University of Tartu: Water-Sludge-Energy Cooperation Model

Introduction and background

In today’s climate conscious society, the pressure of climate change lays heavily on most sectors and businesses. While consumers can influence most businesses indirectly by their shopping behaviour and expect companies to adapt to climate neutrality in order to keep their customers, municipalities are often held in different respect and expected to be the forerunners of climate mitigation. As the wastewater treatment plants (WWTPs) are one of the largest sources of greenhouse gases under the municipalities management, significant changes are expected from the sector.

Historically the aim for wastewater treatment has always been to clean the wastewaters to acceptable quality in the most financially feasible way. Very expensive technologies are not used, as the price of wastewater treatment is paid by the public and their collective interest has been towards the cheapest available options. At the same time, the list of substances WWTPs are required to keep an eye on has become significantly longer – from organic carbon, nitrogen and phosphorus compounds to heavy metals, specific organic substances, pharmaceutical residues etc. The standard of what we now call “clean water” is completely different than 10 or 20 years ago.

To achieve this updated standard, new technologies and ideas must be taken into use. At the same time, total costs and financial feasibility is still the key factor. Many advanced technologies for example increase the electricity or chemical demand of the WWTP. Therefore, one way of mitigating some of the advanced treatment costs is to achieve good energy production in the WWTPs themselves. Larger WWTPs already use anaerobic digestion and utilise the biogas to produce either exportable biomethane fuel or electricity and heat. Increasing these productions could be a potential way to counter the increased costs of advanced treatment and some technologies could even kill two birds with one stone – increase energy production and degrade organic substances at the same time.

In order to move towards energy or climate neutral/positive operation or achieve better-quality effluents and sludge, large scale cooperation between different sectors is necessary. Good industrial cooperation can result in lower hazardous substance inflow to the WWTP and increased biogas production, cooperation with public can change the WWTP influent quality, reduce the amount of litter, microplastics and hazardous organic substances in the wastewater. Cooperation with other municipalities and WWTPs can make sludge treatment more efficient and increase the biogas production in the larger central WWTPs, decrease the amount of diluted stormwater inflow or provide good additional financial measures. In some cases, with political decisions some financially unfeasible technologies or approaches for the WWTP, could even be balanced with positive financial measures. At the same time the public could benefit from the production of biomethane for the municipal public transportation network.

Cooperation model

The BSR WATER project has collected expertise from the different associated projects and examples from good cooperation in the region. The Water-Sludge-Energy Cooperation Model is one of the planned outputs of the project, showing various ways the WWTP can cooperate with other industries, reach energy and climate neutrality and potentially save on costs. The model should be seen as an example outlining opportunities and highlighting possibilities for the near future.

Several Points of Cooperation are highlighted in the Water-Sludge-Energy Cooperation Model – points in the wastewater treatment where the addition or extraction of new liquid or solid streams or even energy production is possible. These points include wastewater influent (industrial influent, stormwater), influent to digesters, production of recycled fertiliser materials from water, sludge or incineration ash, heat energy production from different sources and even renewable energy production from unused land area at the WWTP. These points have been outlined through the BSR WATER partner meetings, where the possibilities for cooperation in the water sector have been discussed at length.

Each Point of Cooperation has several different recommendations attached, outlining different options for cooperation. Not all of the cooperation options are inherently positive for the WWTP, therefore each of the recommendations has following subsections:

• Recommended for – outlining which types or sizes of WWTPs could benefit from the recommendation
• Short description of the cooperation idea – explaining the idea in length
• List of important parameters to consider – listing important parameters and properties to consider with the recommendation
• Potential effects – showing common positive and negative effects the cooperation could result in
• Financial feasibility – evaluating the financial side of a recommendation if possible with current data
• Example – giving case examples and often links to the Smart Water HUB to provide information and contacts with different WWTPs and municipalities already benefitting from given recommendation.

The Water-Sludge-Energy Cooperation Model is currently in development and is planned to be published by Spring 2021. The document should be used as a guide to identify possible cooperation options for a specific WWTP, consider important factors and parameters and find good examples and potential sources for extra information around the Baltic Sea region. Only by learning from one another and cooperating can we achieve a climate-neutral environment for us and the future generations!

Markus Raudkivi
University of Tartu