| Formaldehyde is a kind of volatile organic pollutants. During the manufacturing process of man-made board, the formaldehyde waste-gas will be released into the air, which is harmful to our health and environment. This study targets at the dry exhaust from medium density fiberboard(MDF) plant, chooses formaldehyde gas as the research object and adsorption materials of bamboo charcoal as fillers to study the biodegradation of formaldehyde waste-gas in biotrickling filter. The study processes with the control experiment, the hanging film and the screening of conditions to provide data support for the MDF plant. The experimental results are as follows:(1) The control experiment is carried out before hanging membrane. It is found that the removal rate of formaldehyde is only 63-79% in empty water tower, but in charcoal water tower the rate is 93-99%. With the increase of inlet formaldehyde waste-gas concentration, the formaldehyde concentration dissolving into circulating liquid will also be increased. The formaldehyde concentration adsorbed in wet bamboo charcoal is directly related to the liquid formaldehyde concentration. The higher the liquid formaldehyde concentration is, the more formaldehyde adsorption into wet bamboo charcoal. If the liquid formaldehyde concentration is below 270mg/L, the formaldehyde in bamboo charcoal will not be detected. After the formaldehyde gas entering charcoal water tower, 96% is absorbed in circulating liquid, 3% is absorbed in bamboo charcoal, and the remaining will go outlet.(2) Choosing the method of circling hanging membrane to culture microbes, the process goes on about 30 days. After membrane hanging, start the orthogonal test by 43×21. the optimum operating conditions are as follows: the inlet formaldehyde waste-gas concentration is 110mg/m3, the gas velocity is 120m/h, the spray density of circulating liquid is 0.91m3/(m2·h), and pH is 7. Under this condition, the system has the biggest biodegradation of 14.09g/(m3·h). The liquid formaldehyde concentration is always first falling after rise up to 18mg/L. So this concentration will not poison microbes, and the wet bamboo charcoal will not formaldehyde, then the complexity of the test is reduced.(3) The biofilm's morphology of bamboo charcoal is characterized by scanning electron microscopy. It is found that the microbes on the middle filler grow closely in the form of biofilm. And the lower filler grows lots of coccus and filamentous bacteria. It is speculated that these microbes are formaldehyde degradation bacterium, and they choose formaldehyde as carbon source. But on the upper bamboo charcoal, the coccus and filamentous bacteria are not observed. The reason is that the carbon source is not enough at the upper filler.(4) The parameters such as inlet gas concentration, gas velocity, spray density, pH, inlet gas temperature are tested. The results are as follows: the formaldehyde waste-gas removal rate does not change along with these factors, and remaining above 99%. With the increase of inlet formaldehyde waste-gas concentration, the system biodegradation increased linearly. When the gas velocity increases, the biodegradation will also increase. When the spray density increases up to 0.45m3/(m2·h), the biodegradation is leveling off. When the pH value is 7-8, the system has the biggest biodegradation. Increase the inlet gas temperature from 25 ? to 75 ?, then the biodegradation rises after first drop to 8g/(m3·h). Under the condition of 144m/h gas velocity, the formaldehyde waste-gas is removed for 65.49% at the height of 0.5m. Then the remaining formaldehyde waste-gas is removed at the height of 1m. When the formaldehyde waste-gas entering the biotrickling filter, 10% of formaldehyde waste-gas is absorbed into circulating liquid, and 90% is degraded by microbes.(5) In order to save costs, we can start the circulating liquid intermittently. Intermittent time can be set as stopping for 4 hours, then spraying for 2 hours. If factories shut down for 3 days due to malfunction, we should run the system for 10 hours to restore the original state. Shutting down for 5 days, and running for 21 hours for recovery. Shutting down for 7 days, and running for 40 hours for recovery.(6) Start the biotrickling filter packed with sand and gravel. The sand and gravel filter has the lower biodegradation than the bamboo charcoal in biotrickling filter. The biotrickling filter filling with sand and gravel has the removal rate of 93%, in which 80% of the formaldehyde gas is degraded by microbes, 13% is dissolved in circulating liquid, and the remaining is discharged from the outlet. |
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