3.2.3. Microbial Transport

The detection of *E. coli* and faecal coliforms (>1 CFU/100 mL) in soil and water resources above the guideline threshold [37–39] have a high risk on human health [16]. Presence of these bacteria indicates recent pollution from a faecal source such as pit latrine sanitations [13]. Bacteria can be infiltrated through the soil towards groundwater or move through overflow across the surface [16]. This threat to public health has urged investigation into microbial migration in soils, for which biochar amendments may be a solution [14,15].

When amended with soil, biochar can raise soil pH, which is essential for the mitigation of micro-organic pathogens such as *E. coli* and faecal coliform bacteria [22]. An increase in the organic matter, pH, conductivity, and dissolved organic C in a sandy soil using poultry manure biochar resulted in decreased soil *E. coli* and faecal coliforms migration [13]. Individually, these soil properties have been related to bacterial transport through soil [112–114]. Bolster and Abit [14] also demonstrated that biochar application rate, pyrolysis temperature, and *E. coli* surface properties largely contribute to the likely soil migrations. The higher temperature biochar (700 ◦C) exhibited a larger decrease in pathogen transport, possibly owing to the reduced negative surface charge of high-temperature biochars. The

improved surface area of high-temperature biochars provides a higher adhesion of *E. coli* cells [15]. Biochar can also assist in dehydrating excreta because of its high water holding capacity, reducing malodour by adsorption [23] and thereby helping to keep insects such as flies away.

Biomass type used for biochar pyrolysis also plays a role in the transportation of soil *E. coli*, and faecal coliforms [16]. Comparison between poultry litter and pine chip biochars indicated that the internal pore structure of the woody biochar retained or adsorbed more bacteria [15]. Additionally, soils with higher clay contents have fewer detachments because of the electrostatic attraction force of the negatively charged microbes and the positive clay functional groups [15]. The influence of biochar on microbial movement through soil relies on biomass material, temperature, and soil texture [16]. Results from literature on the effect of biochar use in faecal sludge and contaminant reduction are presented in Table 5.


