Quantifying the performance of a hybrid anion exchanger/adsorbent for phosphorus removal using mass spectrometry coupled with batch kinetic trials.

Increasingly stricter phosphorus discharge limits represent a significant challenge for the wastewater industry. Hybrid media comprising anionic exchange resins with dispersions of hydrated ferric oxide nanoparticles have been shown to selectively remove phosphorus from wastewaters, and display greater capacity and operational capability than both conventional treatment techniques and other ferric-based adsorbent materials. Spectrographic analyses of the internal surfaces of a hybrid media during kinetic experiments show that the adsorption of phosphorus is very rapid, utilising 54% of the total capacity of the media within the first 15 min and 95% within the first 60 min. These analyses demonstrate the importance of intraparticle diffusion on the overall rate in relation to the penetration of phosphorus. Operational capacity is a function of the target effluent phosphorus concentration and for 0.1 mg P L-1, this is [Formula: see text], which is 8-13% of the exhaustive capacity. The adsorbed phosphorus can be selectively recovered, offering a potential route to recycle this important nutrient. The main implication of the work is that the ferric nanoparticle adsorbent can provide a highly effective means of achieving a final effluent phosphorus concentration of 0.1 mg P L-1, even when treating sewage effluent at 5 mg P L-1.

Carbonaceous and nitrogenous disinfection by-product formation from algal organic matter.

Seasonal algal blooms in drinking water sources release intracellular and extracellular algal organic matter (AOM) in significant concentrations into the water. This organic matter provides precursors for disinfection by-products (DBPs) formed when the water is subsequently chlorinated at the final disinfection stage of the potable water treatment process. This paper presents results of AOM characterisation from five algal species (three cyanobacteria, one diatom and one green) alongside the measurement of the DBP formation potential from the AOM of six algal species (an additional diatom). The character was explored in terms of hydrophilicity, charge and protein and carbohydrate content. 18 DBPs were measured following chlorination of the AOM samples: the four trihalomethanes (THMs), nine haloacetic acids (HAAs), four haloacetonitriles (HANs) and one halonitromethane (HNM). The AOM was found to be mainly hydrophilic (52 and 81%) in nature. Yields of up to 92.4 µg mg-1 C carbonaceous DBPs were measured, with few consistent trends between DBP formation propensity and either the specific ultraviolet absorbance (SUVA) or the chemical characteristics. The AOM from diatomaceous algae formed significant amounts of nitrogenous DBPs (up to 1.7 µg mg-1 C). The weak trends in DBPFP may be attributable to the hydrophilic nature of AOM, which also makes it more challenging to remove by conventional water treatment processes.

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.

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.

The influence of ultrasound frequency and power, on the algal species Microcystis aeruginosa, Aphanizomenon flos-aquae, Scenedesmus subspicatus and Melosira sp.

We report on the effectiveness of sonication on controlling the growth of four problematic algal species which are morphologically different and from three algal divisions. Two cyanobacterial species Microcystis aeruginosa (unicellular) and Aphanizomenon flos-aquae (filamentous), one green alga Scenedesmus subspicatus (colonial) and lastly a diatom species Melosira sp. (filamentous) were subjected to ultrasound of selected low to high frequencies ranging from 20 to 1144 kHz. Microcystis aeruginosa and Scenedesmus subspicatus highest cell removal rates were 16 +/- 2% and 20 +/- 3% when treated with the same ultrasound frequency of 862 kHz but differing energy levels of 133 and 67 kWh m(-3), respectively. Aphanizomenon flos-aquae best removal rate was 99 +/- 1% after 862 kHz and 133 kWh m(-3) of energy, with Melosira sp. achieving its highest cell removal at 83% subsequent to ultrasound of 20 kHz and 19 kWh m(-3). Microcystis aeruginosa and Scenedesmus subspicatus are considered non-susceptible species to ultrasound treatment from a water treatment perspective due to their low cell removal rates; however, photosynthetic activity reduction of 65% for Microcystis aeruginosa does indicate the possible utilization of ultrasound to control bloom growth, rather than bloom elimination. Conversely, Aphanizomenon flos-aquae and Melosira sp. are deemed species highly susceptible to ultrasound. Morphological differences in shape (filamentous/non-filamentous) and cell wall structure (silica/peptidoglycan), and presence of gas vacuoles are probable reasons for these differing levels of susceptibility to ultrasound.

Comparison of UV/H2O2 and UV/TiO2 for the degradation of metaldehyde: Kinetics and the impact of background organics.

The kinetics of photodegradation of the pesticide metaldehyde by UV/H(2)O(2) and UV/TiO(2) in laboratory grade water and a natural surface water were studied. Experiments were carried out in a bench scale collimated beam device using UVC radiation. Metaldehyde was efficiently degraded by both processes in laboratory grade water at identical rates of degradation (0.0070 and 0.0067 cm(2) mJ(-1) for UV/TiO(2) and UV/H(2)O(2) respectively) when optimised doses were used. The ratio between oxidant and metaldehyde was significantly higher for H(2)O(2) due to its low photon absorption efficiency at 254 nm. However, the presence of background organic compounds in natural water severely affected the rate of degradation, and whilst the pseudo first-order rate constant of degradation by UV/H(2)O(2) was slowed down (0.0020 cm(2) mJ(-1)), the degradation was completely inhibited for the UV/TiO(2) process (k' = 0.00007 cm(2) mJ(-1)) due to the blockage of active sites on TiO(2) surface by the background organic material.

Biologically and chemically mediated adsorption and precipitation of phosphorus from wastewater.

Biologically and chemically mediated adsorption and precipitation processes offer a range of approaches for removing phosphorus (P) from agricultural, domestic and industrial effluents. Technologies implemented at full-scale include filtration by adsorbent media, such as steel slag, and recovery of phosphorus as struvite, which has been successfully commercialised as a fertiliser. Other promising technologies under investigation include P removal by polymers and nanomaterials as well as struvite formation by bacteria. There is a need to focus future research on improving the efficiency of P removal by adsorption and precipitation. This can be achieved by techniques such as regenerating filters, polymers and nanomaterials for renewed P removal. Research is also needed to optimise the fertiliser potential of struvite precipitates.

Comparison of coagulation performance and floc properties using a novel zirconium coagulant against traditional ferric and alum coagulants.

Coagulation in drinking water treatment has relied upon iron (Fe) and aluminium (Al) salts throughout the last century to provide the bulk removal of contaminants from source waters containing natural organic matter (NOM). However, there is now a need for improved treatment of these waters as their quality deteriorates and water quality standards become more difficult to achieve. Alternative coagulant chemicals offer a simple and inexpensive way of doing this. In this work a novel zirconium (Zr) coagulant was compared against traditional Fe and Al coagulants. The Zr coagulant was able to provide between 46 and 150% lower dissolved organic carbon (DOC) residual in comparison to the best traditional coagulant (Fe). In addition floc properties were significantly improved with larger and stronger flocs forming when the Zr coagulant was used with the median floc sizes being 930 µm for Zr; 710 µm for Fe and 450 µm for Al. In pilot scale experiments, a similar improved NOM and particle removal was observed. The results show that when optimised for combined DOC removal and low residual turbidity, the Zr coagulant out-performed the other coagulants tested at both bench and pilot scale.

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.

The role of polymer in improving floc strength for filtration.

Dosing polymer to improve floc characteristics is a widely practiced method in water treatment to improve floc strength, and there is strong operational evidence showing the benefit of polymer dosing. However, there is a paucity of information on how polymer operates in terms of quantifying the resulting floc size and strength over different size scales. A dual particle sizing approach was used to monitor large floc that contain most of the sludge volume and small floc that can cause downstream treatability problems for systems with and without polymer dosing. The polymer investigated was a slightly anionic polyacrylamide dosed in water collected post dissolved air flotation at concentrations of 0-0.03 mg L(-1). With increasing polymer dose, median floc size increased from 228 to 325 microm. Floc responses to increased shear rate showed that polymer dosing increased resistance to floc break-up. While all of the flocs showed high potential to regrow, regrowth was greatest in polymer-dosed systems, where flocs exceeded the size that they had reached previously. Increasing the dose of polymer showed increased removal of small particles (<8 microm) showing that polymer was able to effectively remove particles that are liable to cause downstream problems.

Polymers as bubble surface modifiers in the flotation of algae.

Previous research has shown that dosing polymers directly to the saturator of a dissolved air flotation (DAF) process in replacement of upstream coagulation can achieve algae removal comparable to that of conventional treatment, as a result of bubble modification. In this paper we further explore the application of polyDADMAC as a bubble modifier in this adapted DAF process. It was determined that removal improved with increasing polyDADMAC molecular weight (MW). Removal efficiencies obtained for Microcystis aeruginosa were much greater than those predicted theoretically, and were attributed to a potential projection of the polymer into the aqueous phase, increasing the swept volume of the bubble. PolyDADMAC dose and the resultant removal efficiency were dependent on the character of the associated algogenic organic matter (AOM). The AOM with high MW, low charge and significant hydrophobicity and protein content enabled co-operative binding, while that of high charge and low hydrophobicity hindered attachment.

The impact of differing cell and algogenic organic matter (AOM) characteristics on the coagulation and flotation of algae.

The aim of this study was to compare the coagulation and flotation of different algae species with varying morphology and algogenic organic matter (AOM) composition in order to link physical and chemical algae characteristics to treatment. Microcystis aeruginosa (cyanobacteria), Chlorella vulgaris (green algae), Asterionella formosa and Melosira sp. (diatoms) were treated by coagulation with aluminium sulphate and flotation. The AOM was extracted and treated separately. Analyses included cell counts, dissolved organic carbon, aluminium residual and zeta potential. Removal efficiencies in the range 94-99% were obtained for each species. Cells, AOM and aluminium were concurrently removed at a coagulant dose that was related on a log-log basis to both cell surface area and total charge density, although the relationship was much stronger for the latter. This was attributed to a significant proportion of the coagulant demand being generated by the AOM. The implications of such findings are that relatively simple charge measurements can be used to understand and control coagulation and flotation of algae.

The impact of barley straw conditioning on the inhibition of Scenedesmus using chemostats.

The current paper investigates the role of barley straw conditioning on inhibiting the alga Scenedesmus. Fresh, pre-rotted and white rot fungi (WRF) augmented straw was tested in a series of chemostat experiments over 15 weeks. All three systems were effective at inhibiting the alga with differences observed in the lag time before inhibition occurred and the rate of alga decline. Lag times of 8, 4 and 1 week(s) were recorded for the fresh, rotted and fungi-treated straws, respectively, with a maximum inhibition rate of >7x10(4) cellsweek(-1) observed for the fungi pre-treated system. Overall, the results indicate that pre-treatment is a viable method to enable barley straw to be used in a more reactive manner. Explanation is postulated that during pre-treatment no alternative sources of nitrogen are available, thereby leading to greater bacterial decomposition of straw lignin to release inhibitory substances. The principle of utilising an engineered pre-treatment by inoculating barley straw with WRF to enhance the impact of the straw on algal inhibition has been clearly demonstrated. Further work is required to understand how the straw pre-treatment stage can be reduced to minimise its duration while maximising the inhibitory effect of adding barley straw.

Comparison of the disinfection by-product formation potential of treated waters exposed to chlorine and monochloramine.

The formation of disinfection by-products (DBPs) from chlorination and monochloramination of treated drinking waters was determined. Samples were collected after treatment at 11 water treatment works but before exposure to chlorine or monochloramine. Formation potential tests were carried out to determine the DBPs formed by chlorination and monochloramination. DBPs measured were trihalomethanes (THMs), haloacetic acids (HAAs), halonitromethanes (HNMs), haloacetonitriles (HANs), haloaldehydes (HAs), haloketones (HKs) and iodo-THMs (i-THMs). All waters had the potential to form significant levels of all the DBPs measured. Compared to chlorine, monochloramination generally resulted in lower concentrations of DBPs with the exception of 1,1-dichloropropanone. The concentrations of THMs correlated well with the HAAs formed. The impact of bromine on the speciation of the DBPs was determined. The literature findings that higher bromide levels lead to higher concentrations of brominated DBPS were confirmed.

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 microg L(-1) in raw water to 144 microg 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.

Comparison between disintegrated and fermented sewage sludge for production of a carbon source suitable for biological nutrient removal.

There is a need to investigate processes that enable sludge re-use while enhancing sewage treatment efficiency. Mechanically disintegrated thickened surplus activated sludge (SAS) and fermented primary sludge were compared for their capacity to produce a carbon source suitable for BNR by completing nutrient removal predictive tests. Mechanically disintegration of SAS using a deflaker enhanced volatile fatty acids (VFAs) content from 92 to 374 mg l(-1) (4.1-fold increase). In comparison, primary sludge fermentation increased the VFAs content from 3.5 g l(-1) to a final concentration of 8.7 g l(-1) (2.5-fold increase). The carbon source obtained from disintegration and fermentation treatments improved phosphate (PO(4)-P) release and denitrification by up to 0.04 mg NO(3)-Ng(-1)VSS min(-1) and 0.031 mg PO(4)-Pg(-1)VSS min(-1), respectively, in comparison to acetate (0.023 mg NO(3)-Ng(-1)VSS min(-1)and 0.010 mg PO(4)-Pg(-1)VSS min(-1)). Overall, both types of sludge were suitable for BNR but disintegrated SAS displayed lower carbon to nutrient ratios of 8 for SCOD:PO(4)-P and 9 for SCOD:NO(3)-N. On the other hand, SAS increased the concentration of PO(4)-P in the settled sewage by a further 0.97 g PO(4)-P kg(-1)SCOD indicating its potential negative impact towards nutrient recycling in the BNR process.

A comparison of disinfection by-products found in chlorinated and chloraminated drinking waters in Scotland.

Seven water treatment works were selected to compare disinfection by-products (DBPs) formed when using chlorination and chloramination. DBPs measured included trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), trihalonitromethane, iodinated THMs and nitrosamines. Generally treatment works that used chloramination were able to meet the European THM regulatory limit of 100 microg L(-1) whereas the chlorinated works found it significantly more difficult. There were no significant differences in the levels of nitrogenous DBPs between the treatment works using chlorination or chloramination with the exception of the nitrosamine N-nitrosodimethylamine (NDMA) which was present at one treatment works in one season.

Isolation and characterization of haloacetic acid-degrading Afipia spp. from drinking water.

Haloacetic acids are a class of disinfection byproducts formed during the chlorination and chloramination of drinking water that have been linked to several human health risks. In this study, we isolated numerous strains of haloacetic acid-degrading Afipia spp. from tap water, the wall of a water distribution pipe, and a granular activated carbon filter treating prechlorinated water. These Afipia spp. harbored two phylogenetically distinct groups of alpha-halocarboxylic acid dehalogenase genes that clustered with genes previously detected only by cultivation-independent methods or were novel and did not conclusively cluster with the previously defined phylogenetic subdivisions of these genes. Four of these Afipia spp. simultaneously harbored both the known classes of alpha-halocarboxylic acid dehalogenase genes (dehI and dehII), which is potentially of importance because these bacteria were also capable of biodegrading the greatest number of different haloacetic acids. Our results suggest that Afipia spp. have a beneficial role in suppressing the concentrations of haloacetic acids in tap water, which contrasts the historical (albeit erroneous) association of Afipia sp. (specifically Afipia felis) as the causative agent of cat scratch disease.

Fouling control of a membrane coupled photocatalytic process treating greywater.

Fouling in membrane coupled photocatalytic reactors was investigated in the case of greywater treatment by establishing the link between product type, dose, irradiation time and fouling rates in a cross flow membrane cell fitted with a 0.4 microm pore sized polyethylene membrane. Rapid fouling occurred only with shower gels and conditioners and was linked to changes in the organo-TiO(2) aggregate size postulated to be caused by polymers within the products. Fouling was reduced to a negligible level when sufficient irradiation was applied demonstrating that the membrane component of the process is not the issue and that scale up and implementation of the process relates to effective design of the UV reactor.