# Ozonized biochar filtrate effects on the growth of Pseudomonas putida and cyanobacteria Synechococcus elongatus PCC 7942

## TL;DR

Ozonized biochar filtrates support the growth of Pseudomonas putida but inhibit cyanobacteria at high concentrations.

## Contribution

The study reveals that ozonization detoxifies biochar filtrates, making them safe for soil bacteria but harmful to cyanobacteria at high DOC levels.

## Key findings

- Ozonized biochar filtrates do not inhibit Pseudomonas putida growth even at 300 ppm DOC.
- Synechococcus elongatus PCC 7942 growth is inhibited by ozonized biochar filtrates at DOC >75 ppm.
- Ozonization reduces inhibitory compounds like terephthalic acid and p-toluic acid in biochar filtrates.

## Abstract

Biochar 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.

In 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.

Ozonized biochar substances can support soil environmental bacterium Pseudomonas putida growth, since ozonization detoxifies the potential inhibitory aromatic molecules.

The online version contains supplementary material available at 10.1186/s40643-021-00491-2.