Recent interest has arisen in the potential use of biochar as a low-cost adsorbent for control of organic micropollutants in water. However, compared with commercial adsorbents such as activated carbon (AC), biochar adsorption capacity is typically one to two orders-of-magnitude lower. To-date most (≥85%) studies of organic compound adsorption by biochar use high (mg/L) adsorbate concentrations and organic free background water matrices – conditions that are not representative of environmental systems. This study reports batch mode adsorption of anionic (2,4-D; C0 100 μg/L) and neutral (simazine, SZN; C0 1.5 μg/L) herbicides from surface water containing dissolved organic matter (DOM) at 4 mg/L total organic carbon concentration. Enhanced adsorption was observed by biochars generated from low-cost gasification devices of the top-lit updraft typology under conditions of single stage co-pyrolysis/thermal air activation (PTA). Herbicide adsorption by PTA biochars is compared with adsorption by biochars generated from a conventional anoxic pyrolysis (CAP) furnace retort. 2,4-D adsorption by ≥850 oC biochars was more than ten times greater on a mass basis when generated under PTA conditions compared with CAP conditions, and was equivalent to AC reference adsorbents on a surface area normalized basis. Pore volume analysis assesses the influence on herbicide adsorption of microporosity, mesoporosity and possible increased pore interconnectivity formed through thermochemical widening of pores and/or removal of pyrolysis tars due to PTA versus CAP generation conditions. 2,4-D adsorption from water containing background DOM was shown to correlate strongly with biochar H:C molar ratio within but not between groups of biochars generated from PTA or CAP reactors. Comparing trends in biochar adsorption of 2,4-D and SZN with increasing temperature and intensity of PTA conditions indicated that herbicide interaction with biochar surface functional groups, e.g., through formation of H-bonds, did not play a significant role in overall herbicide uptake.

High temperature co-pyrolysis/thermal air activation modifies biochar porosity and enhances capacity for uptake of herbicides from surface water

255th National Meeting (2018)

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