Grundfos disinfects Czech drinking water with electrical chlorination

The conventional water treatment technology originally included a disinfection method suited for water featuring the composition and characteristics of raw water (surface water). Applied was chlorine gas, which was dosed by outdated vacuum controllers into pressure water and then supplied to two application points – i.e. pre-chlorination of the raw water and post-chlorination of the final treated drinking water.

The raw water disinfection is first of all adopted during summer months to prevent excess microbiological life in the water. At the maximum chlorine feed rate in the two application points, the chlorine gas demand ranged around 25 kg Cl2 per 24 hours.

The above described disinfection method calls for increased safety at work, regular inspections of the equipment and building, increased costs in connection with the filling of the pressure gas cylinders, as well as transportation and storage of chlorine gas.

The Grundfos Solution

In the course of considering a change of the disinfection method, the water treatment plant management contacted its well-proven partner and supplier of pumping and dosing equipment – Grundfos, who at that time presented through its marketing campaign “Disinfection Road Show 2009” their new suggestions for the sphere of water disinfection including the electrical chlorination method effected through the Selcoperm system.

At that time, Grundfos had no reference Selcoperm unit in operation within the Czech Republic and the Slovak Republic. With this in mind and upon the Customer´s request, a visit was organised in cooperation with Grundfos colleagues in Switzerland to the Waterworks of Geneva, whose water source type and characteristics were very close to those of the Žlutice water treatment plant, with a view to introduce to the Customer a reference Selcoperm unit installed there. The high level of the individual technological stages of the water treatment process and the employed technological units including the electrical chlorination system dominated by Selcoperm 1000 made a strong impression on the representatives of VAK Karlovy Vary. Based on offers elaborated for a total of four larger waterworks, it was subsequently the Žlutice water treatment plant that was selected from among four operated large waterworks as a typical medium size treatment plant for the implementation of the new disinfection system.

A prerequisite condition for the implementation was the approval of the local hygienical authority - KHS Karlovy Vary who required from the State Health Institute of the Czech Republic a standpoint toward the adoption of the electrical chlorination method  and its use with drinking water. Upon submittal of the required documents and fulfilment of the conditions, the approval with the new method of drinking water disinfection through electrical chlorination and the Selcoperm system was issued.

Another pre-condition for establishing smooth operation of the Selcoperm system was the selection of a suitable sort of pelleted salt in line with the manufacturer´s requirements, and installation of a water pre-heater, which is recommendable especially during the winter season with the temperature of the water being treated varying around 1°C, while the required limiting range of the water entering the electrolytic process within 10°C through 20°C must also be met.

Selected and delivered out of the Selcoperm product range was Selcoperm 2000 producing 2 kg Cl2/h whose reserve capacity is sufficient to cover possible emergency demands.

A 5,000-litre sodium-hypochlorite holding tank was delivered to keep a stock of the product ready for application. The tank´s capacity is sufficient to cover the periods needed for possible service interventions and maintenance. For emergencies calling for prolonged downtimes of the Selcoperm system, which would not be covered by the product stock contained in the 5,000-litre holding tank, a standby suction assembly was installed to serve for dosing the commercial concentrated sodium hypochlorite solution, which will also be applied by chemical metering pumps DDI 150-4 AF as the product of the electrical chlorination.

Installed for applying the product is an assembly of a total of three (1 duty + 2 standby) digital chemical metering pumps of the type DDI 150-4 AF including a flow monitor, which provides for continuous check of the individual dosing stages, thus creating conditions for absolutely reliable, even and accurate application of the disinfection agent covering the demands of the pre-chlorination and post-chlorination systems. The fully automated control of the output and run of the chemical metering pumps is effected by pulses generated by the superior control system of the water treatment plant.

The Outcome

The first installation of the disinfection method using electrical chlorination and the Selcoperm system at the Žlutice water treatment plant has heralded a new era in the application of the water disinfection technique offered by Grundfos within the Czech Republic.

This successfully implemented reference unit will become a significant tool for the promotion of the new disinfection method, also contributing to the process of acquiring prospective clients that show interest in replacement of an existing water disinfection method with an efficient, safe, cost-effective and reliable method of disinfection.

And last but by no means least, this installation has confirmed to the owner and the operator himself that the new disinfection method has been the right choice and that he can count upon it for his further implementations of similar nature that call for effective disinfection of water.