Michael Gardner

Performance of UK wastewater treatment works with respect to trace contaminants

This study examined the performance of 16 wastewater treatment works to provide an overview of trace substance removal in relation to meeting the objectives of the Water Framework Directive (WFD). Collection and analysis of over 2400 samples including sewage influent, process samples at different stages in the treatment process and final effluent has provided data on the performance of current wastewater treatment processes and made it possible to evaluate the need for improved effluent quality. Results for 55 substances, including metals, industrial chemicals and pharmaceuticals are reported. Data for sanitary parameters are also provided. A wide range of removal efficiencies was observed. Removal was not clearly related to the generic process type, indicating that other operational factors tend to be important. Nonetheless, removals for many substances of current concern were high. Despite this, current proposals for stringent water quality standards mean that further improvements in effluent quality are likely to be required.

Determination of trace concentrations of hexavalent chromium

A simple and sensitive solvent extraction-atomic spectrometric technique has been developed for the determination of hexavalent chromium in fresh and saline waters. The technique is based on the reaction of chromium with diphenylcarbazide. The method has been tested on a variety of water samples over an analytical range of 0-2 microg l(-1). A limit of detection of 0.024 microg l(-1) was achieved. Spiking recoveries in the range 87-115% were achieved in river water, drinking water and marine waters.

Zinc inputs to coastal waters from sacrificial anodes

Abstract The importance of sacrificial anodes as a source of zinc inputs to marinas, harbours and estuaries has been investigated. The study shows that the increase in dissolved zinc levels where anodes are used is likely to be small in relation to the current Environmental Quality Standard (40 μg Zn l −1 ). Nevertheless, sacrificial anodes can be expected to lead to measurable increases in concentrations of dissolved zinc in marinas and to a lesser extent, in nearby estuary areas. The local increase in concentrations of dissolved zinc near open marinas may be between 2 and 5 μg l −1 , with levels in enclosed marinas being as high as ca. 20 μg l −1 . Increases in zinc concentrations in marina sediments of up to twice background levels (by up to 200 μg g −1 ) were observed.

Chromium redox speciation in natural waters.

Dissolved hexavalent chromium concentrations were determined in river, estuarine and coastal waters of the Humber catchment in north-east England. Samples were collected, filtered, extracted on site and after storage for up to eight days. Hexavalent chromium concentrations did not change by more than 0.05 microg l(-1) (not significant, p = 0.05) over this period. Total chromium concentrations in the catchment were less than 1.0 microg l(-1). This is low in relation to the proposed Environmental Quality Standard. Hexavalent chromium accounted for between 27% and 100% of the total dissolved concentration, with an average of approximately 50%. The proportion of Cr(III) and Cr(VI) in the rivers and estuary were of the same range as previously measured in 1993. The addition of Cr(III) and Cr(VI) to fresh and saline water samples illustrates the complexity of the factors controlling chromium speciation in natural waters. The presence of oxidisable organic matter and the stabilising role of complexing organic ligands are proposed as the main controlling influences of redox speciation in filtered samples.

Kinetics of trace metal sorption to estuarine suspended particulate matter

Complex multi-step processes, with equilibration times varying from minutes to weeks, are observed to control trace metal sorption to particulate matter. A three-step first order reversible kinetic model is used to fit mesured data for sorption and desorption over periods of up to 200h. This is likely to perform better than the equilibrium partitioning approach under the rapidly changing environmental conditions which exist in estuaries.

Domestic source of phosphorus to sewage treatment works

Phosphorus is an element essential for life. Concerns regarding long-term security of supply and issues related to eutrophication of surface waters once released into the aquatic environment have led governments to consider and apply measures for reducing the use and discharge of phosphorus. Examples of source control include legislation to reduce phosphorus use in domestic detergents. This research shows that other domestic sources of phosphorus also contribute significantly to the domestic load to sewer and that overall, domestic sources dominate loads to sewage treatment works. Estimates provided here show that although the natural diet contributes 40% of the domestic phosphorus load, other potentially preventable sources contribute significantly to the estimated 44,000 tonnes of phosphorus entering UK sewage treatment works each year. In the UK, food additives are estimated to contribute 29% of the domestic load; automatic dishwashing detergents contribute 9% and potentially increasing; domestic laundry 14%, including contributions from phosphonates, but decreasing; phosphorus dosing to reduce lead levels in tap water 6%; food waste disposed of down the drain 1%; and personal care products 1%. Although UK data is presented here, it is anticipated that similar impacts would be expected for other developed economies. Consideration of alternatives to all preventable sources of phosphorus from these sources would therefore offer potentially significant reductions in phosphorus loads to sewage treatment works and hence to the aquatic environment. Combining all source control measures and applying them to their maximum extent could potentially lead to the prevention of over 22,000 tonnes-P/year entering sewage treatment works.

Reactive aluminium in UK surface waters

The determination of chemically reactive forms of aluminium in 20 major UK rivers is reported. The reaction of aluminium with 8-hydroxyquinoline followed by a 15 second extraction of chelated forms...

Development of a chemical source apportionment decision support framework for catchment management.

EU legislation, including the Water Framework Directive, has led to the application of increasingly stringent quality standards for a wide range of chemical contaminants in surface waters. This has raised the question of how to determine and to quantify the sources of such substances so that measures can be taken to address breaches of these quality standards using the polluter pays principle. Contaminants enter surface waters via a number of diffuse and point sources. Decision support tools are required to assess the relative magnitudes of these sources and to estimate the impacts of any programmes of measures. This work describes the development and testing of a modeling framework, the Source Apportionment Geographical Information System (SAGIS). The model uses readily available national data sets to estimate contributions of a number of nutrients (nitrogen and phosphorus), metals (copper, zinc, cadmium, lead, mercury, and nickel) and organic chemicals (a phthalate and a number of polynuclear aromatic hydrocarbons) from multiple sector sources. Such a tool has not previously been available on a national scale for such a wide range of chemicals. It is intended to provide a common platform to assist stakeholders in future catchment management.

Copper complexation in English Rivers

Abstract Data for copper complexation capacity (CC), determined by cathodic stripping voltammetry, are presented for 36 English rivers. Values for CC were between 40 and 500 nM. No predictive relationship between major water quality parameters and CC was found. A comparison of determinations made on the same water bodies over several years points towards consistency of CC with time. It is concluded that, in river waters of a wide range of types, forms of copper complexed by organic matter predominate substantially over free or inorganic forms of the metal.

Measurement of Absorbance and Fluorescence as Potential Alternatives to Bod

The measured Biochemical Oxygen Demand (BOD) of a range of water samples, including river waters, sewage effluents and industrial effluents, has been compared with (a) absorbance and (b) fluorescence determinations on the same samples. Absorbance at 650 nm showed a moderately high, positive correlation with BOD for settled sewage effluent samples. This raises the possibility of the use of absorbance measurements in the development of a relatively inexpensive field instrument (or on-line monitor) which would provide an early warning of deteriorating quality in a sewage effluent discharge. The relationship between the relative importance of true absorbance (by dissolved species) and attenuation by particulate matter, as indicators of oxygen, demand should be investigated further. No clear association between absorbance and BOD was observed for industrial effluents or river waters. Sample fluorescence was not associated with BOD for sewage effluents, industrial effluents, or river waters.