Abstract
BackgroundMonitoring and providing early warning are essential operations in the anaerobic digestion (AD) process. However, there are still several challenges for identifying the early warning indicators and their thresholds. One particular challenge is that proposed strategies are only valid under certain conditions. Another is the feasibility and universality of the detailed threshold values obtained from different AD systems. In this article, we report a novel strategy for identifying early warning indicators and defining threshold values via a combined experimental and simulation approach.ResultsThe AD of corn stalk (CS) was conducted using mesophilic, completely stirred anaerobic reactors. Two overload modes (organic and hydraulic) and overload types (sudden and gradual) were applied in order to identify early warning indicators of the process and determine their threshold values. To verify the selection of experimental indicators, a combined experimental and simulation approach was adopted, using a modified anaerobic bioconversion mathematical model (BioModel). Results revealed that the model simulations agreed well with the experimental data. Furthermore, the ratio of intermediate alkalinity to bicarbonate alkalinity (IA/BA) and volatile fatty acids (VFAs) were selected as the most potent early warning indicators, with warning times of 7 days and 5–8 days, respectively. In addition, IA, BA, and VFA/BA were identified as potential auxiliary indicators for diagnosing imbalances in the AD system. The relative variations for indicators based on that of steady state were observed instead of the absolute threshold values, which make the early warning more feasible and universal.ConclusionThe strategy of a combined approach presented that the model is promising tool for selecting and monitoring early warning indicators in various corn stalk AD scenarios. This study may offer insight into industrial application of early warning in AD system with mathematical model.
Highlights
Monitoring and providing early warning are essential operations in the anaerobic digestion (AD) process
Gaseous parameters The CH4 yield and content of the two reactors were seen to have stabilized in the full-load phase, at 0.20 L CH4/g volatile solid (VS) (62.20% of C H4) on average with organic loading rates (OLR) of 1.50–2.24 g VS/(L day) in Reactor 1 (R1) and at 0.20 L CH4/g VS (58.73% of CH4) with OLR between 1.87 and 2.24 g VS/(L day) in Reactor 2 (R2)
Regarding the sudden overload phase of R1, the CH4 yield showed a stepwise rise with elevated OLR, up to 0.37 L C H4/g VS on day 155 with OLR at 3.37 g VS/(L day), and sharply decreased to 0.12 L CH4/g VS
Summary
Monitoring and providing early warning are essential operations in the anaerobic digestion (AD) process. There are still several challenges for identifying the early warning indicators and their thresholds. One particular challenge is that proposed strategies are only valid under certain conditions. Another is the feasibility and universality of the detailed threshold values obtained from different AD systems. We report a novel strategy for identifying early warning indicators and defining threshold values via a combined experimental and simulation approach. Straw has a great potential to serve as a feedstock for anaerobic methane (CH4) production, due to its abundance and suitable bioconversion characteristics [2]. In China, straws are produced at a high annual rate of approximately 1 billion metric tons [3], and about 30% of those were underutilized [3, 4]. Some previous studies reported that the moderate organic loading
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