss. With a 1 ″ hose (inner diameter 25 mm), 180 m hose length, 400 liters flow rate and 200 bar, there is a pressure loss of exactly 50%. The next layer (s) are load-bearing layer (s). Similar to a car tire, they are braided diagonally and hold the tube together, otherwise it would burst immediately. It consists of a textile fabric (rarely also steel fabric). The outermost layer is a highly abrasion-resistant layer made of plastic or rubber . It protects the two load-bearing layers from abrasion on shafts or edges.

High pressure hoses are manufactured in various sizes and lengths. Many hoses are tested after manufacture by applying a set pressure to them for a period of time. There are different designs for the necessary couplings at the beginning and at the end of the hose: pressed, screwed couplings or those with a bridge system (Band It).

Occasionally, rubber and plastic tubing are combined. A few meters, usually 5–10 m, of rubber hose are coupled to the beginning of a plastic hose. The heavier rubber hose at the beginning prevents, especially when using a light nozzle, that it unintentionally changes direction at obstacles.

jet

Feed nozzle

The so-called nozzle takes over the effective cleaning of the sewer. The water pressure generated by the high pressure pump and transported through the high pressure hose emerges at the nozzle in the form of a sharp water jet. This beam is extremely dangerous and can cause extremely serious injuries. Each nozzle must be precisely matched to the vehicle used, so that optimum cleaning and flushing performance is achieved.

Basically, nozzles always have "holes" pointing backwards. The nozzle is drawn into the channel through the water outlet to the rear. This creates great tensile forces that enable distances of several hundred meters. There are also nozzles that have water outlets to the front. They are useful for clearing blockages. So z. B. ice can also be dissolved using cold water. Depending on the angle of the water outlet, a nozzle is suitable for clearing capacity (amount of solid matter), degree of cleaning (cleanliness of the pipe wall) or pulling capacity (for long distances). The pressure and the liter output arise in connection with the diameter of the individual nozzle holes and their number. The smaller the holes, the greater the water backflow in the “high pressure pump, hose, nozzle” system. Pressure and liter output are adjusted via these nozzle holes in connection with the available speed range of the truck, number of holes in the nozzle, hose length and hose type (plastic or rubber).

There are different nozzles depending on the type of use and location:

  • Normal sewer cleaning nozzles : For normal cleaning work without special follow-up orders
  • Rotary nozzles, fan nozzles : For all-round cleaning; is mostly used when a sewer TV examination is due after cleaning. The cleaning takes place via the rotating part of the nozzle.
  • Front jet nozzles : They have one or more forward jets that are used to remove obstructions.
  • Floor nozzles : They usually have a high pulling and clearing capacity. The nozzle holes are usually aligned very straight back and hit the floor.
  • Ejector-based nozzle : A special type of nozzle is an ejector- based nozzle, which is based on the principle of an ejector . If the sewer carries a certain minimum amount of water, it can achieve enormous flushing performance. The water present in the canal is massively accelerated by the water escaping at the right angle in the right amount. The water that flows in is sucked in, so to speak, and the flow rate is greatly increased. This nozzle is not suitable for clean pipe wall cleaning, but for flushing out solids.
  • Eccentric nozzles : They are used to loosen layers adhering to the pipe wall, such as lime, grease or the like. An eccentric bearing creates an imbalance which "knocks or even hits" on the pipe wall. This nozzle should be used with care because it can damage pipes that are old or improperly installed.
  • Cutters or chain knives: These types of nozzles are used to remove extremely hard deposits such as concrete , lime, etc. and are used as a last resort due to their aggressiveness. When using these devices, the greatest risk arises that a pipe will be destroyed. With the chain scraper, a kind of strong, larger Velo chain is used, adapted to the pipe wall. It brushes along the pipe wall and knocks off everything that protrudes or gets in its way. The wear on the chain varies depending on the material and pipe to be removed. The milling head is similar to a tunnel boring machine. It rotates at up to 3000 rpm. Its "teeth" are equipped with hardened steel or diamond attachments. The removal rate is increased by additional blows in the axial direction.
  • Propeller nozzles : They are shaped like a propeller and have nozzle holes at the end that clean the pipe wall. They are suitable for larger canals> ~ 60 cm in diameter. They can even be used in egg-shaped tubes. The propeller nozzles are designed exclusively for cleaning the pipe wall and therefore have poor clearing performance.
  • Water recycling nozzles: Most of the mentioned nozzles can also be used in connection with water recycling if they meet certain conditions. Storage must be independent or separate from the water supply. When water recycling is used, the smallest solid fractions (<0.1–0.3 mm) are always washed away, which would destroy the storage within a few minutes or hours. These nozzles usually have separate oil storage. These nozzles also require special nozzle inserts. These inserts must be made of very hard steel, special alloys or all-ceramic, otherwise the nozzle inserts will be very heavily washed out. If the holes are washed out, less pressure, which is necessary for a clean cleaning of the pipe wall, can be produced. The water then flows out through the openings rather unhindered.
  • Special nozzles : One type of this is equipped with TV cameras at the front to enable immediate control of whether further cleaning is necessary. They are not used for sewer inspection , but only for assessing cleanliness. Furthermore, there are nozzles that activate additional nozzle holes from a certain pressure. This takes place in a mechanical process that is triggered hydrodynamically (medium water pressure). There are also steering nozzles, with these nozzles individual nozzle holes are closed or smaller. This creates a non-uniform jet that causes the nozzle to deflect in a certain direction.
  • Intermediate thrust nozzles: They serve as additional pulling power when rinsing longer positions. They are used for hose connections.

Water consumption and water recycling

Large amounts of water are required due to the high volume flows of the high-pressure pumps. With a 15,000 l capacity of the vehicle and 400 l / min of the high pressure pump, you can flush for almost 40 minutes, after which it has to be refueled. This means that over 100,000 liters (100 m³) of clean water can be used in one working day.

The use of so-called water recycling significantly reduces water consumption. With the water recycling system, you have a suction and flushing vehicle in one. The accumulating material (solids and wastewater) is sucked in and filtered in a filter system to such an extent that only particles smaller than ~ 0.1-0.3 mm are allowed through. With piston pumps, a multi-stage filtration system <~ 0.1 mm is required, with the pressure converter a slotted screen with <~ 0.3 mm is sufficient. The filtered water is then made available again to the high-pressure pump. This means that the water that has already been “used” can be reused several times. Depending on the circumstances, water never has to be topped up for days or until the proportion of sludge in the vehicle tank is too high. Rinsing with fresh water is recommended every day after the end of use so that no solids are deposited. Depending on the system, this cleaning takes less than a minute per day.

The first side effect is the increased profitability of the water recycling system. While a sewer cleaning vehicle is being refueled with fresh water, a water recycling vehicle continues to work. The second side effect is the saving of a suction vehicle to suck up the washed-up waste from sewer cleaning. A water recycler sucks the washed up waste directly from the sewer.

With water recycling, however, the wear and tear of the individual parts and the fuel consumption of the vehicle are higher than with classic sewer cleaning vehicles, so a surcharge is usually charged for the work. However, this almost always pays off if you take into account the standing costs to be paid (for water refueling) and an additional suction vehicle.

security and environment

Entry into sewer systems

Entry into sewers or pits can involve risks in the form of gas, explosion, drowning, slipping or falling. Pits and channels should only be entered correctly after they have been checked using a gas warning device (at breathing height). Deposits make the surfaces very slippery, so correct securing is always required. The consequences of non-compliance with such safety measures can range up to death from suffocation, poisoning, or drowning through fainting. Adequate ventilation should always be provided before climbing a canal.

In general, the employer's liability insurance association guideline BGR 126 "Working in enclosed spaces in wastewater systems" must be observed. In most cases, BGR 117-1 “Working in containers, silos and confined spaces” will also be relevant. The information document of the statutory accident insurance GUV-I 8755 "Assessment of hazards and pollution at workplaces in sewage disposal companies" should be used for risk assessment.

Disposal of waste from sewer cleaning

The European Waste Catalog of 2001 assigns waste from sewer cleaning to waste code number 200306; likewise the Waste Catalog Ordinance (AVV). Accordingly, they are to be disposed of in compliance with the Recycling Management Act and the provisions for municipal waste.

Specific regulations and assignments apply to sludge from cleaning internal waste water pipes, and this applies equally to specialist companies.

Web links

Individual evidence

  1. Falk Schönherr: Sewer deposits and their significance for the discharge of contaminants from sewer systems , GRIN Verlag, 2007, ISBN 3638715329 , page 42ff
  2. ^ Matthias Geib, Martin Wielenberg, Matthias Heyer: Cleaning sewers by high pressure flushing , Volume 11 of series of publications from the Institute for Pipeline Construction at the Oldenburg University of Applied Sciences, Institute for Pipeline Construction Oldenburg, Vulkan-Verlag, 2007, ISBN 3802753488 , page 63ff