Olivier Autin

The impact of background organic matter and alkalinity on the degradation of the pesticide metaldehyde by two advanced oxidation processes: UV/H2O2 and UV/TiO2

The impact of background constituents on the degradation of trace levels of micropollutants by two advanced oxidation processes: UV/H₂O₂ and UV/TiO₂ was studied. Experimental results demonstrated that the background scavenging rate rather than the concentration of micropollutant controls the required UV irradiation dose. The character of the natural organic matter had a limited impact on scavenging when the water source remains unchanged, however, a periodic bleed of hydrophobic material may substantially increase the minimum UV dose required to reach the desired micropollutant concentration. Moreover, in the case of UV/TiO₂, high concentrations of background organic matter do not only act as scavengers but also saturate the TiO₂ surface. Alkalinity inhibits the efficacy of UV/TiO₂ photocatalysis due to the formation of large TiO₂ aggregates. The study also demonstrated that the use of synthetic waters for treatability test purposes was an acceptable approach as long as both the background organic matter and the alkalinity were matched to that of the projected application. Finally spiking micropollutants at higher concentrations does not alter the significance of the findings as long as the background constituents represent more than 85% of the total scavenging rate.

Evaluation of a UV-light emitting diodes unit for the removal of micropollutants in water for low energy advanced oxidation processes.

There is growing interest in using light emitting diodes (LEDs) as alternative to traditional mercury lamps for the removal of micropollutants by advanced oxidation processes due to their low energy consumption and potential for high efficiency and long lifetime. This study investigates the penetration and coverage of the light emitted by LEDs in order to build an optimised LED collimated beam apparatus. From the experimental data, cost analysis was conducted in order to identify when LEDs will become economically viable. It was observed that if their development follows the predictions, LEDs should be a viable alternative to traditional lamps within 7yr for both UV/H2O2 and UV/TiO2 processes. However, parameters such as wall plug efficiency and input power need to improve for LEDs to become competitive.

Evaluating the impact of LED bulb development on the economic viability of ultraviolet technology for disinfection.

Ultraviolet (UV) technologies have been very successful in disinfection applications due to their ability to inactivate microorganisms without producing harmful disinfection by-products. However, there have been a number of concerns associated with the use of conventional UV systems such as hazardous mercury content, high capital investment and reduced electrical efficiency. These concerns have set limitations for the use of UV processes. The study evaluates the development of light emitting diode (LED) technology as an alternative UV source over the last 5 years, analyses the projections provided by the researchers and UV LED manufacturers and presents the information in a cost model with the aim to predict the timeline at which UV LED will compete with traditional UV low pressure high output technology in the commercial market at full-scale residential and industrial disinfection applications.

Incorporating biodegradation and advanced oxidation processes in the treatment of spent metalworking fluids.

The treatment of spent metalworking fluids (MWFs) is difficult due to their complex and variable composition. Small businesses often struggle to meet increasingly stringent legislation and rising costs as they need to treat this wastewater on site annually over a short period. Larger businesses that treat their wastewater continuously can benefit from the use of biological processes, although new MWFs designed to resist biological activity represent a challenge. A three-stage treatment is generally applied, with the oil phase being removed first, followed by a reduction in COD loading and then polishing of the effluents quality in the final stage. The performance of advanced oxidation processes (AOPs), which could be of benefit to both types of businesses was studied. After assessing the biodegradability of spent MFW, different AOPs were used (UV/H2O2, photo-Fenton and UV/TiO2) to establish the treatability of this wastewater by hydroxyl radicals (•OH). The interactions of both the chemical and biological treatments were also investigated. The wastewater was found to be readily biodegradable in the Zahn–Wellens test with 69% COD and 74% DOC removal. The UV/TiO2 reactor was found to be the cheapest option achieving a very good COD removal (82% at 20 min retention time and 10 L min−1 aeration rate). The photo-Fenton process was found to be efficient in terms of degradation rate, achieving 84% COD removal (1 M Fe2+, 40 M H2O2, 20.7 J cm−2, pH 3) and also improving the wastewaters biodegradability. The UV/H2O2 process was the most effective in removing recalcitrant COD in the post-biological treatment stage.

Change in haloacetic acid formation potential during UV and UV/H2O2 treatment of model organic compounds.

Haloacetic acids (HAAs) are disinfection by-products produced by the chlorination of organic matter, including amino acids. Advanced oxidation processes are expected to be effective for the destruction of HAA precursors; however, recent studies have reported the possible failure of these processes to reduce HAA formation potential. This study examined HAA formation potential during the course of UV or UV/H2O2 treatment of three organic compounds: leucine, serine, and resorcinol. HAA formation potential decreased in the treatment of resorcinol, while the potential increased slightly in the treatment of serine and greatly increased for leucine. The chemical structure required for HAA formation was assumed to be produced during the course of UV/H2O2 treatment of leucine and serine. Also, H abstraction from the δ carbon was assumed to result from the initial degradation of leucine by the hydroxyl radical during the UV/H2O2 treatment. The hydroxyl radical may have further reacted with leucine moiety to shorten its carbon chain. This would have produced a chemical structure capable of forming HAA, thus increasing HAA formation potential.

Impact of fouling, cleaning and faecal contamination on the separation of water from urine using thermally driven membrane separation

ABSTRACT In this study, membrane distillation is evaluated as a technology for non-sewered sanitation, using waste heat to enable separation of clean water from urine. Whilst membrane fouling was observed for urine, wetting was not evident and product water quality met the proposed discharge standard, despite concentration of the feed. Fouling was reversible using physical cleaning, which is similar to previous membrane studies operating without pressure as the driving force. High chemical oxygen demand reduction was achieved following faecal contamination, but mass transfer was impeded and wetting occurred which compromised permeate quality, suggesting upstream intervention is demanded to limit the extent of faecal contamination.