Application of soil slurry respirometry to optimise and subsequently monitor ex situ bioremediation of hydrocarbon-contaminated soils

A protocol to monitor respiration as O2 consumption in soil slurries using the Strathtox® respirometer was developed and tested on four soils from brownfield sites. Respiration rates (mg l−1 h−1) of soil slurries in the Strathtox® were compared with rates (μl min−1) of field moist soils analysed using the Columbus Oxymax® ER10 respirometer. One of the soils (99612B), historically contaminated with diesel, was further studied by monitoring the effect of inorganic NH4NO3 liquid nutrient on enhancing respiration rate. Soil microcosms were monitored continuously on the Oxymax® or sampled at 24, 48 and 72 h intervals, prepared as soil slurries, and analysed on the Strathtox®. On the full-scale remediation project (∼6000 m3) soil 99612B was treated as a biopile with spent mushroom compost (SMC) amendment and respiration rates monitored in samples over an 8-week period. In the laboratory microcosm experiment and full-scale bioremediation treatment described, correlation was found for respiration rates between the two respirometry systems.