Modelling of biobarrier of remediation at lead contaminated sites

Abstract

The purpose of this research is to study the microscopic flow in porous media and interaction among soil, microbe and Pb(II) by using the developed mathematical biobarrier model on lead remediation sites as a research sequence from Assistant Professor Dr. Thidarat Bunsri’s developed mathematical model. This theses evaluate and investigate the efficiency of laboratory scale biobarrier in immobilising soluble Pb(ll) by using the MATLAB program. The main mechanisms occurred in the permeable reactive biobarrier are biosorption and bioaccumulation. The PRB consisted of microbe and media. The microbes attached on the highly permeable media, in a meantime they consume Pb(II) from contaminated water. The biological reaction between lead and microbial cell was strong enough to store Pb(II) and the microbes were able to transform the soluble Pb(II) from the influent to insoluble Pb(II) and accumulate them in their cells. Recent studies have demonstrated that microbes might be applied to immobilise the ions of lead Pb(II) Sequential extraction, biosorption and bioaccumulation of lead both batch and column, as well as Fourier Transform Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) technique and biological studies through the rate growth of microorganisms, PCR-DGGE, SEM. The sand-manure and zeolite are used as organic and active media, respectively. Hereby, the result of organic media was a maximum biosorption of lead equaled to 6.2 mg of lead per gram of sand-manure (cow dung). The microbial strains that were isolated from matured sand-manure biobarrier determined with PCR-DGGE of partial 16S rRNA genes fragments showed the predominant species, namely are Bacillus sp., Sporolactobacillus nakayamae sp., Clostridium sp., and Clostridium pasteurianum sp. The case studies of sand-manure column use for verification processes and the simulation had presented the constants of Darcy’s velocity, averaged volumetric moisture content and Pb(II) dispersion coefficient are -0.00034 cm/h, 0.2032 cm3/cm3, and 0.001346 cm2/h, respectively. The Pb(II) dispersion coefficient is higher than zeolite column. High dispersion and low velocity condition could provide a benefit to Pb(II) retardation in biobarrier. While, the zeolite is utilised as an active media for Pb acclimatised microbial seed. In a startup process, the microbes seed are incubated and acclimatised by feeding molasses solution with a concentration of 0.5 g COD/L and molasses mixed with 0.2 mg/L of Pb(NO3)2, respectively. After 50 days, the removal efficiencies of COD and Pb(II) are constant at 70 and 90%. The substrate feeding rate to the column surface is 100 mL/d and controlled by the peristaltic pump. The quality and quantity of influent and effluent samples are daily determined. The zeolite itself has a maximum Pb(II)sorption capacity of 54.24 g Pb(II)/kg, while the maximum sorptive capacity of fabricated biobarrier is increased to 70.12 g Pb(II)/kg. X-ray diffraction (XRD) technique is introduced to identify the forms of Pb in the biobarrier. Precipitants of lead phosphate (Pb2P2O7) are observed on the surface of biobarrier. Fourier Transform Infrared (FT-IR) spectroscopy can reflect that the same functional groups of biopolymer on zeolite and biobarrier are governed, they are H-bonded OH groups (polysaccharides) and NH2 stretching (proteins), Aliphatic C-H stretching (fatty acids), PO43-and P-O-C, P-O-H stretching (phospholipids and ribose phosphate chain pyrophosphate). The results confirmed that biobarrier can retard Pb(II), forming a complexation with inorganic P species and organic ligands. Microbial strains are isolated from matured biobarrier namely, Bacillus sp., Nostoc sp., and Bradyrhizobium sp. They are Pb resistant microbe, which stay in root of plants. These can promote the immobilisation of Pb via metabolic and non-metabolic processes. The Pb(II) resistant microbe can partially retard Pb(II) via biosorption and bioaccumulation. Simulation results for the hydraulic pressure head and moisture content in zeolite columns matched the observed data well. The highest Pb(II) removal was observed at top of 10 cm column. Concentration of Pb(II) was reduced in this layer and Pb(II) remained in the effluent was very low, with a concentration of 0.018 mg/L. The overall Pb(II) removal efficiency was 93% of Pb(II) applied. The simulation had presented the constants of Darcy’s velocity, averaged volumetric moisture content and Pb(II) dispersion coefficient are -0.00389 cm/h, 0.1893 cm3/cm3, and 0.00985 cm2/h, respectively.