How Many Small Agglomerations Do Exist in the European Union, and How Should We Treat Their Wastewater?

Abstract

The European Union (EU)’s legislation on urban wastewater requires all agglomerations with a population equivalent (PE) above 2000 people to undergo a secondary (mechanical/physical and biological) wastewater treatment. Agglomerations below 2000 PE, though, fall outside the scope of the current EU’s legislation. As such, their regulation is heterogeneous across the various EU member states, and there is no systematic collection nor reporting of data enabling an estimation of their actual significance as a source of pollution for the receiving water bodies. Here we present a spatial model to delineate agglomerations in a GIS, based on population distribution and land cover. From the model results, in the EU, we identify 364,650 agglomerations with 2000 PE or less, housing a cumulative population of about 75 million inhabitants. We then calculate the organic matter and nutrient loads these agglomerations can discharge, assuming they presently undergo primary wastewater treatment, and the reduction of loads that can be expected under different treatment scenarios, together with the corresponding treatment costs based on a simple cost model. Using a conventional shadow price for the organic matter and nutrients removed, we show that all treatment scenarios show a benefit-to-cost ratio (B/C) above (or close to) 1. However, only a scenario of secondary treatment applied to all agglomerations above 1000 PE provides sufficient safety margins on the B/C. This suggests the opportunity to expand the scope of the current legislation down to agglomerations of this size, while addressing smaller agglomerations depending on their actual impacts on the receiving water bodies, through “appropriate treatments” defined by the local authorities.

Responses of Freshwater Invertebrates to Imhoff Tank Sewage Effluents: A Preliminary Study in Four Watercourses with Different Ecological Status (Abruzzo, Central Italy)

“…Their low efficiency and their incorrect maintenance often contribute to environmental deterioration, with a large quantity of inadequately treated sewage dispersed in the soil or discharged in superficial watercourses [11][12][13]. In Italy, more than 10% of the population is living in small agglomerations served by decentralized WWTPs [14]. In the Abruzzo region, the most common decentralized treatment system is represented by Imhoff tanks with only a primary treatment and with effluents that are discharged directly into superficial waterbodies.…”

Towards a Safe and Sustainable Future

“…or less -corresponding to circa 75 million inhabitants-have been identified and are predicted to impact receiving water bodies. The percentage of small agglomerations was on average higher in Czechia, Slovakia, Croatia, Slovenia, Romania and Poland (Pistocchi et al, 2022b). Future 'Present' scenario, Panel B the 'Full Compliance' scenario, and Panel C the ' Advanced Treatment' scenario, with a respective pharmaceutical emission reduction potential of 48% (±27), 52% (±28) and 69% (±22).…”

“…Given that not all substances are sufficiently removed by advanced treatment techniques and that it is not feasible to update all STPs (Pistocchi et al, 2022b), other measures focussing on input prevention need to be considered as well (Kümmerer et al, 2019;van Wezel et al, 2017).…”

“…In addition, other environmental burdens than risks of chemicals need to be assessed. Treatment with ozonation is for example associated with higher environmental impacts due to its high energy consumption (Ganora et al, 2019;Pistocchi et al, 2022b). One of the aims laid down in the UWWTD proposal is to achieve energy neutrality in the wastewater sector by 2040 (European Commission, 2022d).…”

“…It is not realistic to implement advanced treatment everywhere, considering the extra costs and e.g. increased energy and material demand (Ganora et al, 2019;Pistocchi et al, 2022b). The OECD estimated that extra investments of 129 to 206 billion euros are needed in order to realise the implementation of advanced treatment at large STPs (OECD, 2020).…”