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PRACTICAL TIPS: STANDARD- AND 4.0 EQUIPMENT FOR MODERNIZATION AND NEW CONSTRUCTION OF STORM WATER BASINS – PART 1 OF 2

Focus: BASIN CLEANING

INTRODUCTION OF BASIN CLEANING

For decades, municipal wastewater treatment could rely on almost constant operating conditions and sufficient experi­ence in wastewater engineering operations. In recent years, however, the boundary conditions have been subject to ever greater fluctuations. The prolonged dry periods of drought in the last few years recent years have shown what a lack of water and hence an insufficient dry weather flow can mean for the removal of deposits in sewer systems and for the oper­ation of sewer systems and the associated special structures.

On the other hand, more extreme periods of heavy rain require larger storage capacities and, as a result, new cleaning strategies.

Less than two decades ago, basins and reservoirs were still being cleaned manually by the operating personnel. This was not only physically tiring, but also very time-consuming and therefore very costly. Furthermore, depending on the geometry and location of the basin or reservoir, it was some­times difficult to reach all points and thus to clean sufficiently.

Faced with these challenges and the increasingly extreme conditions, the development of mechanical and automated basin cleaning got underway…

“Basin and reservoir cleaning”

But why do rainwater basins and reservoirs become soiled?

Particularly after heavy rainfall and the resulting impound­ing of basins and other storage volumes, the dirt and sludge from the sewers and roads remain in the basin. It accumulates on the bottom of the basin, on the walls and, in the case of underground reservoirs, even under the ceiling.

Fig. 1 Manual cleaning of a storm water basin with fresh water

SURGE FLUSHING OR JET CLEANERS –WHAT IS THE RIGHT SOLUTION?

During the impoundment of storm water basins, the sediments in the wastewater are settled and deposited on the bottom of the basin. The sediments remaining on the bottom of the basin after the end of the impoundment are removed or prevented by means of flushing and cleaning devices in the form of surge flushing (Fig. 2) or flow generators. Surge flushing in the form of flushing buckets (or tipping buckets), flushing gates or vacuum surge flushing removes deposits after the basin has been completely emptied by a powerful flushing surge. The selection of the appropriate flushing technology is generally related to the hydraulic, structural and operational conditions. One thing they all have in common is the need for a flushing sump, which is particularly important to consider when retrofitting. Tipping buckets are very cost-effective for structure and discharge heights greater than 3 m and do not require any additional structural space for flushing water supplies like flushing gates or vacuum flushing systems. Tipping buckets and vacuum flushing systems have a common operational advantage – they are not located in the medium and therefore there is no functional damage due to deposits or contamination as with valves located in the medium. In conjunction with the use of surge flushing, the noise emissions of the flushing process should also be addressed. Flow generators for basin cleaning already work at the beginning of basin emptying, but only with a safe falling tendency. They remobilize sedimentation or prevent sedimentation by generating flows in the basins. 2D- and 3D-Jet cleaners (Fig. 3) clean the released basin surface by a directional focused water jet. The advantage of jet solutions lies in the fact that they are largely independent of structural characteristics such as the shape of the basin, gradient and installations such as supports, etc.
Fig. 2 Vacuum surge flushing
Fig. 3 HST 3D-Jet Cleaner cleans the wall
Fig. 4 AWS Flush Sluice
Fig. 5 Flushing Gate discharges
Fig. 6 Flushing buckets

JET CLEANERS

1-DIMENSIONAL

(for e. g., reservoir channels, small basins)

The technically simplest but, at the same time, weakest variant for cleaning by means of flow generators and aerators are static, one-dimensional jet cleaners.

A pump conveys the accumulated water into the injector set via which air is simultaneously drawn in. The resulting air/water mixture leaves the injector set as a bundled cleaning jet in a preset direction and has a comparatively narrow spray width. This method of cleaning is therefore best suited for cleaning hose-shaped/narrow basins and reservoir channels.

Fig. 7 AWS Jet Cleaner (static) in reservoir channel

2-DIMENSIONAL

(for e. g., rainwater reservoirs, sedimentation basins)

If you wished to clean a basin that has a larger surface, several static one-dimensional jet cleaners would have to be placed next to each other in order to reach the whole of the base of the basin with the cleaning jet. This would result in high purchasing and operating costs.

For this reason, two-dimensional “pivoting” jet cleaners were developed as flow generators and aerators. They have a swivel drive that enables the cleaning jet to be rotated horizontally about an axis and to thus cover a large area.

Fig. 8 AWS Swivel Jet Cleaner in an open rainwater retention basin

3-DIMENSIONAL

(for e. g., large pump stations, central rainwater reservoirs)

Two-dimensional basin cleaning offers significant technical benefits compared with manual and one-dimensional jet cleaners. 2D jet cleaners clean large areas of the basin bottom and the lower wall area. 3D jet cleaners can clean the whole wall area and the ceiling of the building.

Three-dimensional jet cleaners significantly expand the cleaning area. The multidimensional range of movement enables almost 100% of the surfaces in the structure to be cleaned. This flexibility allows even surfaces which are further away to be reached.

Fig. 9 Cleaning jet of the AWS 3D Jet Cleaner cleaning three rainwater retention basins at the Herten sewage treatment plant
Fig. 10 2-dimensional
Fig. 11 3-dimensional

SYSTEM COMPARISON: 2D VS. 3D

Comparison of the range of movement and accessible cleaning area between AWS Swivel Jet Cleaner (2D) (Fig. 10) and AWS 3D Jet Cleaner (Fig. 11):

The additional dimension (height) allows the 3D Jet Cleaner to reach a significantly larger cleaning area and thus ensures even more extensive cleaning.

AWS JET CLEANERS – INTELLIGRID PROCESS AND MACHINE CONTROL AUTOMATION LEVELS

Basic: HydroMatic

With the standard HST automation, the Jet Cleaners operate with filling level-dependent switching points. During the whole cleaning process, the pump and swivel drive are in operation intermittently or continuously, depending on the filling level. In addition, routine movements (e. g., daily, weekly, etc.) can be performed to ensure operability.

Level I: IntelliGrid

When degrees of soiling are entered by the operator at the display or are detected by camera, the Jet Cleaner operates independently, depending on the degree of soiling. The automatic adaptation of the cleaning intensity, depending on the swivel position, allows energy to be saved or optimum use to be made of the available cleaning time when emptying the basin.

Level II: IntelliGrid.IoT

The expansion of the IntelliGrid automation system to include precipitation data from data portals, such as NiRA.web® and information from the sewage network and the upline system network (IntelliNet) enables the software to learn from the data so that it can decide pro-actively whether and to what extent cleaning is necessary.

Fig. 12 HydroMatic
Fig. 13 IntelliGrid
Fig. 14 IntelliGrid.IoT
Fig. 15 Automation levels of AWS Jet

NON-INTELLI SYSTEM

Without IntelliGrid, the Jet Cleaners are controlled by means of fixed parameters. Each basin has individual flow conditions. As a result, dirt zones build up that can become thicker and thicker. If action is not taken in good time, failure of the complete basin is possible.

INTELLI SYSTEMS

With IntelliGrid, the system learns from operation. The experience and dirt zones are stored and more efficient cleaning is guaranteed at each cleaning event. Clean areas are cleaned only briefly. The formation of dirt accumulations is reduced at each impoundment.

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APPLICATION EXAMPLE

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ADVANCED TECHNOLOGY

A two-chamber rainwater basin has been built directly next to the Porsche painting line in Stuttgart. A high-gloss finished is not only being ensured for the luxury limousines, but also the rainwater basin that collects the surface water from the factory premises. As for its own production, the luxury car brand has chosen to rely on quality “Made in Germany”. A total of six AWS Swivel Jet Cleaners remove all the soiling from the smooth concrete floor after rainfall. The complete basin equipment – including SECURA floor gates and stainless steel stairs – was installed by HST.

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MODERNISATION AND UPGRADE

During the modernisation measures for the above-ground canals of the Emscher Genossenschaft in Dortmund-Scharnhorst, not only the new buildings were equipped with technology from HST. In order to upgrade the rainwater basins on the sewage treatment plant site, eight AWS Swivel Jet Cleaners with surface-mounted swivel drives were installed. As the original cleaning performance of the old units was no longer sufficient due to the higher dirt load, the pump capacity was increased. In order to save as much energy as possible, energy-efficient single-channel impellers for mixed water applications were installed instead of free-flow impellers.

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FUTURE-PROOF DECISION

For years, cleaning of the deposits in the storage basins of the Aschaffenburg sewage plant inlet was part of the daily work. “Normal” jet cleaners could not handle this soiling. Particularly in this region, the increase in the number of moist cloths is quite significant. Pumps have clogged and moist cloths have built up in layers in the impeller until the machine failed. Through the use of appropriate pump technology and an optimised arrangement of the flow generators, the basins are now cleaned completely until empty without the need for subsequent cleaning.

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