Phosphate, fluoride and calcium removal from Saravan landfill leachate using calcium carbonate bioprecipitation process

In recent years, environmental friendly methods have been considered for managing hazardous chemicals in landfill leachates to prevent their entrance to surface and groundwater resources. This research was done in 2022 at University of Guilan. An ureolytic bacterium with the ability to precipitate calcium carbonate was isolated from the Saravan landfill leachate (SLL) firstly. Then, its potential was investigated along with the indicator bacteria Sporosarcina pasteurii</em> in removing phosphate, calcium and fluoride ions from LLA through the calcium carbonate bioprecipitation process (MICP). The experiment was carried out as a 3 × 2 × 2 factorial in a completely randomized design with three replicates (36 samples). Factors include biocementing bacteria at three levels (no inoculation, inoculation with strain isolated from LLA and inoculation with S.  pasteurii</em>), urea at two levels (0 and 2% (v/v)), and calcium chloride at two levels (0 and 50 mM). The highest phosphate removal rate (93%) was observed in the presence of calcium chloride without bacteria inoculation, and urea addition. However, ureolytic bacteria were needed for fluoride removal where the treatments of indicator bacteria and isolated strain in the presence of urea and calcium chloride removed 77% and 48% of fluoride, which was 14.4 and 9 times greater than the control treatment, respectively. The calcium removal rate in treatments with indicator and isolated bacteria was 93% and 90%, respectively. Although the removal rate of phosphate, calcium and fluoride was higher in the presence of the indicator bacteria compared to the isolated strain, there was no significant difference between them. Therefore, considering the application of native microorganisms, in addition to reducing costs, also creates less environmental concern than the indicator bacteria, it can be used to remove hazardous chemicals from landfill leachates through the MICP process.