Wastewater as a Resource

“Everything supposed to be green is dried up and brown!” – The astronaut Alexander Gerst was shocked when he saw the drought in Germany in summer 2018. Kompetenzzentrum Wasser Berlin (KWB) is working on local solutions to a global problem.

At 19.2 degrees Celsius, the temperature in Germany was nearly about three degrees Celsius above the value of the years from 1961 to 1990, according to the German Meteorological Service. Thus, the summer of 2018 was the third hottest since regular measurements started in 1881 – and also the third driest.

In future, climate change will probably lead more often to what was previously considered an extreme summer in the Federal Republic of Germany. One consequence of this is water stress. International comparisons speak of this when 20 or more percent of the available water resources is used. Kompetenzzentrum Wasser Berlin (KWB) is working on a series of projects to prevent this water stress. Wastewater plays an important role here. It is itself a reusable resource from which other valuable materials can also be obtained. Based on new research results, it can create regional water cycles that improve local life and help mitigate climate change.

Agriculture needs and consumes the most

The biggest consumption of our global freshwater resources is down to agriculture. In addition, more than a quarter of energy worldwide is used in the production and supply of food. “The critical areas of water, agriculture and conventional energy generation are inseparable,” says engineer Dr Ulf Miehe. “We take that into consideration in the way we conduct our work and arrive at new, integrated solutions.” The European Commission proposed new rules in 2018 to facilitate the re-use of water for agricultural irrigation. This should help farmers make the best use of purified wastewater so as to reduce the shortage of water, whilst protecting the environment and consumers at the same time. “The minimum requirements formulated by the EU will promote the re-use of water in agriculture, even if there are still reservations in some Member States,” says the KWB divisional manager for process innovation. “Using different approaches, our research projects are delivering the know how to release hitherto untapped potential in the future.”

Site visit of a constructed wetland for wastewater treatment for water reuse, AquaNES project; Antiparos, Greece

The AquaNES project, for example, has demonstrated the advantages of combining natural and technical water treatment processes in real operation at 13 test sites worldwide. The natural systems are bank filtration, groundwater recharge and constructed wetlands, which are combined with different technical pre- or post-treatment processes.

The project has involved 30 partners from Europe, Israel and India. “We have brought together various methods in Berlin: on the one hand ozonation with a natural post-treatment for the elimination of trace substances at the Schönerlinde site,” explains Miehe. ” On the other hand, at the Tiefwerder Waterworks location, we have examined the combination of bank filtration with nanofiltration for sulphate and trace substance removal.” In addition to the work in Berlin, Kompetenzzentrum Wasser Berlin has coordinated a work package on combinations of sewage treatment plants or retention ground filters with various technical systems. The trial sites are located in Germany, Great Britain and Greece. “Here we havetested with a view to practicality,” says Miehe, “to see how plants like this can comply with the various limit values in the EU Member States.” The results of the project, which ended in 2019, are included in the planning of the large-scale ozonation system at the Schönerlinde sewage treatment plant.

Sewage treatment plants to power plants

In 2018, the POWERSTEP project was devoted to the energy aspect – and in a big way. The initial situation is that Europe’s sewage treatment plants use as much energy as two large-scale power plants produce. Here, the organic fraction of urban wastewater in Europe contains a chemical energy totalling 87,500 gigawatt hours per year, which corresponds to the output of twelve large power plants.

“Recent studies show that wastewater treatment plants can become a renewable energy source through innovative methods without compromising purification,” says engineer Dr Christian Remy, research assistant at Kompetenzzentrum Wasser Berlin. POWERSTEP has demonstrated novel concepts like this for every significant process stage on an industrial scale. “On this basis, with the technologies currently available, sewage treatment plants can be designed that they even deliver energy.” This is made possible, among other things, by improved carbon extraction, new methods of removing nitrogen, power-to-gas technology in conjunction with an smart power grid and efficient use of waste heat.

Currently Kompetenzzentrum Wasser Berlin will be examining new process variants during ongoing operations within the scope of E-VENT. The project will optimise energy use at the Berlin sewage treatment plants. Prior to the examinations, measures were being taken to save energy. In addition, the plants use the biogas produced during the treatment process to generate power and heat. Even so, the average annual electricity consumption of all six Berlin sewage treatment plants still amounts to more than 90,000 megawatt hours, which in the same period leads to greenhouse gas emissions of 40,000 tonnes. “On the test bench are alternative methods to remove nitrogen and carbon, as well as to increase the biogas yield in the sludge treatment,” says Remy. “For some of the options we are testing, data are already available from previous KWB projects, which will be transferred to the process conditions of the large-scale sewage treatment plants as the next step. We are currently testing two promising methods under real conditions.”

Sustainability means that things run smoothly

The central theme in the water industry, as in agriculture, is to operate in cycles. In organic farming, for example, an attempt is made to minimise the consumption of finite resources. Sustainability here means closing regional nutrient cycles as far as possible, which has so far not proved sufficiently successful. This applies in particular to the nutrient phosphorus, an essential component of many fertilisers. “A lot of progress can be achieved here with the recovery of nutrients from biogenic, renewable wastes such as sewage sludge,” says Remy. The nurec4org project, completed in 2018, looked at the extent to which phosphorus-containing products that can be produced using currently available recycling processes are accepted in organic farming and are licensable. The Kompetenzzentrum Wasser Berlin researchers gained scientific knowledge which is now being made available to German and European licensing bodies. “The European regulation governing organic farming can be modified on this basis, ” says Remy. “Farmers, trade and science were involved in the investigations as key players.”

Heat management at WWTP in Copenhagen

Our researchers also keep their eye on the future. The EU project SMART-Plant which will run until 2020, is testing existing technological approaches to resource recovery in wastewater treatment plants on a large technical scale.

Seven pilot systems are being optimised at five sewage treatment plants throughout Europe over a period of more than two years and tested under real conditions, along with two technologies for processing recyclable materials. Biopolymers (e.g. for the production of biodegradable synthetic materials), cellulose, plant nutrients and fertilisers were recovered and processed into commercially usable end products. “It will take a few more years until it is widely used in practice,” says Remy. “But with these tried and tested solutions, which are energy efficient and ecologically efficient, we can close the value-added chain – and thus achieve recycling.”

 Teaser Picture © Abwasserverband Braunschweig