Development of an alternative biofilter system for odor treatment

Biofiltration has been used successfully to control odors, both organic and inorganic in nature. The most common and unsubstantiated assumption for packed bed operation is the plug flow behavior, which is impossible to duplicate in practice. The objectives of this study are: a) to investigate the residence time distribution (RTD) of a tracer gas passing through the biofilter; b) to determine a model to describe the hydraulic characteristics of the biofilter; c) to measure the ammonia removal efficiency and elimination capacity; and d) to determine the order of reaction and the related kinetic parameters. The standard biofilter with vertical gas upflow and the modified biofilter with horizontal gas flow were studied. The latter system design was novel. First, step tracer tests were conducted on these lab-scale biofilters to determine the RTD of CO2 passing through the filter. Both biofilters consisted of two layers. Matured compost materials were used as the filter medium. Next, the kinetic parameters were calculated from the break-through results and the RTD's as previously determined. The hydraulic characteristics can be modeled in terms of the number of continuous stirred tank reactors (CSTR) in series. The second bed had a better removal efficiency than the first bed. The merits of the modified system lie with a greater ammonia removal efficiency compared to the standard biofilter system. Given an improved removal efficiency, the size and therefore the capital cost of biofilter could be reduced. Porosity differences in the beds may explain the larger microbial population in the second bed. The modified biofilter was better than the standard biofilter, in terms of elimination capacity. The biodegradation of ammonia was found to be first-order at low substrate concentration. Each of the beds in the two-bed biofilter had significantly different reaction rate constants. These differences were explained by measurements of bacterial concentrations and surface area. These findings have helped in the development of a quantitative understanding of the principle and operation of a biofilter. This study is a first attempt in testing the RTD of non-column type reactors with practical measurements to model the flow as the number of CSTR's in series.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat