Energy from water

Energy from water

When we think of green energy, we often think of solar energy or wind energy. But energy can also be generated from water. Iv-Water is currently working on a series of projects that focus on generating energy from water.

Sludge fermentation

Obtaining energy from water is no new concept for water boards. When wastewater is treated, sludge is collected and is often fermented, whereby biogas is produced. This biogas can be used in a combined heat and power installation (CHP). A gas engine powers a generator to generate electricity. The heat released in this process is reused to optimise the sludge fermentation process and to heat adjacent buildings at the treatment plant.
“This works differently at the Sleeuwijk Energy Factory,” Paul Kloet, Deputy Director of Iv-Water explains. “At Sleeuwijk, the sludge is collected from the nine surrounding wastewater treatment plants. Because of the size of this operation, a large amount of green gas is produced with the help of sludge fermentation. Given the scale of the treatment plant, it was an attractive option to upgrade the quality of the gas to that of natural gas to make it suitable for consumption by third parties. In fact, the water board has become a gas supplier, which places high demands on the operational management at the wastewater treatment plant. There are many other aspects related to safety which must be considered.” In Sleeuwijk, approximately two million cubic  metres of natural gas is now produced per year. This is undoubtedly an exciting project in light of the objective for the Netherlands to be natural gas-free by 2050. Iv-Water provided the integral design of the Energy Factory and supported the water board with the land permit application. In addition, Iv-Water took care of the start-up and coordinated the entire installation’s technical process.
The Dutch water boards produce approximately 125 million cubic metres of biogas. This is approximately 17% of the biogas production in the Netherlands; currently, only a small portion of this biogas is upgraded to green gas for external consumption.

Thermal energy

Sludge fermentation is not the only way to produce energy from water. Aquathermal heat is another variant. After all, water is a crucial carrier of heat and is suitable as both a transport medium and an energy source. Aquathermal technology can heat and cool buildings using heat and cold recovered from surface water, wastewater, or drinking water. If necessary, heat extracted from the water can be stored in subsurface reservoirs and upgraded with a heat pump when necessary. This type of centralised heat generation requires a heating network to transport the water to the adjacent buildings. A ’Green Deal’ was concluded in 2019 to encourage initiatives to use these types of heat sources.
“Iv-Water is involved in several projects related to heating networks,” says Paul. “The water temperature of, for example, effluent (treated wastewater) has a constant temperature of 10-15 degrees Celsius, by using an electric heat pump, this heat can be extracted. This heat can be used to heat another medium to around 45 degrees Celsius, making it ideal for heating buildings and processes.”
Aquathermal heat is used at the Sleeuwijk Energy Factory as an alternative heat source for the fermentation process. The energy here is not gained from waste but from the heat of the supplied wastewater. Thanks to this initiative by our Project Manager Ronny Faasen, we avoided construction hindrance in the context of unexpected restrictions resulting from the nitrogen problem (Programma Aanpak Stikstof or PAS). Through this alternative, using a portion of the biogas to provide heating was no longer necessary, meaning that approximately 10-15% more green gas can be produced and supplied. In this specific project, a heat pump with an output temperature of roughly 70 degrees Celsius was chosen. There is a drawback to this method of heating because wastewater is not continuously supplied to the installation. By introducing a small buffer, the hydraulic fluctuations in the day/night pattern can be appropriated, continuously supplying the sludge digestion process with the required heat.

Other high-quality heat sources can also be applied, but then the source is usually residual heat from an industrial process or geothermal energy.
“Iv-Water is currently involved in a Vattenfall project via Inenergie.” Paul continues, “This project concerns the coupling of low-quality and high-quality heat sources, using a robust heat network with high availability. This project aims to bring heat and cold from multiple sources to a single distribution station. It concerns a combination of heat, and cold storage (ATES) supplemented with district heating. We are currently working on the design and determining the space required for the installation and it’s requirements. Vattenfall attaches great importance to safety.”

Creating a source

It sounds straightforward, extracting energy from water, but is it? Paul explains: “With sludge fermentation, a certain scale has to be achieved to make it lucrative. There are many stakeholders involved to ensure the achievement of a sound business model. Besides this, these types of projects often have a major impact on the surrounding environment. It’s not just about fermenting the sludge and the associated control measures to prevent the risk of explosion. Collecting sludge from different treatment plants creates more transport movements and impacts the surroundings.”

“With thermal energy, it’s even more complex to organise. Creating a source close to the end-users is, in many cases, a significant challenge. Direct proximity to a sufficient capacity of wastewater, effluent or surface water is essential for this. Moreover, most existing homes are built for being heated by high-temperature sources. These new low-grade heat sources are therefore much more suitable for new builds. The use of Aquathermal heat, therefore, requires intensive exploration for the feasibility.”

Energy neutral

The energy transition is an essential theme for the water boards. Most water boards aim to operate energy-neutral in the long term, and some aspire to achieve this by 2030. “For the future, there is no single solution in terms of energy source choices,” Paul continues. “Energy from water provides a good contribution to the energy transition. But replacing fossil fuels will have to be covered by multiple sources. Which source will always depend on the best solution for the location and situation in question. We examine every option integrally; customisation will always be a part of it.”