Feasibility of Using Traditional Kiln Charcoals in Low-Cost Water Treatment: Role of Pyrolysis Conditions on 2,4-D Herbicide Adsorption

Abstract

Abstract

Prior research has established that pyrolysis temperature during charcoal production is the primary variable influencing adsorption capacity. The first objective of this work was to monitor thermal conditions during charcoal production within three common traditional kiln models. Then, a programmable laboratory furnace pyrolyzer was used to generate chars from eucalyptus, pine, and longan woods and bamboo under a similar range of thermal conditions as identified in the field study. Using chars produced from the furnace, the second objective of this study was to investigate the influence of biomass feedstock and grain size, peak pyrolysis temperature, and duration of thermal treatment on 2,4-D herbicide sorption capacity. A third objective was to determine if chars produced in the laboratory furnace using thermal profiles similar to those observed in the horizontal drum kiln would exhibit similar adsorbent characteristics to kiln charcoals. Field observations revealed significant variability in temperature profiles during pyrolysis in traditional charcoal kilns, and laboratory experiments indicated corresponding variability in equilibrium 2,4-D uptake from surface water ranging from virtually no adsorption to around 10% of the adsorption capacity of commercial activated carbon. Increasing pyrolysis temperature or duration increased 2,4-D adsorption capacity, whereas feedstock did not affect adsorption capacity for the materials studied. Similar herbicide adsorption capacity was observed for furnace chars and kiln charcoals generated using similar thermal profiles. The difficulty of achieving precise temperature control with traditional charcoal production systems contributes to wide thermal variability within and between batches, which translates to wide variability in adsorption of organic compounds.