NUTRIENT LIMITATION IN A COMPOST BIOFILTER DEGRADING HEXANE

A laboratory-scale compost-based biofilter was operated over a six-mon th period to study the requirements for removal of n-hexane from air. Hexane is a relatively short chain aliphatic hydrocarbon with a high H enry's coefficient and a low water solubility. Acclimation of the biof ilter was slow, but removal efficiencies around 80% were achieved afte r one month of operation. However, performance decreased during the ne xt two months of operation to 50% removal efficiency. Nutrient limitat ion was proposed as a reason for the decrease in reactor performance. After the addition of a concentrated nitrogen solution, reactor perfor mance increased almost immediately to >99%. Removal efficiency remaine d above 99% for the following two months of operation at inlet concent rations of 0.7 g/m(3) (200 ppmv), at superficial bed velocities approa ching 50 m/h, and empty bed residence times of about one minute. Thus, nutrient availability may well limit biofilter performance even in co mpost-based units. It was shown that nutrients can be added effectivel y in a soluble form if compost quality is poor and a method is propose d for the evaluation of compost quality.