Biochar–Microbial Synergistic Systems for Nitrogen and Phosphorus Removal in Polluted Waters: Mechanisms, Studies, and Insights

Tianqi Zhu, Di Liu

Eutrophication caused by increasing non-point source pollution has resulted in the
accumulation of nitrogen and phosphorus in water bodies, leading to severe algal blooms,
oxygen depletion, and ecosystem degradation. However, conventional remediation
technologies often face limitations in efficiency and sustainability. Biochar, derived from
organic waste, has gained attention for its strong adsorption capacity. Recent advances show
that combining biochar with functional microorganisms—forming biochar-microbial synergistic
systems—can significantly enhance the removal of nitrogen and phosphorus from polluted
water. For example, laboratory studies have reported that microbial-immobilised biochar can
achieve over 90% removal of ammonium and phosphate, far exceeding the performance of
single biochar or free bacteria. Such ecological and environmental benefits are due to the
physical and chemical properties of biochar and its ability as a multifunctional carrier for
microorganisms, which therefore form a comprehensive purification mechanism of physical
adsorption, biological transformation and chemical precipitation. This review systematically
summarises the mechanisms, advantages, and recent progress of biochar-microbial
synergistic systems, including key factors influencing removal efficiency and the prospects for
in-situ application. Additionally, comparative analyses between biochar-microbial synergistic
technology and traditional technologies are presented, discussing economic feasibility and
current challenges. This review highlights the unique potential of biochar-microbial composites
to achieve high efficiency, environmental friendliness, and practical scalability in water
pollution remediation, providing a reference for future research and large-scale applications.