In order to determine the size of the reactor, the conditions that are given within GreenCycle are as follows:Flow rate to be treated: 85 000 m3/hOdor concentration in raw gas: 20 000 OU/m3Odor concentration in clean gas: 500 OU/m3Firstly, to calculate the required volume of the biofilter, the odor degradation rate of the packing material that is used in the biofilter has to be known. The sources for the packing material that are going to be used are mature compost and woodchips.There are certain reasons behind choosing compost and woodchips as packing materials and they are as follows:These materials meet the necessary requirements (like moisture holding capacity, porosity, microorganisms, nutrient content etc.) as the packing material in the biofilters.Compost provides nutrients for microorganisms and high permeability for air and water.Porosity can be improved by using wood chips, thereby reducing the pressure drop.Easily available in the plant and inexpensive.Accordingly, a pilot test is performed that is specific to a biofilter design with a particular filter media. After the test is performed, a graph can be plotted for the odor degradation rate (r) versus the average logarithmic mean concentration (Cm).Experimental conditions are given as follows:Flow rate = 290 m3/hTest Biofilters Volume = 1.7 m3Packing material: a coarse screen fraction (>20mm) of mature compost. Table xx: Biofilter Experimental Results Cin (OU/M3) Cout (OU/M3) 497 104 558 62 939 22 11925 348 15792 608 16384 484 21720 966 32500 966 45823 1916 74698 2246 94646 2506Odour Degradation Rate: r = (Cin -Cout) V´V(OU/m3/h) (Eq 7.1)Where,r = Degradation rateCin = Concentration of raw gas Cout = Concentration of clean gas V* = flow rate (m3/h)V = Volume of filter (m3)Logarithmic Mean Concentration: Cm = Cin – Coutln CinCout (Eq 7.2)Using equations 7.1 and 7.2 the results for ´r` and ´Cm´ can be calculated as shown in the Table XX. By plotting degradation rates over logarithmic mean concentration a graph can be drawn as shown in Figure XX. Table xx: Calculations of r and Cm using experimental results Cin (OU/M3) Cout (OU/M3) V’ (M3/h) V (M3) Cm (OU/M3) r (OU/M3)4971042901.7251.246783967041.18558622901.7225.739328284611.76939222901.7244.2875458156429.4119253482901.73275.715381974900157926082901.74661.8387982590212163844842901.74514.5116582712353217209662901.76667.2557573540388325009662901.78969.14419753793294582319162901.713830.9520574900187469822462901.720675.15598123594599464625062901.725372.7447415718000Using above calculations , we plot a graph to obtain the linear regression line equation.Figure xx:For the above experiment, the overall logarithmic mean concentration is, Cm = 20000 – 500ln 20000500= 5286.16 OU/m3 (Eq 7.3) From first order kinetics, we have: r = k1 . Cm (Eq 7.4)Therefore,The overall degradation rate for the logarithmic mean concentration (Cm) from the above diagram can be given as,r = 607.69 5286.16 -165673 = 30,46,673.57 (OU/m3/h) (Eq 7.5)Now, the Volume of Biofilter is calculated as follows: V = Cin -Cout V´r (Eq 7.6) V = 20000 – 500 850003046673.57= 544 m3 (Eq 7.7)Biofilter surface area is calculated by the amount of flow rate to be treated times the filter area load:The flow rate = 85 000 m3/hThe filter area load = 100 m3/m2h.Biofilter surface area, A = 85000100= 850 m2 (Eq 7.8)The Packing height is: H = VA= 544.035850= 0.64m (Eq 7.9)7.4.6 Other Dimensions of biofilter:Length: 30 mWidth: 29 mpH: 6-8 Temperature: 20-40 oC EBRT: 23 sVolumetric loading rate: 156 (m3m-3.h-1) Relative humidity: > 95%Efficiency: 97.5 % 7.3 Various Components of BiofilterThe overall biofilter plant comprises of various components such as high pressure fans with negative pressure to collect the exhaust air from different process units (composting, pretreatment etc.). Long pipes with holes to allow the polluted gas to flow through the filter bed. Humidifiers that eliminates the drying effect by providing sufficient moisture content Sprinklers are placed above the filter bed that sprinkles necessary water to maintain the sufficient moisture on the filter bed medium. Filter bed constitutes the medium and microbes where the biodegradation process takes place due to which the concentration of contaminants decreases and gets converted into water and carbon dioxide. The bottom of the biofilter is equipped with support that contain gravels which provides support to the bed medium and thereby maintains the structure of the biofilter.7.4 Important Parameters Affecting the Biofilter Operation There are various parameters such as temperature, moisture, nutrients attainability, pH and flow direction of polluted gas that effects the functioning and performance of the biofilter.In this chapter, the details about each of these parameters are discussed below.7.4.1 Flow Direction of Odorous GasesIn biofilters two different types of flow modes namely downflow and upflow are available. In our green cycle facility, we preferred to use down flow mode to the closed type of biofilter. Firstly, the polluted gases flows across the long pipes with many holes at the sides so that the air gets distributed evenly throughout the entire bed. In the down flow mode the inlet for the pollutants will be at the top of the biofilter and the outlet for the cleansed air will be at the bottom. For the larger flow rates the down flow mode for the closed biofilter is desirable.7.4.2 TemperatureThe microbial activity is a key factor for the successful biofilter operation. The temperature has a major effect on this microbial activity, therefore it is essential to maintain the temperature at favourable conditions. Increased temperature fast up the rate of the microbial activity but decrease the rate of adsorption and lower temperatures works in the reverse manner. Usually the gases coming out from the composting unit has high temperatures and as soon as these gases are intermixed with the exhausted air that are released from other different units and flows through the humidifier, where the temperature will get decreased. The humidifiers play a significant role in operating the biofilter at the desired conditions. The temperature that ranges from 20-40 oC is generally esteemed as the optimal temperature conditions for the effective biofilter operation and also for the microorganisms to survive and proliferate.It is a good safety measure to incorporate a high temperature alarm near the air inlet and also regular monitoring (once in every 8 hours per day is preferable) of the temperature of the filter bed is necessarily important