Granulation process in an expanded granular sludge blanket (EGSB) reactor for domestic sewage treatment: Impact of extracellular polymeric substances compositions and evolution of microbial population
Graphical abstract
Introduction
Anaerobic granular sludge technology is a promising method for the treatment of organic pollutants due to its energy effectiveness, limited nutrients requirements and low sludge production (Chi et al., 2018, Chong et al., 2012, Huang et al., 2016). Numerous advanced anaerobic reactors, including internal circulation (IC) reactors and expanded granular sludge blanket (EGSB) reactors, have been developed and applied for the treatment of various high-concentration industrial wastewaters (Stazi and Tomei, 2018, Teng et al., 2018). However, these anaerobic reactors usually require a long-term and high-concentration of substrates to start-up (Ghangrekar et al., 2005, Hulshoff Pol et al., 2004, Zhang et al., 2017), resulting in limited engineering applications of anaerobic processes for the treatment of low-strength wastewater such as domestic sewage (Liu et al., 2018a).
The key to achieving start-up of an anaerobic reactor is to cultivate granular sludge with excellent settleability and high biomass concentration. This depends on the biodegradation function of the microorganisms in the sludge, as well as other operational parameters (e.g., hydraulic retention time (HRT) and up-flow velocity (Vup)) (Hulshoff Pol et al., 2004, Yang et al., 2017). Mounting evidence supports that extracellular polymeric substances (EPS) excreted by microorganisms play a key role during sludge granulation despite certain discrepancies (Bala Subramanian et al., 2010, Chen et al., 2016, Shi et al., 2017). One report shows that the acetotrophic methanogen Methanosaeta is responsible for sludge granulation (Hulshoff Pol et al., 2004), while other studies suggest that the granulation process is due to the excessive amount of EPS excreted by Methanobacterium (Suarez et al., 2018, Torres et al., 2018). Thus, the fundamental mechanisms responsible for sludge granulation have not yet been fully elucidated.
An often-overlooked fact is that granulation largely depends on a high level of biomass growth (Liu et al., 2018a). Current studies suggest that the biomass accumulation can be enhanced by adding multivalent cations (e.g., calcium and iron), and/or a support material (e.g., granular activated carbon) during start-up (Hulshoff Pol et al., 2004, Yang et al., 2018, Zhang et al., 2018). However, this will inevitably increase the cost of cultivation and the complexity of operation (Li et al., 2018, Wang et al., 2005). Alternatively, sludge granulation can also be achieved by increasing the organic loading rate (OLR) and controlling the operational parameters (e.g., HRT and Vup) of reactors (Liu et al., 2018a).
There are few reports available on the application of anaerobic granular sludge technology for the treatment of low-strength domestic sewage. Not surprisingly, all these anaerobic reactors were performed by direct inoculating mature granular sludge, rather than cultivating the granular sludge from seed sludge (Stazi and Tomei, 2018). Thus, several important questions remain. For example, which types of EPS are essential during sludge granulation? What are the key components of EPS during sludge granulation? What is the impact of other operational parameters? What is the feasible start-up strategy for the treatment of low-strength domestic sewage? Also, the spatial distribution of EPS during sludge granulation for the treatment of low-strength domestic sewage is unknown. Therefore, an in-depth study of the sludge granulation during the treatment of low-strength domestic sewage is warranted.
In this study, we adopted the strategy of increasing the OLR and Vup to accelerate the growth of sludge granules. The main objective was to evaluate the granulation and microbial population dynamics in an EGSB reactor by treating low-strength domestic sewage. To achieve the-above objectives, the change in volatile fatty acids (VFAs), specific methanogenic activity (SMA) and EPS contents were determined during sludge granulation. The microbial community distributions and EPS distributions of the microbial aggregates during the granulation process were correlated, and a corresponding granulation mechanism is proposed. This work may bring new insights into the mechanism of anaerobic sludge granulation.
Section snippets
Reactor set-up and operational conditions
A typical EGSB reactor with an effective working volume of 28.6 L was employed to treat the synthetic domestic sewage. The reactor consists of a bottom column (with an internal diameter of 10 cm and a height of 100 cm), an upper three-phase separator (25 × 25 × 25 cm), and an external circulation system. Three sampling ports (A, B, and C) were established along the EGSB column at a height of 25, 50 and 75 cm, respectively. One run lasted 135 days. The whole experiment can be divided into four
Performance of the EGSB reactor
Fig. 1 shows the change of influent and effluent COD concentrations, and the relevant COD removal efficiency with the operation time. During the operation, HRT was gradually reduced from 8 to 4 h. Consequently, the relevant OLR increased from 1.35 to 2.70 kg COD/m3/d. Influent and effluent COD concentrations were in the ranges of 322–554 mg/L and 76–280 mg/L, respectively. In Period I (days 1–24), COD removal efficiency increased linearly with time at an HRT of 8 h, due to increased biomass.
Conclusions
The granules in an EGSB reactor using domestic sewage as the influent were cultivated successfully for 107 days. The optimal HRT was 5 h at an OLR of 2.16 kg COD/m3/d. A corresponding average COD removal efficiency of 71.5 ± 2.3% was obtained. The EPS distribution and composition suggest that the TB-EPS content had a positive impact on the formation of the granular sludge. In addition, high-throughput sequencing analysis indicated that the metabolism shifted during the sludge formation from
Acknowledgements
This work was supported by Shanghai Pujiang Program (No. 18PJ1400400), the Shanghai Science and Technology Committee (No. 17DZ1202204), the Natural Science Foundation of Shanghai, China (No. 18ZR1401000), and the National Key Research and Development Program of China (No. 2018YFF0215703 and No. 2016YFC0400501). Y.L. thanks Donghua University for the start-up grant (No. 113-07-005710).
References (43)
- et al.
Neighborhood social stressors, fine particulate matter air pollution, and cognitive function among older U.S. adults
Soc. Sci. Med.
(2017) - et al.
Extracellular polymeric substances (EPS) producing bacterial strains of municipal wastewater sludge: Isolation, molecular identification, EPS characterization and performance for sludge settling and dewatering
Water Res.
(2010) - et al.
Accumulation of propionic acid during consecutive batch anaerobic digestion of commercial food waste
Bioresour. Technol.
(2017) - et al.
Membrane fouling in a membrane bioreactor: high filtration resistance of gel layer and its underlying mechanism
Water Res.
(2016) - et al.
Influent characteristics affect biodiesel production from waste sludge in biological wastewater treatment systems
Int. Biodeterior. Biodegrad.
(2018) - et al.
The performance enhancements of upflow anaerobic sludge blanket (UASB) reactors for domestic sludge treatment – a State-of-the-art review
Water Res.
(2012) - et al.
Inhibitory effect and mechanism of azo dyes on anaerobic methanogenic wastewater treatment: can redox mediator remediate the inhibition?
Water Res.
(2016) - et al.
Influence of synthetic and natural polymers on the anaerobic granulation process
Water Sci. Technol.
(1998) - et al.
Characteristics of sludge developed under different loading conditions during UASB reactor start-up and granulation
Water Res.
(2005) - et al.
Role of sludge volume index in anaerobic sludge granulation in a hybrid anaerobic reactor
Chem. Eng. J.
(2016)
Fluorescence excitation–emission matrix spectra coupled with parallel factor and regional integration analysis to characterize organic matter humification
Chemosphere
Volatile fatty acids (VFAs) production from swine manure through short-term dry anaerobic digestion and its separation from nitrogen and phosphorus resources in the digestate
Water Res.
The role of hydrogenotrophic methanogens in an acidogenic reactor
Chemosphere
Anaerobic sludge granulation
Water Res.
Adhesion characteristics of nitrifying bacteria in activated sludge
Water Res.
Microbial population dynamics during aerobic sludge granulation at different organic loading rates
Water Res.
Direct contact membrane distillation for the treatment of industrial dyeing wastewater and characteristic pollutants
Sep. Purif. Technol.
Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge
Water Res.
Effect of heavy metals on the methanogenic UASB granule
Water Res.
Enhanced granulation and methane recovery at low load by downflow sludge circulation in anaerobic treatment of domestic wastewater
Bioresour. Technol.
Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor
Water Res.
Cited by (0)
- 1
Both authors contributed equally to this work.