Synchronous Removal of Ca²⁺, Cd²⁺, Zn²⁺, and NO₃⁻ from Water Using Magnetic Biochar-Based Bioceramsite Reactor: An Advanced Technique for Water Remediation

Remediation of contaminated water using biosorbents is of great interest. Modification of pristine biochar using biogum and ceramsite with metal oxides under magnetic medium and its application for water decontamination has not yet been investigated. Therefore, a chia seeds gum (g) and synthetic ceramsite-impregnated hybrid magnetic biochar (g-MBC) filled reactor was established to assess the synchronous removal of Ca²⁺, Cd²⁺, Zn²⁺, and NO₃⁻ from contaminated water. The potential removal mechanisms have been investigated using microscopic, spectroscopic, and microbial techniques. The removal rates of Ca²⁺, Cd²⁺, Zn²⁺, and NO₃⁻ by the novel g-MBC bioreactor reached 79.9, 100.0, 99.8, and 99.9%, respectively, at carbon to nitrogen (C/N) ratio of 6, pH of 6.50, and hydraulic retention time of 6 h. Most of the NO₃⁻ was converted to gaseous nitrogen (N₂: 99.8%) in the g-MBC bioreactor without accumulation of toxic nitrite (NO₂⁻). The SEM images showed different and numerous forms of biological precipitates attached to the g-MBC filler, whereas EDS, XRD, and FTIR analyses showed the composition of mineralized products like CaCO₃, Ca₃(PO₃)₂, CdCO₃, and ZnCO₃. Sphingomonas, Dechloromonas, Acinetobacter, and Aquabacterium were the dominant genera in the microbial community in the g-MBC bioreactor with strong biomineralization capability and specific adaptability to high concentrations of Cd²⁺ and Zn²⁺. We concluded that chia seeds gum and ceramsite effectively enhanced the adhesion between the biofilm and filler due to its high viscosity. Therefore, the g-MBC bioreactor exhibited a good ability to synchronously remove Ca²⁺, Cd²⁺, Zn²⁺, and NO₃⁻ from water. These findings may help in the sustainable management of contaminated water.