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No description available.

Horizontal Subsurface Flow Treatment Wetlands (HSSF TWs) are used by Severn Trent Water as a low-cost tertiary wastewater treatment for rural locations. Experience has shown that clogging is a major operational problem that reduces HSSF TW lifetime. Clogging is caused by an accumulation of secondary wastewater solids from upstream processes and decomposing leaf litter. Clogging occurs as a sludge layer where wastewater is loaded on the surface of the bed at the inlet. Severn Trent systems receive relatively high hydraulic loading rates, which causes overland flow and reduces the ability to mineralise surface sludge accumulations. A novel apparatus and method, the Aston Permeameter, was created to measure hydraulic conductivity in situ. Accuracy is ±30 %, which was considered adequate given that conductivity in clogged systems varies by several orders of magnitude. The Aston Permeameter was used to perform 20 separate tests on 13 different HSSF TWs in the UK and the US. The minimum conductivity measured was 0.03 m/d at Fenny Compton (compared with 5,000 m/d clean conductivity), which was caused by an accumulation of construction fines in one part of the bed. Most systems displayed a 2 to 3 order of magnitude variation in conductivity in each dimension. Statistically significant transverse variations in conductivity were found in 70% of the systems. Clogging at the inlet and outlet was generally highest where flow enters the influent distribution and exits the effluent collection system, respectively. Surface conductivity was lower in systems with dense vegetation because plant canopies reduce surface evapotranspiration and decelerate sludge mineralisation. An equation was derived to describe how the water table profile is influenced by overland flow, spatial variations in conductivity and clogging. The equation is calibrated using a single parameter, the Clog Factor (CF), which represents the equivalent loss of porosity that would reproduce measured conductivity according to the Kozeny-Carman Equation. The CF varies from 0 for ideal conditions to 1 for completely clogged conditions. Minimum CF was 0.54 for a system that had recently been refurbished, which represents the deviation from ideal conditions due to characteristics of non-ideal media such as particle size distribution and morphology. Maximum CF was 0.90 for a 15 year old system that exhibited sludge accumulation and overland flow across the majority of the bed. A Finite Element Model of a 15 m long HSSF TW was used to indicate how hydraulics and hydrodynamics vary as CF increases. It was found that as CF increases from 0.55 to 0.65 the subsurface wetted area increases, which causes mean hydraulic residence time to increase from 0.16 days to 0.18 days. As CF increases from 0.65 to 0.90, the extent of overland flow increases from 1.8 m to 13.1 m, which reduces hydraulic efficiency from 37 % to 12 % and reduces mean residence time to 0.08 days.

A novel method was developed to collect samples of surface sediment that had accumulated upon a road surface with high traffic loading over a period of 17 months. The method was designed to remove the smallest size fraction of sediment from a set area on the road surface by washing with water and collecting the effluent. The sediment collected was analysed for total mass and particle size distribution, ‘total’ sediment attached metal concentration of Zn, Cu, Pb and Cd (2 - 500 <span style='font-family:Symbol'>mm), dissolved pollutants consisting of the ionic species F^-, C1^-, SO₄^2-, NO₃^- PO₄^3-,NH₄⁺, total carbon (TC), total organic carbon  (TOC) and pH. Road run-off was also measured, both continuously and discretely. Continuous measurement parameters (temperature, conductivity, pH, turbidity, depth) were correlated with climate and rainfall characteristics but no consistent relationship was found. Levels of pollutant in run-off (Zn, Cu, Pb, Cd, F^-, C1^-, SO₄^2-, NO₃^-, PO₄^3-, NH₄⁺ TC, TOC, pH) were related to levels of the same pollutants collected on the surface. Levels of sediment and dissolved pollutants collected on the surface showed distinctive seasonal and spatial variation, and were elevated due to the application of road de-icing salts during periods of cold weather. Concentrations of heavy metals tended to increase with decreasing particle size and a seasonal variation was observed with higher concentrations found during the summer months. Little evidence was found to indicate that rainfall patterns were influencing concentrations of pollutants deposited, although a slight correlation (r = 0.55, p = 0.04) was observed between certain parameters and antecedent dry weather period during the summer.

In metal machining processes, the regulation of heat generation and lubrication at the contact point are achieved by application of a fluid referred to as metalworking fluid (MWF). This has the combined features of the cooling properties of water and lubricity of oil. MWFs inevitably become operationally exhausted with age and intensive use, which leads to compromised properties, thereby necessitating their safe disposal. Disposal of this waste through a biological route is an increasingly attractive option, since it is effective with relatively low energy demands when compared to current physical and chemical options. However, biological treatment is challenging since MWF are chemically complex, including the addition of toxic biocides which are added specifically to retard microbial deterioration whilst the fluids are operational. This makes bacterial treatment exceptionally challenging and has stimulated the search and need to assess technologies which complement biological treatment. In this study the remediation, specifically of the recalcitrant component of a semi-synthetic MWF, employing a novel hybrid treatment approach consisting of both bacteriological and chemical treatment, was investigated. Three chemical pre-treatment methods (Fenton’s oxidation, nano-zerovalent iron (nZVI) oxidation and ozonation) of the recalcitrant components followed by bacterial degradation were examined. The synergistic interaction of Fenton’s-biological oxidation and nZVI-biodegradation led to an overall COD reduction of 92% and 95.5% respectively, whereas pre-treatment with ozone reduced the total pollution load by 70% after a post-biological step. An enhancement in biodegradability was observed after each of the chemical treatments, thus facilitating the overall treatment process. The findings from this study established that the use of non-pathogenic microorganisms to remediate organic materials present in MWF wastewater is a favourable alternative to energy demanding physical and chemical treatment options. However, optimal performance of this biological process may require chemical enhancement, particularly for those components that are resistant to biological transformation.

There have been no previous studies carried out on the impact of urban runoff in the Coventry City centre area. The culverted nature of the River Sherbourne, and many of its tributaries, makes the investigation of intermittent pollution and rainfall events expensive and impractical, when using traditional spot sample methods. Storm events have been monitored over a period of over 60 months upstream and downstream of the City, using continuous water quality monitors and auto-spot sample methods. The receiving waters of the River Avon had previously suffered annual fish mortalities as a result of summer storm events causing oxygen depletion. Previous studies (Clifforde and Williams 1997) on the impact of Coventry Sewage Treatment Works effluent on the watercourse, have suggested a major component of the intermittent pollutant load arising from the City (upstream of the Sewage Treatment Works), which requires evaluation and remediation. This research identifies the contaminants found during a series of storm events impacting on the River Sherbourne culvert, and discusses the relationship between them and the increased flow measured. The methodology was divided into 3 Phases; Phase 1 examined all of the watercourses in the River Sowe catchment, and identified the culverted streams and drainage system giving an indication of the presence of pollutant sources. Continuous monitors were deployed within the four identified drainage systems to pinpoint intermittent and illegal contaminated discharges, and these discharges were subsequently redirected to the foul sewer or stopped. Phase 2 examined the quality of the River Sherbourne culvert upstream and downstream of the city centre, and demonstrated (using continuous monitors and automated sampling), that six combined sewer overflows discharging to the watercourse upstream of the culvert were opening unsatisfactorily. The dissolved oxygen levels were significantly reduced during rainfall events (with a loss of diurnal variation), and total ammonium levels exceeded current water quality standards. The results were used to instigate a remediation scheme to replace the overflows with additional foul sewage capacity, and a single high-level storm relief. Phase 3 examined the impact of urban runoff during rainfall events after the improvements made following Phases 1 and 2. The results suggest a marked improvement in the water quality, with little impact from organic pollutants. Dissolved oxygen concentrations remained high during many of the post-remedial rainfall events, and ammonia levels remained largely insignificant. The results indicated a fall in pH levels during the rainfall events and increases in all of the heavy metals analysed, though not beyond current water quality guidelines. The efficiency of using continuous monitoring in Coventry was assessed and likely sources of the contaminants in urban runoff were considered. The statistics of compliance with percentile standards do not allow for short-term pollution or storm events, which may kill all aquatic life whilst not breaching water quality standards. Using continuous monitors to identify intermittent and illegal discharges in underground drainage systems was an efficient and cost-effective method of reducing the impact of urban runoff in a failing watercourse. The methodology can be applied to other urban areas to identify unidentified illegal and intermittent point sources. Routine monthly monitoring of an urban watercourse may not identify the peaks and troughs associated with rainfall events that may breach toxicological guidelines, and will not identify intermittent and unknown pollutant sources; particularly when discharging outside of normal working hours. This research was a unique and comprehensive investigation into the nature and composition of urban runoff in the City of Coventry, and local data gathered will be invaluable in promoting further research, improving local knowledge of the urban environment in preparation for the Water Framework Directive (2000/60/EC), and in planning for environmental improvements in the future.