Development and characterization of the 2,4,6-trichlorophenol (2,4,6-TCP) aerobic degrading granules in sequencing batch airlift reactor

https://doi.org/10.1016/j.ibiod.2014.03.019Get rights and content

Highlights

  • Glucose and acetate were used as co-substrates to promote granule formation.

  • The specific degradation rate of 2,4,6-TCP peaked at the concentration of 400 mg L−1.

  • EPS contents of the 2,4,6-TCP aerobic degrading granules decreased compared with seed sludge.

  • The fluorescence and components of EPS was changed identified by 3-D EEM.

Abstract

2,4,6-trichlorophenol (2,4,6-TCP) aerobic degrading granules were successfully developed in the sequencing batch airlift reactor. The key strategy used in cultivation of the granules was dosing glucose and acetate as co-substrates. After granulation, average concentrations of 2,4,6-TCP and COD in the effluent were less than 8 mg L−1 and 59 mg L−1, respectively. The removal efficiencies of 2,4,6-TCP and COD were above 93% and 90%, respectively. The specific degradation rate of 2,4,6-TCP peaked at 61 mg 2,4,6-TCP g VSS−1 h−1 when inoculated at the concentration of 400 mg L−1. The extracellular polymeric substance (EPS) contents of the 2,4,6-TCP aerobic degrading granules were decreased compared with the contents in seed sludge. Two peaks attributed to the protein-like fluorophores were identified by three-dimensional excitation emission matrix (EEM) fluorescence spectra. The decrease of fluorescence parameters, e.g., peak locations, intensities, indicated quenching effect of 2,4,6-TCP on the EPS fluorescence. Meanwhile, the shift of peak position indicated chemical changes of the EPS.

Introduction

Chlorophenols are a group of chemicals in which chlorines (between one and five) have been added to phenol (Polcaro and Palmas, 1997). They were mainly produced in industries, such as petrochemical, oil refinery, plastic, pharmaceuticals, pesticides, biocides, wood preservers, pulp, insulation materials and so on (Hameed et al., 2008). These compounds are among the most hazardous anthropogenic materials, as they are carcinogenic, mutagenic and teratogenic (Xu et al., 2010). In order to avoid the biomagnified toxicity to aquatic flora and fauna through various food chains, wastewaters containing chlorophenols have to be decomposed or treated before discharging into the environment. Due to their structural stability and persistence in the environment, the removal of chlorophenols from the environment is crucial (Ren et al., 2011).

Several physical, chemical and biological methods such as activated carbon adsorption, chemical oxidation, electrochemical and biological bioremediation methods have been used for the removal of chlorophenols from industrial wastewaters (Armenante et al., 1999). Most of them presented some limitations such as poor capacity, generation waste products, incomplete mineralization and high operating costs (González et al., 2010). Biodegradation of chlorophenols was more specific, relatively inexpensive and could be realized under aerobic or anaerobic conditions (Annachhatre and Gheewala, 1996). But there were limited studies reported on biological treatment of wastewaters containing chlorophenols (Eker and Kargi, 2008). Performance of biological treatment processes used for wastewaters containing chlorophenols was usually low due to the toxic effects of chlorophenols on microorganisms yielding toxic effluents. Therefore, in treatment of wastewaters containing chlorophenols, effluent toxicity levels should be controlled along with the other effluent parameters such as COD, nutrients and chlorophenols.

Nowadays aerobic granulation in biological treatment processes was considered to be the most effective route for wastewater treatment containing chlorophenols (Khan et al., 2011). Aerobic granules were considered to be a special case of self-immobilized microbial consortium (Seviour et al., 2010). Aerobic granules have the advantages of compact microbial structure, good settling ability, high biomass retention and the ability to withstand high organic loading rate (Kong et al., 2013). Formation of granules in aerobic conditions had been possible and appeared as a promising technique for high strength or highly toxic wastewater treatment (Ni et al., 2010).

In several cases, aerobic bacteria degrading xenobiotic pollutant (such as chlorophenols) grew on the xenobiotic pollutant as the sole carbon source (Knackmuss, 1996). The performance of the aerobic bacteria was usually low due to the toxic effects of the xenobiotic pollutant. However, some results suggested that the addition of some conventional carbon sources (glucose or acetate etc.) as co-substrate might contribute to reducing the toxicity and growth inhibition of xenobiotics on cells, consequently, the transformation rates of xenobiotics increased (Khan et al., 2011). The presence of easily degradable carbon sources could stimulate the growth of microbial population and the biodegradation of target contaminants such as chlorophenols (Robinson et al., 2001, Di Iaconi et al., 2007). These additional carbon sources may also be able to act as an inducing agent or provide reducing power for degradation of recalcitrant organic compounds. This strategy has been used by many researchers in order to prevent the xenobiotics' unfavorable impact on microbial metabolism (Haritash and Kaushik, 2009).

Most of the available literature dealing with biodegradation of chlorophenols were isolated in pure culture (Matafonova et al., 2006). Limited study has concerned with mixed culture which addition glucose or acetate and the xenobiotic pollutant as mixed culture (Eker and Kargi, 2009). The study of chlorophenols degradation in presence of glucose and acetate as co-substrates by mixed culture has not been reported. In addition, extracellular polymeric substance (EPS) has a significant effect in promoting microbial aggregation, adhesion and enhancing the communication between cells. Characterization of the EPS from 2,4,6-TCP aerobic degrading granules has not been carried out previously.

Therefore, the main objective of this study was to explore the feasibility of cultivating 2,4,6-TCP aerobic degrading granules involving the addition of glucose and acetate as co-substrates by mixed culture. Furthermore, the EPS was characterized by three-dimensional excitation emission matrix (EEM) fluorescence spectra technology targeting the EPS fluorescence and components. The process reported in this study could potentially be applied to remove 2,4,6-TCP in industrial effluents and contaminated groundwater.

Section snippets

Experimental set-up and operation

A double-walled cylindrical column sequencing batch airlift reactor (SBAR) (Fig. 1) was used in cultivation of the 2,4,6-TCP aerobic degrading granules, with a height of 100 cm and an internal diameter of 8 cm. The SBAR contained an internal riser (80 cm high, 5 cm internal diameter, bottom clearance 1.5 cm) with a working volume of 3.6 L. Air was introduced via a fine bubble aerator at the bottom of the reactor through a porous stone diffuser with the airflow rate of 200 L per hour during the

Formation and characterization of 2,4,6-TCP aerobic degrading granules

Activated sludge collected from a municipal wastewater treatment plant with nearly complete nitrogen removal was initially acclimated over a 21 days period to allow the biomass to adapt to 2,4,6-TCP. The SBAR was started up with acclimated activated sludge. The initial sludge had a MLSS value of 3.26 g L−1, while the MLSS concentration increased to 4.93 g L−1 after the acclimation period.

Fig. 2 showed the MLVSS and effluent VSS (EVSS) responding to decreasing the settle time during startup of

Conclusions

2,4,6-TCP aerobic degrading granules were successfully achieved. Glucose and acetate were used as co-substrates to promote granule formation. After granulation, the 2,4,6-TCP and COD removal efficiencies were above 93% and 90%, respectively. The specific 2,4,6-TCP degradation rate peaked at 61 mg 2,4,6-TCP g VSS−1 h−1 at the 2,4,6-TCP concentration of 400 mg L−1. The EPS contents of the 2,4,6-TCP aerobic degrading granules decreased compared with seed sludge. The decrease of fluorescence

Acknowledgments

This work was supported by the Open Research Fund Program of Shandong Provincial Key Laboratory of Eco-Environmental Science for Yellow River Delta (Binzhou University) (No. 2013KFJJ01), National Natural Science Foundation of China (21177075), Program for New Century Excellent Talents in University (No. NCET-10-0554) and Natural Science Foundation for Distinguished Young Scholars of Shandong Province (JQ201216).

References (29)

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