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Headspace monitoring and control of fixed-film anaerobic digesters
Abstract
The development of high rate anaerobic processes has reached a point where there is a need for better monitoring and control strategies. The general objective of this research was to evaluate the potential of headspace gas monitoring and control of fixed-film anaerobic digesters. Laboratory-scale fixed-film anaerobic digesters treating a synthetic soluble carbohydrate waste were used. Trace gases, hydrogen and carbon monoxide, and final gases, methane and carbon dioxide, were monitored on-line. The effects of liquid recirculation on the rate of gas transfer from the generation site to the headspace of the reactor were evaluated. It was found that liquid recirculation rates do not affect mass transport rates significantly. Gas transport was primarily taking place by rising bubbles. Methane and carbon dioxide were transported from the bubbles to the surrounding liquid, whereas hydrogen was transported from the liquid to the bubbles. The rate of substrate uptake by the biofilm was significantly affected by liquid recirculation rates. The responses of trace gases to toxic stress by cadmium and formaldehyde were evaluated. Trace gases proved to be sensitive indicators of toxic stress. Comparison with previous studies revealed that fixed-film digesters were several times more resistant to toxicity than suspended-growth digesters. Adaptation to formaldehyde was fast and degradation of the compound was consistently observed. On-line control of effluent COD concentration using headspace parameters was possible when changes in influent strength were imposed to the system. A new parameter for digester monitoring was proposed in this study. The new parameter was named the methanogenic activity index, MAI. The MAI provides a simple criterion to determine when the reactor is reaching its maximum loading rate and also, provides a clear signal of the occurrence of toxicity events in the process.
Subject Area
Civil engineering|Sanitation|Microbiology
Recommended Citation
Giraldo, Eugenio, "Headspace monitoring and control of fixed-film anaerobic digesters" (1991). Doctoral Dissertations Available from Proquest. AAI9207403.
https://scholarworks.umass.edu/dissertations/AAI9207403