حذف فنل از پساب های اشباع از نمک در راکتور غشای بیولوژیکی (MBR): مشخصه سازی عملکرد و میکروبیولوژی Phenol removal from hypersaline wastewaters in a Membrane Biological Reactor (MBR): Operation and microbiological characterisation

۱٫ Introduction Although phenolic compounds are hardly present in municipal wastewaters, they are frequently found in some industrial wastewaters, such as pulp and mill, textile and petrochemical industries and refineries. Phenols are chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group. Several methods can be used for phenol degradation, such as advanced oxidation processes (AOPs) and/or biological processes. For economic reasons, biological treatments are preferred when the studied wastewater does not contain toxic compounds that inhibit biomass activity. Some industrial wastewaters containing phenol can be efficiently treated by means of a biological Sequencing Batch Reactor (SBR) due to its flexibility of operation (resistance to changes in phenol concentration), compactness and easy control (Brenner et al., 1992; Buitrón and Ortiz, 1997; Macé and Mata-Álvarez, 2002). Since microorganisms responsible of phenol degradation have a relatively low growth rate, biomass is usually attached in porous materials to improve biomass retention in the digesters (Puhakka and Järvinen, 1992; Buitrón and Ortiz, 1997; González et al., 2001; Sá and Boaventura, 2001; Sgountzos et al., 2006). However, the application of Membrane Biological Reactors (MBR) could assure the retention of phenol degrading microorganisms without risk of an eventual wash-out of biomass (Cornel and Krause, 2006; Lesjean and Huisjes, 2007). In fact, the MBR technology has lead to a very good biomass retention capacity in reactors working with microbial consortiums characterised by slow growth rates (Trigo et al., 2006; Lesjean and Huisjes, 2007). Very few experiences are reported for phenol biodegradation in MBRs: Barrios-Martinez et al. (2006) studied the treatment of synthetic wastewater representative of petrochemical effluents from a refinery (1.01 mg phenol L1 ). These authors operated a MBR with an external membrane module configuration obtaining phenol removal efficiencies around 100%. On the other hand, Marrot et al. (2006) examined phenol biodegradation in a MBR (submerged hollow fiber membrane module) for the treatment of synthetic wastewater with high phenol concentration (0.5–۳٫۰ g phenol L1 ) obtaining high removal rates. Ahn et al. (2008) used an MBR (submerged hollow fiber membrane module) to treat a phenol loaded wastewaters, reporting good removal efficiencies when phenol was fed at low (0.1 g L1 ) and high (1.0 g L1 ) concentration levels. Moreno-Andrade et al. (2008) studied the treatment of a synthetic wastewater with 4-chlorophenol (600 mg L1 ) in a sequencing batch MBR (submerged tubular membrane module) obtaining removal efficiencies higher than 99%. Recently, Carucci et al. (2010) reported high removal efficiencies (99–۱۰۰%) of 50 mg L1 of 4-chlorophenol in a lab-scale MBR (3.1 L of capacity, hollow fiber membrane unit) operated as a sequencing batch reactor at Hydraulic Retention Times (HRT) between 12 and 24 h, depending on cycle length. Phenol contaminated industrial wastewater holds microorganisms belonging to different phylogenetic taxons (Van Schie and Young, 2000; Watanabe et al., 1998). Particularly, gammaproteobacteria have been found to constitute a major part of the phenol-degrading bacterial population in some industrial phenol waste bioremediation systems (Whiteley and Bailey, 2000), however, the role of specific bacterial components in the removal of phenol from those bioreactors has scarcely been addressed. In this study, a lab-scale MBR and a pilot plant MBR were tested for the treatment of an industrial wastewater characterised by low phenol concentrations and high salinity. When both reactors worked under steady state conditions and high phenol degradation, their microbial composition was studied by culture independent and culture dependent methods and phenol degrading isolates were obtained and characterised. ۲٫ Methods ۲٫۱٫ Lab-scale Membrane Biological Reactor (MBR) The lab-scale MBR (5 L) used in this study is schematised in Fig. 1a. It was operated as a SBR. The digester was a rectangular methacrylate reactor containing a submerged flat membrane (0.3 lm) and a pH probe (Crison pH 25). Aeration was supplied by means of two air blowers (300 L h1 ) connected to a porous stone to assure a homogeneous oxygen distribution in the mixed liquor. Two peristaltic pumps (Ismatec REGLO and Selecta PERCOM-1) performed the feeding and the permeation of the MBR. The operation of the lab-scale reactor was controlled by means of a Programmable Logic Controller (PLC; Siemens LOGO!).