Gotland, Sweden

Technology performance and best practices

Decentralised membrane treatment

Without the NextGen solution for sewage treatment, no water would be reused. How much water could be recovered as a percentage of the treated flow is a key parameter for evaluating the direct potable reuse from municipal sewage. During the early pilot tests in Burgsvik, there was little impact related to a high recovery rate. This is positive since a higher recovery rate results in reuse of more wastewater for irrigation, infiltration to the groundwater water, or other uses. The tests indicate that the recovery rate for the UF RO combination could be at least 80 %.

The higher the recovery rate, the smaller the concentrate volume. At a recovery rate of 80 % the retentate will be 20 % of the original sewage volume, which reduces energy for pumping the concentrate, improves the efficiency for biological treatment (e.g. by anaerobic USAB technology), and improves nutrient recovery efficiency. Anaerobic treatment of the concentrate is estimated to lower the energy consumption by > 50 % compared to conventional aerobic wastewater treatment. Additionally, the biogas yield should almost double. The KPIs for reused water quality compare the RO permeate quality with the Swedish drinking water standard. More information about the results can be found in D1.3.

Innovative floodgate for storage of rainwater

Mjölhatteträsk is an example of where a ditching carried out during the 1950s lowered the lake to make use of previously soaked areas for arable land and grazing. Here, modelling has shown that recreating the previous level (about 20 cm higher than today's maximum level) would mean that just over an additional 200 000 m3 of water can be stored in the lake and would make a good contribution for a full-scale test bed that can produce 500 000 m3 of water for Gotland's drinking water network.

The implementation of an innovative floodgate for rainwater harvesting was evaluated to quantify the water savings, in terms of drinking water demand. The study shown that more than 100,000 m³ should be able to be stored in the lake and without the floodgate, this volume of fresh water would have flowed into the Baltic Sea via the ditch. More information about the results can be found in D1.3.

Real time measurements of the water balance

The Gotland study evaluated the same catchment surface and water storage as in the aforementioned rainwater harvesting system. Based on the results of the water balance measurements for Storsudret and the use of the systems, it was shown a system which could produce 450,000 m3 of drinking water and 100,000 m3 of irrigation water annually. Half of the annual drinking water supply would take place during the critical supply period from May to October. Irrigation water could be produced through collecting and storing rainwater to ensure the continued local commitment to the case study area Storsudret, which so far has been very large. More information about the results can be found in D1.3.

Outcome of assessments

Quantitative microbial risk assessment (QMRA)

At the case study in Gotland, the QMRA tool was used the explore the opportunity of implementing direct potable reuse from raw wastewater, i.e. wastewater is treated to the extent that it is suitable for human consumption in the absence of an additional environmental buffer. More details can be found in D2.1.

Legislation and policy recommendations

In NextGen, we analysed the policy and regulatory landscape to identify relevant opportunities for and barriers to upscaling circular economy in the water sector. Our recommendations, targeted at the revised Urban Wastewater Treatment Directive, are summarised in our policy brief. These recommendations focus on creating meaningful incentives and policy drivers towards circular systems (e.g., through energy and carbon neutrality targets, and additional guidance on water recycling) and simplifying the route to market for recovered products (e.g., fertilisers and other materials). Check out our policy brief.