Urban wastewater disinfection by iron chelates mediated solar photo-Fenton: Effects on seven pathogens and antibiotic resistance transfer potential.

The effects of solar photo-Fenton (SPF) process mediated by the iron chelate Fe3+ imminodisuccinic acid (Fe:IDS) on both the inactivation of seven relevant pathogens and the potential for antibiotic resistance transfer (degradation of antibiotic resistance genes (ARGs) and after treatment regrowth), in real secondary treated urban wastewater, were investigated for the first time. A comparison with results obtained by sunlight/H2O2 process and Fe3+ ethylenediaminedisuccinic acid (Fe:EDDS) SPF was also carried out. ARGs were quantified by polymerase chain reaction (PCR) in samples before and after (3 h) the treatment. The persistence of the selected pathogens and ARGs was also evaluated in regrowth tests (72 h) under environmentally mimicking conditions. Fe:IDS SPF resulted to be more effective (from 1.4 log removal for Staphylococcus spp. to 4.3 log removal for Escherichia coli) than Fe:EDDS SPF (from 0.8 log removal for Pseudomonas aeruginosa to 2.0 log removal for Total coliphages) and sunlight/H2O2 (from 1.2 log removal for Clostridium perfringens to 3.3 log removal for E. coli) processes for the seven pathogens investigated. Potential pathogens regrowth was also severely affected, as no substantial regrowth was observed, both in presence and absence of catalase. A similar trend was observed for ARGs removal too (until 0.001 fold change expression for qnrS after 3 h). However, a poor effect and a slight increase in fold change was observed after treatment especially for gyrA, mefA and intl1. Overall, the effect of the investigated processes on ARGs was found to be ARG dependent. Noteworthy, coliphages can regrow after sunlight/H2O2 treatment unlike SPF processes, increasing the risk of antibiotic resistance transfer by transduction mechanism. In conclusion, Fe:IDS SPF is an attractive solution for tertiary treatment of urban wastewater in small wastewater treatment plants as it can provide effective disinfection and a higher protection against antibiotic resistance transfer than the other investigated processes.

Improving organic matter and nutrients removal and minimizing sludge production in landfill leachate pre-treatment by Fenton process through a comprehensive response surface methodology approach.

Landfill leachate (LL) represents a very complex effluent difficult to treat and to manage which usually requires a chemical pre-treatment. In this study, response surface methodology (RSM) was used to identify the optimum operating conditions of the Fenton process as a pre-treatment of LL in order to reduce the high organic content and simultaneously optimize the BOD5:TN:TP ratio. The dosages of Fenton process reagents, namely Fe2+ and H2O2, were used as variables for the implementation of RSM. Chemical oxygen demand (COD), five-days biochemical oxygen demand (BOD5), total nitrogen (TN), total phosphorus (TP) removals (and simultaneously BOD5:TN:TP ratio), sludge-to-iron ratio (SIR) and organic removal-to-sludge ratio (ORSR) were selected as target responses. This approach considered the SIR and ORSR parameters which are a useful tool for assessing sludge formation during the process along with organic matter removal. The variables (H2O2 and Fe2+ concentrations) significantly affected the responses, as the role of oxidation mechanism is dominant with respect to coagulation one. The pH for the process was fixed to 2.8 while the treatment time was set to 2 h. The optimum operational conditions obtained by perturbation and 3D surface plot, were found to be 4262 mg/L and 5104 mg/L for Fe2+ and H2O2, respectively (H2O2/Fe2+ molar ratio = 2) with COD, BOD5, TN and TP removals of 70%, 67%, 84% and 96% respectively, while SIR and ORSR final values were 1.15 L/mol and 33.79 g/L respectively, in accordance with models-predicted values. Moreover, the initial unbalanced BOD5:TN:TP ratio (9:1:1) was significantly improved (100:6:1), making the effluent suitable for a subsequent biological treatment. The investigated approach allowed to optimize the removal of organic load and nutrients as well as to minimize the sludge formation in Fenton process, providing a useful tool for the operation and management of LL pre-treatment.

Chelating agents supported solar photo-Fenton and sunlight/H2O2 processes for pharmaceuticals removal and resistant pathogens inactivation in quaternary treatment for urban wastewater reuse.

In this work, Fe3+-iminodisuccinic acid (Fe:IDS) based solar photo Fenton (SPF), an Italian patented method, was investigated in quaternary treatment of real urban wastewater and compared to Fe3+-ethylenediamine-N,N'-disuccinic acid (Fe:EDDS) for the first time. Three pharmaceuticals (PCs) (sulfamethoxazole, carbamazepine and trimethoprim) and four pathogens (Escherichia coli, somatic and F-plus coliphages, Clostridium perfringens, consistently with the new EU regulation for wastewater reuse (2020/741)), were chosen as target pollutants. SPF with Fe:EDDS was more effective in PCs removal (80%, 10 kJ L-1) than the SPF with Fe:IDS (58%), possibly due to the higher capability of generating hydroxyl radicals. On the contrary, Fe:IDS was more effective (4.3 log inactivation for E. coli) than Fe:EDDS (1.9 log) in pathogens inactivation, possibly due to a lower iron precipitation and turbidity which finally promoted an improved intracellular photo-Fenton mechanism. Fe:L based SPF was subsequently coupled to sunlight/H2O2. Interestingly, while its combination with Fe:EDDS based SPF slightly increased disinfectant efficacy (2.3 vs 1.9 log inactivation for E. coli), the combination with Fe:IDS decreased inactivation efficiency (3.4 vs 4.3 log reduction). In conclusion, due to the good compromise between PCs removal and disinfection efficiency, Fe:IDS SPF alone is an attractive option for quaternary treatment for urban wastewater reuse.

Landfill leachate treatment by a combination of a multiple plant hybrid constructed wetland system with a solar photoFenton process in a raceway pond reactor.

The sustainable and green treatment of landfill leachate (LL), produced by municipal solid waste, represents one of the most relevant challenges in the integrated waste management systems. Accordingly, in this work a green solution was investigated by coupling an innovative hybrid constructed wetland (HCW) to a solar photo-Fenton (SPF) process. A multiple layers HCW pilot plant including different medium substrates (sand, solid compost and carriers) and plant species (Phragmites australis, Arundo donax and A. plinii) was designed. The HCW was functionalised with compost tea solution to simultaneously provide high nutrient content for plants and increase the microorganism biodiversity. Process efficiency was investigated using different real LLs (young and mature) in terms of chemical oxygen demand (COD), nitrogen compounds, chlorides and metals. Removals in the range 75-95% were observed for all the parameters after ten days of leachate recirculation in the pilot plant. Subsequently, the SPF process was carried out in a raceway pond reactor (RPR) as polishing step, significantly improving COD removal (further 49%). HCW combined with SPF in RPR would allow to meet the corresponding limits according to the final use/fate of the effluent by modulating the main parameters of the process.

Co-treatment of landfill leachate with urban wastewater by chemical, physical and biological processes: Fenton oxidation preserves autochthonous bacterial community in the activated sludge process.

The impact of Fenton oxidation (FO) and Air stripping (AS) pre-treatments on the bacterial community of a biological activated sludge (B-AS) process for the co-treatment of mature landfill leachate (MLL) and urban wastewater (UWW) was assessed. In this work high-throughput sequencing was used to identify changes in the composition of the bacterial communities when exposed to different landfill leachate's pre-treatments. The combination of FO and AS to increase biodegradability (BOD5/COD) and reduce ammonia concentration (NH3) respectively, allowed to successfully operate the B-AS and effectively treat MLL. In particular, BOD5/COD resulted to be the key factor for bacterial community shifting. The microbiological community of the B-AS, mainly composed by the phylum Bacteroidota (Saprospiraceae, PHOS-HE51, Chitinophagaceae) after FO pre-treatment, shifted to Pseudomonadota (Caulobacteraceae and Hyphomicrobiaceae) when FO was not used. At the same time a drastic reduction in BOD5 removal was observed (90%-58%). On the other hand, high NH3 concentration affected the abundance of the family Saprospiraceae, known to play a key role in the degradation of complex organic compounds in B-AS. The results obtained suggest that a suitable combination of pre-treatments can reduce the negative effect of MLL on the B-AS process, reducing the pressure on autochthonous bacteria and therefore the acclimatization time of the biological process.

Combination of flow cytometry and molecular analysis to monitor the effect of UVC/H2O2 vs UVC/H2O2/Cu-IDS processes on pathogens and antibiotic resistant genes in secondary wastewater effluents.

The efficiency of a new Advanced Oxidation Process (AOP), namely the photo Fenton like process UV-C/H2O2/IDS-Cu, in removing determinants of antibiotic resistance and pathogenic bacteria was compared to a consolidated AOP (namely UV-C/H2O2) in a secondary treated municipal WasteWater (WW). A reductionist experimental laboratory-based approach was applied on real WW and the parameters were collected by an alternative integrated approach using (i) flow cytometry to enumerate bacteria and test for the fitness of the bacterial communities and (ii) molecular analyses to define the community composition (16S rRNA amplicon sequencing) and the abundances of Antibiotic Resistance Genes (ARGs) and of the class 1 integron (intI1 gene) (by quantitative PCR). The same approach was applied also to post-treatment regrowth tests (24 h) to define the potential persistence of the tested parameters. These experiments were performed in both, human pathogens favorable conditions (HPC, in rich medium and 37°C) and in environmental mimicking conditions (EMC, original WW and 20°C). UV-C/H2O2/IDS-Cu process resulted to be more effective than the UV-C/H2O2in inactivating bacterial cells in the EMC post-treatment regrowth experiments. Both AOPs were efficiently abating potential human pathogenic bacteria and ARGs in the HPC regrowth experiments, although this trend could not be detected in the measurements taken immediately after the disinfection. In comparison with the UV-C/H2O2, the UV-C/H2O2/IDS-Cu process did not apparently offer significant improvements in the abatement of the tested parameters in the WW effluent but, by evaluating the results of the regrowth experiments it was possible to extrapolate more complex trends, suggesting contrasting efficiencies visible only after a few hours. This study offers a detailed view on the abatement efficiency of microbiological/genetic parameters for the UV-C/H2O2/IDS-Cu process, calling for technical adjustments for this very promising technology. At the same time, our results clearly demonstrated the inadequacy of currently applied methodologies in the evaluation of specific parameters (e.g. determinants of antibiotic resistance and pathogenic bacteria) in WW.