TKI- Wetlands as pre-treatment for mild desalination
Dow, Evides and HZ University of Applied Sciences are working on a TKI subsidized project aiming to investigate how a combination of wetlands as pre-treatment and desalination processes can effectively remove micro-pollutants, nutrients and salinity from wastewater treatment plant effluent. The hypothesis is that wastewater treatment plant effluent is one of the most difficult streams to treat for removal of micro-pollutants and nutrients, so if it can be achieved on this stream then it can also be applied to other streams such as (brackish) surface water. It is believed that the micro-pollutants will be adsorbed in the root zone of the wetland vegetation and the nutrients will be taken up by the plants, meaning that the remaining impurities such as salts are removed with a combination of ultrafiltration (UF), ion exchange (IX) and reverse osmosis (RO).
Research on the wetlands alone is carried out independently from summer 2019 to summer 2020. Research on the “brackish water line”; namely the treatment train consisting of ultrafiltration, ion exchange and reverse osmosis in sequence, began in January 2020 and will run until summer 2020 when the wetlands will be connected to the brackish water line as a pre-treatment step. A polishing step such as a mixed bed which would be needed to achieve demi water quality is out of the scope.
The influent water used in the research consists of effluent from a local Membrane Bio Reactor (MBR) and effluent from an industrial wastewater treatment plant (Biox). These influents will be tested separately and also as a mixed stream, with and without wetland treatment.
Student Experiences
Louis Johnston: Aquatic Eco-Technology
As part of my 3rd year studying Aquatic Eco-Technology B.Sc. at the HZ University of Applied Sciences, I was offered an internship at DOW Benelux on a new pilot project looking to reduce the company’s reliance on fresh water taken from the Biesbosch. I applied for the internship because I wanted to gain more of an insight into DOW’s operations as a global company and sustainability activity. Furthermore, I wanted to establish how such a global company acts on its sustainability goals and how easily environmental issues can be made economically viable.
The pilot project at DOW explores the reduction of the company’s reliance on Biesbosch water (currently at 20%) on a pilot scale, with the goal of running a full scale system once optimization of the treatment steps have been fully explored. The company objective is to reuse 100% of used water by 2025, with a constructed wetland as the first pre-treatment step.
My role between September 2019 and January 2020 consisted of optimizing and maintaining the wetland before its connection to further pre-treatment pilots in June 2020. Over 4 months, I encountered troubleshooting difficulties, carried out dissolved oxygen tests, tracer tests, and performed daily grab sampling, comparing the COD and NO3 with the analyser results to test reliability becoming an important task. I also monitored the dissolved oxygen, temperature, pH, flow, and total suspended solids of the wetland, reporting weekly and monthly to the larger team.
Upon comparing myself to when I first started at DOW, I can see that I have gained important professional qualities which will be incredibly useful in the future. Students from UGent and TU Delft, Evides, lecturers from the HZ, and companies in the construction industry were all involved with this project created a very dynamic working environment. I was able to realise the importance of what I was doing and the responsibility that I had, and could then find a way to support the team whilst gaining a great deal myself. I am thankful for the opportunity.
