Veolia Water

Zinc oxide is a semiconductor material with an interesting potential for photocatalysis of organic pollutants. It has been prepared according an eco-friendly green method, using five various plant extracts (banana, rosemary, bitter orange, olive tree, comfrey). Two different synthesis processes were tested: a hotplate synthesis and a hydrothermal method. Metal precursor used was zinc acetate. Plants present in the process allowed the formation and the self-assembling of ZnO during the crystal growth thanks to the large chemical family of polyphenol which act as reductants. Crystalline and organic matter-free compounds obtained after annealing were characterized with diffractive reflectance spectroscopy (DRS) to determine gap energies and confirm ZnO belonging to semiconductors, X-ray diffraction to verify the crystalline structure and its features, Fourier transform infrared spectroscopy (FTIR) to check the characteristic functional group and scanning electron microscopy (SEM) to reveal the self-assembling forms of ZnO. Data about the shapes, dimensions and crystal planes of zinc oxide were regarded in the light of the plant and the synthesis method used. This work has highlighted the morphologies of ZnO obtained on the basis of the synthesis method and the plant extracts.

Stainless steels are successfully used in the range of water compositions encountered during wastewater treatment. Austenitic stainless steels are the most often used grades in water treatment applications. S30403 and S31603 are known to be suitable for municipal and industrial wastewater with respectively moderate and increased chloride contents. Considering the comprehension of economic cost, good corrosion resistance and higher mechanical properties, lean duplex stainless steels can be a good alternative to these commonly used austenitic grades but they are still too rarely chosen, probably due to a lack of case studies. The present paper deals with the localized corrosion performance of lean duplex (S32101, S32202 and S32304) in solutions simulating pre-treatment unit waters, using electrochemical testing. The localized corrosion was compared with austenitic stainless steels (S30403 and S31603) and with more alloyed duplex grades (S82441 and S32205). Pitting corrosion methods were adapted from standard electrochemical test methods ASTM G150 ASTM G61 to assess critical pitting temperature (CPT) and pitting potential (PP) respectively. Environmental parameters (chloride content, pH and temperature) were selected to be representative of the different environments that can be encountered in urban wastewater treatment plants. All the results permit to have an overview of corrosion properties according to the environmental parameters and to choose properly the best stainless steel grade for urban wastewater treatment units. This study allows also to have a clearer view of the behavior of duplex stainless steel grades versus austenitic grades in such environments. It confirms that lean duplex grades S32101 and S32202 can be used as alternatives to S30403 and S31603 respectively.

Thanks to their good corrosion resistance and ease to shape and weld, austenitic stainless steel grades (e.g. EN 1.4404 / 316 L / UNS S31603) are used as standard materials for the construction of urban wastewater treatment plants (WWTP). The main factors influencing the corrosiveness of the fluids in WWTP are halide concentration (more specifically chlorides), H2S, low pH, high temperature and their combined action. Considering the comprehension of moderate material cost, good corrosion resistance and high mechanical properties, lean duplex stainless steels are good alternatives to the commonly used austenitic grades, but they are still too rarely chosen, probably due to a lack of case studies. To define the limit of use of lean duplex stainless steels for urban wastewater treatment units, a European project was initiated, involving stainless steel manufacturers, end-users, corrosion and microbiological laboratories. The present paper deals with the localized corrosion performance of lean duplex EN 1.4062 / DX2202 / UNS S32202 in solutions simulating pre-treatment unit waters, compared to the austenitic stainless steel 316 L and the more alloyed duplex grade EN 1.4462 / DX2205 / UNS S32205. Crevice corrosion testing was performed using crevice formers defined in ISO 18070: 2015. Both laboratory screen tests and field exposure in urban wastewater treatment plants were performed. This study confirms that lean duplex grade DX2202 can be used as an alternative to 316 L in aerated wet atmospheres in case of moderate contamination of H2S (<10 ppm) and chloride (<200 ppm). For higher contaminations (e.g. H2S around 100 ppm and chloride content around 1000 ppm) the duplex grade DX2205 should be preferred.

With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred.

Normalizations by TSS or P-PO(4)(3-)initial concentrations are consistent as they are correlated to the Jar-test performances. Jar-tests results are independent of the wastewater quality variations in terms of TSS and P-PO(4)(3-)and independent of the WWTP origin of the water. A notable variability in the TSS results indicates that the pollutant's initial load has to be taken into account even with normalizations. This variability is lower with normalization by P-PO43-, indicating that this is the best indicator to consider. It is possible to determine that the optimal cation dosage is 60 mol Fe3+/ kg P-PO(4)(3-)as it guarantees a residual concentration of 0.7-1.0 mgP/L and a good removal of TSS. Then, six commercially available cationic coagulants were compared, demonstrating a comparable effect at a comparable normalized molar dose, whatever the coagulant on both TSS and P-PO43-, as well as on soluble carbon and nitrogen. The differences observed between these types of coagulants in the literature are then probably due to methodological issues. Settling velocity distribution charts were also very similar for the different coagulants. This confirms that the source of cation and the type of cation have no significant effect on physico-chemical settling performances.