Efficient degradation of polyacrylate containing wastewater by combined anaerobic–aerobic fluidized bed bioreactors
Graphical abstract
Introduction
Polyacrylate is widely used in sizing (Zhou et al., 2020), printing and finishing of the water jet weaving industry due to its good adhesion, aging resistance and fast production characteristics. Polyacrylate is formed by the polymerization of acrylic acids, and it has high molecular weight and good thermal stability. The wide application of polyacrylate makes the world more colorful, but it also caused an undesirable visible pollution. Among the industries generating PCW, the textile industry is prominent. It is traditional industry in China, with more than 36 thousand factories spread nationwide. According to the statistics China's total filament manufacturing will account to 60 million tons by 2020, which accounts for more than half of the global production. Meanwhile, the sewage discharged by the textile industry will grow up to 2.05 billion tons per year. PCW is one of the typical wastewaters of the sizing process in the textile industry. It contains a high concentration of organic compounds with extremely poor biodegradability. The conventional treatment of PCW is by chemical methods, which have problems such as high cost and secondary pollution (Show et al., 2020). Therefore, it is necessary to develop an efficient, economical and environmentally friendly method for the treatment of PCW.
A combined anaerobic–aerobic biological treatment process has been regarded as the most logical concept for the treatment of refractory pollutants (van der Zee & Villaverde, 2005). In this process high molecular weight organic matter such as polyacrylate are anaerobically biodegraded to low molecular weight organic matter, which could be further biodegraded aerobically (Liu et al., 2020). The step anaerobic treatment is essential, because the refractory pollutants are recalcitrant to an aerobic bio-treatment (dos Santos et al., 2007). This holds for some bacterial strains, for which refractory pollutants are recalcitrant under aerobic but easily biodegradable under anaerobic conditions (Deng et al., 2008).
In order to provide a good and efficient anaerobic treatment, a high efficiency anaerobic reactor with own intellectual property rights, the Spiral Symmetry Stream Anaerobic Bioreactor (SSSAB) (Chen et al., 2016) was developed. In the reaction zone of SSSAB three elliptic plates were spirally and symmetrically set. Then the reaction zone was divided into three zones by the elliptic plates. Each zone was provided with a gas collection pipe to achieve respective biogas collection. The division was based on the anaerobic three stage theory. The dominant bacteria for the different stages of the microbial anaerobic fermentation are enriched in different zones of the reactor, which improves the reactors processing efficiency. The superior operating performance of the SSSAB has been proven in previous studies (Chen et al., 2016, Chen et al., 2017, Dai et al., 2017, Dai et al., 2016). Taking methanol-sodium acetate wastewater treatment for example, the super-high-rate OLR, volumetric removal rate (VRR) and improved volumetric methane production (VMP) were 361.5 kg COD/(m3·d), 268.3 kg COD/(m3·d) and 73.0 m3/(m3·d), respectively, which have a leading position in literature. The reactor has been applied also for the treatment of other wasters, such as azo dye wastewater (Dai et al., 2018), soybean waste water and Chinese pharmaceutical wastewater (Chen et al., 2019). According to this study the treatment of PCW by SSSAB has been tested and a good performance was obtained. The air-lift external circulation vortex enhancement nitrogen removal fluidized bed bioreactor (AFB) (Hu et al., 2017) has also been developed, to use for a post aerobic treatment. The AFB is divided into an aerobic space and anoxic space. Thus, it can perform biological nitrification and denitrification on its own. According to the previous experiment, if AFB is used to treat synthetic wastewater made of sucrose and ammonium chloride, the OLR and nitrogen loading rate (NLR) can reach 8.5 kg COD/(m3·d) and 0.56 kg TN/(m3·d), respectively. This is obviously higher than the values for a similar bioreactor (Bhuvanesh et al., 2013, Feng et al., 2021, Omena et al., 2013).
Co-metabolism is an effective approach to increase the degradation of refractory pollutants by anaerobic treatment. The improvement by co-substrates addition can be attributed to the induction of oxidizing enzyme and causing the bacteria proliferation supported by the biodegradable carbon resource (Friman et al., 2013). Glucose is known for a good co-metabolic substrate for enhancing the degradation of the refractory pollutants (Tian et al., 2020). In this study the enhancement of glucose as co-metabolic substrate for PCW treatment was studied. While it is uneconomical to add glucose to wastewater, a substitute for glucose is need. Therefore, domestic sewage was introduced in a pilot-scale experiment and used as co-metabolism substrate since it is cost-free and nutritive (Guo et al., 2013).
The objective of this study was to provide a novel biological method for the treatment of PCW to replace the chemical methods. The experiment was divided into three steps. First, a batch experiment was carried out to verify the feasibility of the anaerobic biological technique for treating PCW. Second, a lab-scale experiment using a SSSAB with glucose as co-substrates to improve the degradation. The performance of the SSSAB is discussed. And third, a pilot-scale experiment using an AFB with the SSSAB for an improved treatment of PCW. Besides the chemical oxygen demand (COD), the high concentration of NH4+-N was also removed. Additionally, the stability of the SSSAB and the AFB was assessed by OLR shock experiment and statistical analysis.
Section snippets
Inoculated sludge
For inoculation of the SSSAB, anaerobic granular sludge obtained from SSSAB in a soybean product processing plant in Jiangxi province, China was used. The average particle size of the sludge was 2.25 mm, the density was 1.17 g/cm3, and the VSS / SS value was 0.77.
The sludge dosage accounted for about 35% of the effective volume of the SSSAB. The sludge used for the AFB was obtained from the aeration tank of the municipal sewage treatment plant. The dosage accounted for 40% of the total volume
Optimum influent concentration of COD
The biogas production relies strongly on the stability of the anaerobic microbial community growing in the bottle (Calusinska et al., 2018). Fig. 2 depicts the methane production, COD removal and methane production for different dilution ratios. As can be seen from Fig. 2A, when the COD increased from 2040 mg/L to 16300 mg/L, the methane production also increases. If the COD concentration of the PCW is 178800 mg/L (a dilution ratio of 0), little methane is produced which resulted from the
Conclusion
The application of co-substrate theory and the use of a SSSAB alleviated the inhibitory effect of polyacrylate and effectively improved the biodegradability. The SSSAB-AFB process is efficient particularly for the treatment of PCW. The COD removal reaches up to 95.2%, which is higher than the value obtained by other chemical methods (the highest COD removal is 92.7%) (Yu et al., 2019b). High-throughput sequencing analysis indicated the relative abundance of Proteobacteria, Firmicutes and
CRediT authorship contribution statement
Qi Song: Methodology, Writing - review & editing. Zheng Sun: Conceptualization. Yong Chang: Project administration. Weifeng Zhang: Software. Yingzhi Lv: Writing - review & editing. Jiayi Wang: Visualization. Fenghao Sun: Validation. Yanxue Ma: Supervision. Yuling Li: Resources. Fengbo Wang: Data curation, Investigation. Xiaoguang Chen: Formal analysis, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was sponsored by the Bashan Weaving Group Co., Ltd, Shanghai Pujiang Program (No: 2020PJD001), Key Laboratory of Water Pollution Control and Environmental Safety of Zhejiang Province, China, and Graduate Student Innovation Fund of Donghua University (No: GSIF-DH-M-2021009).
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