Enhanced degradation of azo dye alizarin yellow R in a combined process of iron–carbon microelectrolysis and aerobic bio-contact oxidation
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- Liang, B., Yao, Q., Cheng, H. et al. Environ Sci Pollut Res (2012) 19: 1385. doi:10.1007/s11356-012-0785-4
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With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process.
Materials and methods
The combined ABO (with effective volume of 2.4 l) and ICME (with effectively volume of 0.4 l) process were studied with relatively short hydraulic retention time (HRT) of 4 or 6 h.
At the HRT of 6 h with the reflux ratio of 1 and 2, the AY degradation efficiency in the final effluent was >96.5%, and the total organic carbon (TOC) removal efficiency were 69.86% and 79.44%, respectively. At the HRT of 4 h and the reflux ratio of 2, TOC removal efficiency and AY degradation efficiency were 73.94% and 94.89%, respectively. The ICME process obviously enhanced the total AY removal and the generated micromolecule acids and aldehydes then that wastewater backflow to the ABO where they were further biodegraded.
The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.
KeywordsAzo dyesAlizarin yellow REnhanced degradationMicroelectrolysisCombined processAdvanced treatment
China is undergoing a rapid transition from a rural to an urban society (Zhu et al. 2011). Obviously, the city clusters have played a leading role in the economic growth of China, owing to their collective economic capacity and interdependency. However, the economic boom has led to a general decline in environmental quality (Shao et al. 2006). The rapid industrialization development originated from urbanization is resulting in the soil or water environment pollution and has attracted a considerable amount of attention.
Among different industry types, the textile industry is very water-intensive (80–100 m3/ton of finished textile), about 280,000 tons of textile dyes are discharged in such industrial effluents every year worldwide (Jin et al. 2007; Savin and Butnaru 2008). The varied synthetic dyestuffs pose a great threat to environmental safety (Saratale et al. 2011). The characteristics of the typical textile industry wastewater with biochemical oxygen demand (BOD)/chemical oxygen demand (COD) ratio of around 0.25 indicate that it contains large amounts of non-biodegradable organic matter (Oller et al. 2011). In particular, most pollution in textile wastewater comes from dyeing and finishing processes (Al-Kdasi et al. 2004) and many azo dyes and their metabolites are toxic, mutagenic, and carcinogenic (Myslak and Bolt 1988). To reach the permit discharge standard, the removal of color from textile and dyestuff manufacturing industry wastewaters as well as thorough degrade these dyes represents a major environmental concern (Savin and Butnaru 2008).
Globally, different groups have carried out azo dyes wastewater treatment extensively, including the physical–chemical methods, such as adsorption, coagulation–flocculation, electrochemical and electro-Fenton process (El-Desoky et al. 2010; Raju et al. 2009; Wang et al. 2010; Zhao et al. 2010) and advanced oxidation (O3, O3/UV, O3/TiO2, O3/internal micro-electrolysis, O3/H2O2/UV, H2O2/UV, Fe2+/H2O2, TiO2, TiO2/UV, TiO2/H2O2/solar, Fenton and photo-Fenton, internal microelectrolysis/ultrasound) (Ay et al. 2009; Azbar 2004; Baban et al. 2003; Cisneros et al. 2002; de Moraes et al. 2000; Ledakowicz and Gonera 1999; Ledakowicz et al. 2001; Liu et al. 2007a; Liu and Chiou 2005; Liu et al. 2007b; Pérez et al. 2002; Reddy and Kotaiah 2005; Ruan et al. 2010; Szpyrkowicz et al. 2001; Torrades et al. 2004), aerobic and anaerobic biological process as well as diverse hybrid treatment technology (Damodar and You 2010; Hai et al. 2007; Kanagaraj and Mandal 2011; Oller et al. 2011; Saratale et al. 2011; Singh and Arora 2011; You et al. 2010). Although high dye removal efficiency can be achieved in these reports, implementation of physical/chemical methods have the inherent drawbacks of being economically unfeasible (as they require more energy and chemicals), being unable to completely remove the recalcitrant azo dyes and/or their organic metabolites, generating a significant amount of sludge that may cause secondary pollution problems, and involving complicated procedures (Forgacs et al. 2004; Saratale et al. 2011; Zhang et al. 2004). Furthermore, the pre-oxidation applied did not always lead to a significant improvement in biological degradation (Hörsch et al. 2003). Therefore, advanced treatment and increasing the potential of reuse of the enormous wastewaters and plant effluents represent an economical and ecological challenge for the entire textile industry (Rosi et al. 2007).
It is obvious that a single process is unrealistic, and combination of different techniques is an economically feasible option (Oller et al. 2011), especially biological hybrid technologies for the dye wastewater treatment appear to be the most promising (Hai et al. 2007). Dye and an effluent from an integrated dyeing wastewater treatment plant were successfully degraded by an integrated photochemical (Fenton oxidation and photo-Fenton) and a MBR and SBR, respectively (Feng et al. 2010; García-Montaño et al. 2006). Biofilm process combined electrochemical oxidation (pilot scale) or advanced oxidation processes (photo-Fenton, H2O2/UV and TiO2/UV) for the dyes’ wastewater treatment that could obtain high removal efficiency (García-Montaño et al. 2008a, b; Kim et al. 2002; Kim and Park 2008; Sudarjanto et al. 2006). Anaerobic biological process combined with photocatalysis (with TiO2 as a pre- or post-oxidation treatment) to treat raw solutions (containing azo, anthraquinone and phthalocyanine textile dyes) (Harrelkas et al. 2008), or with O3 as post-treatment for azo dyes removal (83% mineralization) (García-Montaño et al. 2008a) were also studied.
Considering the characteristics of dye wastewater and the shortages in the presence of wastewater treatment process discussed above, the exploitation of combined advanced treatment process has become increasingly important. With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) (still with ecological risk and toxicity) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process. This case will provide some theoretical references and may also become an economic, feasible and environment-friendly hybrid biotechnology scheme for the azo dyes wastewater advanced treatment.
2 Materials and methods
AY, p-nitraniline and p-phenylenediamine all with the purity of 98% were obtained from Aladdin Chemistry Co. Ltd (Shanghai, China). 5-Aminosalicylic acid (98.5% purity) and HPLC-grade methanol were purchased from J&K Scientific Ltd (Shanghai, China) and Sigma-Aldrich (St. Louis, MO, USA), respectively.
2.2 Configuration of the combined process
The packing material used in this study with polyporous characteristics was beneficial for the immobilization of active AY-biodegrading microbial community.
2.3 Analytical methods
p-Nitraniline, 5-aminosalicylic acid, p-phenylenediamine and p-aminophenol were determined by reverse-phase HPLC (model e2695; Waters Co., USA) with UV detection at 288 and 368 nm, respectively. The separation was conducted at 30°C on a C18 column (5 μm; 5 × 250 mm; Waters Co., USA) with mobile phase methanol/H2O (containing 0.03% acetic acid) (8:2) at a flow rate of 1.0 ml/min. The retention time of p-nitraniline, 5-aminosalicylic acid and p-phenylenediamine were 5.3, 3.1 and 1.6 min, respectively. AY concentrations were measured with a wavelength range from 200 to 900 nm at 372 nm using UV–vis spectrophotometer (Shimadzu UV2550, Japan).
To deduce the metabolic pathway of the AY degradation in the combined process, the sample from the effluent of the ICME process (HRT = 80 min, pH = 5 and the Fe/carbon = 3) was determined by HPLC (the method mentioned above) and HPLC-MS (Thermo Finnigan LCQ Deca XP Max LC/MS, Germany) for this control condition containing more surplus TOC than other conditions, which could detect more metabolites from AY degradation. The sample from the effluent of the initial ABO (HRT = 4 h) was determined by HPLC and HPLC-MS for the identification of metabolites from AY biodegradation. The operating conditions of HPLC-MS (ion trap) was on a zorbax XDB-C18 column (150 × 4.6 mm i.d., 5 μm) with mobile phase methanol/H2O (8:2) at a flow rate of 1.0 ml/min. The metabolites scanned in the normal mass range from 50 m/z (mass-to-charge ratio) to 800 m/z were separated and confirmed by first-order MS with the full scan mode, ionized by electrospray with a positive polarity or negative polarity. Measurement of COD was performed according to standard methods (APHA 1995). TOC was determined by the TOC determinator (Shimadzu TOC-VCPN, Japan).
2.4 Startup of the combined ABO–ICME process and operation
Considered the practical advanced degradation in the biological secondary effluent of azo dyes treatment, the route of the AY degradation in the combined ABO–ICME process was as followed: AY and its metabolites degraded in the secondary effluent of the ABO, further removed by the enhanced treatment process ICME, and then partial effluent of the ICME backflow to the ABO again to further treated for that the effluent contained some micromolecule acids, aldehydes and simple benzene ring substances which were viable to the ABO process. Importantly, the final step of backflow could offer the further total TOC removal efficiency. In our experiment, the inoculated sludge was obtained from the aerobic biofilter of a textile industry wastewater treatment plant (Shaoxing, China). The packing material and sludge were combined into the ABO process that containing synthetic azo dye wastewater (300 mg/l glucose that represents easily biodegradable organic, 100 mg/l AY that represents the refractory pollutant, 1% mineral medium with the content as followed (per Liter): 75 mg CH3COONa, 125 mg NaHCO3, 4.17 mg KCl, 250 mg Na2EDTA, 70 mg (NH4)2SO4, 25 mg KH2PO4, and 0.1% trace element solution (Lovley and Phillips 1988) with pH adjusted to 6.8–7.0) for the enrichment of the active AY and its metabolites biodegrading microbial community and further formation of biofilm. During the enrichment and entire test process, dissolved oxygen monitor was employed for the dissolved oxygen control in the ABO (2–3 mg/l). COD removal, AY decolorization and degradation efficiency were used for evaluating the microbial biodegrading activity.
2.5 Effect of hydraulic retention time (HRT) and reflux ratio on AY degradation
The combined ABO–ICME process was started with the influent COD of 500 mg/l (with almost 300 mg/l glucose and 100 mg/l AY). To investigate the effect of HRT and reflux ratio (the ratio of the flow rate of the effluent from ICME backflow to the ABO and that of the initial influent to the ABO, keeping the constancy of total flow rate in consistent with the no backflow conditions) on the degradation of AY, COD and total organic carbon (TOC) at room temperature (24 ± 2°C), the hybrid process was operated with different reflux ratios (r = 0–2) at the HRT 6 and 4 h, respectively. The effluent of the initial ABO and the final effluent of the hybrid process were sampled at the regular intervals for the analysis of TOC degradation, AY decoloration efficiency and AY concentrations. At the HRT 4 h, the original influent, the effluent of the initial ABO and the ICME were scanned by the UV–vis spectrophotometer with the wavelength between 200 and 900 nm.
3 Results and discussion
3.1 Performance of the combined ABO–ICME process
After the successful startup of ABO (requiring 36 days), it could decolor AY of 30.04%, biodegrade AY of 34.52%, and the COD and TOC removal efficiency were 65.83% and 59.64%, respectively, with initial COD of 500 mg/l (300 mg/l glucose and 100 mg/l AY) at HRT 6 h. The lower decoloration and degradation efficiency of AY by single ABO process indicated that most TOC was biodegraded from the contribution of the glucose as an easily biodegradable organic. The COD removal was consisted of the glucose and AY degradation because some recently papers had proved that some azo dyes biodegrading bacterial strains had oxygen-insensitive azoreductase, which was responsible for the azo dyes biodegradation at aerobic conditions (Bafana et al. 2008; Blumel et al. 2002).
3.2 Enhanced performance of ABO by ICME at different HRT and reflux ratio conditions
3.3 The deduced metabolic pathway for the AY degradation in combined process
The sample from the effluent of the initial ABO (HRT = 4 h) was determined by the HPLC-MS for the identification of metabolites from AY biodegradation, an obvious deprotonated molecular ion at m/z 256.13 [M–H]− was identified as p-aniline-azo-salicylate. However, the prominent deprotonated molecular ion at m/z 97.27 represented an unknown metabolite (Fig. 4c) that need further research in the future. Collecting the results of HPLC and HPLC-MS, the deduced metabolic pathway for the AY degradation in the combined ABO–ICME reactor was presented in Fig. 4d.
Owing to the multivariate characteristics of azo dye wastewater, the exploitation and combination of diverse treatment processes for the depth and strengthening treatment which can achieve the final purpose of abundant dye wastewater reuse has become increasingly important in the highly developing industrialization and urbanization period. In the present study, we performed the combined ABO–ICME process for the enhanced degradation of azo dye AY and further removal of LsRM of the secondary effluent as much as possible with a relatively short HRT of 4 or 6 h. The ICME process obviously enhanced the AY removal efficiency and the generated micromolecule acids and aldehydes, then the wastewater backflow to the ABO where they were further biodegraded. The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.
This research was supported by the National Natural Science Foundation of China (Grant No. 50878062; No. 51078100 and No. 30870037), Project 50821002 (National Creative Research Groups) and State Key Laboratory of Urban Water Resource and Environment (Grant No. 2010DX11).