Enhanced nitrate removal in aquatic systems using biochar immobilized with algicidal Bacillus AK3 and denitrifying Alcaligenes M3: a synergistic approach

This study investigates the effectiveness of biochar immobilized with algicidal Bacillus AK3 and denitrifying Alcaligenes M3 in mitigating harmful algal blooms (HABs) and reducing nitrate pollution in aquatic environments. Over a six-day period, we analyzed changes in Microcystis density, chlorophyll-a levels (indicative of algal biomass), nitrate concentration, and microbial community composition in water treated with biochar and biochar-immobilized bacteria. In the Biochar+AK3+M3 treatment, Microcystis density decreased from 600,000 cells/mL to 80,000 cells/mL, and chlorophyll-a concentrations also substantially reduced, from 85.7 µg/L initially to 42.8 µg/L. The results showed significant shifts in bacterial communities, with a decrease in Microcystis, highlighting the specific algicidal activity of Bacillus AK3. Nitrate concentrations in the Biochar+AK3+M3 treatment significantly decreased from approximately 23 mg/L to around 14 mg/L by Day 6, demonstrating the enhanced denitrification capabilities of the immobilized Alcaligenes M3 and associated bacterial communities. The study underscores the potential of biochar-based treatments as a sustainable and effective approach for improving water quality and mitigating the environmental impacts of nutrient pollution and HABs.