General future work

An important issue with traditional biofilter is its huge size (3000 m2 per m3 of pollutants treated in an hour) (Theodore, 2008). Use of membrane reactors could solve this size issue to a great extent. Membrane reactors have been previously studied for biological gas treatment. As reviewed by Kumar et al (2008) the major advantages of membrane reactors over traditional packed beds are oxygen supply is received equally by the whole membrane resulting in more degradation and less clogging, higher inlet loading rate with greater elimination capacity, smaller foot-print and lower maintenance cost. A smaller foot print, plug flow biofiltration reactor needs to be developed from the existing differential biofiltration reactor system with biofilm on the gas side of the membrane. This reactor will be similar to a shell and tube heat exchanger. The biofilm will be developed in the gas-side of the membrane inside the tube side rather than shell side (Fig. 8.1). It will also eliminate the membrane mass transfer resistance, as the contaminant will transfer directly from the gas phase to the biofilm, with only water and dissolved species exchanging across the membrane. In regards to practical operation, excess biomass will be more easily controlled with direct access to the biofilm for physical or chemical treatment. This will allow both non-growth and growth systems to be easily tested in the same apparatus. However, with the biofilm directly exposed to the contaminated gas, the build-up of recalcitrant compounds such as dust or fats/oils or the displacement of the preferred microbial community by

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contaminants or predators is more likely compared to traditional membrane reactors. However, standard biofilters and trickle beds are subject to the same problems.

Preliminary design calculations have given satisfactory results which will help us to develop a plug flow reactor efficiently for treating higher volumes of pollutants per unit volume of reactor. This novel work will pave the way for developing a cost effective biofilter reactor occupying less area and involving less manpower in treating higher volume of pollutants and higher specific productivity. Moreover, this reactor will also help to introduce the metabolic uncouplers in a controlled way/environment similar to the existing differential biofilter reactor system. This idea is one of the future ideas for our current research group, and hence it has to be first proved in a lab scale before scaling it up.

Figure 8.1 – A comparison of the biofilm location in a membrane reactor (a) – saturated

biofilm on the water-side; (b) – traditional shell and tube configuration of a membrane bioreactor; (c) – an unsaturated biofilm on the gas-side of the membrane.

Additional work could include testing different substrates (pollutants) in the biofiltration reactor set-up. In particular methane gas is a possible replacement to toluene for similar studies as it is a greenhouse gas and posing a great threat to the increased global warming.

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Similar to toluene degraders, methane degrading organisms (Chu and Alvarez-Cohen, 1998; Lontoh and Semrau, 1998) may be used in our biofilm reactor in presence and absence of metabolic uncouplers to study the degradation rate.

Finally a modelling study to understand and calculate the maintenance energy during the action of metabolic uncouplers in a pure culture biofilm reactor needs to be done. This study is one of the ways to quantitatively explain the metabolic uncoupling in pure biofilm under non-growth conditions.

8.6 References

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Deshusses, M.A., 1997, Transient behavior of biofilters: Start-up, carbon balances, and interactions between pollutants. Journal of Environmental Engineering (ASCE) 123, 563-568.

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Appendix A