Using Ozone To Remove Micropollutants From Wastewater
By Dan Johansson, Susanna Rehn Hedlund, Primozone
Micropollutants in our wastewater are a growing problem and so is the concern for the long-term hazard to the ecosystem. The effects of these contaminants have been investigated in many large-scale studies over a long period of time, and the results are worrisome. Today’s wastewater treatment plants are not built to remove these pollutants. But there are solutions available.
Micropollutants are contaminants that are persistent and bioactive, which means that they are not completely biodegradable and cannot be removed with conventional water treatment technologies. The continued release of micropollutants with wastewater effluent is believed to cause long-term hazards as the contaminants are bioaccumulating and even forming new mixtures in our waters. The exact effects of micropollutants in our environment are not fully known.
The ecological impact of a specific group of micropollutants, called endocrine disrupters (EDCs), is known to a larger extent. Endocrine disruptive compounds may interfere with the endocrine, i.e. hormone system of humans and animals. Studies on different species of fish have shown a negative effect on the reproductive system (for example feminization of male fish) and alteration of behavior that may ultimately change the natural evolution of these species. But in the short run the declination of the population is the most urgent negative effect.
Pathways To The Water
Hazardous micropollutants end up in wastewater treatment plants usually as a result of domestic uses of textiles, electronics, pharmaceuticals, and cosmetic and hygiene products. Other sources are industrial discharge, storm water runoff from cities and surface runoff from agricultural areas. Studies show that 70 percent of the pharmaceutical residue in the wastewater comes from household use, while 20 perecent comes from livestock farming and only 5 percent from hospital effluent, although variations might be large in different regions and countries.
Reducing micropollutant concentrations requires a long-term strategy.
According to Rik I. L. Eggen et al (Reducing the Discharge of Micropollutants in the Aquatic Environment: The benefits of upgrading Wastewater treatment plants) there are currently 100 000 commercially registered compounds in Europe and residue from the majority of these will eventually end up in the water cycle. Furthermore the production of chemicals is predicted to increase.
There are at least two different approaches that need to be adopted to reduce concentrations of micropollutants in the long run: source control and end of pipe removal. Source control is a long term measurement that includes prohibiting toxic contaminants and promoting green chemistry. When it comes to pharmaceuticals, prohibition of effective drugs is an ethical dilemma as both humans and animals may rely on these for their survival. End of pipe solutions, ie waste water treatment, will thus also in the long run be of high importance.
Within the European Union, legislative action is taken and a list of prioritized substances that are seen as a threat to surface and ground water has been published. To live up to the environmental standards laid out by EU, member countries needs to monitor the prevalence of the substances on this list, starting in September 2015. (Directive 2013/39/EU (priority substances in the field of water policy) and Directives 2000/60/EC (Water Framework Directive))
Switzerland is one step ahead and has already decided to reduce micropollutants and toxicity in their wastewater. They have decided to upgrade its 100 WWTp’s (which represents about 50 percent of the municipal wastewater in Switzerland) during the next 20 years.
Available Water Treatment Technologies
Conventional biological as well as mechanical water treatment methods are not sufficient for reduction of micropollutants. This is mainly due to the fact that the objectives with traditional wastewater treatment is to protect receiving waters and therefore focuses mainly on removal of organic compounds, nitrogen and phosphorus.
For reduction of micropollutants, traditional water treatment plants need to add an additional barrier with advanced water treatment technologies.
There are several available technologies that have been proven to work. According to Rik I. L. Eggen et al (Reducing the Discharge of Micropollutants in the Aquatic Environment: The benefits of upgrading Wastewater treatment plants) the large scale studies that preceded the Swiss decision suggest that ozonation and powdered activated carbon (PAC) are the technically most feasible methods. Both methods, according to the above article, reduces the load of broad range micropollutants with over 80 percent and should be followed by a polishing step such as sand filtration to eliminate any bioavailable oxidation products and particles.
The cost aspect is also important and in Switzerland they experience the cost to be more or less the same for these two technologies. Studies in Sweden suggests differently (Läkemedelsrester i Stockholms vattenmiljö. Cajsa Wahlberg et al). They have found that the cost for ozone treatment is 50 percent lower than the cost for PAC treatment.
New Governmental Founding For Swedish Research
In early 2014, the Swedish government announced that they are dedicating 32 million Swedish kroner (3.5 million Euro) over the next four years for the facilitation of advanced water treatment technologies for wastewater. On behalf of the government the Swedish Agency for Marine and Water management awarded 10 million (1 million Euro) Swedish kroner of this money to six different projects.
The Swedish water treatment company, Primozone, is providing ozone generators and ozone knowledge to several of these projects.
Earlier this year Primozone built a mobile pilot scale ozone system for removal of pharmaceutical residue. The aim was to be able to prove the concept on existing wastewater treatment plants and to test and confirm the system design on different water flows and environmental conditions.
This mobile ozone plant is used by one of the projects and makes it possible to collect a large number of samples from many different wastewater treatment plants as opposed to conducting a longer pilot installation at one water treatment plant. The approach is unique and the benefits are the possibility to compare samples from wastewater treatment plants that differ in size, treatment methods, process technology, and population structure, and all this during a short period a time.
When Will Theory Come Into Practice?
Much effort has been put into studying the effects of micropollutants in the water cycle. Even more studies have been performed on how to tackle this problem at wastewater treatment plants. Switzerland has been brave enough to put theory into practice. Other countries will follow, the question is when. The limited access to fresh water is creating great problems in different parts of the world already. The water scarcity will increase the need for reusing wastewater for drinking water purposes. We know for a fact that the load of micropollutants in our wastewater will increase, but so far we are not completely aware of the impact of the bioactivity of the contaminants in our nature. For how long do we dare to wait before we take action? The solutions are readily available and the cost is surprisingly low.
About The Authors
Dan Johansson, specialist in municipal water treatment at Primozone, Sweden. Co-author Susanna Rehn Hedlund, Market Communications, Primozone.