A combined process for haloacetic acid (HAA) removal was proposed which takes advantage of the high reactivity of zero-valent iron (ZVI) to trichloroacetic acid (TCAA) and brominated HAAs and the good biodegradability of dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA) in biologically active carbon (BAC). The reaction kinetics of the two consisted operations at different temperatures was investigated for the optimization of the combined process. With a controlled temperature range from 5 to 35 �C, the observed rate constants for HAA reduction by ZVI were from 0.02 to 2.80 1/min, and that for HAA degradation by BAC were from 0.01 to 0.40 1/min. The activation energies of HAA reduction by ZVI ranged from 11.4 to 49.0 kJ/mol and that of HAA degradation by BAC from 63.4 to 89.1 kJ/mol. Temperature had negligible effect on the removal of bromine-containing HAAs by ZVI. The biodegradation of DCAA and MCAA in BAC were crucially dependent on the water temperature; the degradation rates were substantially higher at 25 �C than at 15 �C. By assuming TCAA reduction by ZVI follows sequential hydrogenolysis, the obtained kinetic rate constants could be used for the simulation of TCAA (and its degradation products) removal in the sequential ZVI�BAC process. The simulated results matched well with that obtained by experiments. Under a arbitrary temperature at 25 �C and by assuming the raw water contains TCAA, DCAA and MCAA all at 100 �g/L, a pass through a ZVI column of 0.35 m and a BAC column of 2 m at a rate of 8 m/h can achieve a 98.3% removal of total HAAs, as compared to a 73.6% removal by passing through the 2 m BAC. The kinetic data can be also used for the design of the sequential ZVI?BAC process for cost-effective removal of various HAA combinations from swimming pool water, wastewater and drinking water.

Kinetics of haloacetic acid removal by the combined process of zero-valent iron and biologically active carbon

248th National Meeting (2014)

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