Microbial Carbonate Precipitation In Heavy Metals Immobilization With Rhizobacteria And Poly-lysine

Heavy metals are the most common pollutant of soil and water and are being the center of attention due to their toxicity and carcinogenic nature for environment and human health.Microbially induced carbonate precipitation?MICP?,a type of urease-based biomineralization,is one of well-known bioremediation process in recent years for metals immobilization that can effectively decontaminate metal stressed soil.It's known to have preference of MICP for divalent metal over other multivalent metal ions.Despite of success of MICP in heavy metal immobilization,the efficiency of this process remains in question.Poly?amino acids?are known to enhance enzymatic activity.In recent years,application of Plant Growth Promoting Rhizobacteria?PGPR?exhibited great trait in increasing the production of biomass.Thus,combining PGPR with MICP process could be beneficial to plant growth with effective metal immobilization.Further,although the process of MICP has been a well-researched technique in recent years for heavy metal immobilization;the efficiency of the process remains in question.The present thesis carried out important research to solve above problems with three objectives:?1?As one of first objectives,the research mainly focused on the MICP for the remediation of divalent Pb?II?and hexavalent Cr?VI?in solution using ureolytic Staphylococcus epidermidis.The urease activity led to the metal removal in MICP process,and the removal efficiency of Pb?II?and Cr?VI?was up to 86%and 76.8% ?with initial metals concentration 25 mg/l?,respectively.The FTIR spectra revealed number of peaks indicative of CO₃ bonding and formation of carbonate compounds in MICP samples;however,such peaks were clearly identified in MICP-Pb than MICP-Cr?VI?due to direct precipitation or immobilization ability of similar valency(Ca²⁺and Pb²⁺).The results depicted clear efficacy or preference of MICP in the immobilization of divalent over multivalent metal ions.?2?The application of plant-growth-promoting rhizobacteria?PGPR?supports the growth of plants in contaminated soil while ureolytic bacteria can immobilise heavy metals by carbonate precipitation.Thus,dual treatment with such bacteria may be beneficial for plant growth and bioremediation in contaminated soil.This study aimed to determine whether the PGPR Pseudomonas fluorescens could work in synergy with ureolytic bacteria to assist with the remediation of cadmium?Cd?-and lead?Pb?-contaminated soils.Pot experiments were conducted to grow radish plants in Cd-and Pb-contaminated soils treated with PGPR P.fluorescens and the results were compared with dual inoculation of P.fluorescens combined with ureolytic Staphylococcus epidermidis HJ2.The removal rate of the metals from the soil was more than 83%for Cd and Pb by the combined treatment compared to 17%by PGPR alone.Further,the dual treatment reduced the metal accumulation in the roots by more than 80%.?3?Then,third objective of this thesis focused on carbonate precipitation induced by ureolytic Staphylococcus epidermidis HJ2,poly-Lysine?poly-Lys?was added to obtain higher enzyme activity,and Response Surface Methodology-Central Composite Design was used to identify the optimum conditions for this process.Following this,the effect of poly-Lys was investigated in lead?Pb?immobilization in aqueous solution by MICP.The results concluded that the addition of poly-Lys increased the Pb removal rate by around 8%compared to the control.The addition of poly-Lys gave a strongly confirmation that it is an effective and stable way to enhance the MICP efficiency.