Monitoring quaternary treatments for municipal wastewater – DEMO3

Monitoring and control of quaternary treatments for municipal wastewater: Pilot-Scale demonstrators from the European CARDIMED Projects 

Lorenzo Tombolini1,2, Massimiliano Sgroi1, Daniele Caterino1, Alessia Foglia1, Anna Laura Eusebi1, Ike Olivotto1, Luigi Ledda1, Attilio Toscano3, Giuseppe Mancuso3, Francesco Fatone1  

1 WWEELab (https://www.wweelab.it; https://it.linkedin.com/company/wweelab-research-group) /SIMAU (Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica – Un sito dipartimentale dell’Università Politecnica delle Marche), D3A (Dipartimento di Scienze Agrarie, Alimentari ed Ambientali), DISVA (Home | DISVA), Università Politecnica delle Marche (UNIVPM – Università Politecnica delle Marche Home), Ancona, Italia 

2Dipartimento di Ingegneria Industriale – DII Dottorato Nazionale in Scientific, Technological and Social Methods Enabling Circular Economy, Università di Padova (Università di Padova), Via 8 Febbraio, 2 – 35122 Padova, Italia 

3Dipartimento di Scienze e Tecnologie Agro-Alimentari (Dipartimento — Scienze e Tecnologie Agro-Alimentari), Alma Mater Università di Bologna (Università di Bologna), Bologna, Italia 

The term contaminants of emerging concern, or organic micropollutants of emerging concern (commonly referred to by the acronym CECs), refers to synthetic organic compounds produced by the chemical and pharmaceutical industries that, as a result of their use, have been released into the environment and can be detected in various environmental matrices. Examples of contaminants of emerging concern include pharmaceuticals, personal care products, pesticides and industrial chemicals, surfactants and flame retardants, disinfection by-products and pathogens (such as bacteria capable of developing antibiotic resistance). Over the past few decades, these contaminants of emerging concern have been detected in various water matrices, including wastewater, surface water and drinking water, at concentrations ranging from µg/L to ng/L1,2. Although the effects of these emerging organic contaminants on public health at typically detected concentrations are often uncertain and still under investigation, toxicological evidence has shown that some of these contaminants can have severe effects on aquatic organisms at concentrations typically found in wastewater effluents. Moreover, the presence of “cocktails” of pharmaceuticals and synthetic organic compounds in water can produce synergistic effects on certain organisms3. In particular, studies conducted in Italian watercourses have shown that the presence of these compounds in water can interfere with the endocrine system of aquatic species, potentially leading to sex changes. Some of these compounds have become widespread in the environment and have also been detected in human serum and blood4. 

Wastewater treatment plants (WWTPs) have been identified as hotspots for the release of these contaminants into aquatic environments. This is because conventional wastewater treatment plants rely on primary, secondary and tertiary treatment processes, often based on activated sludge systems operated in different configurations, which provide limited removal of several CECs. In contrast, achieving high removal efficiencies for these micropollutants requires advanced treatment technologies, commonly referred to quaternary treatments5. These treatments are often implemented according to a multi-barrier approach, in which different processes are applied in series to achieve the removal of a broad range of contaminants with widely varying physicochemical properties. Quaternary treatments include adsorption processes, advanced oxidation processes (AOPs), and membrane filtration technologies, such as nanofiltration and reverse osmosis6. 

Following the widespread detection of emerging micropollutants in drinking water, surface water, and groundwater, the European Union has introduced regulatory measures aimed at mitigating and addressing this issue. In particular, the new Directive (EU) 2024/30197 on urban wastewater treatment requires the implementation of quaternary treatment processes in wastewater treatment plants (WWTPs) with a treatment capacity of 150 000 population equivalents (PE) or more. For smaller WWTPs (>10 000 PE), quaternary treatment is required only in areas identified as sensitive to micropollutant pollution, following a health and environmental risk assessment-based approach. These areas should include sites where treated urban wastewater is discharged into receiving water bodies with limited dilution capacity or into waters intended for drinking water production, shellfish production, or bathing. In particular, the new Directive requires the implementation of quaternary treatment to achieve at least 80% removal of a set of representative micropollutants, including amisulpride, carbamazepine, citalopram, clarithromycin, diclofenac, hydrochlorothiazide, metoprolol and venlafaxine. The removal of contaminants of emerging concern is also addressed by Regulation (EU) 2020/741, which establishes minimum requirements for water reuse in agriculture, when a risk assessment identifies potential adverse effects on human health and the environment8. Another key aspect of the new Directive (EU) 2024/3019 concerns the energy transition, requiring Member States to ensure that energy audits are carried out every four years for urban wastewater treatment plants and sewerage systems. These audits are intended to identify measures to reduce energy consumption and increase the use of renewable energy, thereby contributing to the reduction of greenhouse gas emissions and supporting the EU’s goal of achieving climate neutrality by 2050. This aspect is particularly relevant given the need to implement quaternary treatments for the removal of contaminants of emerging concern, which are known to be energy-intensive processes.  

One of the largest innovation actions funded under the Horizon Europe programmes, aimed at developing innovative solutions for the monitoring and control of quaternary treatments for municipal wastewater and the removal of contaminants of emerging concern is the CARDIMED (Climate Adaptation and Resilience Demonstrated in the MEDiterranean region) project, in which the Università Politecnica delle Marche and Università di Bologna are involved as a project partners. The objective of the project is to foster systemic transformations towards climate resilience in the Mediterranean region by promoting the implementation of nature-based solutions and technologies relying on renewable energy sources for wastewater treatment and agricultural irrigation. The Italian case study aims to promote the decarbonisation of agricultural activities in Sardinia through an integrated system for water management and sustainable energy production. The experimental site is in Alghero (SS) and covers an area of approximately six hectares. The project includes two pilot-scale quaternary treatment lines, integrating advanced monitoring systems and nature-based solutions to promote wastewater reuse for agricultural irrigation. 

The project includes two pilot-scale quaternary treatment lines with different configurations. The first line combines sand filtration for suspended solids removal with a UV/H₂O₂ advanced oxidation process (AOP), while the second line integrates GAC filtration with the same UV/H₂O₂ process. Both treatment lines are equipped with the same online monitoring system, including fluorescence and absorbance sensors for monitoring organic matter and CEC removal, as well as pH and electrical conductivity sensors for assessing the overall quality of the reclaimed water. 

Following quaternary treatments, the treated water will be used for agricultural irrigation. Runoff generated from the irrigated areas will subsequently be collected and treated using nature-based solutions (NBS), including constructed wetlands, buffer strips and microalgae-based systems. These systems will provide an additional treatment barrier for pollutant removal before the treated water is discharged into the receiving surface water body. The entire treatment and irrigation system will be energy supplied by a pilot photovoltaic system with an installed capacity of approximately 20 kW, which will provide the energy required to operate the electromechanical components installed within the experimental area. This configuration is intended to demonstrate the measures required to move towards the energy-neutrality objectives established by Directive (EU) 2024/3019. The proposed approach is therefore consistent with current requirements on energy neutrality, contributing to the reduction of CO₂ emissions while promoting a circular model for water and energy resource management and reducing the energy costs associated with system operation. Figure 2 illustrates the process flow diagram of the first line of the project, with particular emphasis on the quaternary treatment processes and the associated monitoring instrumentation. 

Figure 2 – Description of the Quaternary Treatment Train Implemented in the CARDIMED Project 

The first water treatment line is currently under installation, while the second treatment line has already been tested in a different experimental site. In particular, innovative online spectroscopic sensors based on fluorescence measurements were tested for the long-term monitoring of organic micropollutant removal by two different quaternary treatment processes: granular activated carbon (GAC) filtration and the UV/H₂O₂ advanced oxidation process (Figure 2). Fluorescence spectroscopy is a technique commonly used to investigate and monitor organic matter content in aquatic systems. In natural waters and wastewater, a fraction of the dissolved organic matter that absorbs light is also capable of fluorescing at characteristic wavelengths within the UV and visible regions of the electromagnetic spectrum. Moreover, measuring fluorescence intensity at specific wavelengths can provide information on specific components of organic matter and enable their removal and transformation to be monitored during both wastewater and surface water treatment processes. Fluorescence is considerably more sensitive than other spectroscopic measurements commonly used for monitoring water treatment processes, such as UV absorbance at 254 nm (UV254), and allows improved process monitoring in water matrices with low organic matter concentrations, such as the influents of quaternary treatment processes. During the experimental activities carried out in the experimental trials, changes in fluorescence signals measured using in situ sensors were correlated with the removal of several contaminants of emerging concern, including carbamazepine, clarithromycin, and diclofenac, which are among the indicator compounds listed in Directive (EU) 2024/3019. These correlations were investigated for both adsorption and advanced oxidation processes. 

Figure 2 – Pilot plants for quaternary treatment of municipal wastewater and sensor-based monitoring system 

Figure 3 shows, as an example, the correlation observed for clarithromycin, one of the indicator compounds included in Directive (EU) 2024/3019, during the monitoring of the GAC filtration process. The results obtained in the experimental trial represent an important achievement that can support both water utilities and companies operating in drinking water and wastewater treatment, as well as regulatory and monitoring authorities, by providing an indirect approach to assess compliance with the requirements established by recent European legislation. 

Figure 3 – Example of the correlation observed between clarithromycin removal and fluorescence measurements