Using of hydrogen peroxide for increasing of biologically active carbon filter work efficiency.
Advancing the chemical engineering fundamentals
Interfacial & Colloidal Phenomena (T2-6P)
Keywords: Activated carbon, Bioregeneration, Hydrogen peroxide
Using of activated carbon (AC) with inoculated microorganisms (BAC) is the most effective method for the advanced removing of the organic compounds from natural and waste water. Inoculation of AC by microorganisms and supporting of the optimal condition of their life is one of the most fundamental circumstances of the BAC successful using.
Hydrogen peroxide, except enrichment of liquid by oxygen, can be oxidizing agent for the dissolved organic matters in presence such catalyst as AC. Ability of AC to be catalyst in oxidation-reduction reaction is well known. Granulated activated carbon (GAC) is successfully used as adsorbent and catalyst in heterogenic catalysis owing to well developed surface, porous structure and flexible regulated characteristics.
The main goal of this work was to estimate hydrogen peroxide influence on fulvic acids filtration efficiency through BAC. Another aim was to determine rational condition of H2O2 using in BAC filtration processes.
As sorbent was used activated carbon KAU with such structural and sorption characteristics: effective mesoporous surface Sme = 630 m2/g; volume of adsorption space Va=0,39 sm3/g; volume of micropores Vmi= 0,12 sm3/g. As adsorbate were used fulvic acids (FA). They were receive by Forsit method [] from high-moor peat. Plant work was controlled by analysis of the water samples, which were taken from different height of the column. They were analysed on content of fulvic acids (COD, TOC) and dissolved oxygen.
Decomposition degree of H2O2 under initial concentration 1 mg/l is 94-96%. Therefore concentration of the released oxygen is not more than ~0.95 mg/l. Under H2O2 initial concentration H2O2 10 mg/l the decomposition degree is 86-88% at the first moments. It is apparently conditioned by the spending of some part of hydrogen peroxide on the reaction with AC surface. At H2O2 initial concentration 5 mg/l the quantity of H2O2 released after oxidation at AC surface is ~4.8 mg/l. If dissolved in water oxygen is taken into account this value of oxygen will prevent of anaerobic process in AC loading.
Value of limit specific adsorption of fulvic acids without H2O2 is 102.5 mg/g and in presence of H2O2 (10 mg/l) – 135 mg/g. As we can see from this date presence of H2O2 in the system leads to some increasing of a∞ value. It is probably stipulated for catalytic oxidation of some part of dissolved fulvic acids (up to 20-21%). Changing in the surface oxygen content groups on the AC KAU after contact with H2O2 can confirm trustful of this assumption.
Thus, using of hydrogen peroxide solution with concentration 5 mg/l is the most expedient because it allows enrichment fulvic acids solution by oxygen without using it for AC surface oxidation and partly use of catalytic reaction of fulvic acids oxidation.
Experimental dates were compared in the both columns on the height of 15 sm where experimental was going for 14 months. Native biofilms was formed on AC for this time.
Earlier we showed that efficiency of organic matters solution filtration through the BAC is expediently estimated by comparing of equal and dynamic adsorption capacity of AC. It is known when biodegradation processes in the layer of AC is absence, equal capacity is always bigger or in ideal case at the absence of mass transfer resistance is equal to dynamic capacity. Increasing of the dynamic capacity above equal is evidence that the bioregeneration of AC is going on as a result of adsorbed compound biodegradation. Presence of hydrogen peroxide in fulvic acids solution which is entered to the BAC filter lead to the increasing of adyn value for 81 %. At the same time aeq in presence of H2O2 is bigger aeq at it absence for 27 %. That is why we can suppose that in biofiltration process influence of hydrogen peroxide is stipulate for both catalytic oxidation of part of organic substrate and intensification of the biological processes in BAC layer. The last is probably conditioned by amount of oxygen solution which is passed through BAC filter.
Amount of oxygen in solution decreased from 3.8 mg/l at height 15 sm to 1.8 mg/l at height 90 sm after setting of stationery regime of filtration. According to the dates from [2] such amount of oxygen is not enough for normal life of aerobic biocenose.
Under filtration of the fulvic acids solution with H2O2 though AC layer oxygen concentration was not lower than 3 mg/l both at the top and the bottom of the AC layer. The initial concentration of the oxygen was 4-4.5 mg/l. It is confirmation that the oxygen released at the catalytic decomposition of H2O2 is consumed by microorganisms.
Conclusion
Using of Н2О2 at concentration 5 mg/l is the most expediently because it allows to enrichment NOM solution such as fulvic acids by oxygen without using it for AC surface oxidation. Oxygen can be partly used for catalytic oxidation of the fulvic acids. This approach may be recommended for the enrichment of the waste and natural water by oxygen during advanced treatment by biologically active carbon.
Presented Thursday 20, 13:30 to 15:00, in session Interfacial & Colloidal Phenomena (T2-6P).
