Introduction
Reclaimed water aquaculture for food production exists outside Europe, especially in resource-poor regions. However, currently there is no capacity for reclaimed water aquaculture or aquaponics in Europe mainly due to low public acceptance and lack of regulations [1 , 2] . The EU Water Reuse Regulation of 2020/741 [2 ] regulates the use of reclaimed water for agriculture, laying the groundwork for an extension to aquaculture . The novelty in this work pioneers the use of reclaimed water to farm fish and vegetables fit for human consumption in an aquaponic system, leading not only to a notably water scarcity alleviation but also a reduction of produce prices and carbon footprint avoiding transport costs.
For the first time in Europe, an experimental aquaponic farm has been coupled to a nearby urban wastewater treatment plant in Castellana Grotte, Puglia, Italy within the frame of the project Aquaponics from wastewater reclamation (AWARE) GA N. 101084245. Advanced (post-tertiary) treatment of wastewater has been tailored to feed the aquaponic farm to produce lettuce and Tilapia. The performance of advanced post- tertiary treatment and the aquaponic farm has been evaluated not only in terms of chemical and microbiological water quality, but also fish welfare, plant health and food safety . H ere, we report on water quality.
Materials and Methods
The advanced tertiary treatment has been developed by Aquasoil . MITO3X technology i s composed of an ozonation step with the ability to perform ozonation at a dose of 4.5 mg/L O3 with nearly zero contact time (< 10 seconds) excluding the formation of brominated byproducts (bromates), follow by a vacuum ultraviolet (VUV) with an emission at a wavelength of 185 nm. This radiation can directly photolyze water and produce hydroxyl radicals and hydrated electrons, both species able to effectively degrade micropollutants . Then, a reactive storage (biofilter) is used downstream the ozone/VUV system . The biofilter is comprised of two tanks with a total dimension of 15 m3 (5 m x 3 m x 1 m) . Water is first subjected to granular activated carbon (GAC) and then, expanded clay and lava rock. This adsorption step can assure total retention of micropollutants. Assuming a n average flow rate of 1 m3/h, this ensures an average empty bed contact time (EBCT) of 15 hours . The biofilter is aerated using oxygen wasted by the ozone generator.
These systems comprise various compartments (in this case: fish tank, biofilter, sump, DWC floating raft crop cultivation system, settler, and aerobic digester, provided by Green in Blue). In this study two aquaponic lines were studied to ensure reproducibility. Each aquaponic system was set up with three tanks of 350 L each, filled up with reclaimed wastewater, and stocked with a total of 140±6 Nile tilapia ( Oreochromis niloticus L. , initially stocked at 37.5±0.95 g per system) and a 5 m2 of crop planting surface with 36 lettuces . The experiment was conducted in a small scale, closed-loop, simple recirculating aquaculture system (RAS) running for three months . A n aquaponic line with dechlorinated tap water was used as control.
Several physico -chemical and biological parameters were monitored not only after the water advanced (post- tertiary) treatment, but also throughout the cycle in the sump of the aquaponic system . In particular, microplastics; metals; organic emerging micropollutants; human enteroviruses such as Sapovirus (SaV) , Norovirus (NoV GI, NoV GII) , Hepatitis (HAV, HEV), crAssPhage , and Pepper Mild Mottle Virus (PMMoV) which is considered as potential indicator of fecal contamination in aquatic environments ; parasites (18S rRNA gene metabarcoding) ; fe cal contamination bacteria indicators such as enterococci , t otal c oliforms, Escherichia coli ; and antibiotic resistance biomarkers and the bacterial community (16S rRNA gene metabarcoding) were analysed.
Results
Regarding the efficacy of the advanced (post-tertiary) treatment for the removal of contaminants , 77±5 organic micropollutants were detected in the inlet of the advanced (post-tertiary) treatment using non targeted screening conducted by high-resolution mass spectroscopy. A fter the treatment, an overall removal of 51.1 % was measured in terms of sum of micropollutants. Furthermore, the stage of the reactive storage was able to achieve an additional removal of micropollutants reaching (relative to the influent) nearly two logs reduction (i.e., 98.7%). Suspect PFAS were not detected in the effluent. Metals were detected in trace concentrations in the inlet and effluent. Mi croplastics were reduced in 66% . The crAssPhage and PMMoV concentration were quantified in the inlet corresponding to 8.57·102 and 2.55·105 gc/L respectively. Moreover, 30% of PMMoV particles showed infectivity. SaV , NoV GI, GII, HEV, HAV were not detected (<LoD) or detected below LoQ. After treatment crAssPhage was totally inactivated and PMMoV was reduced to 1-log but no infectivity was confirmed. Bacterial counts were also below LoD.
Regarding microbial water quality evolution in the aquaponic system, no viruses were detected through time , not even PMMoV . Accumulation of bacterial contamination was observed through time in the sump, but no E. coli was observed . The water microbial community was observed to change during the experimental cycle, and mirrored that of the biofilter, but not of the of fish and plants being cultivated. Various parasitic species were identified, but none have pathogenic significance. Interestingly, n o differences in water quality were detected within the aquaponic system using dechlorinated tap water and reclaimed urban wastewater.
Conclusions
A dvanced post- tertiary treatment was demonstrated to provide high quality reclaimed water . The combination of oxidation processes coupled to a final adsorption led to high reduction of microbial pathogens, micropollutants and microplastic particles. Its reuse in aquaponics showed promising results in comparison with potable water systems.
Literature
[1 ] Official Journal of the European Union, 2020 “REGULATION (EU) 2020/741 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 25 May 2020 on minimum requirements for water reuse”.
[2 ] Health guidelines for the use of wastewater in agriculture and aquaculture: report of a WHO scientific group [meeting held in Geneva from 18 to 23 November 1987].