Influence of nitrogen on the degradation of toluene in a compost-based biofilter

Two identical laboratory-scale bioreactors were operated simultaneously, ea ch treating an input air flow rate of 1 m(3) h(-1). The biofilters consiste d of multi-stage columns, each stage packed with a compost-based filtering material, which was not previously inoculated. The toluene inlet concentrat ion was fixed at 1.5 g m(-3) of air. Apart from the necessary carbon, the e lements nitrogen, phosphorus, sulfur, potassium and other micro-elements ar e also essential for microbial metabolism. These were distributed throughou t the filter bed material by periodic 'irrigations' with various test nutri ent solutions. The performance of each biofilter was quantified by determin ing its toluene removal efficiency, and elimination capacity. Nutrient solu tion nitrogen levels were varied from 0 to 6.0 g dm(-3), which led to elimi nation capacities of up to 50 g m(-3) h(-1) being obtained for a toluene in let load of 80 g m(-3) h(-1). A theoretical analysis also confirmed that th e optimum nitrogen solution concentration lays in the range 4.0-6.0 g dm(-3 ). Validation of the irrigation mode was achieved by watering each biofilte r stage individually. Vertical stage-by-stage stratification of the biofilt er performance was not detected, ie each filter bed section removed the sam e amount of pollutant, the elimination capacity per stage being about 16 g m(-3) h(-1) per section of column. (C) 2001 Society of Chemical Industry.