Enhanced Biofiltration Using Cell Attachment Promoters

The use of positively charged polymers to enhance attachment of bacteria to surfaces, for enhancing biofiltration of odors and volatile organics, has been investigated. Preliminary batch experiments on polyurethane (PU) foam cubes submerged in a bacterial broth for 40 days showed that a 25 mg/L Polyethyleneimine (PEI) aqueous solution yielded the highest solids attachment to the PU foam. Based on this result, two columns operating as biotrickling filters packed with polyurethane (PU) foam cubes, one with cubes coated with a solution of 25 mg/L of PEI (coated reactor) and the other containing just plain PU foam cubes (uncoated reactor) were tested in order to determine the effect of the coating on the performance of the reactors operating at Empty Bed Residence Times (EBRT) ranging from 6 to 60 sec and inlet hydrogen sulfide (H2S) concentrations up to 235 ppmv (inlet overall loads of up to 44 gH2S/m3bed/hr). After acclimatization was achieved, both reactors showed overall removal efficiencies (RE) mostly in the range of 90-100% over a period of 125 days. The lower and upper halves of the coated reactors exhibited elimination capacities (EC) of 63 and 77 gH2S/m3bed/hr, respectively, and retention of Total Volatile Solids (TVS) of 42 and 30 mg TVS/cube, while the uncoated reactor gave lower and upper half values of 27 and 40 gH2S/m3bed/hr for the elimination capacity (EC) and 23 and 24 mg TVS/cube for the TVS retention. The experimental data was fitted to a model which included the airflow distribution through and around the foam packing media including the water and biofilm layer thickness, and the best–fit maximum Monod's biodegradation velocities were 6.69×10−4 and 2.56×10−4 sec−1 respectively, for the coated and uncoated reactors. Denaturing Gradient Gel Electrophoresis (DGGE) performed on the collected biomass showed that the predominant bioactive species in both reactors belonged to the genus Acidithiobacillus, with no differentiation within each reactor itself.