Abstract
BackgroundBiochar ozonization was previously shown to dramatically increase its cation exchange capacity, thus improving its nutrient retention capacity. The potential soil application of ozonized biochar warrants the need for a toxicity study that investigates its effects on microorganisms.ResultsIn the study presented here, we found that the filtrates collected from ozonized pine 400 biochar and ozonized rogue biochar did not have any inhibitory effects on the soil environmental bacteria Pseudomonas putida, even at high dissolved organic carbon (DOC) concentrations of 300 ppm. However, the growth of Synechococcus elongatus PCC 7942 was inhibited by the ozonized biochar filtrates at DOC concentrations greater than 75 ppm. Further tests showed the presence of some potential inhibitory compounds (terephthalic acid and p-toluic acid) in the filtrate of non-ozonized pine 400 biochar; these compounds were greatly reduced upon wet-ozonization of the biochar material. Nutrient detection tests also showed that dry-ozonization of rogue biochar enhanced the availability of nitrate and phosphate in its filtrate, a property that may be desirable for soil application.ConclusionOzonized biochar substances can support soil environmental bacterium Pseudomonas putida growth, since ozonization detoxifies the potential inhibitory aromatic molecules.Graphical
Highlights
The pyrolysis of biomass to biochar may produce some chemical compounds such as polyaromatic hydrocarbons (PAH’s), furans, and dioxins that may be toxic to microorganisms (Lyu et al 2016)
While the results presented here are empirical evidence that the ozonization of biochar reduces its inhibitory effect on the growth of P. putida KT2440 and S. elongatus PCC 7942, to the best of our knowledge this is the first study that investigated the effect of ozonized biochar filtrates on microorganisms
We previously showed that ozonization can significantly improve the cation exchange capacity (CEC) of biochar (Kharel et al 2019)
Summary
The pyrolysis of biomass to biochar may produce some chemical compounds such as polyaromatic hydrocarbons (PAH’s), furans, and dioxins that may be toxic to microorganisms (Lyu et al 2016). The effect of ozonization was shown to create some oxygen functional groups on the biochar surface, which resulted in an increase in cation exchange capacity (CEC) (Sacko et al 2020; Huff et al 2018), a key property for fertilizer retention in soil; we recently showed the biochar CEC increased by up to almost 10 times upon ozonization under dry conditions (Kharel et al 2019). The potential soil application of ozonized biochar warrants the need for a toxicity study that investigates its effects on microorganisms
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