Results and conclusions

1. The monitoring of the secondary effluent of Benidorm WWTP showed the conventional treatment was not prepared to remove all the micropollutants present in wastewaters, evidencing the need to apply the tertiary treatments proposed by EMPORE project.

2. The most efficient combination of technologies for eliminating micropollutants in the permeate line of the EMPORE plant was: PRETREATMENT (conventional filtration followed by ultrafiltration) + REVERSE OSMOSIS + ACTIVATED CARBON.

2.1. The pretreatment carried out in EMPORE plant (conventional filtration followed by ultrafiltration) removed scarcely the micropollutants, except for chlorpyrifos.

The average removal efficiencies reached by this step were low (0 - ~50%) for diuron, diclofenac, erythromycin, carbamazepine, sulfamethoxazole, glyphosate, ketoprofen, fluoxetine, DEHP, isoproturon, estrone and ibuprofen. Chlorpyrifos was completely removed; due to its hydrophobicity, this compound was probably associated to the suspended matter and was derived to the ultrafiltration (UF) concentrates.

2.2. An effluent of high quality, almost free of micropollutants and with low conductivity, was obtained from reverse osmosis (RO). In the RO permeates, only traces of glyphosate, carbamazepine, diclofenac and sulfamethoxazole were detected in a few specific samples.

The objectives of the project were complied after the combination of technologies Pretreatment+Reverse Osmosis. The concentrations of all priority substances detected in the secondary effluent of Benidorm WWTP (chlorpyrifos, DEHP, diuron and isoproturon) were reduced below the Directive 2013/39/EU threshold and the average concentrations of the pharmaceutical compounds erythromycin, ibuprofen, fluoxetine, estrone and ketoprofen were reduced by 99% of their original concentration.

2.3. The filtration by activated carbon of the RO permeates removed the traces of the above mentioned micropollutants. Therefore, no further treatment by advanced oxidation processes (AOPs) was required.

After the subsequent filtration by activated carbon, the average concentration of the pharmaceutical compounds diclofenac, carbamazepine and sulfamethoxazole and the pesticide glyphosate were reduced by 99% of their original concentration.

3. The methodology used in this project to eliminate micropollutants in the rejection line was ADVANCED ELECTROXIDATION (EAOP’s).

3.1. The rejections or concentrates of UF and RO processes contained several micropollutants such as diclofenac, glyphosate, fluoxetine, among others. The elimination efficiencies of the electrochemical process (EAOP) were diverse, depending on the nature of the compounds: glyphosate, isoproturon, estrone and ketoprofen were highly removed (60-90%); sulfamethoxazole, diclofenac, erythromycin, ibuprofen and chlorpyrifos were partially removed (35-60%); and diuron, carbamazepine and fluoxetine were slightly removed (< 35%).

3.2. The objectives of the project were analysed comparing the concentration of each micropollutant in the UF/RO concentrates with the concentration in the effluents of the line concentrates. The priority substances diuron and isoproturon detected in the UF/RO concentrates generally complied with their reduction below the Directive 2013/39/EU threshold after the treatment by electro-oxidation. This objective was not achieved for chlorpyrifos. After the electro-oxidation, the average concentrations of the pharmaceutical compounds diclofenac, erythromycin, carbamazepine, ibuprofen, fluoxetine, estrone, ketoprofen and sulfamethoxazole and the pesticide glyphosate were not reduced by 99% of their inlet concentration, but, the removal efficiencies were high for glyphosate, ketoprofen and estrone. The electro-oxidation reduced the discharge of micropollutants to the environment.

4. The average energy consumption ratios related to the water produced per process were: EAOPs (2.93±2.02 kWh·m-3) > RO (2.77±0.83 kWh·m-3) > AOPs (1.49±0.73 kWh·m-3) > Pre+UF (0.33±0.13 kWh·m-3). The ratios of energy consumption of reverse osmosis process were slightly smaller than those corresponding to EAOP’s process.

5. In general, there was a good correlation between the removal efficiencies reached by the UF and RO units of EMPORE pilot plant and IRAD Benidorm (full-scale plant), which supports the extrapolation of the technology to a large-scale level, as it was detailed in action B7.

6. The proposed methodology allows for the elimination of priority substances and other micropollutants present in the WWTP effluents, reducing the environmental impact of the discharge of these effluents into the aquatic environment.

6.1. To compare the environmental state before and after the EMPORE treatments in Benidorm, the dimensionless Canadian Water Quality Index was applied, considering as parameters the concentrations of the studied micropollutants, index referred as CWQI-EC. Additionally, as a new scientific contribution to this project, a modification of this index was used, which we call the Emerging Pollutants Water Quality Index (WQIEC), which includes a penalty factor that depends on the category of the compound in the calculation. of the parameter called excursion. Both indices improve the interpretation of the presence of microcontaminants for a general public, since, instead of considering the concentrations, the quality is provided by a dimensionless scale of 0 to 100, where 100 is the best value.

6.2. The secondary effluent of Benidorm WWTP (influent of EMPORE plant) possessed low quality due to the presence of micropollutants (WQIEC=42-53). After the line of permeates of the EMPORE plant (Pretreatment + Reverse Osmosis + Activated Carbon), the quality of the effluents was excellent (WQIEC= 100). On the other hand, the quality of the rejections improved in the line of concentrates; the effluents of electro-oxidation possessed a similar/superior quality than the secondary effluent (WQIEC=43-85).

7. During the project, EMPORE members made a great effort to raise awareness of the need to remove micropollutants from the secondary effluents of conventional wastewaters treatment plants, highlighting their participation in 24 congresses and 14 networking sessions with other LIFE projects, among other activities. On the other hand, the social acceptation of reclaimed water was assessed considering the opinion of irrigators, water experts and researchers and members of the academical community in Spain. The use of the quality indexes CWQI-EC and WQIEC will contribute to the social acceptation of reclaimed water because these indexes allow a simple interpretation of water quality.

7.1. Despite some disadvantages related to the use of reclaimed water (price, difficulty to guarantee traceability and food safety, pumping and storage infrastructures), irrigators would use more reclaimed water if the prices were competitive and the quality of the resource was fully guaranteed and suitable for any type of agricultural use.

7.2. Both the academic community and water experts are aware of the presence of emerging pollutants in wastewaters and agree on the need to combine technologies to remove them efficiently, since conventional wastewaters are not currently prepared for that purpose. In general, they consider that the elimination of micropollutants could have positive impact mainly on public health, environmental and sustainability and in integrated management of water resources.

7.3. Considering the opinion of the academic community, the three main factors that can make difficult the detection/removal of micropollutants in waters are: development of analytical methods and cost of analytical equipment, requirements of the current regulation and high cost of the existing technology to remove emerging pollutants.

8. The lack of a policy framework for wastewater treatment and water reuse regarding micropollutants hinders the implementation of removal technologies such as the proposed by EMPORE methodology. Future regulations in the European framework should include quality standards for micropollutants in the effluents of wastewaters. In case of reuse, new regulations should focus on different uses of reclaimed water and set quality standards for micropollutants. In that sense, the proposal “Proposal COM (2018) 337 final 2018/0169(COD)” focused on the use of reclaimed water for irrigation, set that when necessary and appropriate to ensure sufficient protection of the environment and human health, specify requirements for water quality and monitoring will be considered, such as the environmental quality standards for priority substances and certain other pollutants laid down in in Directive 2008/105/CE.

8.1. EMPORE project proposes to improve the current regulation of wastewater treatment with the obligation of analysing the occurrence of a list of micropollutants in all the European urban WWTPs, submitting the concentrations and the removal efficiencies reached by treatment in a common database. The initial list of compounds to be monitored in WWTPs should include at least, the priority substances included in Directive 2013/39/UE and the micropollutants included in the Watch List proposed by Decision 2018/840/UE or subsequent directives and decisions. The collection of that information will help the European Union to include these pollutants or not as priority compounds in future regulations.

9. The DSS (Design Support System) software developed in EMPORE project has proved to be a useful tool for analysing the transferability of the methodology taking into account the characteristics of the country and specific location analysed.

9.1. From the study of the results obtained from applying the DSS tool on four scenarios, corresponding to four WWTPs in Europe (2 in Croatia, 1 in Spain, 1 in Holland), the capacity of the installation seems to be, together with the cost of water production (euros/m3), the determining parameters in the viability of the technology, since it is a strong economic indicator in the evaluation.