Key Takeaways & Executive Findings
- •• • MAP precipitation pretreatment elevated hydrogen production from <0.50 mmol/(kg·d) in raw wastewater to 48.17 mmol/(kg·d) at COD 1800 mg/L, a >96-fold increase, enabling energy recovery from high-strength organic waste. • • Co-treatment of MAP supernatant with sludge heat-treated at 75°C for 0.5 h further boosted hydrogen production to 71.44 mmol/(kg·d), a 48% improvement over MAP alone, demonstrating effective enrichment of hydrogen-producing bacteria. • • At pH 4.0, maximum hydrogen production rates reached 0.10, 7.74, and 8.83 mol/(kg·d) for raw, MAP-pretreated, and co-treated reactors, respectively, underscoring pH as a critical operational parameter for process optimization. • • MAP pretreatment increased methane concentration to 14.2% at COD 2400 mg/L versus 10.8% in raw wastewater, indicating enhanced overall anaerobic digestion efficiency, though COD removal was inversely affected (78.9% > 70.8% > 52.5%), likely due to accumulation of volatile fatty acids.
Abstract
Swine wastewater, a high-strength organic effluent, offers a viable substrate for anaerobic biohydrogen production, aligning with clean energy recovery. This study compared hydrogen production in three anaerobic sequencing batch reactors (ASBRs) treating: raw wastewater (R1), supernatant after MAP (magnesium ammonium phosphate) precipitation for nitrogen and phosphorus recovery (R2), and the same supernatant with anaerobic sludge heat-treated at 75°C for 0.5 h (R3). Without pH adjustment, hydrogen production in R1 remained below 0.50 mmol/(kg·d). At an influent COD of 1800 mg/L, R2 and R3 achieved hydrogen production rates of 48.17 and 71.44 mmol/(kg·d), respectively. At COD 2400 mg/L, methane concentrations in R1, R2, and R3 were 10.8%, 14.2%, and 9.1%, respectively, indicating MAP pretreatment enhanced both hydrogen and methane production. As COD increased, R1's methane concentration rose to 14.6%, while average COD removal efficiencies for R1, R2, and R3 were 78.9%, 70.8%, and 52.5%, respectively. Under pH adjustment, all reactors peaked at pH 4.0, with hydrogen production rates of 0.10, 7.74, and 8.83 mol/(kg·d) for R1, R2, and R3, respectively. These findings demonstrate that MAP pretreatment combined with sludge heat treatment significantly enhances biohydrogen production, offering a promising strategy for swine wastewater valorization.
1. Introduction
Anaerobic digestion of swine wastewater conventionally targets methane production, yet biohydrogen offers a higher-value energy carrier with lower greenhouse gas footprint. However, process instability and low yields have hindered commercial adoption. The four-stage anaerobic theory suggests that arresting fermentation before methanogenesis can maximize hydrogen recovery, but practical implementation requires effective pretreatment to suppress hydrogen-consuming microorganisms and optimize substrate composition.
This study addresses these bottlenecks by integrating MAP precipitation—which recovers nitrogen and phosphorus while altering the carbon-to-nitrogen balance—with thermal pretreatment of anaerobic sludge to selectively enrich hydrogen-producing bacteria. The comparative evaluation across three ASBR configurations provides quantitative evidence on how these pretreatments influence hydrogen yields, methane generation, and COD removal, offering a data-driven pathway for scaling up biohydrogen production from agricultural waste streams.
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SUN Jian, YANG Zhipeng, ZHANG Dongmei, ZHANG Ling, WANG Haoyu, ZHONG Jiaxing, WANG Xiaoling, DU Juli (2026). Comparative Study on Hydrogen Production Characteristics of Pre-treated Swine Wastewater in ASBR Process. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202606018
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Frequently Asked Questions
What is the underlying mechanism by which MAP precipitation enhances hydrogen production in swine wastewater?
MAP precipitation removes ammonium and phosphate, adjusting the C/N ratio to a more favorable range for hydrogen-producing bacteria. This reduces the buffering capacity that favors methanogens, thereby shifting metabolic pathways towards hydrogen production. The study observed a >96-fold increase in hydrogen yield (from <0.50 to 48.17 mmol/(kg·d)) at COD 1800 mg/L, indicating that nutrient recovery not only adds value but also improves fermentative efficiency.
How does sludge heat treatment at 75°C for 0.5 h influence the microbial community and hydrogen yield?
Heat treatment selectively inactivates non-spore-forming hydrogen consumers like methanogens, while preserving spore-forming hydrogen producers such as Clostridium species. This enrichment led to a 48% higher hydrogen production (71.44 vs. 48.17 mmol/(kg·d)) compared to MAP alone, demonstrating that thermal pretreatment is an effective strategy to enhance biohydrogen yields.
What is the optimal pH for maximizing hydrogen production in the ASBR system, and how does it affect reactor performance?
The optimal pH was 4.0 for all reactors, yielding maximum hydrogen production rates of 0.10, 7.74, and 8.83 mol/(kg·d) for raw, MAP-pretreated, and co-treated reactors, respectively. At this acidic pH, hydrogenase activity is favored, and methanogenic activity is suppressed, leading to higher hydrogen yields. However, such low pH may inhibit overall COD removal, as evidenced by lower removal efficiencies in pretreated reactors.
What are the trade-offs between enhanced hydrogen production and COD removal efficiency?
While MAP and heat pretreatment significantly boost hydrogen production, they reduce COD removal efficiency: 78.9% (raw), 70.8% (MAP), and 52.5% (co-treated). This is likely due to the accumulation of volatile fatty acids (VFAs) from partial acidogenesis, which increases soluble COD. For industrial application, a two-stage process—first optimizing hydrogen production, then methanogenic digestion of the effluent—could maximize both energy recovery and pollutant removal.
How does the methane concentration in the reactors vary with influent COD, and what implications does this have for process control?
At COD 2400 mg/L, methane concentrations were 10.8% (raw), 14.2% (MAP), and 9.1% (co-treated). The higher methane in MAP reactor suggests enhanced overall anaerobic activity, but in co-treated reactor, heat treatment likely suppressed methanogens more effectively, favoring hydrogen. As COD increased to higher levels, raw reactor methane rose to 14.6%, indicating that methanogenesis becomes more competitive at higher organic loads. This suggests that to maintain hydrogen production, influent COD should be carefully controlled, and pH or hydraulic retention time may need adjustment to suppress methanogens.
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