The use of constructed wetlands for domestic wastewater treatment and effluent reuse for irrigation

Laburpena

Climate change is a global phenomenon that affects water availability and the distribution of water resources. Southern Europe is one of the areas that can expect water scarcity in the future and therefore it has to increase its resilience to it. In order to assess this area’s risk of water shortage, a simple index called Water risk was created using different parameters. The analyses showed that the Water risk is the highest for The Former Yugoslav Republic of Macedonia and Malta, and the lowest for Portugal and Slovenia. In order to increase their resilience to climate change and water shortage, the Southern European countries should rely more on non-renewable water resources, such as treated wastewater. In South Europe, only Greece, Italy, Portugal and Spain (GIPS) have guidelines for wastewater reuse. When the values required by them are compared, it can be said that the Greek and Italian standards are stricter than the other two. Wastewater reuse is particularly suitable in agriculture since wastewater already contains nutrients needed for plant growth. A technology that could help smaller communities with lower financial resources to achieve that goal is constructed wetlands (CWs), environmentally friendly wastewater treatment systems with low energy requirements. However, their possible role in wastewater reuse in agriculture has still not been examined on a bigger scale. In order to assess their potential to treat wastewater for reuse, effluents from CWs in four Southern European countries that have guidelines for wastewater reuse in agriculture (GIPS) were compared to the qualities required by these guidelines. However, it was concluded that the CWs alone can rarely reach those standards, and that is especially difficult regarding microbiological parameters. Therefore, their performance has to be improved in order to be used as wastewater treatment and reuse systems. Since, the role of the plants in CWs is still not clear and, in addition, some studies have shown that integration of earthworms in these systems can have certain benefits, an experiment was developed in order to test effect of these components. A pilot plant based on CWs (four vertical flow systems) was built in 2015 and one year experimental period has assessed effect that earthworms and plants have on the operation of these systems. On average, no significant difference could be found for either plants or earthworms effect on wastewater treatment. However, during the summer period these components did affect total nitrogen removal. Therefore, although plants and earthworms can have a certain effect on their efficiency, other ways to improve operation of CWs should be investigated, for example their integration with disinfection systems.