Feasibility study on a combined spray absorber-activated sludge process for volatile organic compound removal

The purpose of this study was to explore the feasibility of a combined spray absorber - activated sludge process for the removal of gas phase volatile organic compounds (VOCs). Three different solvents – water, bacteria slurry, and powdered activated carbon (PAC) slurry, were evaluated for this process. Methyl-ethyl-ketone (MEK) was studied as the target VOC. The rate of VOC removal in a spray absorber was the major concern for reactor volume reduction. Using PAC slurry as solvent. experimental results showed that the gas-to-liquid mass transfer rate was increased by a factor of 2. The effects of PAC to the subsequent activated sludge process were also explored. Experiments were conducted to evaluate the three major VOC fate mechanisms in the activated sludge unit: stripping, biodegradation, and adsorption on PAC. The results indicate that stripping is negligible if the VOC is readily biodegradable. and PAC can be biologically regenerated if the adsorption is reversible. PAC also serves as a reservoir to prevent stripping losses, especially at high concentration fluctuations. Therefore, PAC slurry is a promising solvent in this combined process. Experimental results and theoretical investigations indicate that a slurry of bacteria will not have significant enhancement to the efficiency of a spray absorber. Water is considered to be a feasible solvent for removal of relatively soluble and biodegradable VOCs. Gas retention time in a spray absorber can be within seconds. Design examples were given for MEK gas removal in this process. Further study on the mass transfer rate using PAC slurry as solvent and other aerobic bioreactor for volume reduction is recommended.