Municipality, drinking water

The municipality of Kungälv needed a wa­ter treatment plant that is very effective in dealing with Natural Organic Matter (NOM). It also required a robust produc­tion capacity that is easily upgradable. The process devised for the new Kungälv water plant was tested for a full year to see if it would be up to the task in different conditions. The pilot trials were executed by Purac, a leading Scandina­vian contractor in water and wastewater treatment.

As the ultrafiltration system is the heart of the overall drinking water treatment plant, Purac has worked together closely with Pentair X-Flow, who delivered the UF pilot unit and full-scale UF units, as well as engineering support.

The town of Kungälv in Sweden decided to build new treatment facilities for producing drinking water. In a process of close cooperation, the Küngalv municipality, process partners including Purac,

and Pentair engineers went through every step from development to operational excellence for building state-of-the-art facilities that will eventually also supply drinking water to neighboring communities.

The municipality of Kungälv in western Sweden near the city of Gothenburg was facing two main challenges concern­ing its drinking water supply. First, a fast-growing number of households is increasing local and regional demand for drinking water, while at the same time the existing ground infiltration plant was at maximum capacity and could not be expanded. Second, the design of a new treatment plant to take water directly from a river susceptible to varying water quality conditions. The treatment plant is located near Kungälv on the bank of Sweden’s largest river: the Göta river. The COD levels in this surface water are on the rise, and climate change is only going to push them higher. The river is also a strategic transport route and has several wastewater treatment plants that discharge into it.

Higher average temperatures will bring much more pre­cipitation that will have a marked effect on the quality of raw water sources for drinking water. Excess surface runoff brings high humus levels and algal blooms fed by nutrients from fertilizers, entering the aquatic system and causing excessive growth. Microbial contamina­tion will increase in raw water sources as a result. The existing drinking water treatment process in Kungälv was strug­gling to meet the required microbiolog­ical barrier levels, as several wells were being increasingly affected.

The selected process scheme comprises four treatment steps to reduce or eliminate the risks posed by NOM, viruses, and pathogens. In the first treatment step, the river water is naturally aerated in an aeration cascade. The water passes through rapid gravity filters containing Filtralite®, a highly porous media filter that removes iron and turbidity and improves water quality and biostability. 
The second step is UF membrane filtration, in which bacteria, viruses, and parasites are removed. Furthermore, in combination with coagulants, the membranes will remove more than 50 percent of NOM, measured by UV254.

The in-line coagulation is controlled by feed forward control. 
In the third step, the water is treated with activated carbon filters in order to remove the last traces of chemical substances, odor, and taste. In the fourth and final step, the water is alkalized with sodium carbonate and carbon dioxide. Before distribution, the water is also UV-treated to provide a second and independent microbiological barrier.

To increase the overall system water recovery and to reduce the waste stream, there are two successive ultrafiltration stages. The primary UF system uses the Pentair X-Flow Xiga Solution, the highest surface area-to-footprint ratio in the market, and its backwash waste is treated with the secondary UF system that uses the Pentair X-Flow Aquaflex Solution, the proven technology for high solids membrane filtration applications. 

Membrane+ is the X-Flow approach to ensuring success in every filtration project through close involvement and cooperation from the first concept to full-scale operations. Expert assistance, especially from an early stage onward, will always make the difference in terms of quality, safety, efficiency and reliability. The Pentair X-Flow engineers are committed to provide all practical support you need in every one of the four main project phases.

Pentair Pilot Engineer Martijn Lesscher was involved in the development phase, working together with Purac on the piloting. ‘The combined effort of all operators has made this trial a success. performance.’ During the design phase, various calculations were made for the complete UF system, including all equipment specifications and selection guidelines for a robust system design that meets best engineering practices for operational efficiency and reliability. ‘Our process design and calculations also covered the neutralization system, and the tank dimensioning for the UF system.

The frequent interactions and meetings with the Purac engineering team helped me to understand and meet their specific requirements. Working together closely in every project phase enables us to deliver successful and sustainable ultrafiltration solutions.’