Concurrent transport and removal of nitrate, phosphate and pesticides in low-cost metal- and carbon-based materials.

Low-cost magnesium- and/or carbon-based materials have a great potential to remove soluble contaminants from surface and ground water. This study examined mechanisms that control the removal of nitrate, phosphate and pesticides (tricyclazole, malathion and isoprothiolane) during their transport through calcined magnesia (MgO) and corn stalk biochar. Various miscible column breakthrough experiments were carried out and morphology and crystallographic structures of reactive materials were examined. Approximately 96% (78,950 mg-NO3-/kg) and 48% (27,455 mg-NO3-/kg) of nitrate were removed from biochar and MgO columns, respectively. Chemical adsorption dominated nitrate removal during early phase (i.e., <11 PVs for biochar and <100 PVs for MgO, respectively), and microbial denitrification dominated during the following phase. 92% of the applied phosphate (6168 mg-PO43-/kg) was removed in MgO column, while much less in biochar column (4%, 347 mg-PO43-/kg). Mineral surface analyses confirmed that electrostatic attraction, ligand exchange, and chemical precipitation were responsible for phosphate removal. For the three pesticides, biochar exhibited larger removal capacity (1260-2778 mg/kg) than MgO (28-2193 mg/kg) due to the functional groups on biochar. The removal of pesticides based on their physico-chemical properties. Malathion had highest removal rate (98-100%), attributing to chemical sorption and bio-degradation, followed by isoprothiolane (47-79%) and tricyclazole (6-64%).

Adsorption of Pyrene onto the Agricultural By-Product: Corncob.

The adsorption behavior of pyrene on corncob was studied to provide a theoretical basis for the possible use of this material as an immobilized carrier for improving the bioremediation of PAH-contaminated soil. The results were as follows. Kinetic experiments showed that the adsorption processes obeyed a pseudo-second-order model. The intraparticle diffusion of Weber-Morris model fitting showed that the film and intraparticle diffusions were the key rate-limiting processes, and the adsorption process mainly consisted of three steps: boundary layer diffusion and two intra-particle diffusions. Experimental adsorption data for pyrene were successfully described by the adsorption-partition equilibrium model. The maximum adsorption capacity at 25°C was 214.8 µg g(-1). The adsorption contribution decreased significantly when the Ce/Sw (the equilibrium concentration/solubility in water) was higher than 1. Adsorption decreased with increased temperature. Based on the above results, the corncob particles could be helpful in the bioremediation of pyrene-contaminated soil.

[Effect of Decomposing Products of Immobilized Carriers on Desorption of Pyrene in Contaminated Soil].

Batch experiments were conducted to investigate the effect of soluble and insoluble decomposing products (decomposed for 1 day and 120 day; noted by DP1 and DP120, respectively) from immobilized carriers (corncob) on the desorption of pyrene in PAH-contaminated soil (120 d ageing, 20 mg x kg(-1)). It was found that (1) adding decomposing products of immobilized carriers could not only increase the rapidly desorbing fraction, but also improve the desorption rate of pyrene. The desorption rates of pyrene increased from 20% to 81.8% and 84.5% because of adding insoluble DP1 and DP120, and from 40% to 89.6% and 88.5% because of adding soluble DP1 and DP120. (2) The sorption amounts of pyrene by insoluble DP1 and.DP120 were 9. 4 and 16. 6 times higher than that by natural corncob, respectively. The sorption amounts of XAD-2 resins were increased by 1.5 and 3.1 times due to the added soluble DP1 and DP120, respectively. These results indicated that decomposing products of immobilized carries could improve the desorption of pyrene by sorption or activation in contaminated soil.