The effects of residual concentration and moisture content on pollutant removal and carbon recovery in a soil biofilter. (2019)
Type of ContentElectronic Thesis or Dissertation
Thesis DisciplineChemical Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsDang, Quang Anhshow all
This study quantitatively determined the importance and potential interaction between operating conditions – combination of residual pollutant concentration and water potential and soil type on %CO2 recovery and biofilter performance (elimination capacity - EC). A 2 x 3 factorial design was adopted, which included two levels of operating conditions: (1) low residual pollutant concentrations and wetter conditions and (2) high residual pollutant concentrations; and drier conditions. This experimental design was done for three types of soil (Soil 1, Soil 2, Soil 3).
A continuous lab-scale differential biofilter was used as a research tool to control the environmental conditions. The biofilter was operated without supplemental nutrient addition to remove a variety of pollutants (toluene and methane) in an air stream. The carbon flux was rigorously tracked through the biofiltration system. Over the range of operation, the carbon balance closure for 37 experiments was 96.1 ± 5.3%. The carbon fraction found in the liquid phase was less than 5% of the degraded carbon. Majority of the biodegraded carbon (> 90%) ends up in the form of either CO2 or active biomass/EPS.
In general, operating the toluene biofilters at low residual concentrations (5 ppm to 49 ppm) and wetter condition (-10 cmH₂O) resulted in a 20% higher EC and a 20% higher CO₂ than operating at high residual concentrations (115 ppm to 146 ppm) and drier condition (-100 cmH₂O). Conversely, operating the methane biofilters at low residual concentrations (1709 ppm to 1942 ppm) and wetter condition (-10 cmH₂O) resulted in a 35% lower EC and a 45% higher CO₂ than operating at high residual concentrations (8590 ppm to 9054 ppm) and drier condition (-100 cmH2O).
Soil type had a strong effect on the EC and %CO₂ recovery in methane biofilters and on the EC in toluene biofilters. Among three soil types, Soil 2 had the lowest EC. The interaction between soil type and operating condition was not significant. Preliminary microbial analysis suggested the differences in the community structure was mainly attributed to the soil type rather than the operating conditions, type of substrate during acclimation.
A feedback control system was developed to maintain the residual toluene to the desired value. The impact of residual toluene concentration on biofilter performance packed with Soil 2 was investigated. Substrate inhibition occurred when the residual toluene concentration exceeded 250 ppm. Start-up concentration studies showed that starting the reactor at a lower residual concentration (20 ppm) then increasing it to higher value (65 ppm) increased the EC by 22% compared to starting the reactor at a high residual concentration (65 ppm).