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Wastewater treatment and nature-based solutions: how is the Central and Eastern European region doing?

The Global Water Partnership in Central and Eastern Europe (GWP CEE), which includes 12 countries from the Baltic to the Black Sea (Estonia, Latvia, Lithuania, Poland, Czech Republic, Slovakia, Slovenia, Hungary, Romania, Bulgaria, Moldova and Ukraine), is an international network of organisations involved in water resources management. Among other things, the network deals with the assessment of wastewater collection and treatment in the rural areas of the region and advocates for sustainable sanitation and nature-based solutions.

Since the adoption of the EU Urban Waste Water Treatment Directive (UWWTD 91/271/EEC) in 1991, the level of wastewater collection and treatment has improved significantly throughout Europe, including the Central and Eastern European region (CEE), resulting in improved freshwater quality. However, as reported by the European Environment Agency, urban wastewater remains a major source of water pollution. Stormwater overflows, poorly designed, monitored and maintained individual treatment systems and wastewater treatment plants for small communities of less than 2,000 PE place significant pressure on surface and groundwater bodies (Evaluation of the Urban Waste Water Treatment Directive). The problems listed are recognised by the EU and will be addressed in the revised UWWTD, which is expected to be adopted soon.

In the case of small settlements, it must be remembered that the concept of wastewater collection and treatment differs significantly from that of larger cities and towns with dense urbanisation. Small settlements are scattered across the landscape and are often located in rough terrain or on agricultural land. A decentralised approach, in which wastewater from individual settlements or houses is collected and treated, is often more appropriate than a centralised approach, in which wastewater from multiple settlements is collected and treated at a centralised treatment plant. Centralised and decentralised approaches differ in many aspects such as investment, management, stakeholder involvement and also in the most appropriate treatment technologies. While nature-based treatment technologies are less suitable for centralised treatment plants due to the large areas required, they are the preferred solution for small settlements because they are reliable and sustainable, simple and inexpensive to operate and maintain, easy to construct, provide high effluent quality and are multifunctional. Recently, nature-based solutions have evolved from marginal, lesser-known technologies and measures to an approach that is also supported by EU strategic documents (European Green Deal) and funding (H2020, Horizon Europe).

In Central and Eastern Europe, there are numerous small settlements (with less than 2,000 inhabitants) where about one-third of the population lives. The situation of wastewater collection and treatment in these settlements is difficult to assess because in some countries there is no central database on the number and capacity of small public wastewater treatment plants and many countries do not have data on individual (private) wastewater treatment plants. Therefore, the assessment of wastewater collection and treatment in small settlements is only an estimate and shows that only about 16 per cent of the population living in small settlements is connected to public or private wastewater treatment plants.

Because wastewater treatment in small public and private wastewater treatment plants is not specifically addressed in the UWWTD, different regulations apply in different countries of the region. All countries require the removal of organic matter (BOD, COD and/or TSS) for wastewater treatment plants with a capacity of 50-2,000 PE and more than half of the countries require the removal of nutrients (either various forms of nitrogen and/or phosphorus compounds). Only a few countries also require the removal of E.coli. The most stringent requirements are in Romania, where the removal of chlorides, phenols, detergents, and sulphides is also required for individual systems. Regarding monitoring requirements, most countries monitor effluents from small wastewater treatment plants (50-20,00 PE) 2, 4 or 6 times per year, while for individual wastewater treatment plants below 50 PE there is usually no monitoring.

There are various technologies used for wastewater treatment in small communities, from simple watertight septic tanks to conventional activated sludge systems and nature-based solutions. The latter is applied in all countries covered by GWP CEE and includes soil infiltration systems, short-rotation willow coppice (irrigation), waste stabilisation ponds, different types of treatment wetlands, sludge drying reed beds, vermifilters and separate treatment of urine and faeces (Ecosan technology). Treatment wetlands are used in all countries and in some (for example, in Poland) in very large numbers.

Treatment wetlands are an established technology for wastewater treatment that includes numerous variants: free water systems, subsurface vertical or horizontal wetlands, so-called French treatment wetlands that can be fed with raw wastewater without primary treatment and a group of intensified wetlands that include recirculation for improved nitrogen removal, aeration for improved per-area pollutant removal and wetlands with various types of reaction media that increase phosphorus removal and/or reduce land requirements.

Different types of treatment wetlands. Source: Cross et al., 2021.

Although there are some nature-based treatment systems in the region, their implementation in CEE is still far behind that of many Western and Northern European countries where nature-based treatment systems such as treatment wetlands are widely used and often supported by national legislation (for example, Denmark, France and Austria). The main obstacle to the introduction of nature-based treatment systems in CEE is the lack of knowledge about these technologies and their benefits. In addition, some countries report negative past experiences when improperly designed or managed treatment wetlands failed to meet effluent limits.

Negative experiences can be overcome by presenting existing or newly built, efficient and well-performing examples by practitioners and supported by experiences of local decision-makers and communities. Because nature-based solutions require a lot of lands compared to conventional approaches, the lack of land (area) is often a bottleneck to their implementation. However, with proper design, nature-based treatment systems can adapt to landscape conditions and by placing them on degraded or less valuable sites, we can overcome this bottleneck and also restore degraded sites. The multifunctionality of nature-based solutions can also substitute for the landscape tradeoffs required to implement them.

Long winters, high altitudes and rough terrain are also frequently reported as barriers to implementing nature-based solutions in CEE. However, there are numerous examples of nature-based treatment systems working well even under these conditions, so these barriers may also be related to a lack of knowledge about the potential and variability of such systems. Institutional barriers and lack of legislation are not major problems in most countries in the region, suggesting that there are no legal barriers to implementing nature-based solutions. In addition, the lack of engineering or technical knowledge, which was one of the main problems 10 years ago, seems to have been overcome by numerous scientific and expert open-access literature that provides design guidelines and detailed descriptions of case studies.

Despite the small percentage of the population connected to public and private wastewater treatment plants in small communities in the CEE region, there are many examples of applied nature-based solutions. Insufficient national databases on the number, capacity and technologies applied in private treatment systems may result in good practices remaining hidden from decision-makers. Therefore, it is important to identify the hidden gems of the best solutions in the regions and use them to build awareness and knowledge of real systems.

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