Vallei en Veluwe is situated in the Netherlands provinces of Gelderland, Overijssel and Utrecht – it services an area of 37 municipalities, overseeing 1.1 million residents and more than 24 000 businesses. Ede is one of its main plants.
There is a growing concern about the release of micropollutants, such as pharmaceutical residues, pesticides and household chemicals into the environment. Since the current generation of technology employed by treatment plants don’t remove all of them, plant effluent becomes a major source of these micropollutants.
Whilst there are no European effluent standards for micropollutants getting into surface water, a special forum at the 2018 IFAT trade fair in Munich addressed the need for legislation to ensure a more comprehensive wastewater treatment strategy. Many viewed an additional fourth treatment step using new technologies as inevitable.
In the Netherlands, already some plants have been piloting several new technologies, whilst in 2018 government earmarked 60 million euros to regional water authorities for plant upgrades.
It’s further worth noting that the ministry of Infrastructure and Water Management is funding projects that remove micropollutants, if the removal efficiency (of 12 indicator substances) is raised to at least 70%. (A standard wwtp will only remove 30-50% of these substances.)
IFor especially Vallei en Veluwe, taking the initiative to advance wastewater treatment methods and gaining more insight into the implementation of innovative tech has become primary directives.
Micropollutants in the form of pharmaceutical residues with an increased life expectancy are central to the problem. In addition, and due to this age of climate change causing longer periods of no rain, there’s a rise of wwtp effluent and resultant concentrations of these micropollutants in many Dutch water courses.
For Vallei en Veluwe the challenge is twofold: how to further combat Ede’s effluent, whilst also minimising climate impact of the treatment technology chosen. The water authority subsequently approached Royal HaskoningDHV to help devise a solution – one that will also complement the plant’s current treatment process.
Royal HaskoningDHV’s engineers – with their extensive track record in consultancy and technology seletion for various projects – did a comprehensive study of the Ede WWTP treatment process and decided that ozonation, PACAS technology and cloth media filtration will augment current plant operations. .
PACAS (Powdered Activated Carbon in Activated Sludge) technology
PACAS treatment is a dynamic process incorporating two approaches. First, powdered activated carbon can be added directly to effluent tanks – this leads to a binding step followed by a filtration step.
As an alternate solution, powdered activated carbon can also directly be added to activated sludge. The activated sludge process uses a mass of organisms to aerobically treat wastewater and remove biodegradable organics. Overall, powdered activated carbon added to activated sludge can lead to a higher quality of treated wastewater and also significantly benefit the production of reusable water. For instance, the amount of especially pharmaceuticals in the treated wastewater is negligible – as little as a nanogram to a milligram per liter.
What’s more, many times it was shown that treated effluent is toxic to many aquatic organisms, and by decreasing the amount of pharmaceuticals the toxicity is also lowered. With current measuring methods to quantify toxicity, the effluent could be considered as almost non-toxic after treatment with powdered activated carbon..
In the Ede case particularly, cloth media filtration was further considered as an option to separate the carbon from the treated wastewater. One of the questions was whether cloth media filtration could be used to replace Ede’s existing disc filter..
Considering the technological setup and performance of the installation, it was decided that any of these solutions can be implemented. And of course, ozonation..
Using ozone to treat water goes as far back as the late 1800s and is well documented. Today its use has spread across the globe. Ozonation has become such a preferred technology because of its powerful oxidising effect – it removes as much as 99% of bacteria, and even pathogens and chlorine resistant cryptosporidium. .
Ozonation further reduces colour intensity, improves odour, and increases the biodegradability of wastewater. In fact, ozonation increases the ratio of COD/BOD by as much as 10 times. (The BOD to COD ratio is an indicator of the proportion of biologically degradable organic matter to total organic matter.).
Projected outcomes at Ede WWTP
Compared to standard treatment technologies, and besides ozonation, the two technologies selected – dosing of PAC and cloth media filtration – will use less resources, leading to a 20% lower CO2-footprint, which makes them rather environment friendly. Additionally, they will also remove more hazardous components such as microplastics. Do note that combining these technologies is a first for both Ede and the Netherlands.
The next step for Ede is a pilot trial of the technologies. With only favourable outcomes predicted, the future is looking promising with the prospect of more Netherlands wastewater treatment plants benefitting from implementing them.