REMOVAL OF PYRIDINE BY ADSORPTION IN CONTINUOUS REACTOR AND BY BIODEGRADATION USING BACILLUS SUBTILIS

Abstract

Pyridine (Py) and its derivatives are volatile, toxic and flammable with a pungent and unpleasant odor. Pyridine is the parent of a series of chemicals, and is used in many industries like paint, rubber, insecticides and herbicides. Pyridine and its derivatives are also used to make different products such as medicines, vitamins, food flavorings, dyes, adhesives, and in water proofing for fabrics. When heated to decomposition, pyridine emits highly toxic vapors of NO„ in an oxidative atmosphere. It has very high half-life when released in the atmosphere. It is also mildly toxic by inhalation; its vapour is skin and severe eye irritant and exposure to it can cause depression, gastrointestinal upset, liver and kidney damage, headache, nervousness, dizziness, insomnia, nausea, anorexia, frequent urination and dermatitis. The typical concentration of Pyridine in wastewaters is in the range of 20-300 mg/I. However, the vapor (odor) concentration may be as low as 7 μg/I, while the threshold odor concentration can be —0.3 μg/l. The various physical methods which are available for treatment of pyridine from various sources are thermal catalytic incineration, deep well injection, soil percolation, ultrafiltration, chemical coagulation and adsorption on various materials. Various chemical methods, required for the treatment of pyridine are based on UV/ ozone gas scrubbing, chemical/ photochemical oxidation and wet oxidation etc. Advanced oxidation processes (AOPs) are another major group of chemical treatment processes used for treatment of heterocyclic compounds like pyridine. The AOPs are associated with generation of highly reactive radical intermediates, mainly the hydroxyl radicals. Another attractive method to eliminate pyridine is biodegradation in which the organic compound is essentially converted to harmless compounds such as CO2, H2O, and NH2- etc. In literature different aerobic and anaerobic microorganisms have been reported for degradation of pyridine. In the present study pyridine contaminated air stream had been treated in continuous fixed bed column, reactors. Soybean and puffed rice which have no mention of use in literature as adsorbents had been chosen as the adsorbents. The characterizations of these compounds were also performed. The data from adsorption study was used to validate Yoon and Nelson mode! for gas phase continuous reactor. In the next part of the present work where pyridine had been treated by biodegradation, Bacillus Subtilis was chosen as the microorganism to be used. Parameters like pH and temperature were III optimized through batch studies for degradation by B. Subtilis. The growth of microorganism was studied for various initial pyridine concentrations and subsequently the growth kinetics was also studied. Finally continuous biotrickling filter was run at a definite contaminant load, flow rate and empty bed residence time. Soybean was used as the packing material. The adsorption study of pyridine laden air stream was carried out in continuous reactors by varying inlet concentration and total flow rate to the reactor. Soybean was found .to give better results than puffed rice. The validation of Yoon and Nelson model showed that rate constant as well as proportionality constant reduced with increase in concentration for both adsorbents. When the model was validated for variation in flow rate the rate constant increased for soybean but decreased for puffed rice with increase in flow rate. The proportionality constant though decreased in both cases.- The optittifiatiOn study for biodegradation of pyridine by B. Subtilis showed that optimum temperature was 30 °C and optimum pH was 7. At this optimized pH and temperature conditions the growth of B. Subtilis was studied for initial pyridine concentration ranging from 50 to 500 ppm. The specific growth rate appeared to increase with increase in concentration thus indicating Monod growth kinetics. Hence double reciprocal plot was plotted to find the maximum specific growth (tmax) rate as 0.0349 VI and Half saturation constant (Ks) as 121.65 mg/1 or ppm. The continuous process with soybean packing though did not work as soybean started to rot in 3 days and the bed also collapsed. IV