New solutions: sustainable sewage sludge treatment
Step by step, Germany is phasing out coal, with renewable energy taking its place. There has long been a general consensus that sustainable strategies are needed to help shape this transformation – and ensure that future generations inherit an environment worth living in. Since 2012, EnBW has already parted with around one third of its carbon-intensive generation capacity and wants to phase out coal at its remaining sites by embracing more climate-friendly fuels in a first step (known as a fuel switch) and then making them emission-free operations – by using green hydrogen, for example.
As there will soon be an ever dwindling number of coal power plants, new solutions must also be found for other important aspects of daily life. Like sewage sludge, for instance. Every year, people in Germany produce between seven and eight million tons of sewage sludge – taking a “detour” via the sewage treatment plants. This is where the wastewater from the cities and municipalities is purified. What remains is the sewage sludge, which in many cases has hitherto been disposed of by incinerating it in coal power plants in a simple but unsustainable manner. Since these will soon no longer be available for this purpose – even though the sludge also contains valuable phosphorus – a new sustainable disposal and recycling method is needed.
That is why the first sewage sludge recycling plants have already been built in Germany in recent years, with many more set to follow. This is because proximity is important in order to avoid having to transport the waste product across the country by truck. The state of Baden-Württemberg currently estimates that up to six new sewage sludge incineration plants will be needed by 2029.
Efficient and emission-free: modern sewage sludge incineration plants
Modern sewage sludge incineration plants are virtually emission-free and produce sewage sludge ash with a high phosphorus content as a residual product of the incineration process. It is used as a raw material in the manufacture of vital phosphorus products such as fertilizers.
Fertilizer plays a key role in agriculture and has hitherto had to be completely imported in Germany. For this reason, legislators have decided that from 2029/2030, sewage sludge must be used to recover phosphorus. To this end, the ash produced during incineration will be transported to a special plant, where the phosphorus is recycled.
A forward-looking plant of this nature is set to be built in Walheim in the form of a state-of-the-art sewage sludge combined heat and power plant on the current site of the coal power plant. In turn, parts of the coal power plant will be dismantled. The project is set to be accompanied by a wide range of concepts aimed at promoting e-mobility and generating sustainable heat, to name but two examples. As such, the sewage sludge combined heat and power plant in Walheim is expected to play a key role in a sustainable energy transition, while supporting local interests and thus attracting attention far beyond its regional borders.
Phosphorus: an important raw material for agriculture
Sewage sludge contains phosphorus and nitrogen – important nutrients for crops in agriculture. However, the waste product from our sewage treatment plants also contains substances that should not be introduced into the soil in an uncontrolled manner, such as microplastics and organic pollutants.
The new regulation should now ensure that phosphorus is recovered from sewage sludge – it applies to cities and larger municipalities from 2029 and to smaller municipalities with their own sewage treatment plants from 2032. They must all ensure that up to 80 percent of the phosphorus is recovered – in other words, recycled – from the sewage sludge or its ash.
Phosphorus is vital to all biological organisms and is involved in the function of key areas such as DNA and the supply of energy to cells. It enters the soil naturally by means of weathering on the one hand or through the decomposition of organic matter on the other..
Artificial fertilizers used in agriculture increase the soil’s phosphorus content in order to improve growth and yields. The spreading of sewage sludge on the fields – which contains phosphorus, among other things – has the same function. Since the agricultural use of sewage sludge has now been severely restricted by the German Fertilizer Ordinance (DüMV) due to the aforementioned pollution, there has also been a drop in the amount of phosphorus that is introduced into the fields.
Eighty percent of the mineral deposits containing phosphorus are located in Africa, China and the USA. Germany has no noteworthy deposits and has to import 100 percent of its phosphorus. Recycling is therefore necessary in order to meet increasing demand on the one hand and embrace the concept of sustainability on the other. After all, phosphorus is an important substance. It is obtained from a waste product of sewage treatment plants and helps us to reduce our dependence on phosphorus imports. Consistent recycling of phosphorus from all sewage sludge in Germany could replace up to 40 percent of imports..
Sustainable for Baden-Württemberg’s northeast
Until now, sewage sludge destined for incineration from northeastern Baden-Württemberg sometimes had to be transported over long distances to other states, such as Lippendorf near Leipzig in Saxony. The plant in Walheim will dispose of local sewage sludge in northeastern Baden-Württemberg in the future and is one of a whole series of plants whose future viability is set to be secured by means of further development with sustainability in mind.
EnBW’s sewage sludge combined heat and power plant in Walheim will provide a regional disposal option for municipal sewage treatment plant operators, meeting all legal requirements that will need to be taken into account in the future and constituting an important component for the safe disposal of such waste in the region
With an incineration capacity for around 180,000 metric tons of dewatered sewage sludge per year, the plant partly represents the region’s first step toward sustainable sewage sludge recycling, but also provides an optimal basis for the future recycling of phosphorus.
The heat generated in the plant can be used to supply local heating to nearby communities.