Jitka MacAdam

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.

Photocatalytic oxidation of natural organic matter surrogates and the impact on trihalomethane formation potential

Natural organic matter (NOM) consists of a complex mixture of organics and acts as precursors for a range of disinfection by-products (DBPs) including trihalomethanes (THMs). The characteristics of these precursors are still not well identified and here we have used a range of NOM surrogates that allows us to investigate how the characteristics of NOM relate to treatability with photocatalytical oxidation. Nine surrogates of NOM (five amino acids, two carbohydrates, two phenolic compounds) were evaluated and the impact of retention time on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP) measured. Adsorption of the compounds onto TiO(2) was evaluated and electrostatic forces played a significant role in their removal although photocatalytic oxidation was found to be unselective. DOC and THMFP decreased significantly with retention time except for l-leucine where the by-products formed during photocatalytic oxidation were significantly more reactive with chlorine than the parent compound.

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.

Photocatalytic oxidation, GAC and biotreatment combinations: an alternative to the coagulation of hydrophilic rich waters?

This study investigated the photocatalytic oxidation of a raw water rich in hydrophilic natural organic matter (NOM) and the impact on the removal of: dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254) and trihalomethanes formation potential (THMFP). Dissolved organic carbon and UV254 removals were 40% and 55%, respectively, after 1 min irradiation time and 1 g L−1 dose of TiO2. The THMFP content was reduced from 305 µg L−1 in raw water to 144 µg L−1 after 10 min treatment, whereas chlorine reactivity was stable with treatment. The results showed that larger molecular weight species were preferentially degraded during the process. Dissolved organic carbon and THMFP removals reached 60% and 70%, respectively, after photocatalytic oxidation and granular activated carbon (GAC) columns.

An investigation into advanced oxidation of three chlorophenoxy pesticides in surface water

The performance of Fentons reagent in removing 2,4-D, MCPA and mecoprop from surface water has been evaluated here. Initial trials were undertaken at a pesticide concentration of 4.5 x 10(-5) mol l(-1) in deionised water at pH 3 and two different stoichiometric ratios of pesticide: Fe(II): H(2)O(2) (1:1:10, 1:10:10) were evaluated. At the 1:1:10 ratio, approximately 10 minutes were required to achieve a 50% removal of the pesticide. At the higher ratio the removal achieved after 1 minute, was >90%. Subsequent experiments studied the performance of Fenton (4.5 x 10(-4) mol l(-1) Fe(II): 4.5 x 10(-4) mol l(-1) H(2)O(2)) in surface water spiked with pesticides and the impact of pH on the rate and degree of pesticide degradation was investigated. The removal was significantly improved at pH 3 in comparison to pH 6.5. The effect of Fenton on DOC removal from surface water was followed. Experiments investigated the performance of Fenton at pesticide concentrations of 7.5 x 10(-9) mol l(-1) in surface water. Fenton was shown to be an effective treatment for removing low levels of pesticides from surface waters at pH 3 & 4.

Water-Formed Scales and Deposits: Types, Characteristics, and Relevant Industries

Precipitation of mineral deposits is caused by sparingly soluble salts. The primary agents responsible are the carbonates and sulfates of calcium and magnesium with barium salts, silicate, and phosphate scaling also causing problems in some industries. Mineral scale formation is a considerable issue in domestic, commercial, and industrial applications. The formation of mineral deposits is affected by a number of factors including supersaturation, temperature, pH, pressure, flow velocity, and presence of impurities. Different areas and processes, where equipment comes into contact with scaling water either with or without temperature gradient, are being affected by this problem; steam generators, cooling systems, membrane surfaces, and evaporators, just to name a few. The main mineral deposits described or mentioned in this chapter are calcium carbonate, calcium and barium sulfate, magnesium-based scales, silica scales, iron scales, calcium phosphate, and struvite.Abstract Precipitation of mineral deposits is caused by sparingly soluble salts. The primary agents responsible are the carbonates and sulfates of calcium and magnesium with barium salts, silicate, and phosphate scaling also causing problems in some industries. Mineral scale formation is a considerable issue in domestic, commercial, and industrial applications. The formation of mineral deposits is affected by a number of factors including supersaturation, temperature, pH, pressure, flow velocity, and presence of impurities. Different areas and processes, where equipment comes into contact with scaling water either with or without temperature gradient, are being affected by this problem; steam generators, cooling systems, membrane surfaces, and evaporators, just to name a few. The main mineral deposits described or mentioned in this chapter are calcium carbonate, calcium and barium sulfate, magnesium-based scales, silica scales, iron scales, calcium phosphate, and struvite.

The Effect of Metal Ions on Calcium Carbonate Precipitation and Scale Formation

Scale formation in domestic heating appliances is a widespread problem in the UK. Scale affects the life of energy intensive domestic devices such boilers with a potentially significant impact on their energy efficiency. A number of metallic cations, such as copper and zinc have been reported to affect CaCO3 precipitation and scale formation. This study aimed to investigate closely the effect of zinc and copper on calcium carbonate (CaCO3) formation and two sets of laboratory tests were performed. The effect of both metals on CaCO3 precipitation was investigated using a standard jar tester. The longest delay in precipitation was obtained by zinc. To study CaCO3 formation on a heated surface, a rapid scaling test was developed. This test was conducted at 42°C and 70°C to examine the effect of zinc dosing on CaCO3 scale formation. The results show that zinc is effective in inhibiting scale formation on a heated surface particularly at 42°C.

Intake of lead (Pb) from tap water of homes with leaded and low lead plumbing systems

Methods of quantifying consumer exposure to lead in drinking water are increasingly of interest worldwide, especially those that account for consumer drinking habits and the semi-random nature of water lead release from plumbing systems. A duplicate intake protocol was developed in which individuals took a sub-sample from each measured drink they consumed in the home over three days in both winter and summer. The protocol was applied in two different water company regional areas (WC1 and WC2), selected to represent high risk situations in England, with the presence or absence of lead service pipes or phosphate corrosion control. Consumer exposure to lead was highest in properties with lead service pipes, served by water without P dosing. The protocol indicated that a small number of individuals in the study, all from homes with lead service pipes, consumed lead at levels that exceeded current guidance from the European Food Standards Agency. Childrens potential blood lead levels (BLLs) were estimated using the Internal Exposure Uptake Biokinetic model (IEUBK). The IEUBK model predicted that up to 46% of children aged 0-7 years old may have elevated BLLs (>5 μg/dL) when consuming the worst case drinking water quality (>99%ile). Estimating blood lead levels using the IEUBK model for more typical lead concentrations in drinking water identified in this study (between 0.1 and 7.1 μg/L), predicts that elevated BLLs may affect a small proportion of children between 0 and 7 years old.