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Biofiltration is proven technique for the degradation of Volatile Organic Compounds
(VOCs) and toxic or odorous compounds, such as
H2S and NH3 (Sheridan et
al., 2002). A biofilter is a column containing biologically active biomass. Biofiltration is a process which
utilizes micro-organisms in the form of a biofilm on the surface of porous carriers such as,
peat, soil, compost and synthetic substances, or their combinations. As the polluted air
stream passes through the filter bed, the pollutants are transferred from the gas stream to the
biofilm developing on the carrier (Ramirez-Lopez
et al., 2003). The micro-organisms metabolize
the pollutants (Bohn, 1992; Wani et al., 1997; and Morgan-Sagastume
et al., 2001). The carrier material provides a favorable environment in terms of pH, temperature, moisture,
nutrients and oxygen supply to the microorganisms (Ramirez-Lopez
et al., 2003). These removal processes take place on the carrier in the packed bed, so the carrier is an important
factor which determines the characteristics of gas removal. According to Clark and
Wnorowski (1991), almost all organic compounds can be used as biofilter carriers. Thus, the
physical and chemical characteristics of several low-cost organic carriers have been studied by
many researchers. These include, rice husk, maize stubble, bagasse and coconut
(Ramirez-Lopez et al., 2003), coconut fiber (Baquerizo
et al., 2005), Peat (Tarja Hartikainen et
al., 1996) and Pine bark (Leson and Winer, 1991). In this study, the physical and chemical
characteristics of durian (Durio zibethinus
Murray) shell as a potential carrier material in biofilters
is examined. Durian is a tropical fruit, familiar in the Association of Southeast Asian
Nations (ASEAN), because it grows in warm and wet conditions, and belongs to the
family Bombacaceae (Martin, 1980). Durian is nearly round-shaped with an average size
weighing between 2 and 4.5 kg depending on the variety. The shell which usually weighs more
than half of the total fruit weight is green to yellowish brown, thick and semi-woody with
sharply pointed pyramidal thorns (Hokputsa et
al., 2004), which make peeling a difficult task
for untrained people. Only one-third of durian is suitable for eating, whereas, the seeds
(20–25%) and the shells are usually thrown away. Due to high utilization of durians, a
large amount of shells (as waste products) are disposed, causing a severe problem in
the community (Hameed and Hakimi, 2008). In the interest of the environment, we propose
to use this agricultural waste after examining its physical and chemical characteristics, as a
low-cost alternative biofilter carrier material.
Raw Durian shells (DS) were obtained from the market in Serdang, Selangor,
Malaysia. They were cut into small pieces of about 30-50 mm, by using a wooden chipper. A
small portion of the cut piece was analyzed for pH, density and moisture content in
triplicate according to the Association of Official Analytical Chemists (AOAC, 1975)
methods. The small DSs were washed with distilled water for several times to remove all the
dirt and dried at 70 OC for 48 h in an oven. Then, the samples were ground to a powder
(0.5 mm) by pulverisette machine. The powdered DS was mixed with
calcium hydroxide (Ca(OH)2) in the ratio of 23:1 (w/w) dry basis in order to adjust the pH
to be within 7-8. The mixture was made into pellet form (30 mmØ) by hydraulic
hand pressure (5 psi). |
