March 5, 2018
In Sweden, the circular economy is already a reality. The REVAQ certification system, which started in 2008, recycles nutrients back to agricultural land
To ensure high quality digestate from the anaerobic digestion of sewage sludge in Sweden, REVAQ, a certification system, was established in 2008. REVAQ is operated by the Swedish Water & Wastewater Association, the Federation of Swedish Farmers, the Swedish Food Federation and the Swedish Food Retailers Federation, in cooperation with the Swedish Environmental Protection Agency.
Today, more than 50% of the population is connected to a waste water treatment plant (WWTP) that is certified through REVAQ and the number is growing. The work performed by certified WWTPs is focused on removing heavy metals and other contaminants before they reach the WWTPs, and ensuring the safe recycling of nutrients.
In 2008, the first 14 WWTPs were certified through REVAQ. Today, there are 42, and every year, more plants are joining. The plants certified through REVAQ ensure that:
- The quality of the incoming waste water is continuously improved.
- Information is available about the treatment methods used and the quality of the digestate.
- The quality of the digestate fulfils requirements.
Excellent phosphorous source
One of the main drivers behind the creation of REVAQ is to increase the recirculation of nutrients in our society (Figure 1). Special attention is given to phosphorous, a limited resource, but also to nitrogen, micronutrients and organic matter which are important components of fertilisers and which contribute to soil quality improvement.
Phosphorus is given special importance due to Europe’s dependence on imported phosphate rocks. Today, mineral fertilisers containing 10.000 tonnes of phosphorus and manure containing 26.000 tonnes of phosphorus are used in the Swedish agricultural sector. In 2015, the REVAQ-certified digestate contained almost 3.000 tonnes of phosphorous, out of which 1.300 tonnes was used in the agricultural sector. If the entire Swedish population were to be connected to REVAQ-certified WWTPs and the acceptance for using WWTP digestate in agriculture further improved, more than 50% of mineral fertilisers could be replaced by digestate from WWTPs.
The future price of phosphorus and the volume of contaminants, such as cadmium, are expected to increase for mineral fertilisers due to reduced availability and quality phosphorous resources. The reasoning is that phosphorous rock is imported from outside the EU. It is a limited resource, polluted with cadmium, a hazardous substance.
There is no full-scale technology in place to remove cadmium from phosphorous rock. As supplies of phosphorous with low levels of cadmium run out, at the same time as the EU’s new Fertilisers Regulation introduces maximum cadmium limits in mineral fertiliser, there will be two options:
- Price increases as manufacturers turn to the limited reserves of phosphate rock with low levels of cadmium or producers of mineral fertilisers have to introduce technology to remove cadmium from the produced fertiliser.
- Increase the recirculation of phosphorous in order to ensure future food production for the growing world population. If the proposed Fertilisers Regulation would open the market to the phosphorus contained in sewage sludge of good quality, regardless of its form (compost, digestate, struvite or ashes), we could certainly have a sustainable source of phosphorus for the farmers.
Cadmium: one of our main challenges
Finding and eliminating cadmium sources requires a lot of investigation but also information campaigns promoting better consumer behaviour; for example, on what can and cannot be flushed. Another example is the specific type of paints used by artists, which contain high levels of cadmium. A proposed ban on cadmium in hobby and artist paints failed this year, though information campaigns targeted artists who use these paints, making them aware of the problem and stating that they should no longer flush paint down the sink.
Removal of organic contaminants
The most efficient way to remove undesired organic substances from the sewage system is to encourage reduced usage of specific compounds at the source, e.g. industries and services, either by legislation or information, or both. In the long term, it is important to influence amendments to laws and regulations controlling what substances are allowed to be used by various industries and which eventually end up in WWTPs.
Certified WWTPs identify where undesired compounds are used, and in cooperation with local environment authorities, the identified industry actors take action so these compounds are removed from their process and from the sewage system.
The Swedish Chemicals Agency has a list of 2.500 substances whose use should be phased out by industry. The WWTPs also have the right to express their opinion when new companies apply to start up activities in their area so as to avoid the establishment of companies that will pollute sewage.
During 2015, most of these 2.500 substances were no longer used. The general impression from REVAQ’s work is that cooperation with the industries causing the pollution in the first place usually goes a long way to solving the overall problem.
The Swedish REVAQ certification system was launched in 2008 to coordinate and strengthen the WWTPs’ systematic work with control-at-source and the elimination of contaminant sources by laying down strict requirements on the reuse of nutrients in sludge on agricultural land.
REVAQ certification is the result of long term cooperation between stakeholders in agriculture, the food industry, retailers and the water sector. The REVAQ certification system has shown that it is possible to simultaneously build confidence, reduce contaminants and increase the recycling of nutrients and organic matter by implementing a transparent and goaloriented cooperation between WWTPs and key stakeholders.
By Anna Linusson, CEO and Anders Finnson, Senior Environmental Adviser, Svenskt Vatten
Read more: Water MattersAuthor : EurEau