Biomedical subjects

Sujit Banerjee

Publications and source records attributed to Sujit Banerjee.

6 recordsLinked to original sources

PubMed2006

Process-based control of HAPs emissions from drying wood flakes.

Industrial wood flake drying generates methanol, formaldehyde, and other hazardous air pollutants (HAPs). A simple theoretical model shows that particles smaller than 400 microm will begin to thermally degrade and release disproportionately large quantities of HAPs. This is confirmed in full-scale practice where particles smaller than 500 microm show visible signs of charring. Laboratory measurement of the activation energy for the breakdown of wood tissue into methanol and formaldehyde led to a value of about 17 kcal/mol. The apparent activation energy measured in the field was higher. This result was obtained under nonisothermal conditions and is biased high by the fines fraction of the furnish, which is exposed to elevated temperatures. It is proposed that a combination of screening out the fines fraction smaller than 500 microm and reducing the dryer inlet temperature will substantially reduce emissions, possibly to the point where control devices can be downsized or eliminated. Our findings allow these HAPs reductions to be semiquantitatively estimated.

Air Pollutants↗

PubMed2005

Controlling formaldehyde emissions with boiler ash.

Fluidized wood ash reduces formaldehyde in air from about 20 to <1 ppmv. Methanol is removed to a much lower extent. The efficiency of formaldehyde reduction increases with increasing moisture content of the ash. Sorption of formaldehyde to ash can be substantially accounted for by partitioning to the water contained in the ash followed by rate-controlling binding to the ash solids. Adsorption occurs at temperatures of up to 165 degrees C; oxidation predominates thereafter. It is proposed that formaldehyde could be stripped from an air stream in a fluidized bed containing ash, which could then be returned to a boiler to incinerate the formaldehyde.

Adsorption↗

PubMed2005

Spark-induced agglomeration of aqueous polymeric suspensions.

Discharging a high-energy spark underwater creates a shock wave that dissipates through an acoustic field. Colloidal acrylate polymers suspended in water containing dissolved calcium are agglomerated as a result. The degree of agglomeration increases with the number of sparks applied and with increasing calcium content. The calcium decreases the charge on the colloidal particles and thereby increases their propensity to be agglomerated by the acoustic wave. These observations are confirmed in full-scale trials in paper recycling mills where sparking improves the efficiency of centrifugal cleaners by increasing the particle size of the contaminants.

Journal Article↗

PubMed2005

Spark-induced consolidation of biological sludge.

Subjecting a suspension of biological sludge to underwater sparks (3kV, 50kA) leads to its consolidation, decreases the charge density on the solids, and increases its settling rate. The cake solids increase, but by only one percentage point. High-speed video images show that the spark generates a steam bubble. The dynamics of bubble growth could be estimated through the Rayleigh model. The bubble collapses into an acoustic field, which then agglomerates the particles. Sparking does not affect the settling rate of an aqueous slurry of softwood pulp because the fibrous particles are too large to be aggregated by an acoustic pulse.

Acoustics↗

PubMed2002

Fate of resin acids in pulp mill secondary treatment systems.

Profiles of resin and fatty acids (RFAs), COD, and aquatic toxicity were measured across the secondary treatment systems of three pulp mills. The RFAs sorb to suspended solids, principally fiber, and are partially removed through settling. An activated sludge system is more efficient in removing RFAs than an aerated stabilization basin (ASB) because of its higher solids level. Dehydroabietic acid accounts for a significant fraction of the effluent toxicity in the two ASBs studied. The microorganisms in an ASB are unable to respond rapidly to an RFA spill, and effluent toxicity can be elevated for a prolonged period because of hydraulic backmix. The applicability of several laboratory studies to field situations is assessed.

Adsorption↗

PubMed2001

Dual Reactive Domain Model for Sorption of Aqueous Organics by Wood Fiber.

An experimental study of 2,4,5-trichlorophenol (2,4,5-TCP) sorption to kraft papermaking fiber demonstrates that the dual reactive domain model (DRDM) effectively characterizes the process over a broad concentration region. Isotherm data were deconvoluted into linear partitioning and nonlinear adsorption contributions in accordance with the model demonstrating the importance of both mechanisms to the overall process. DRDM accurately fit concentration-dependent distribution coefficient, K(d)(C), data that could not be characterized with the Freundlich or Langmuir equations, and the model predicts the asymptotic movement toward a limiting K(d)(C) value at high solute or cosolute concentrations observed in experiments. Competitive effects were accounted for by modifying the adsorption portion of the model. With its limitations understood, the extended Langmuir equation was utilized and provided an effective fit of data. Langmuir fitting parameters for competitive data with five different n-alcohol homologs allowed estimates of free energy values per methylene linkage, which were in agreement with previously reported values. Also obtained from competitive data were relative sorption values for various benzene analogs, indicating that interactions in addition to those stemming from solute hydrophobicity often contribute in driving the overall sorption process. These results have implications for papermaking given the ubiquitous nature and importance of sorption in the process. Copyright 2001 Academic Press.

Journal Article↗