European legislation

Aligning to the Directive 2000/60/EC of the European parliament and of the council of 23 October 2000 establishing a framework for Community action in the field of water policy, where one of the environmental objectives of the Directive is to protect enhance and restore water bodies across the Member States, additionally to the management of water scarcity, the demo sites were compared to the current European legislation of the minimum requirements for reclaiming water use (EU 2020/741) that states that depending on the quality of the water output it can be used for specific agricultural irrigation systems or environmental purposes, ensuring the protection of the environment and of human and animal health (OJ L 177, 5.6.2020, p. 32–55, Annex 1). According with the objectives of the BIODAPH₂O project, a minimum of quality class C must be achieved to assure the possibilities of use of each demo site.

Figure 1. EU 2020/741 normative Section 2 Table 1 of the classification of water quality and the water use that it authorizes and their corresponding quality requirements.

Quart WWTP demo site

The implementation of the BIODAPH system at Quart WWTP is designed to treat up to 40% of the secondary wastewater with the aim of enhancing the chemical and ecological status of the Onyar River's ecosystems. This initiative goes significantly beyond compliance with the minimum standards set by the European Commission's Water Framework Directive (Directive 2000/60/EC) by including the evaluation of the removal of emerging contaminants, microplastics and antibiotic resistance genes by the BIODAPH system.

The system, featuring two reactors (T1 and T2) with a capacity of 100 m³ each, was evaluated over the months of March, April, and May at the WWTP of Quart. The two reactors were filled in November 2023 with secondary wastewater to promote biofilm growing and Daphnia inoculation was done in December 2023. Both reactors were left to stabilize for two months. Biofilm and phytoplankton communities have been monitored periodically since January 2024. Both communities have shown development oscillations influenced by water quality changes, with differences between reactors. Phytoplankton had had greater fluctuations, while biofilm has steadily increased and stabilized, reaching similar levels in both reactors. Each reactor operates independently, adapting to biological conditions (i.e number of Daphnias and biofilm maturity) as well as sun irradiation.

Over a three-month trial with a hydraulic retention time (HRT) of 1.5 days, the Daphnia magna population thrived, reaching 293.3 individuals per litre in T1 and 227.6 individuals per litre in T2. These concentrations are optimal for the system's performance.

Despite the variations in the system’s environmental conditions and the D. magna dynamics, the microbiological analysis of the outlet water from both reactors now reaches a classification that enables water to be reused for drip irrigation of crops (C and D classes of water quality of the EU 2020/741 regulation on minimum requirements for water reuse).

Table 1. Quality parameters at the end of the first trial at the BIODAPH reactors T1 and T2, at the Quart WWTP in Girona, Spain. Operation period: 01/03 to 31/05. HRT=1.5.

Figure 2. Pictures of the Quart demo site: a) Onyar river located next to Quart WWTP b) the two (T1 & T2) BIODAPH reactor installation at the Quart demo site

As can be seen in Table 1, the BIODAPH tertiary system is highly effective in reducing both the turbidity and the total suspended solids. The disinfection achieved in Reactor T1 meets the limits established by the EU 2020/741 regulation with E.coli < 1000 u.f.c/100 mL to classify as Class C water whereas Reactor T2 classifies as Class D in this legislation, allowing drip irrigation for crops in both cases.

The reactors are designed to produce a high sedimentation rate of the largest particles in the first compartment whereas D. magna mainly work in the second compartment (the largest part of the reactors) filtering the small edible particles (<30 microns). Therefore, the BIODAPH reactors improve the elimination of suspended particles from the inlet water due to both the filtration capacity of D. magna and the particle sedimentation. Both mechanisms result in a global improvement of the water quality. The efficiency of the system was addressed by monitoring the particles and their size distribution, linking the particle size with the agent responsible for the water clarification. During Trial 1 (HRT of 1.5 days), at the end of the stabilization trial, an elimination of between 70-80% of particles by D. magna was observed. The removal of the particles is associated with a decrease in pathogens such as coliforms and E. coli from secondary wastewater. Moreover, this nature-based technology has the capacity of improving the quality of the treated wastewater by removing organic micropollutants (pharmaceuticals and personal care products, and PFAs), microplastics, and antibiotic resistance genes allowing the reduction of pollutants being introduced in the aquatic systems as there are removed in the origin source. Finally, it is also worth mentioning that during this first period of trials, it has been possible to detect a reduction of between 70 and 100% of antibiotic resistance genes as in the case of microplastics (size < 350 µm), their presence in the effluents was reduced by 90 %. About the composition of the microplastics, the only polymer identified in the influent was PVC whereas this was not detected in the effluents, demonstrating the high efficiency of the BIODAPH system in removing this microplastic. Concerning PFAs, an efficient removal of these compounds (> 80 %) was achieved in both BIODAPH reactors.

Antissa WWTP demo site

At the Antissa WWTP, the BIODAPH reactor is undergoing optimization trials with different HRTs (0.4, 1, and 1.4 days). In this case the goal is to produce reclaimed water for the irrigation of different kinds of crops, meeting the water reuse regulations (Regulation (EU) 2020/741). However, the testing periods were different from those of Quart, as they were adapted to the availability of wastewater.

The reactor was filled with wastewater from the constructed wetlands (Fig. 5 a) to give time for the biofilm to grow. In May 2024, two months after the inoculation of D. magna when the population was fully developed, the full start-up of the system was set in motion with an HRT of 1.4 days.

The initial results, based on the monitoring of general parameters (Table 2), indicate that the effluent meets the limits for treated wastewater reuse. The reclaimed water is nutrient-rich, making it highly suitable for agricultural reuse as intended. Given the low levels of TSS, COD, and turbidity in the reactor inlet, there is no need for significant reduction within the BIODAPH unit, although there is a notable reduction in turbidity levels. The system also demonstrates effective removal of microbiological content, achieving a 2.6-3.8 log reduction in E. coli (99.78%). An interesting observation underscoring the system’s consistency, is that despite the exceeding of water temperature >25C, —initially proven to affect Daphnia—the population recovered quickly after the initial shock, with an average of 358 individuals per liter, showcasing the system's resilience.

Table 2. Physicochemical quality parameters of the inlet and outlet of the BIODAPH system, at the Antissa WWTP in Lesvos, Greece. Operation period: 15/04 to 28/06. HRT=1,4.

Figure 5. Pictures of the BIODAPH reactor installation at the Antissa demo site: a) constructed wetlands and b) BIODAPH reactor with the buffer tank (left) and the monitoring unit (right)

Future trials

After the first trial, a second trial will be undertaken during the hottest months of the year (June, July and August) at the Quart WWTP demonstration site to study the behaviour of the system and the D. magna dynamics in adverse environmental conditions. The upcoming activities will also include the evaluation of the system at HRTs of 1 and 2 days across different seasons. Furthermore, the effluent quality achieved by the BIODAPH technology still contains a significant amount of N and P nutrients, which means that additional actions will be conducted in order improve their removal.

In the case of Antissa WWTP demonstration site, sampling campaigns are currently being conducted to analyze emerging contaminants, microplastics, PFAs, and ARGs. Once these campaigns are completed, the current operational period will conclude, and new trials will commence with HRTs of 0.4 and 1 day, tailored for both summer and winter periods.

Conclusion

The BIODAPH tertiary treatment system has so far shown a high level of efficiency in improving water quality at both demonstration sites, with potential for widespread application in agricultural irrigation as well as in improving the chemical and microbiological quality of the treated effluents. Further trials will validate its performance under different environmental conditions.

References

Regulation (EU) 2020/741 of the European Parliament and of the Council of 25 May 2020 on minimum requirements for water reuse (OJ L 177, 5.6.2020, p. 32–55).                                           < http://data.europa.eu/eli/reg/2020/741/oj>

Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy (OJ L 327, 22.12.2000, p. 1–73).          < http://data.europa.eu/eli/dir/2000/60/oj>