Key Takeaways & Executive Findings
- •• • COD removal efficiency reached 90% under microaerobic-biochar coupling (0.2 mL/(g VS·d) micro-aeration, 15 g/L biochar, 37 °C), a 10.6 percentage point improvement over anaerobic control, demonstrating enhanced organic mineralization for high-strength industrial wastewater. • • Effluent propionate concentration was reduced to 0.15 g/L, a 98.4% decrease versus control, mitigating the key inhibitor in anaerobic digestion of 1,2-propanediol-rich wastewater, thus preventing acidification failure. • • Biogas production increased to 1.64 times that of the anaerobic control, with maximum methane content of 77.2%, indicating improved energy recovery and process stability. • • FT-IR and SEM analyses confirmed increased –OH, –CH2–, and C–O functional groups and formation of dense microbial aggregates dominated by long bacilli, evidencing biochar's role in enhancing microbial adhesion and syntrophic interactions.
Abstract
Guar gum production wastewater contains 1,2-propanediol, which in conventional anaerobic treatment causes propionate accumulation and microbial inhibition. Microaerobic conditions foster fermentative bacterial metabolism, enhancing organic substrate conversion, while biochar promotes anaerobic microbial aggregation and oxygen tolerance. This study treated actual guar gum wastewater using three configurations: blank control, anaerobic, and microaerobic-biochar (O2/BC) coupled systems. Under mesophilic conditions (37 °C), with micro-aeration at 0.2 mL/(g VS·d) and biochar dosage of 15 g/L, the O2/BC system achieved a COD removal efficiency of 90%, 10.6 percentage points higher than the anaerobic control. Effluent COD and propionate concentrations dropped to 3800 mg/L and 0.15 g/L, respectively, representing reductions of 49.6% and 98.4% versus the control. Biogas production was 1.64 times that of the control, with a maximum methane concentration of 77.2%. Fourier transform infrared spectroscopy (FT-IR) indicated increased abundance of –OH, –CH2–, and C–O functional groups on sludge surfaces, revealing biochar's adsorption enhancement. Scanning electron microscopy (SEM) showed dense microbial aggregates dominated by long bacilli, distinct from conventional anaerobic sludge. Microbial community analysis revealed increased abundance of Clostridium and Comamonas, modulating the propionate-to-acetate ratio and optimizing acidification efficiency, thereby promoting complex organic degradation. This study provides a novel technical pathway for biological treatment of alcohol-rich organic wastewater.
1. Introduction
Guar gum production wastewater, characterized by high concentrations of 1,2-propanediol, poses a significant challenge to conventional anaerobic digestion. The metabolic pathway of 1,2-propanediol often leads to propionate accumulation, which is thermodynamically unfavorable and inhibits methanogenic activity, resulting in process instability and reduced biogas yields. Existing commercial anaerobic systems frequently require long hydraulic retention times and suffer from low organic loading rates when treating such alcohol-rich streams, limiting their economic viability.
This study introduces a microaerobic-biochar coupled system to address these bottlenecks. Microaeration (0.2 mL/(g VS·d)) creates a facultative environment that stimulates hydrolytic and acidogenic bacteria, enhancing the conversion of complex organics. Simultaneously, biochar (15 g/L) provides a conductive surface that promotes syntrophic interactions and microbial aggregation, improving oxygen tolerance and process resilience. The combination synergistically mitigates propionate inhibition, achieving a 90% COD removal efficiency and a 1.64-fold increase in biogas production compared to conventional anaerobic digestion, offering a robust solution for industrial application.
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DONG Yuanyuan, YU Jianchang, SHAN Yu, XU Tian, BU Jiuhe, WANG Tao (2026). Enhancement of Anaerobic Digestion Operational Efficiency for Guar Gum Production Wastewater Using a Microaerobic-Biochar Coupled System. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604010
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Frequently Asked Questions
What is the optimal micro-aeration rate and biochar dosage for treating guar gum wastewater, and how were these parameters determined?
The optimal parameters were micro-aeration at 0.2 mL/(g VS·d) and biochar dosage of 15 g/L, determined through systematic experiments comparing COD removal, propionate concentration, and biogas production. These conditions achieved 90% COD removal and 98.4% propionate reduction, indicating a balanced oxygen supply that stimulates fermentative bacteria without inhibiting methanogens.
How does the microaerobic-biochar system mitigate propionate accumulation compared to conventional anaerobic digestion?
The system enhances the abundance of Clostridium and Comamonas, which are key in acidogenesis and syntrophic propionate oxidation. Microaeration promotes the metabolic activity of these bacteria, while biochar facilitates electron transfer and microbial aggregation, leading to a 98.4% reduction in propionate concentration (from 9.4 g/L to 0.15 g/L) and a more favorable propionate-to-acetate ratio.
What are the implications of the increased biogas production and methane content for energy recovery in industrial applications?
Biogas production increased to 1.64 times that of the anaerobic control, with maximum methane content of 77.2%. This translates to higher energy recovery potential, making the process more economically attractive. For a typical wastewater treatment plant, this could significantly offset operational costs through biogas utilization.
What is the role of biochar in enhancing microbial aggregation and process stability under microaerobic conditions?
Biochar provides a high-surface-area support that promotes biofilm formation and microbial adhesion, as evidenced by SEM showing dense aggregates of long bacilli. FT-IR analysis revealed increased –OH, –CH2–, and C–O functional groups on sludge surfaces, indicating enhanced adsorption and colonization. This aggregation improves syntrophic interactions and protects microorganisms from oxygen stress, contributing to process stability.
Are there any potential scalability challenges or long-term operational issues with the microaerobic-biochar system?
Scalability challenges include ensuring uniform biochar distribution and maintaining optimal micro-aeration control in large reactors. Long-term issues may involve biochar saturation and replacement, as well as potential clogging from dense microbial aggregates. However, the study demonstrates robust performance over the experimental period, and the use of low-cost biochar derived from agricultural waste could mitigate economic concerns.
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