Operational Experiences with Package Filter Sewage-Treatment Plants

This paper describes the operation of four prefabricated'package'biological filter plants which have been installed in Somerset by Wessex Water since 1984. Whilst these, in common with most other package sewage-treatment plants, have advantages of low capital cost and minimum site requirement, some operational difficulties have arisen since commissioning, and effluent quality has been variable.
This paper outlines the problems, and makes some suggestions for improvements.     

The Removal of Bromate from Potable Water Using Granular Activated Carbon

Bromate in drinking water, at a level of microgrammes/litre, is a problem in ozonated waters but can be adsorbed, to a certain extent, by granular activated carbon. The adsorption capacity of granular activated carbon for bromate is significantly lowered when there are high concentrations of other anions, most notably chloride and sulphate, present in the water.     

Mechanisms of Leakage through Synthetic Landfill Liner Materials

The introduction of synthetic lining materials for leachate containment and the prevention of groundwater contamination was an important development in landfill technology. These materials have a low hydraulic conductivity which results in minimal leachate release by bulk fluid flow (advection) provided that the barrier (and its construction) is free from defects. However, the effectiveness of these materials as barriers cannot be confirmed unless contaminant release by diffusion is also taken into consideration.
This paper reviews the mechanisms by which transport through barriers occur. It highlights the role of diffusion as a pathway for organic compounds to migrate through synthetic liners and indicates its importance in terms of environmental impact and landfill design.     

Assessment of Microbial Populations in Activated Sludge Using an Organism Diversity Index

An organism diversity index for use with mixed liquor or wastewater samples was developed to assess the species richness and diversity of activated sludge. The index was used in several studies and was found to be fast and simple to perform using basic laboratory equipment. Two bench-scale and two pilot-scale studies found that the resulting 'organism diversity index'value was a good indicator of process performance and was not influenced by the total concentration of the mixed-liquor suspended solids but by their nature alone. The technique rapidly yielded pertinent information about the health of the sludge and could be used instead of genetic investigations to obtain population information quickly enough for wastewater-treatment plant process control.     

Passive Treatment Systems for the Remediation of Acid Mine Drainage at Wheal Jane, Cornwall

In 1992, Knight Piésold was appointed to formulate a long-term treatment strategy for the remediation of acidic metal-rich minewater issuing from the abandoned Wheal Jane mine in Cornwall, UK. The study has investigated both passive and active treatment technologies. As part of the study, a pilot passive-treatment plant was constructed during 1994, comprising three separate systems. Each system contains the same main treatment stages which consist of five aerobic reedbeds, an anaerobic cell and an aerobic rock-filter. Two of the systems also incorporate pretreatment, one in the form of lime dosing and the other in the form of an anoxic limestone drain. This paper discusses the theory and design criteria used in the construction of the plant and examines performance data during the period June 1995 to November 1996.     

Comparison of Disinfection Techniques for Sewage and Sewage Effluents

This paper reviews operational and experimental disinfection techniques for the removal of pathogens from sewage and secondary effluent prior to marine discharge. Disinfection options considered include chlorine (hypochlorite, chloramines, OSEC), ultraviolet light (UV), ozone, chlorine dioxide, bromine chloride, peracetic acid (PAA) and gamma irradiation. A comparison of alternative systems is made in terms of their inactivation efficiency, safety, environmental impact and cost. Budget costs were obtained from chemical and equipment suppliers for the disinfection of a theoretical case-study, to enable a direct cost-comparison to be made.