Solar processes and ozonation for fresh-cut wastewater reclamation and reuse: Assessment of chemical, microbiological and chlorosis risks of raw-eaten crops

In this study, a full cycle of agricultural reuse of agro-food wastewater (synthetic fresh-cut wastewater, SFCWW) at pilot plant scale has been investigated. Treated SFCWW by ozonation and two solar processes (H2O2/solar, Fe3+-EDDHA/H2O2/solar) was used to irrigate two raw-eaten crops (lettuce and radish) grown in peat. Two foodborne pathogens (E. coli O157:H7 and Salmonella enteritidis) and five organic microcontaminants (OMCs: atrazine, azoxystrobin, buprofezin, procymidone and terbutryn) were monitored along the whole process. The three studied processes showed a high treatment capability (reaching microbial loads < 7 CFU/100 mL and 21-90 % of OMC reduction), robustness (based on 7 or 10 analysed batches for each treatment process) and high suitability for subsequent treated SFCWW safe reuse: non-phytotoxic towards Lactuca sativa and no bacterial regrowth during its storage for a week. The analysis of the harvested crop samples irrigated with treated SFCWW in all the studied processes showed an absence of microbial contamination (< limit of detection, LOD; i.e., < 1 CFU/99 g of lettuce and < 1 CFU/8 g of radish), a significant reduction of OMC uptake (in the range 40-60 % and > 90 % for solar treated and ozonated SFCWW, respectively) and bioaccumulation in both crops in comparison with the results obtained with untreated SFCWW. Moreover, the chlorophyll content in the harvested lettuces irrigated with SFCWW treated by Fe3+-EDDHA/H2O2/solar was twice than that irrigated with SFCWW treated by H2O2/solar and ozone, indicating the additional advantage of using Fe3+-EDDHA as an iron source to reduce the risk of iron chlorosis in crops. Finally, the chemical (dietary risk assessment for the combined exposure of the 5 OMCs) and quantitative microbiological risk assessment (QMRA) of the harvested crops showed the capability of the studied processes to reduce the risk associated with untreated SFCWW reuse by more than 50 % and more than 4 orders of magnitude, respectively.

Synthetic fresh-cut wastewater disinfection and decontamination by ozonation at pilot scale

In this research, the capability of ozonation and peroxone treatment for the simultaneous disinfection and decontamination of wash water from the fresh-cut industry has been investigated at pilot plant scale (10 L). The removal efficiency of six organic microcontaminants (OMCs) (four of them priority substances) and the inactivation of two foodborne pathogens (Escherichia coli O157:H7 and Salmonella enteritidis) in synthetic fresh-cut wastewater (SFCWW) has been assessed. Ozonation and peroxone (O₃ with 20 mgL^-1 of H₂O₂) process has been investigated under several operational conditions: natural SFCWW pH (6.25) and basic pH (11), and two different initial ozone production (0.09 and 0.15 gO₃ L^-1 h^-1). Results showed that the highest efficiency for OMCs removal (85%) and pathogen inactivation (>5-Log) were obtained with ozonation treatment at natural pH. OMCs degradation was obtained after 120 min of treatment with an ozone dose of 27.4 mgO₃ L^-1. First order kinetic constant of each OMC degradation was obtained, and two clear different groups have been identify based on their degradation profiles, which have been correlated with their chemical structure. G₁-OMC [terbutryn > buprofezin > azoxystrobin] > G₂-OMC [imidacloprid > simazine > thiamethoxam]. As for bacterial inactivation, up to 10 min of treatment time and an ozone dose of <8.6 mgO₃ L^-1 were required to reach the detection limit (2 CFU mL^-1), showing E. coli O157:H7 a higher susceptibility to be inactivated (k: 2.79 min^-1) than S. enteritidis (k: 1.47 min^-1). Moreover, from the techno-economical and toxicological assessment of the treated water with the best operational condition, can be highlighted: i) a slight acute toxicity for V. fischeri (47 ± 2.3% of luminescence inhibition), ii) an acute toxicity for Daphnia magna (100% of immobilization) and iii) a total cost of the treatment of 1.16 € m^-3.

Microbiological evaluation of combined advanced chemical-biological oxidation technologies for the treatment of cork boiling wastewater

This paper contains a multidisciplinary approach that will contribute to design and properly evaluate a treatment line for complex biorecalcitrant wastewaters. To demonstrate this approach a specific industrial wastewater (cork boiling wastewater, CBW) was used. A treatment line based on a coagulation-flocculation step followed by an Advanced Oxidation Process (AOP) (solar photo-Fenton) and combined with an aerobic biological system was evaluated. Applied microbiological techniques: optical microscopy, plate count, DNA extraction and qPCR, indicated that some communities disappeared after the activated sludge adaptation period to the partially treated wastewater, while communities that did not disappear were damaged: 2-log reduction of total heterotrophic bacteria (THB) and a decrease in DNA concentration from 200 ng/μL to 65 ng/μL were observed. Therefore, chemical and microbiological results obtained along the set of experiments, suggested the inefficiency of the combined treatment option between solar photo-Fenton and advanced aerobic biological systems for CBW. This led to the necessity of applying solar photo-Fenton without combining with biotreatment and with the objective of improving the effluent quality enough for being reused in the own industry. Toxicity tests, based on different organisms (after coagulation-flocculation followed by solar photo-Fenton), showed increase on acute toxicity (from 46% to 71% by respirometric assays) and the development of chronic toxicity (from 21-29% to 83-90% also measured by respirometric assays), made evident the incompatibility of this type of wastewater with a biological treatment even after the application of an AOP.