Effects of beach sand properties, temperature and rainfall on the degradation rates of oil in buried oil/beach sand mixtures

Lysimeters located outdoors have been used to evaluate the decomposition of buried oily beach sand waste (OBS) prepared using Forties light crude oil and sand from different locations around the British coast. The OBS (5% oil by weight) was buried as a 12-cm layer over dune pasture sub-sand and over lain by 20 cm of dune pasture topsoil. Decomposition rates of oil residues averaged 2300 kg ha(-1) in the first year and the pattern of oil decomposit ion may be represented by a power curve. Oil decomposition was strongly rel ated to the temperature in the OBS layer, but was also significantly affect ed by rainfall in the previous 12 h. The CO2 flux at the surface of the tre atment lysimeters followed the relationship [log(10) CO2 (mg C m(-2) h(-1)) = 0.93 + 0.058 OBS temp. (degrees C) -0.042 x 12 h rain (mm)]. There was c onsiderable variation in the rate of oil decomposition in sands collected f rom different sites. Sand from Askernish supported most microbial activity whilst sand from Tain was relatively inactive. The decomposition process ap peared to cease when the sand became saturated with water, i.e. temporarily anaerobic. However, decomposition recommenced when the soil dried out. The fastest rate of decomposition occurred in sand from one of the two sites p redicted to have high populations of hydrocarbon-degrading bacteria. Larger particle size and higher Ca content may also be significant factors govern ing the rate of decomposition. (C) 2000 Elsevier Science Ltd. All rights re served.