Simrishamn WWTP - Case Study
Removal of pharmaceutical residuals and micropollutants
The wastewater treatment plant Stengården in Simrishamn, Sweden, is the first full-scale installation of its kind after an expansion with additional advanced treatment steps, which includes DynaDisc, DynaSand, DynaSand Carbon and ozonation. The advanced treatment steps are designed for excessive removal of pharmaceutical residuals and micropollutants as a first potential step towards enabling reusability of wastewater in a region which suffers from seasonal water shortage.
Clean water scarcity is already a global issue which is further stressed by climate change and the ongoing constant pollution of the aquatic environment.
In 2015 the municipality of Simrishamn decided to take concrete actions for the water environment with the aim and objective of removing pharmaceuticals and hormone disturbing substances from the outgoing wastewater. Reduction of microplastics, antibiotics and harmful microorganisms was also within the project scope. It was decided to complement the old WWTP with additional advanced treatment steps. This was also seen as a first step towards making the water consumption in the region more circular. As the region has been facing seasonal water shortage in recent years, the possibility to reuse wastewater from the new WWTP by infiltrating it to the groundwater is under investigation. The project was partly funded by VINNOVA, with stakeholders in IVL Swedish Environmental Research Institute, Nordic Water, SLU and Xylem, even though the major investment costs were covered by the municipality itself.
Supplementing advanced treatment steps after the old final sedimentation basin were installed in a new building. The new configuration was constructed with three separate treatment lines to evaluate the impact and effectiveness of different separation processes in full-scale:
1) Adsorption through granular activated carbon (GAC).
2) Ozonation plus biofiltration.
3) Ozonation plus GAC-adsorption.
A DynaDisc was installed as a pre-treatment to all process lines in the new facility to remove excessive suspended solids and organic matter.
The first treatment line without ozone relies solely on adsorption to GAC in a DynaSand DS7000 2.0 Carbon. The other two treatment lines are led through an ozone contact basin before entering the DynaSand or the DynaSand Carbon.
Adsorption to GAC is a chemical process where a contaminant is fixated to the carbon if it collides with the activated surface. With each fixated contaminant the active surface area of the carbon decreases, i.e. the GAC gets saturated. The saturating time varies, but indicative regeneration or replacement of GAC is required after about 30 000 EBV (Empty Bed Volumes). Recent studies in other projects with DynaSand filters have however shown positive results in terms of creating a biological degradation process of pharmaceuticals, nearly as effective as GAC, established after about 20 000 EBV. Due to the origin of the water and the addition of oxygen to the system from ozone in two of the treatment lines, the expectations are to form a similar bacterial culture to continue achieving high reduction rates even when the GAC inevitably starts losing reactivity. As a result of a biological process, the GAC would not have to be replaced once saturated, which otherwise is a large cost and one of the main drawbacks.
The combination of ozone and the DynaSand Carbon provides the overall highest efficiency of pharmaceutical removal, on average above 97 % reduction with a fairly high ozone dosage, 8 mg/l. At a lower ozone dosage, 6mg/l, the average reduction decreases somewhat but still remains very high. The reduced energy consumption of each produced mg/l ozone is significant and should be carefully investigated. Even at low ozone dosages the average reduction rate stays above 80 %. Although the combination of GAC and ozone will result in the highest removal efficiency, it will also generate the largest investment. Biofiltration in combination with 8 mg/l ozone also resulted in a very high average reduction rate but will be more sensitive and respond more easily to a decreased ozone dosage. With only adsorption in the DynaSand Carbon, a moderate reduction rate was obtained, which would likely be increased with a finer mesh of the activated carbon. A GAC process without ozone will also be the smallest investment with the lowest overall running costs.
The overall WWTP reduction rates of microplastics were about 99.8 %.
Suspended solids escaping the final sedimentation were reduced by over 70 % by the DynaDisc. This also means a significant reduction of organic matter, which in turn results in less required ozone as more ozone can selectively react with pharmaceuticals. The removal efficiency of different pharmaceuticals and antibiotics for all three separate treatment lines is presented in the table beside.