(30d) Biodegradation of Phenol-Polluted Air In Aerobic Granular Reactors

As one kind of toxic Volatile organic compounds (VOC), phenol-polluted air was degraded by aerobic granules. aerobic granulation is a novel biotechnology, which has good ability to tolerate toxicity and to handle high phenol loading rates. The objective of this work is to evaluate the possibility of phenol elimination by aerobic granules and the characteristics of the aerobic granules. In this experiment, phenol was added to reactor at loading rates of 0.5, 1.0, 1.5 and 2.0 kg/m³·d. Aerobic granules showed good degraded ability at different phenol loading rates. At steady state, the phenol removal rate was higher than 96% while COD removal rate was higher than 95%. Phenol loading rate exerted a profound influence on the activity, morphology, structure of aerobic granules. The specific oxygen utility rate of aerobic granules changed from 91 to 32 mg O₂/(g VSS h) when the reactor fed with phenol-polluted air. Then it increased to 74 mg O₂/(g VSS h) at phenol loading rate of 1.5 kg/m³·d. Extracellular polymers, as well as protein, polysaccharides increased with the increasing of phenol loading rates. Sludge volume Index (SVI) and settling velocity were 42.5-44 ml/g and 72.6-80.0 m/h, respectively. The compact structure of aerobic granules was kept after fed with phenol waste gas. This study confirmed the application of aerobic granule technology on VOCs elimination.

Keywords: aerobic granules; phenol-polluted air; biodegradation; microbial activity; ECPs;

  INTRODUCTION

Volatile organic compounds are a group of organic chemicals which boiling point is below 260 at ambient pressure or saturated vapor pressure is above 71 Pa at ambient temperature (de Nevers, 1995). Phenol is a volatile organic compound (VOC) emitted by the chemical process industries, which manufacture many phenolic resins and organic solvents (Wallace et al., 1996). The major sources of phenol containing wastewater and waste air streams are petroleum refineries, petrochemical, steel mills, coke oven plants, coal gas, synthetic resins, pharmaceuticals, paints, plywood industries and mine discharge (Mukherjee et al., 2007). Phenol was listed in the priority list of hazardous substances (ATSDR, 2005) since it was regarded as a Hazardous Air Pollutant under the US Environmental Protection Agency Clean Air Act section 112(b) (USEPA, 2006).

Aerobic granulation, a new form of cell immobilization for exploitation in biological wastewater treatment, has shown good performance in toxic wastewater such as phenol wastewater and high concentration wastewater treatment (Tay et al., 2001; Moy et al., 2002; Jiang et al., 2002; Beun et al., 2000; Arrojo et al., 2004; Dulekgurgen, 2003; McSwain et al., 2005). It had the potential to degrade phenol in air stream. In the present study, a sequencing batch reactor was set up to study the degradation of phenol-polluted air by aerobic granules and the influence of phenol loading rate on the characteristics of aerobic granules.

  MAIN TEXT

A column-type sequencing batch reactor (SBR) (5 cm diameter) with a working volume of 2.4 L was set up. The reactor was operated sequentially in 4-h cycles with a hydraulic residence time (HRT) of 8h at room temperature. Fine air bubbles for aeration were supplied through a dispenser at the reactor bottom at an airflow rate of 3.5 L min^-1. Phenol-polluted air was fed as sole carbon source through dispenser in the reactor.

Aerobic granules were first cultivated in sequencing batch reactors with sodium acetate as sole carbon source. Phenol-polluted air was then added to the reactor at phenol loading rates of 0.5, 1.0, 1.5 and 2.0 kg/m³·d. Aerobic granules showed good degrading ability to phenol with the COD removal rate higher than 95% and phenol removal rate higher than 96% (Table 1). Phenol loading rate exerted a profound influence on the activity, morphology, structure of aerobic granules. Microbial activity of aerobic granules indicated by SOUR decreased from 91 to 32 mg O₂/(g VSS h) when phenol-polluted air was added into the reactor. Then the SOUR increased with phenol loading rate to 74 mg O₂/(g VSS h) at phenol loading rate of 1.5 kg/m³·d after aerobic granules adapted to the phenol-polluted air. Extracellular polymers (ECPs), as well as protein (PN), polysaccharides (PS) increased with the increasing of phenol loading rates. SVI and Settling velocity were 42.5-44 ml/g and 72.6-80.0 m/h, respectively. The aerobic granules possessed more compact structure with the degradation of phenol-polluted air .

These results indicated that aerobic granules had good performance in the degradation of phenol-polluted air. To adapt to the toxic compounds, the microbial activity, settling ability and structure of aerobic granules changed greatly. 

Table 1.Reacter performance at different phenol loading rates

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