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New life in dead river

Green advisor

Effective water treatment breathes new life into a dead river

A significant deterioration in the oxygen balance in stretches of Sweden’s River Vege led the multinational food business Findus to seek immediate help from ÅF to upgrade its wastewater treatment.

In mid-August 2012 reports were received of large numbers of dead fish in the 55-kilometre long River Vege in south-western Sweden. An investigation showed that the Findus wastewater treatment plant upriver in Bjuv was an unwitting contributor to the cause.

Investment in modernisation

High sediment content in water discharged from the plant during processing of the annual pea harvest had led to a critical lack of oxygen in the water of the river. Fragments of oxygen-consuming organic material had passed through the plant without being decomposed, causing hypoxia and killing the fish. Findus responded by investing 1.4 million euros in modernising its treatment plant and donated around 110 000 euros to the River Vege Water Preservation Association for research and fishery conservation projects.

Multiple measures required

Findus discussed different solutions with various experts, including ÅF. It was decided that the necessary improvements could best be achieved by a combination of more reliable measuring methods, new filter processes, a retention basin and a new control system. ÅF was tasked with replacing the old control system and the outdated SCADA system that monitored and controlled certain key processes. The assignment included programming the two new systems and designing an electrical system that could replace the existing set-up and integrate new components into the plant. The SCADA upgrade also incorporates a function for producing reports that facilitate the work of the County Administrative Board’s engineers when they conduct their inspections.

ÅF assists at all stages

During the implementation of the project ÅF consultants took part in technical meetings about the measuring and control functions to ensure an optimum result. They also participated in the work of fine-tuning the new systems both prior to and in connection with the upgraded plant being brought online.

Energy efficient and eco-friendly

During the programming process ÅF introduced a number of functions designed to improve the wastewater treatment plant’s sustainability credentials by reducing its energy use and minimising its impact on the environment. Variable-frequency drives were installed to control the aeration blowers that oxygenate the water in the retention basins. This makes it possible to optimize the speed of the blowers according to the oxygen levels measured at any given time, slashing energy requirements by a staggering 30–50 percent compared with previous operations. 

Extra safety net

ÅF and Findus also collaborated on the development of a facility for continuously measuring the phosphorus content of outgoing flows into the River Vege and set up   boundary values to control when the wastewater treatment plant can discharge water into the river. Excessive levels of phosphorus can be problematical as phosphorus is a plant nutrient, stimulating the growth of algae and other organic material that  consume large amounts of oxygen during the decomposition process. If the phosphorus content in the river exceeds a certain limit, wastewater is now transferred to a storage basin instead. This water is subsequently pumped back to the beginning of the treatment process until the phosphorus content falls within the limit. This innovation has enhanced the system with an additional safety net.

In excess of expectations

The investments in the wastewater treatment plant combined with various measures to conserve the river’s fish stocks have brought about a dramatic turnaround in the health of the river. After many years of absorbing contaminants from many different sources, the River Vege has now been transformed into oxygen-rich fishing waters. Measurements also show that the Findus plant has remained well below the limit values during the two pea-processing seasons since the system was introduced. The representatives of the River Vege Water Preservation Association are satisfied and happy with the results and the County Administrative Board has let it be known that the current situation in the River Vege is far in excess of expectations.

The fish return

Happiest of all, however, are probably the healthy salmon and salmon trout that have once again found their way back to the river’s clear waters. That must surely be the best environmental indicator of all.  

Services involved