DBU German Environmental Prize awarded to Dr Klaus Vossenkaul

European Union Urban Waste Water Treatment Directive: Sewage treatment works face radical change

Bonde speaks of  “new standards for wastewater treatment: the best water quality, minimal energy consumption and maximum space savings. This makes sewage treatment plants future-proof.”  These facilities across the European Union (EU), including hundreds in Germany, are facing a radical transformation: To better protect water bodies from micropollutants, the EU Urban Waste Water Treatment Directive – in German known as KARL for short (Kommunale Abwasserrichtlinie) – which came into force in 2025, must be implemented across the EU by the end of July 2027. It requires a highly efficient fourth treatment stage in addition to the three conventional mechanical, biological and chemical stages used to date. According to Bonde, Vossenkaul’s innovations make this technically and environmentally superior membrane technology cost-competitive with conventional wastewater treatment in both production and operation – now a bonus for many plants that have to retrofit due to KARL. “Vossenkaul’s membrane technology is a flexible modular system – and an elegant solution in the new KARL era, particularly where space is limited,” says Bonde.

Hollow-fibre membrane filters: as thin as ­spaghetti, as hollow as macaroni and 1.6 m long

According to Bonde, Vossenkaul has demonstrated “remarkable courage” through various start-ups in membrane technology. What sets Membion apart: After the company was founded in 2012, Managing Director Vossenkaul and his business partner, process engineer Dirk Volmering, focused exclusively for years on the further development of membrane bioreactor (MBR) technology. The result is hollow-fibre membrane filters: “Thin tubes that filter crystal-clear water from sewage sludge. They look like spaghetti, are hollow like macaroni and about 1.6 m long," says Vossenkaul. They are made from four types of plastic and, most importantly, have pores so fine that the membranes filter problematic substances out of the wastewater – including microplastics, pathogens and multi-resistant germs, as well as residues of medicines and cosmetics using activated carbon. These are just a few examples of the pollutants that burden the sewerage system and wastewater. They come from manufacturing, cooking, washing up, showering, toilets – in short, everything that is disposed of down the drain. A new approach to wastewater treatment via sewage treatment works is essential, says Bonde. “It protects humanity’s most important resource. Without water, there is no ‘us’. This is the best form of water recycling and the basis for ensuring, amongst other things, that crystal-clear water reaches reservoirs - the basis for subsequently producing vital drinking water in several steps", says Bonde. Vossenkaul’s achievement is “of enormous significance”.

Sludge and bacteria: a permanent feature of sewage treatment plants

Even before Vossenkaul’s ideas, MBR technology was already delivering water quality many times better than that of conventional sewage treatment plants. However, the high energy consumption required to flush the membranes – to prevent sludge blockages – often deterred sewage treatment plants operators from installing the system. Sludge and bacteria are a constant feature of sewage treatment plants: bacteria break down the constituents of the wastewater, making the water biologically clean. At the same time, they multiply, and the sludge accumulates. Excess sludge is disposed of, whilst the remainder remains in the treatment plant for the next cycle. There is no longer any need for circular tanks, as found in conventional sewage treatment works, where sludge sinks to the bottom and separates from the water. Instead, the membrane modules are submerged in the sludge, and the water – purified by bacteria – is extracted from the membranes, crystal-clear. It is not drinking water, of course, but it is suitable, for example, for agricultural irrigation. This conserves groundwater reserves, which are essential for drinking water treatment. The heatwave of 2026 demonstrated why this protection is becoming increasingly important.

Vossenkaul’s ideas are at the heart of Germany’s largest membrane sewage treatment plant in Wolfsburg

For almost five years, a pilot treatment plant in the Eifel village of Konzen near Monschau – equipped with both conventional plate-module membrane filters and Membion technology – has been demonstrating what is possible: a reduction of more than 90 % in energy consumption for flushing the membranes and a 75 % reduction in space requirements. Vossenkaul: “The sewage treatment plant operator stands to save a six-figure sum in electricity costs each year.” Membion technology is now in use at Collini, Europe’s leading electroplating company, as well as at McCain, the world’s largest producer of French fries, for treating potato wastewater. What’s more, it is set to become the centrepiece of Germany’s largest membrane wastewater treatment plant in Wolfsburg-Stahlberg: more than 1600 "macaroni" membranes are anchored in a base element and float freely, like seaweed, in enclosed, man-sized housings submerged in the sludge. In Wolfsburg, 3000 such base elements are being used. Vossenkaul’s ingenious solution: so-called "Geyser" elements clipped beneath the base unit, from which pulses of air propel the sludge upwards in a matter of seconds – thereby keeping the membrane pores clean and ensuring a long service life. Vossenkaul calls this "JetSplash" (water splash) – one of his 28 patents in total.

Up to 80 % the world’s 360 billion m³ of wastewater is discharged untreated into the environment

Nationwide, around 130 l of water are used per person per day in Germany – and as much as 7000 l if imported food, clothing and other goods are taken into account. This results in wastewater requiring treatment – in Germany, this is handled by some 8700 public sewage treatment plants, processing 8.3 billion m³ every year. Globally, the situation is dire: of the approximately 360 billion m³ of wastewater worldwide – four times the volume of Lake Geneva – up to 80 % flows untreated into the environment. Bonde: “There is a huge need for action on wastewater.” Its highly efficient treatment is increasingly becoming a lifeline for people and the environment: only around 0.3 % of the world’s total water volume – approximately 120 000 km³ out of a global total of 1.4 billion km³ – is fresh water available for human use. The rest is largely the salt water of the oceans or, as fresh water, locked up in the ice of the Arctic and Antarctic, amongst other places.