As part of a project for the neutralisation of hydrogen sulphide in the sewage system of a medium-size municipality, sera has started over ten innovative dosing systems in September 2008. An effective solution was developed in cooperation with an internationally operating water technology company.
A municipality of approximately 50.000 citizens in the German state of North Rhine Westphalia was literally fed up.
The stress from unpleasant odours from the sewage system, especially in the vicinity of the local sewage plant, had developed into a significant nuisance.
The problem element
Many waste water channel networks in Germany are designed for much higher volumes as is meanwhile actually needed. Low water consumption and extended dwell times of the waste water in the sewage network are, however, ideal growth media for the development of gaseous hydrogen sulphide, both in the sewage systems, in the pump stations and pressure lines. Because from sulphur-containing waste water ingredients high sulphide concentrations develop through a chemical reaction, and thus the gaseous hydrogen sulphide.
The rotten egg „smell“ can already be perceived at a low concentration of less than 0.15 ppm. Although these „side effects“, together with the accompanying corrosion of the construction materials, are unpleasant, they are not yet life-threatening. However, acute danger to life begins at 300 ppm. Furthermore, sulphides eliminated in the waste water hamper the process of waste water treatment (interference with the biocenosis) because the increased occurrence of sulphur bacteria can favour special filamentous bacteria and cause operating problems (flotation).
The special challenge
A remedy against the negative effects of H2S can be provided with several metallic salt solutions. After several months of testing, the local operating company opted for the use of an iron-II-chloride solution with the active ingredient FE 2+ and a pH of 1. Because this chemical is classified as a substance harmful to water, special measures were necessary for the safe and careful use in the residential area. Operating company and municipality emphasized in particular the need for a high-quality and safe system technology which would also withstand extreme external influences.
Besides, the system should blend, „invisibly“ to the residents from the neighbourhood, with the landscape. This challenge was also successfully met by sera.
The intelligent system
The dosing systems were delivered complete and ready to be connected. Because of the proven sera plug & dose system they were ready for operation shortly after the connection was established. The systems were installed in a special outdoor cabinet which blended harmoniously into the scenery. The integrated dosing pallet is equipped with the latest sera dosing pump generation and fitted with a drip pan and leak alarm.
One of the main concerns of the operating company was the simple handling and modification of the dosing program. Apart from the high-quality motor diaphragm dosing pump, the integrated switching cabinet is equipped with a timer programmable via a key. With the easy to operate software and the key the new time control can be programmed in the
office via PC. Subsequently, the software can be transferred to the timer on site via the key.
The systems can thereby be optimally adapted to changing waste water characteristics and saving expensive chemicals in the process. The iron-II-chloride is supplied in the pump well directly below the waste water seal through a dosing valve enabling it to react directly at the location of the H2S development.
The systems are supplied from underground tanks with a volume of 2 m³. This quantity approximately covers the annual demand. The underground tanks are regularly serviced, are thereby protected against leaks and are equipped with driveable lids.
About hydrogen sulphide:
Hydrogen sulphide (H2S) is a gas which consists of the compound of one part hydrogen and two parts sulphur. When protein is broken down from sulphuric amino acids, putrefactive and sulphur bacteria are generated which cause the specific strong odour of hydrogen sulphite. Hydrogen sulphite is flammable, very toxic and hardly soluble in water.
The unobtrusive housing gives the dosing station the appearance of an ordinary electrical distribution box. However, it accommodates innovative dosing technology from sera. The associated tank from which dosing takes place is installed.