Laura Ponce Robles

The use of reclaimed water for crop irrigation can be an important route for pharmaceutical introduction into the food chain. This work aims to investigate the crop uptake, accumulation and translocation of 11 representative pharmaceuticals in radish crop through two realistic agricultural growing conditions (highland and fall radish). For this, radish crops were irrigated with three reclaimed water qualities: (i) WWTP effluent (named real effluent, RE), (ii) RE fortified with 5 µg/L of pharmaceuticals (named higher concentration, HC) and (iii) RE fortified with a concentration of pharmaceuticals 10 times lower than HC (0.5 µg/L, named medium concentration, MC). Results revealed that the pharmaceutical concentration in irrigation water does not play a role in radish quality. However, phytotoxic effects could appear at concentrations above 100 µg/L. A clear relation between irrigation water quality and uptake was obtained (RE < MC < HC). Pharmaceutical concentrations in radish leaves were higher than in roots in all cases. However, the total distribution percentages in radish tissues and soil were directly dependent on the environmental growing conditions (mainly attributed to evapotranspiration rates, ET). Octanol–water partition coefficient (log K _ow) of each pharmaceutical was a critical factor in radish uptake, accumulation and translocation (optimal range 1–4), while organic carbon to water partition coefficient (K _oc) played a key role in soil accumulation rates. The concentration levels of pharmaceuticals detected in the edible part of radish did not pose a risk to human health via dietary intake. However, irrigation with reclaimed water containing pharmaceuticals (mainly caffeine (CAF), carbamazepine (CBZ) and sulfamethoxazole (SMX)) could have a significant environmental impact for aquatic and terrestrial organisms. The link between risk assessment and future prospects was also discussed. Graphical Abstract

Wastewater treatment plant effluents can be an important source of contamination in agricultural reuse practices, as pharmaceuticals are poorly degraded by conventional treatments and can enter crops, thereby becoming a toxicological risk. Therefore, advanced tertiary treatments are required. Ozone (O₃) is a promising alternative due to its capacity to degrade pharmaceutical compounds, together with its disinfecting power. However, mass transfer from the gas to the liquid phase can be a limiting step. A novel alternative for increased ozone efficiency is the combination of micro-nano bubbles (MNBs). However, this is still a fairly unknown method, and there are also many uncertainties regarding their implementation in large-scale systems. In this work, a combined O₃/MNBs full-scale system was installed in a WWTP to evaluate the removal efficiency of 12 pharmaceuticals, including COVID-19-related compounds. The results clearly showed that the use of MNBs had a significantly positive contribution to the effects of ozone, reducing energy costs with respect to conventional O₃ processes. Workflow and ozone production were key factors for optimizing the system, with the highest efficiencies achieved at 2000 L/h and 15.9 gO₃/h, resulting in high agronomic water quality effluents. A first estimation of the transformation products generated was described, jointly with the energy costs required.

Today, the emergence of increasingly restrictive treatment and reuse policies make the implementation of full-scale tertiary treatment, capable of improving the quality of water, a priority. Full-scale TiO₂ photocatalysis systems are resulting in a promising option, since TiO₂ is commercially available. However, questions such as how to work continuously during day/night irradiation cycle, or the removing of TiO₂ in outlet flow are still unresolved. In this work, a full-scale system integrating a solar CPC/UV-LED step combined with commercial microfiltration membranes was installed in a conventional WWTP for agricultural reuse purposes. After optimization, 0.5 g/L of catalyst and combined SOLAR + UV-LED showing the highest pharmaceutical removal percentages, while a self-designed UV-LED included in the own reaction tank resulting in higher efficiencies compared with commercial lamps. Longer membrane surface area decreased fouling problems in the system. However, 60 min of irradiation time was necessary to reach the most restrictive water quality values according with (EU 2020/741). After optimization step, total costs were reduced by 45%. However, it was shown that a reduction in operating and maintenance costs, along with the development of more effective and economical commercial filtration membranes is a key factor; therefore, working on these aspects is essential in the treated water cost reduction. Graphical abstract

Irrigated agriculture is a predominant economic activity in many areas of the Mediterranean region.  However, water scarcity and restrictions on the use of fresh water resources in high agricultural production regions, endangers sustainable agricultural development.  So, alternative water resources are necessary.The use of reclaimed water for agriculture irrigation makes available a low-cost water source, providing an additional source of nutrients for the plants, helping to reduce the amount and costs associated with the consumption of synthetic fertilizers in agriculture. However, this practice is not a remedy for water scarcity free of disadvantages. Among them, the presence of contaminants of emerging concern (CECs) is one of the most worrying to the scientific community. The problem with these compounds is that they are not completely removed during wastewater treatment, which makes their long-term consequences unpredictable. On the other hand, the absorption and bioaccumulation of CECs in food crops is a matter still to be clarified.In this work, the absorption capacity, accumulation and persistence of a selected group of CECs in real crops (baby lettuce) irrigated with reclaimed water from a WWTP were evaluated. Results showed different behaviors depending on CECs properties and concentrations, indicating a progressive accumulation when the culture time increased. So, the chemical quality of reclaimed water is a key issue in safe agricultural irrigation.

Wastewater reuse presents a promising way to mitigate the risk to global water resources and achieve sustainability in water, especially in agricultural areas in the southeast of Spain, such as the Murcia region. However, the risks related to the presence of contaminants of emerging concern (CECs) or pathogenic microorganisms in wastewater treatment plant (WWTP) effluent suggest the need to implement effective and relatively low-cost tertiary treatments. With this aim, a self-sustainable pilot prototype based on three combined modules (disc-filtration, granular activated carbon (GAC) bed adsorption and UV disinfection) assisted by solar panels was installed as an alternative tertiary treatment in a conventional WWTP in the Murcia region. The obtained results clearly confirmed the efficiency of the proposed prototype for CECs removal, and showed optimal results at a workflow of 500 L/h. In all cases, high removal efficiency was obtained for the different indicator microorganisms described in the recently published Regulation (EU) 2020/741 (E. coli, F-specific coliphages, somatic coliphages, total coliphages, and Clostridium perfringens). The protection of the activated carbon by disc-filters and the energy autonomy and self-operation of the prototype resulted in an efficient and economically viable methodology for its implementation in both conventional WWTPs and in isolated areas attached to crops.