Hydrogel microbial reactor based on microbially induced calcium precipitation for the removal of calcium, cadmium and nitrate from groundwater

In this study, hydrogel biocarriers filled with chia seeds gum biochar encapsulated with Pseudomonas sp. LYF26 were prepared using polyvinyl alcohol and sodium alginate. Simultaneous removal of NO3, Ca2+ and Cd2+ from low carbon wastewater was achieved by microbially induced carbonate precipitation and denitrification. In order to investigate the performance of the bioreactor, different conditions of hydraulic retention time, pH, and concentration of Cd2+ were studied, and the optimal operating conditions of the bioreactor were finally determined as HRT of 8 h, pH of 6.5 and initial Cd2+ concentration of 3 mg L-1. The results showed that the optimum removal of NO3- -N, Ca2+ and Cd2+ by the reactor was 100%, 54.02% and 100%, respectively. Three-dimensional excitation-emission matrix (3D-EEM) showed that the microorganisms produced extracellular polymers during the operation of the bioreactor, which promoted the removal of Cd2+. Fourier transform infrared spectroscopy (FTIR) detected the presence of -OH, C-O, C-O-C and C-O-H, indicating the production of CaCO3 and extracellular polymers. Scanning electron microscope (SEM) observed that the filler surface had a rough and porous character with a large amount of biodeposits attached to its surface. X-ray diffraction (XRD) indicated that the sediments contained CaCO3, CdCO3 and Ca-5(PO4)(3)OH. High-throughput sequencing showed that Pseudomonas was the dominant bacterium.