Synthetic flocculants are produced in enormous quantities. These polymers are used to treat wastewater, dewater sewage sludge and harvest valuable particles which cannot easily be separated from water. The major disadvantages of such synthetic flocculants are that they are not sustainable, and may be carcinogenic and neurotoxic. The Environmental Technology Group within Wageningen University and Research (WUR) has partnered with the expertise centre Wetsus to look for sustainable alternatives to these synthetic agents.
Hardy Temmink is an associate professor at WUR, where he works with a team within his chair group on developing green flocculants. “We aim to cultivate microorganisms that purify wastewater and produce natural polymers during the process, which we can then use as flocculants,” he explains. The approach is showing considerable promise. “Two years ago we started with simple experiments on wastewater produced by the biodiesel industry. By varying the amount of nitrogen in the wastewater, we managed to convert 50 to 60% of the organic pollutants by mass into an effective mixture of biopolymers. The wastewater is also purified at the same time.”
Decreasing costs and energy consumption
Temmink and his group have reached the point where returns on their polymers are at least as good as those achieved by synthetic flocculants. The technology has also been shown to work in saltwater with bacteria and polymers that are adapted to salty conditions. It is important, however, that the waste water, whether fresh or salty, is still treated in a highly effective way. Another important advantage is that their method does not require pumping in a lot of oxygen to kick-start the conversion process. In other words, the new technique is doubly advantageous, Temmink concludes: “You save money and energy on the treatment side, while producing a useful end product.”
Interest from the business community
There is a great deal of interest in the new technology, Temmink notes. “We are talking with partners from a range of sectors, from dredging to wastewater treatment, and even a company in the food industry. Possible, one of the polymers produced is. Alginate is a food ingredient that is currently mainly extracted from brown seaweed, which is highly sensitive to weather conditions and therefore difficult to grow. Our technology could ensure a well-controlled production flow in the future. Of course, that would imply the use of a cleaner source of organic matter than wastewater.”
Binding heavy metals
Further research is focusing on two tracks. One is basic research: for example, investigating which mixtures of flocculants are the most efficient. The other is practical applications. “A specialised process needs to be developed for every wastewater or surface water stream,” Temmink states. “Tests have also shown that our flocculants are very effective at binding heavy metals. One gram of flocculant can bind more than a gram of lead, which can subsequently be separated and extracted. This creates a concentrated stream and prevents the lead from getting into surface water.”
Great interest in the US
Temmink’s green flocculants have also attracted attention in the United States where Wetsus, WUR and the Delft University of Technology are competing for the George Barley Water Prize, founded to find ways to solve the issue of excess phosphorus in freshwater and protect the Florida Everglades. “Half of the phosphorus there is found in the form of particles, which we are hoping to remove with our flocculation technology,” Temmink explains. “For the phosphate dissolved in water, an adsorption technique developed by TU Delft is used. We have now passed two rounds and collected €75,000 in research funding. If we win the next round with a pilot installation, we will receive $200,000 that we can use to bring the technology to market.