The Study Of Biofilter Process For Treatment Of Volatile Organic Compounds (VOCs)

Biofiltration has been recognized as a cost-effective technology forvolatile organic compounds (VOCs) control. The characteristics of the packingmaterials are very important for the biofilter to obtain a good treatmentperformance. An ideal packing material should have large surface area, enoughnutrients supply and low pressure drops. Compost is widely used as basicpacking material but often has the problem of clogging and compaction. Soother natural packing materials, such as wood chips and rice hulls have beentested for replacement of compost.The purpose of this paper is to develop a new natural packing material,buck wheat hull (BWH, hereafter) which is easy to find in the rural area ofnorth China. The properties of the packing material and the runningperformance and characteristics of the biofilter are studied here.Before starting the experimental study, the VOC sources in Beijing area isinvestigated for better understanding of VOC pollution.The properties of the raw BWH used here were systematically evaluatedbefore use. The average diameter of the BWH particle is about 5mm and thepore volume is about 65%. The drying curve and pressure drop curve of theBWH is also measured. Nutrient content study showed that the total protein,nitrogen and phosphorus that can be washed out from the raw BWH by waterare 2.5-3.0mg/gBWH (dry weight), 1.0-1.5mg/g and 0.2-0.5mg/g, respectively.A batch test showed that the organic compounds in the surface of BWH maydecrease the toluene elimination rate of microorganisms by substrateinhibition.In this study, a biofilter packed with BWH was set up (100 mm innerdiameter, 1500 mm height) and another biofilter packed with sawdust wasoperated in parallel. Toluene is used as the representative VOC. The inoculumof the biofilter was activated sludge from an industrial wastewater treatmentplant.The two biofilters were operated at a flowrate of 5m3/h for 70 days withinlet concentration of toluene around 200-400 mg/m3 at 19-28 ℃. The biofilterpacked with BWH showed a lower toluene elimination rate of 9 g/m3.h thanthe biofilter packed with sawdust. The pressure drop of the BWH biofilter roseafter 40 days' operation, indicating the overage growth of the microorganismsin the filter bed. The biomass in the packing material reached 175mg/gBWH(dry weight) after 70 days' operation.Based on the results mentioned above, we can conclude that the BWH isan effective new packing material for Biofiltration, but more modificationshould be done to obtain higher removal rate and efficiency of VOC.