The aim of this
research was to characterize plant cell walls as a sorption and filtration
media for ammonia, hydrogen sulfide, propyl acetate (representing hazardous
organic compounds) and micron size particles, by comparison with activated
carbon. Filtration media consisting of cell wall powder were derived by hot
ethanol extraction, filtration and drying of finely ground plant tissues.
Adsorption capacities of cell wall filtration media prepared from primary or
secondary walls from different tissues of monocot or dicot plants were
determined. The influences of different physical factors, such as compaction,
flow rate, path length, surface area and humidity on the adsorption and
filtration capacity of the media were studied. In addition, adsorption
capacities of the major cell wall components (i.e. cellulose, pectin, protein
and lignin) were determined. The influence of chemical modifiers such as weak
acids or strong oxidizers on the adsorption capacity of cell walls and
activated carbon was also investigated. Secondary cell wall material prepared
from dicot pine wood absorbed ammonia with about 60% the efficiency of
activated carbon and with near equivalent efficiency after chemical
modification with citric acid. Other plant sources of primary or monocot cell
walls proved less effective than pine wood. The best results were obtained for
higher densities of filtration media and lower rates of ammonia injection
through the filter. All of the polymer components of cell walls were capable of
some ammonia absorption but the most active component was pectin. The hydrogen
sulfide adsorption capacity of all the studied types of cell walls was low, as
was the adsorption capacity of activated carbon for this gas. Adsorption of
propyl acetate vapor by cell wall media was very low as compared with activated
carbon. Chemical modifications did not improve the adsorption of propyl
acetate. Cell wall powder was able to completely remove microparticles of
smoke, ranging from 0.2 to 0.8 µm diameter, from an air stream during a 3 h
assay. Cell wall powder therefore showed promise as a microparticle air filter,
certainly in comparison with activated carbon and cellulose powder. Moreover,
the cell wall powder reduced particle concentrations in air with a relatively
low pressure drop compared to the other materials studied.
