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Protecting residents from sanitary hazards – HST solutions for combined sewers


The combined sewerage system discharges domestic sewage and rainwater through a common channel. Therefore, in the event of overflows, e.g. during heavy rains, there is a serious risk of exceeding the capacity of the treatment plant and discharging untreated wastewater to the receiving water body. Sludge removal systems and HST flow control devices can provide a solution to such problems.

  • Sanitation risks posed by wastewater decay
  • Technology to prevent wastewater decay
  • HST equipment and comprehensive support from Ecol-Unicon
  • AWS Jet Cleaner aeration and flushing nozzle
  • AWS Flush Gate


Sanitary wastewater decay is a serious sanitary risk

Sewage decay and the accompanying noxious odours are caused by oxygen deficiency in extensive sewer systems and long delivery pipelines. This occurs after the wastewater has been in the pipeline for only a few hours, and its consequences can be hazardous to the health and lives of both residents and maintenance crews. At the same time, treatment of such wastewater becomes less efficient and more energy-intensive.

Insufficient aeration of wastewater results in wastewater decay. It leads to the oxidation of hydrogen sulphide and the formation of sulphuric acid, which is harmful to the wastewater network components.

Hydrogen sulphide causes corrosion of concrete and metal structures and equipment. It also contributes to the foaming of wastewater and the growth of filamentous bacteria and aerobic chemotrophic sulphur bacteria. It is the gas that causes the most poisoning and deaths among workers associated with the operation of water and wastewater systems. It is particularly dangerous because it cannot be smelled in high concentrations.

HST devices

Technologies to prevent decay of wastewater

Contrary to expectations, the investment and operating expenses of solutions aimed at preventing wastewater from decay are not high and should already be foreseen at the design stage of the sewage system. They make it possible not only to operate the wastewater treatment plant more efficiently, but also to seriously reduce operating costs.

The most common systems used are aeration of wastewater or disposal with air or water, such as:

  • pipeline blowing with compressed air
  • aeration of wastewater with compressed air
  • water flushing


Another solution used is the application of chemical agents that bind hydrogen sulphide compounds or inhibit bacterial growth. However, this method generates higher costs and increases the risk of corrosion of concrete or metals. It also requires appropriate dosing pumps and equipment to measure the concentration of hydrogen sulphide. In addition, chemical compounds such as nitrates or iron salts are not completely removed during wastewater treatment and may end up in the environment.


HST devices and comprehensive support from Ecol-Unicon

German-made solutions from HST Systemtechnik, such as sludge removal systems, keep sewer networks in optimum condition. These are innovative and effective products that integrate information technology into the operation and management of facilities.

The exclusive distributor of HST products in Poland is Ecol-Unicon, a company that, together with its German partner, provides comprehensive services from the design itself, through the implementation stage, to service.  Ecol-Unicon offers full support in planning, consultancy, assessment, dimensioning or planning documentation of the entire water and sewage system.


AWS Jet Cleaner aeration and flushing nozzle

The AWS Jet Cleaner aeration and flushing jet is a powerful and highly efficient pump with nozzle set. It can be used in combined sewers, wastewater treatment plants, storage tanks and in process water treatment.

The AWS Jet Cleaner produces a water-air mixture as a driving and cleaning jet. This effectively eliminates wastewater decay processes during prolonged retention.

It is a fully automatic cleaning unit which, in its standard version, consists of a pump unit and a set of injectors. The AWS rotary nozzle is equipped with a set of injectors, which allow a large flushing radius even with very different tank geometries. The contaminants are discharged here as the tank is emptied. During the emptying process, the nozzle operates in intermittent or continuous mode, according to predetermined switching points. In addition, cleaning is assisted by rotating movements.

The HydroMatic software used in the streamer allows for energy-efficient control of the entire process with real-time monitoring of the results. It is also possible to individually adapt the operating mode of the unit to local conditions.

Flushing efficiency data is continuously recorded by a screen located at the bottom of the tank. This makes it easy to monitor the effectiveness of ongoing activity. The location and intensity of sludge can be determined by entering the data manually into the control panel or automatically using an optical camera.


AWS Flush Gate

AWS Flush Gate is an extremely effective and fully automatic system used to remove sludge from combined sewers and holding tanks. It works by using sensors mounted in the tanks and relies on the use of stored water to flush the bottom of the tank. Opening the manhole creates a strong wave that safely flushes out accumulated sludge.

A chamber closed by a flap is placed above the section that requires flushing. This allows the chamber to be opened automatically when it is required to remove the sludge from the system. For the remaining time, water is stored in the chamber, ensuring that the sewer can be cleaned even in dry weather.

Thanks to its lightweight housing and compression system, the AWS Flush Gate does not require additional delayed closing mechanisms, minimises hydraulic losses and allows the tank to be completely emptied.

You can find more about the equipment supporting HST’s combined sewer solutions on our website. We also invite you to sign up to our newsletter to keep up to date with all the latest news from the wastewater industry.