Evidence base for ecotechnologies in wastewater treatment
A global evidence base of ecotechnologies for the recovery and reuse of nutrients, carbon and energy from wastewater

Pollution of the Baltic Sea continues to be a problem. Important terrestrial sources of nutrient emissions to the Baltic Sea are: agriculture and wastewater – both major causes of eutrophication. However, the nutrients and organic matter in wastewater could also constitute valuable products, such as agricultural fertilizers and energy. Thus, the EU’s action plan for circular economy highlights the need for improving waste management and resource utilization.

The integration of resource recovery to wastewater management could provide benefits beyond the wastewater sector, turning the carbon and nutrients from pollution into products. We used systematic mapping methodology to identify a comprehensive list of studies that focus on ecotechnologies for recovering or reusing carbon, energy and nutrients (nitrogen and phosphorus) from wastewater, which includes for example, sewage sludge and wastewater fractions. Here, we present the evidence base visualized in an evidence atlas.

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How to use the atlas

The evidence atlas is an interactive searchable tool that shows the locations of the studies included in the systematic map database along with extracted meta-data. Each dot shows a study reporting on ecotechnology for recovery and/or reuse of carbon and nutrients. By clicking on a specific dot, bibliographical information of the publication, data on study design and characteristics of reported ecotechnology, recovery and reuse, including a link to the publication on Google Scholar are visualized. Different colours of dots represent different types of recovery including recovery of energy, carbon, phosphorus and nitrogen (and their combinations). In 144 studies (30.4%), coordinates of locations where studies were conducted were not reported and, in these cases, the evidence atlas shows locations of lead authors’ institutions.

How we collated the systematic map database

We searched for both academic and grey literature. The searches were restricted to the period 2013 to 2017. English language searches were performed in five bibliographic databases and search platforms, as well as Google Scholar. Searches in 38 specialist websites were performed in English, Finnish, Polish and Swedish. We included any type of ecotechnology undertaken for the purposes of recovery and/or reuse of carbon, phosphorus and/or nitrogen in wastewater treatment. Our methods are described in the peer-reviewed and published protocol.

What is included in the systematic map database?

We found 448 articles studying the effectiveness of ecotechnologies. The majority of eligible articles were in English, originated from bibliographic databases and were published in 2016. The evidence base had a broad geographic basis, with the majority of studies conducted in Europe (220 studies), followed by Asia (158 studies) and North America (47 studies). China was the most represented country, contributing to 16.2% of the evidence base. The three most prevalent ecotechnologies in the evidence base (totalling 34.6%) were: cultivation of microalgae, irrigation with effluents, and reuse of biosolids. Conventional/mixed wastewater was the principal waste source used for recovery of nutrients or carbon, making up 47.1% of all studies in the evidence base, followed by sludge (26.7%). 24.1% of studies reported on joint recovery of nutrients and carbon or energy (for example, by anaerobic digestion) and 8.0% reported on joint reuse.

Who can use systematic map database?

The evidence base can be useful for researchers, decision-makers or any other actors working on transformation from linear to circular economy in the wastewater sector.

The following topics were identified as potential candidates for evidence synthesis:

1. Effectiveness of products recovered from different types of wastewater as soil amendments or fertilizers.
2. Effectiveness of anaerobic digestion as an ecotechnology used for recovery of carbon.
3. Effectiveness of struvite precipitation as an ecotechnology for nutrient recovery.
4. Microalgae cultivation.

We have already started addressing the first three gaps and a methodical plan for this review can be found here.

Please cite as: Johannesdottir S.L., Macura B., McConville J., Lorick D., Haddaway NR., Karczmarczyk A., Ek F., Piniewski M, Księżniak M. & Osuch P: What evidence exists on ecotechnologies for recycling carbon and nutrients from domestic wastewater? A systematic map. Environ Evid 9, 24 (2020). DOI: doi.org/10.1186/s13750-020-00207-7