Bioremediation Using Windrows at Newcastle-upon-Tyne (continued)
BOX FIGURE 5.2.2 Field measurements on windrows. Courtesy of WSP Remediation Ltd., Cardiff, Wales, United Kingdom.
Sample series B
Sample series B
Temperature °C - 30
BOX FIGURE 5.2.3 Three-sample series from windrow 11, showing progress of TPH removal during the bioremediation phase of the contract.
Landfarms also have been proven effective in reducing concentrations of all components of fuels found in USTs, including petrol, diesel, and kerosene, as well as primarily nonvolatile oils such as heating and lubricating oils (324). For the oil industry, it has been seen as a relatively cost-effective and simple technique for dealing with refinery wastes, but there are envi ronmental concerns over landfarming operations (11). In terms of total refinery wastes, a small proportion is landfarmed. Between 1986 and 1993, a mere 4.9% of all refinery sludge was disposed of by landfarming from 89 reporting Western European oil refineries (340); despite being the cheapest reported option, very few refineries in Europe use it. In a number of
5. BIOREMEDIATION OF CONTAMINATED SOILS AND AQUIFERS ■ 159
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countries, the technique is not permitted at all (77).
LANDFARM DESIGN The preparation of the site for a landfarm bears similarity to the methods for preparation of the base for biopiling, but of course the area to be prepared has to be much larger. The amount of land required depends on the volume of materials to be treated and the depth of the landfarm soil. The depth of landfarm soils is usually between 30 and 45 cm, although very powerful soil tillers can till down to about 60 cm. An advisable upper sludge loading is 150 g of sludge per kg of soil (13). Waste is typically applied in layers of no more than 20 cm. Time should be invested to maximize the accuracy of the land requirements, as a key to economical landfarm operation is to size the installation properly and then run it close to capacity (W. Younkin, C. Suaznabar, and S. Parsons, paper presented at the SPE International Conference on Health, Safety, and the Environment in Oil and Gas Exploration and Production, Stavenger, Norway, 26 to 28 June 2000). The most difficult and variable part of the calculation is the residence time (the time taken to reach the treatment target). Younkin et al. reported a variation in residence time to reach a 1 % total petroleum hydrocarbons target of 139 to 218 days. Given variabilities in soil, climate, and sludge quality, treatability studies are highly recommended (Fig. 5.13).
Landfarm Base. Landfarm surface areas are highly variable but may be of the order of 4 ha (40,000 m2). The total land area is divided up into treatment cells, generally square and of variable size. A U.S. Army design specifies a treatment cell size of 1 acre (4,047 m2) (320). A BP Amoco landfarm to treat drilling wastes is a 4-ha site in a rectangle, laid out in 45 treatment cells of 30 by 30 m each. By so dividing the land, wastes can be sequenced in time so that continuous operation can be maintained.
Given the large area and the shallowness of a landfarm, the base has to be properly designed and built to accommodate local climate. Leachate control is essential for wet and temperate climates. To this end, a high-integrity liner is required. A compacted clay layer of 0.6 m with a hydraulic conductivity of 10"7 cm s_1 is suitable. A 1-mm-thick HDPE liner is a suitable alternative, and at permanent sites, both may be used.
The leachate collection system to sit on top of the liner consists of slotted-pipe laterals embedded in a granular drainage layer (Fig. 5.14). The grade of a treatment cell should be between 0.5 and 2%, depending on local rainfall. The granular drainage layer is formed from compacted, well-sorted gravels and coarse sand, with a minimum compacted hydraulic conductivity of 10cm s"1. Gravels greater than 13 mm in diameter may damage the HDPE liner, and it would be advisable in such a case to have a protective layer of sand or geotextile between the granular drainage material and the liner.
Perimeter Dike. The perimeter dike is designed to prevent runoff and storm water run-on based on a 25-year flood. A minimum freeboard of 0.3 m between the top of the dike and the surface of the treatment cells, and also from the top of the dike to the exterior surface of the cell, is recommended.
Stockpile Area. Stockpiling is necessary for the storage of contaminated material for treatment, already treated material awaiting haulage out of the farm, and oversize material. Stockpiling areas should be lined with a chemically resistant impermeable geomembrane to a minimal thickness of 1 mm. Rain is prevented from entering the stockpile with a 0.25-mm-thick impermeable geomembrane.
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