Quantitative and qualitative approaches for CEC prioritization when reusing reclaimed water for irrigation needs - A critical review

The use of reclaimed water for irrigation is an option that is becoming increasingly widespread to alleviate water scarcity and to cope with drought. However, reclaimed water, if used for irrigation, may introduce Contaminants of Emerging Concern (CECs) into the agroecosystems, which may be taken up by the crops and subsequently enter the food chain. The number of CECs is steadily increasing due to their continuous introduction on the market for different uses. There is an urgent need to draw up a short list of potential high priority CECs, which are substances that could be taken up by plants and accumulated in food produce, and/or that could have negative effects on human health and the environment. This review presents and discusses the approaches developed to prioritize CECs when reclaimed water is (re-)used for irrigation. They are divided into quantitative methodologies, which estimate the risk for environmental compartments (soil and water), predators and humans through equations, and qualitative methodologies, which are instead conceptual frameworks or procedures based on the simultaneous combination of data/information/practices with the judgment of experts. Three antibiotics (erythromycin, sulfamethoxazole and ciprofloxacin), one estrogen (17-α ethinylestradiol) and one analgesic (ibuprofen) were found on at least two priority lists, although comparison among studies is still difficult. The review remarks that it is advisable to harmonize the different methodologies in order to identify the priority CECs to include in monitoring programs in reclaimed water reuse projects and to ensure a high level of protection for humans and the environment.

Selection of indicator contaminants of emerging concern when reusing reclaimed water for irrigation - A proposed methodology

Organic and microbial contaminants of emerging concern (CECs), even though not yet regulated, are of great concern in reclaimed water reuse projects. Due to the large number of CECs and their different characteristics, it is useful to include only a limited number of them in monitoring programs. The selection of the most representative CECs is still a current and open question. This study presents a new methodology for this scope, in particular for the evaluation of the performance of a polishing treatment and the assessment of the risk for the environment and the irrigated crops. As to organic CECs, the methodology is based on four criteria (occurrence, persistence, bioaccumulation and toxicity) expressed in terms of surrogates (respectively, concentrations in the secondary effluent, removal achieved in conventional activated sludge systems, Log K_ow and predicted-no-effect concentration). It consists of: (i) development of a dataset including the CECs found in the secondary effluent, together with the corresponding values of surrogates found in the literature or by in-field investigations; (ii) normalization step with the assignment of a score between 1 (low environmental impact) and 5 (high environmental impact) to the different criteria based on threshold values set according to the literature and experts' judgement; (iii) CEC ranking according to their final score obtained as the sum of the specific scores; and (iv) selection of the representative CECs for the different needs. Regarding microbial CECs, the selection is based on their occurrence and their highest detection frequency in the secondary effluent and in the receiving water, the antibiotic consumption patterns, and recommendations by national and international organisations. The methodology was applied within the ongoing reuse project SERPIC resulting in a list of 30 indicator CECs, including amoxicillin, bisphenol A, ciprofloxacin, diclofenac, erythromycin, ibuprofen, iopromide, perfluorooctane sulfonate (PFOS), sulfamethoxazole, tetracycline, Escherichia coli, faecal coliform, 16S rRNA, sul1, and sul2.

Activated carbon coupled with advanced biological wastewater treatment: A review of the enhancement in micropollutant removal

This study consists of a review on the removal efficiencies of a wide spectrum of micropollutants (MPs) in biological treatment (mainly membrane bioreactor) coupled with activated carbon (AC) (AC added in the bioreactor or followed by an AC unit, acting as a post treatment). It focuses on how the presence of AC may promote the removal of MPs and the effects of dissolved organic matter (DOM) in wastewater. Removal data collected of MPs are analysed versus AC dose if powdered AC is added in the bioreactor, and as a function of the empty bed contact time in the case of a granular activated carbon (GAC) column acting as a post treatment. Moreover, the enhancement in macropollutant (organic matter, nitrogen and phosphorus compounds) removal is analysed as well as the AC mitigation effect towards membrane fouling and, finally, how sludge properties may change in the presence of AC. To sum up, it was found that AC improves the removal of most MPs, favouring their sorption on the AC surface, promoted by the presence of different functional groups and then enhancing their degradation processes. DOM is a strong competitor in sorption on the AC surface, but it may promote the transformation of GAC in a biologically activated carbon thus enhancing all the degradation processes. Finally, AC in the bioreactor increases sludge floc strength and improves its settling characteristics and sorption potential.

A review of the occurrence of selected micropollutants and microorganisms in different raw and treated manure - Environmental risk due to antibiotics after application to soil

This study consists of a review based on 104 papers published between 1980 and 2019, which dealt with the occurrence of pharmaceuticals, hormones and a selection of microorganisms in raw and treated manure from different types of animal farms. The selected pharmaceuticals and hormones are those regularly administered to livestock for treating and preventing diseases. Worldwide, manure is commonly spread on soil as a fertilizer due to its nutrient content. However, this practice also represents a potential pathway for micropollutant release into the environment. In this context, this study evaluates the predicted concentrations of some antibiotics in soil after the application of swine slurry on soil and compares them with corresponding measured concentrations found in the literature. Enrofloxacin, oxytetracycline and chlortetracycline were the antibiotics with the highest concentrations that were found in raw and treated manure and that showed a high risk together with sulfamethazine. Future research should focus on monitoring other pathogens, parent compounds and their main metabolites in raw and treated manure, studying the spread and development of antibiotic resistance genes in the environment due to residues of antibiotics in manure applied to soil, and evaluating predicted no effect concentrations of pharmaceuticals and hormones commonly administered to livestock with regard to terrestrial organisms.