TREATMENT OF LEACHATE FROM A CLOSED LANDFILL IN WEST SUSSEX, UK

摘要

Small Dole Landfill Site is located north of Brighton, and about 10km inland from the south coast of England. It is typical of many hundreds of closed landfill sites, having been filled during the 1970s and 1980s in a worked out mineral quarry, adjacent to a medium sized tidal watercourse, the River Adur. The site is located in an area of high landscape value, just north of the newly created South Downs National Park. Small Dole landfill has an area of 30ha and has been restored to pasture, similar to surrounding land, much of which is in the floodplain of the River Adur. Since closure and restoration it has continued to generate several hundred cubic metres of relatively diluted leachate daily as a result of rainfall infiltration, combined with suspected ingress of groundwater in some areas. Leachate at Small Dole is characterised by concentrations of ammoniacal-N in the order of 100mg/l, significant concentrations of iron, but relatively low levels of BOD. A previously-constructed plant had treated leachate over several years, but been unable to comply reliably with relatively strict standards for the discharge of treated leachate into the River Adur. It had also required relatively onerous site attendance in order to operate it manually. What was needed was a modified and fully automated leachate treatment plant, which would use as many of the structures of the existing plant as possible, in order to minimise construction costs. Particular challenges included the need to continue to manage volumes of up to 300m~3 per day of leachate during a construction programme. This paper is a detailed case study that will describe the approach that was adopted, and the innovative process design, based on a modified SBR system, which allowed the plant to be operated on a “temporary” manual basis during the first half of 2010, before being fully commissioned in June 2010. Extensive data are presented to support the study. The challenges involved and detailed operational data for the five years of operation, will be presented and described in particular the ability of the plant to deal successfully with high variatio in flow rate, from typical summer leachate flows of 100m~3 per day to rates as high 700m~3 per day during winter months. The primary issue is the relatively rapid response to rainfall events. Many of the experiences will have widespread application at similar closed landfill sites around the World.