This study investigated the effect of silicic acid to the adhesion of Bacillus subtilis to metal oxide-coated surfaces. The first sets of column experiments were conducted under various concentrations of silicic acid. The second and third experiments were performed under various concentrations of sulfate and nitrate to compare the results from silicic acid. Bacterial breakthrough curves were obtained hy monitoring effluent, and mass recoveries were quantified from these curves. The results show that, at silicic acid concentrations between 0 and 0,2 mM, bacteria were negatively charged, while the charges of metal oxides were changed from positive to negative. Bacterial adhesion to metal oxidecoated surfaces decreased sharply with increasing silicic acid concentration (bacterial mass recovery increased from 11.5 to 82,2%), as a result of the hindrance effect of silicic acid adsorbed onto metal oxide-coated surtaces. Between 0,2 and 10 mM, both bacteria and metal oxides were negatively charged. Bacterial adhesion remained constant (mass recovery were 80,5 to 82.2%), despite the increasing silicic acid concentration, possibly as a result of the hindrance effect of polymerized silicic acid. That is. the bacterial approach to the metal oxide-coated surfaces could be disturbed through steric hindrance of polymerized silicic acid, which compensates the potential enhancement effect from the electrical double layer compression. The results also illustrate that the effect of silicic acid on bacterial adhesion was greater than those of sulfate and nitrate. This study demonstrates that silicic acid can play a significant role in bacterial interaction with metal oxide-coated surfaces. Water Environ. Res.. 83, 470 (2011).
In photochemical reactor, the process conditions of formaldehyde wastewater treatment using UV-Fenton oxidation under the joint action of hydrogen peroxide, ferrous ions, and ultraviolet were studied, and the kinetic curves of formaldehyde degradation in different conditions were obtained. The results showed that: when the original wastewater concentration is 30mg/L, operating temperature is 23℃, pH = 3, the dosage of H 2 O 2 is suitable for 68mg/L (correspond to the theoretic oxygen requirement of wastewater 1Q th ), H 2 O 2 and Fe 2+ dosing ratio n(H 2 O 2 ) n (Fe 2+ ) = 5, reaction to 30 minutes, the removal rate of formaldehyde is up to 91.89%. On this basis, the kinetic model for formaldehyde wastewater treatment in UV-Fenton system was established. By curve fitting and equation solving, the kinetic equation was obtained as follow:The analysis of reaction products by UV spectrum supposed that the further oxidation of the intermediate product, formic acid, is the rate-limiting step of formaldehyde oxidation reaction.
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