Studies on biodegradation of phenols and m-cresols by upflow anaerobic sludge blanket and aerobic sequential batch reactor

Abstract

Wastewaters from fossil fuel refining, pharmaceuticals, and pesticides are the main sources of phenolic compounds. Those with more complex structures are often more toxic than the simple phenol, and yet little is known about the treatment of wastewater containing a mixture of phenolic pollutants.. The present study was aimed at assessing the efficacy of UASB and SBR for the treatment of mixtures of phenolics compounds. The experiments were conducted in a laboratory scale UASB reactor, which had a volume of 1.414 l. A gas-liquid solid separator, GLSS was provided at the top of the reactor. The reactor was operated at constant HRT of 24 h throughout the study. The reactor was seeded with digested sewage sludge obtained from Okhla Sewage Treatment Plant, New Delhi, India. Initially the microbial culture was acclimatized to phenol concentration of 600 mg l-1 in UASB. Thereafter, different phenol: m-cresols ratio were introduced, 10:1, 4.5:1, 2.7:1, 1.75:1 and 1.2:1 and the performance of the reactor was evaluated under each case. The second experiment was conducted in a laboratory scale SBR reactor with a working volume of 1.4 l. The effluent was drawn from a volumetric exchange ratio of 50%. A fine bubble aerator in the bottom of the column was used to introduce air. The reactor was seeded with aerobic digested sludge obtained from Star Paper Mill, Saharanpur, UP, India. A constant HRT of 12h was kept throughout the study. Reactor was operated sequentially with fill, react, settle and draw periods for a cycle of 6h. In order to establish a viable biomass and minimize any potential toxic effects due to presence of phenolic compounds, the sludge was fed with phenol as batch culture up to 1000 mg l-1 concentration. After acclimatization, different phenol: m cresol ratio were introduced 6.5:1, 2:1, 1.1:1, 0.5:1 and the performance of the reactor was evaluated under each case. A start up period of 40 days was required to acclimatize the anaerobic bacterial at HRT of 24 hrs for phenol concentration of 200 mg l-1. UASB reactor successfully biodegraded phenol and m-cresol up to a maximum ratio (1.25:1) (300: 250 mg l-1) with 80% efficiency. A start up period of 30 days was required to acclimatize aerobic bacteria with phenol to concentration up to 1000 mg l-1 as batch culture. The maximum phenol and m-cresol up to (1.1: 1) (800: 700 mg l-1) was successfully treated with efficiency of 95% in SBR. The results indicates that anaerobic treatment by UASB and aerobic treatment by SBR can be successfully used for phenol/cresol mixture, representative of major substrates in chemical and petrochemical wastewater and the results shows proper acclimatization period is essential for the degradation of m - cresol and phenol. Moreover, SBR was found as a better alternative than UASB reactor as it is more efficient and higher concentration of m cresols can be successfully degraded. Copyright © 2008 Global NEST.