Journal of Food, Agriculture and Environment

Effect and mechanism of stirring on cyanobacteria anaerobic fermentation for biogas production

Author(s):

Yaqin Yu  ^{1, 2}, Xiwu Lu ¹*

Recieved Date: 2013-06-21, Accepted Date: 2013-09-30

Abstract:

Stirring is a key factor affecting biogas production via anaerobic fermentation by algae. In this research, the effects of stirring interval, stirring duration and stirring intensity were investigated on algal anaerobic fermentation. Optimal stirring factors were determined by response surface methodology. The optimal stirring conditions, predicted from the simulated quadratic polynomial regression equation, were stirring interval 6 h, stirring duration 20 min/stir and stirring intensity 56 r/min. In a pilot study, the maximum specific production rates of gas and methane were 0.39 L/d.gVS and 0.236 Ld.gVS, respectively. Stirring intensity exerted the greatest effect on algal anaerobic fermentation for biogas production, while stirring duration was the minor factor. Excessive stirring intensity or frequency destroys the condition for anaerobic microbial growth, partially destroying the synergy among different species in the system. Ultimately, levels of protease, dehydrogenase and coenzyme F₄₂₀ in the sludge decline and gas production rate reduce. With the optimal stirring, the dominant bacterial strains producting biogas in the granular sample were Methanosphae, Methanolinea, Methanoregula, Thermogymnomonas, Methanosaeta and Methanomethylovorans by the denaturing gradient gel electrophoresis (DGGE) analysis. At suitable stirring conditions, there were plenty of methanogenic bacteria in granular sludge during the algae anaerobic fermentation. The study found that the suitable stirring could overcome the drawbacks of algae floating and crusting in the reactor and at the same time accelerate the mass transfer in the reactor so as to increase gas production rate. Low-intensity or long stirring interval tends to float the algae, reducing their contact with other sludge microorganisms and thereby lowering the algal conversion efficiency.

Keywords:

Algae, anaerobic fermentation, response surface methodology, stirring

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Journal: Journal of Food, Agriculture and Environment
Year: 2013
Volume: 11
Issue: 3&4
Category: Environment
Pages: 1954-1959

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