The Revaq-certified Sjöstadsverket is responsible for the sludge

In the middle of the Klarälven delta lies Sjöstadsverket, a wastewater treatment plant with the capacity to treat effluent from a population of 97,000. Once treated, the water is discharged into the Klarälven River and Lake Vänern. Meanwhile, raw water is taken from the lake and used to produce drinking water.

Sludge is formed during the treatment of wastewater from organic material, nutrients and other substances that have been flushed down the drain. Sjöstadsverket is responsible for handling the sludge from Karlstad Municipality's nine treatment plants, as well as from private sewage systems. The sludge is then digested in an oxygen-free environment, where microorganisms break down the organic material. During this process, biogas is produced and upgraded for use as vehicle gas. The sludge itself can then be used as fertiliser.

'Our goal is for 100 per cent of sewage sludge to be approved according to the Revaq standard, which is more stringent than the legal requirements. The purpose of recycling sludge is to restore the nutrient cycle, particularly for elements such as phosphorus and nitrogen," explains Hanna Widalm, the environmental engineer responsible for Revaq in Karlstad Municipality.

Charlotte Bourghardt is the Project Manager for Circular Wastewater Systems at RISE:

"In the nearly 20 years since Revaq's establishment, there has been a significant improvement in the quality of sewage sludge. Today, farmers are confident about receiving sludge from Revaq-certified treatment plants. Revaq is a seal of quality," she says, continuing:

For Karlstad and the other municipalities, it has become clear that the better you control your operations and treatment processes, the more influence you have over your sewage sludge and the easier it is to achieve the desired results.

It helps businesses to identify substances that are being phased out.

Every spring, Hanna Widalm and her team at Karlstad Municipality draw up an action plan for the year ahead. This may involve running a certain number of information campaigns aimed at households or specific areas.

'We may also phase out products containing substances that have been phased out, such as those on the Swedish Chemicals Agency's PRIO list. We also have targets for sludge quality — we want it to be the best it can be," says Hanna Widalm.

Both households and businesses send their sewage to the Water Authority. Although both contribute to chemical emissions, they account for different types of pollution. Households are a source of everyday chemicals, whereas industries and businesses often account for more concentrated emissions of specific, environmentally hazardous substances.

"All priority operations in our municipality have been asked to compile a list of products that go down the drain. By examining the safety data sheets for these products and comparing them with lists of phased-out substances, we have identified what changes are required. Many products can be removed entirely or replaced with something that is less harmful to the environment," explains Hanna Widalm, continuing:

"Revaq places great emphasis on eliminating the emission of undesirable substances at source. We do not want these substances in our pipe networks, entering our treatment plants or ending up in the ground through sewage sludge or discharged with treated water."

Karlstad's neighbours are following in its footsteps.

The work of Revaq in Karlstad has increased. In autumn 2023, four neighbouring municipalities joined forces with Karlstad Municipality and hired a colleague to assist Hanna Widalm. The plan is for this new colleague to oversee the certification work in the smaller municipalities and continue the well-established upstream work alongside Hanna Widalm.

‘We also collaborate with other water and sewage companies, as well as municipalities, that face the same challenges as us. Everyone involved in Revaq is very helpful and contributes ideas and solutions. It’s great to have colleagues around the country to bounce ideas off,” says Hanna Widalm.

Maintaining Revaq certification requires continuous improvement. RISE conducts an on-site audit at Sjöstadsverket every year.

'In the first year, I was nervous and thought, "Now someone from RISE is coming to find faults with us". The following year, however, I realised that wasn’t the case; rather, it was an opportunity to drive the work forward. The auditors provide input that helps us find solutions. Although the audit day is long and tough, it’s also very rewarding,” says Hanna Widalm.