Iranian Association of Environmental Health (IAEH)
Abstract
Chlorinated phenols in many industrial effluents are usually difficult
to be removed by conventional biological treatment processes.
Performance of the aerobic sequencing batch reactor treating 4-
chlorophenol containing wastewater at different loadings rates from
0.0075 to 1.2 g4CP/L.d was evaluated. The sequencing batch reactor was
operated with fill, react, settle and decant phases in the order of
10:370:90:10 min, respectively, for a cycle time of 8 h at 10 days
solid retention time and 16 h hydraulic retention time in the stable
period. The effects of 4-chlorophenol loadings on the 4- chlorophenol
and chemical oxygen demand removal percents, yield coefficient (Y),
biomass variation and sludge volume index were investigated. High
chemical oxygen demand removal efficiencies (95±3.5%) and
approximately complete 4-chlorophenol removal (>99%) were observed
even in the absence of growth substrate. The degradation of
4-chlorophenol led to formation of 5-chloro-2-hydroxymuconic
semialdehyde, which was more oxidized, indicating complete
disappearance of 4-chlorophenol via metacleavage pathway. A compact
sludge with excellent settleability (sludge volume index=47±6.1
mL/g) developed during entire acclimation period. High removal
efficiencies with sequencing batch reactor may be due to enforced short
term unsteady state conditions coupled with periodic exposure of the
microorganisms to defined process conditions which facilitate the
required metabolic pathways for treating xenobiotics containing
wastewater
