- Industrial wastewater is a major polluant: it contains chemicals, metals and salts. But more than 40% of industrial wastewater is untreated when discharged into the natural environment.
- Solutions to better treat wastewater include cooling methods to separate salts from water, using bacteria to clean water or using saline wastewater to create energy.
Europe abstracts around 243 billion m3 of water every year to drive its economy according to the European Environment Agency. Industry accounts for about 40 % of that total. “In itself, water usage isn’t an issue,” points out Kitty Nijmeijer, a membrane materials researcher at the Technical University of Eindhoven. “The problem is really the volume of wastewater produced.”
In fact, more than 40% of industrial wastewater is untreated when discharged into the natural environment, despite the fact chemicals, metals, animal proteins, salts and clean water are all valuable recoverable resources and wastewater is a major pollutant. “Without separating potentially valuable components like semi-rare metal or chemicals from wastewater, it’s of no use,” Nijmeijer notes. As a result, Europe’s per capita water resources decreased by 24% between 1960 and 2010.
Against that context, Technologist presents four projects challenging the inertia around wastewater treatment.
1. Separating salts
Chemical contamination may be the most common environmental hazard associated with wastewater, but the impact of salinity is almost as damaging. When brine is dumped into rivers, it disrupts aquatic ecosystems, degrades soils and damages crops. The most sustainable way to utilise saline wastewater would involve retaining onsite for use in further industrial processes, but salt is highly corrosive to machinery, so it must first be removed from the equation.
Cool Separations, which span out from the Delft University of Technology in 2009, has harnessed eutectic freeze crystallization (EFC) – the point at which ice and salt crystals are formed when cooled – to create a crystalliser machine that effectively treats saline wastewater. Traditionally, evaporator machines raise wastewater to high temperatures to separate salt from water, but this consumes a lot of power and generates too much chemical waste run into corrosion problems. This new crystalliser offers low-energy, low-temperature alternative to existing evaporator solutions and outputs clean water and high-purity dry salt that can be used commercially.
“The big advantage is that we don’t require a heat source,” notes Rob van der Meij, the company’s CEO. “Cooling is 30-40% more efficient than evaporation and the process is emission-free.”
The need for salt water disposal exists everywhere, from refining chemicals in the South African mining industry, to recycling fertiliser material in Europe’s farming sector. Cool Separations current partnerships extend to engineering giants Jacobs Engineering and MPR (USA), and multinational water treatment specialists Proxa.
2. Using less water to clean chicken feet
While beef is a well-known offender in terms of its high water consumption, needing 15,415 litres per kg of meat produced, chickens require a substantial 4,325 litres per kg each. Chicken feet are a popular product on the Asian export market, requiring yet more water, meaning the environmental costs start to add up. Against this context, researchers from DTU’s National Food Institute set out to optimise the feet washing process.
The team discovered that water used in the last rinse of a batch of chicken feet can be cleaned using filtration, then reused in the first wash of the next batch. This ability to reuse water reduces consumption by nearly 50%.
In dialogue with the Danish Veterinary and Food Administration, the researchers investigated the regulatory and microbiological challenges, concluding that treated water is unlikely to contain disease-causing microorganisms. However, more research is needed to determine whether the water has sufficiently low chemical traces. The research has been conducted alongside Danish food producers within a public-private partnership, so prospects of commercialisation are high if water purity does meet standards.
3. Bacterial biofilters
The most sustainable forms of water treatment exploit natural phenomena. The iMETland project, led by Abraham Esteve-Núñez from the Madrid Institute of Advanced Studies, has developed and validated the full-scale application of an eco-friendly device that treats urban wastewater from small communities at zero-energy operation cost.
The team developed large basin-like units filled with artificially constructed wetland, including species like reeds and papyrus. The researchers (who work across four EU countries, as well as Argentina, and Mexico) have used the system to remove water impurities at a rate 10 times higher than techniques that don’t include these electroactive and conductive elements.
Electrons run through the biofilter material, creating a current that allows microbial communities to interact with one another at distance. Optimising this ‘electro-talking’ amongst the microbial community enhances their efficiency in cleaning the water.
The intensity with which the electroactive bacteria’s metabolisms convert pollution into electricity is remarkable. “The electroconductive material used in our system shows an unlimited capacity to accept electrons, so bacteria can keep eating pollutants at a higher rate,” project coordinator Dr Abraham Esteve-Núñez explains. “Metland is already a registered brand and the concept is ready to reach the market through a start-up called METfilter, founded for this specific purpose.”
4. From wastewater to blue energy
The usual paradigm around wastewater is to separate clean water from components and impurities, but imagine if the saline water could be used to generate energy? “At the interface of fresh water and saltwater, you can generate energy,” explains Kitty Nijmeijer from the Technical University of Eindhoven.
This phenomenon, known as Blue Energy, is one of the most under-exploited sources of renewable energy. Salt solution and freshwater contain negative and positive charged ions. As they flow through a stack of alternating cathode and anode exchange membranes, they generate voltage. Nijmeijer’s pioneering research led to the construction of the first blue power plant in the world, on the Afsluitdijk, a 90m-wide dam that separates the Zuiderzee (a salt water inlet of the North Sea) from Ijsselmeer (a large freshwater lake in the north of the Netherlands). The total quantity of electricity that could be generated on the Afsluitdijk could power 500,000 households annually.
The implications are far reaching, suggesting that brine from desalination plants could be mixed with low salinity effluent from power plants or data centres to produce energy. About 80% of the current global electricity demand could potentially be covered by this energy source.