Primary Investigation On The New Fillings Of PRB Used For In Site Bioremediation Of Contaminated Groundwater

PRB is a rising technology which was developed in the 1990s and the fillings of PRB is mainly non-biological material, such as zero-valent iron, active carbon, zeolite and so on, PRB has the advantages of low investment, small disturbance and long period treatment for contamination, and it has been rapidly developed in rencent years. But the research on immobilized microbe as PRB filling is singular, especially, the research on using polyvinyl alcohol as bio-immobilization carrier to fill in PRB to remedy contaminated groundwater has not been reported.Bio-immobilization is a rising biotechnology of bioengineering, In contrast with traditional bio-remediation; it has the advantages of high bio-density and toxicity-resistance. Among bio-immobilization techniques, embed method is more outstanding for its advantages and is studied abroad, which immobilizes microbe in the process of high polymer forming gel.Polyvinyl alcohol is a new material of Bio-immobilization with potential practicality, and it has the advantages of high mechanical strength, good chemical stability, innocuity, cheapness.The well-developed technique of making bio-bead with polyvinyl alcohol is: dissolve PVA and sodium alginate in water together, mix the mixed gel with microbe when the gel is cooling, then drop in CaCl2-saturated boric acid solution for a period of time. But the bio-beads making in this way appear some problems, such as expanding, volume augmenting, mechanical strength declining, and conglutination.To solve these problems, bentonite and diatomite were added to the PVA and sodium alginate mixed gel, respectively, and cranked out two kinds bio-beads A and B after the optimal modifying parameters have been determined, and then studied the degradation characters and the tolerance capability of bio-bead A and B, polluted groundwater laboratory simulations were also carried out. And the conclusions as follow:1. The optimal modifying parameters of bentonite modifying PVA bio-bead is: dissolving 10.8%PVA and 0.1%sodium alginate in 95～100℃water together, then mixed together with 1.8% bentonite and 0.9% activated carbon powder, then the mixed gel is disinfected under 120℃for 20min, then the mixed gel is dropped into 1%CaCl₂-saturated boric acid solution to modify for 24 hours, after cooling to room temperature. The mechanical strength and expanse capability of bentonite modifying PVA bio-bead have been improved.2. The optimal degradation parameters of bio-bead A is: pH value is from 6～11, glucose is the best assistant carbon source, the concentration of glucose is above 1.0%.3. The optimal modifying parameters of diatomite modifying PVA bio-bead is: dissolving 9% PVA and 1% sodium alginate in 95～100℃water together, then mixed together with 16% diatomite, then the mixed gel is disinfected under 120℃for 20min, then the mixed gel is dropped into 3%CaCl₂-saturated boric acid solution to modify for 26 hours, after cooling to room temperature. The mechanical strength and expanse capability of diatomite modifying PVA bio-bead have also been improved.4. The optimal degradation parameters of bio-bead B is: the concentration of atrazine is 8mg/L, pH value is 7, glucose is the best assistant carbon source, the concentration of glucose is above 0.4%. The study of the tolerance capability shows that: the immobilized atrazine degradation bacteria has a good tolerance to toxicant, extremity pH value and the lack of assistant carbon source, and the removal rate of atrazine is higher than free cell.5. Simulating underground water environment, study the degradation result of atrazine by bio-beads. The result of the laboratory simulation of bio-bead B shows that: as the atrazine concentration of enter water is 10mg/L, the remove rate is 55%-73% while the atrazine concentration of enter water is 20mg/L, the remove rate is 46%-53%. The result of the laboratory simulation of bio-bead B shows that: when the atrazine concentration of enter water is 16mg/L, the remove rate is 61%-74%.6. In contrastwith bio-bead A , bio-bead B have the advantages of low PVA dosage, no expensive powder active carbon, easy making, lower dosage of glucose-the best assistant carbon source, higher atrazine remove rate and so on. So , bio-bead B is chosen as the new filling of PRB Used for In Site Bioremediation of Contaminated Groundwater, and will be studied in the following research.