Abstract
Biohydrogen production by fermentation has become a promising technology developed in the world. In this study, diluted normal molasses wastewater is used as the raw material, and biohydrogen production efficiency and operation characteristics of an anaerobic baffled reactor (ABR) are studied. The effect of hydraulic retention time (HRT) on biohydrogen production efficiency and operating characteristics of ABR is extensively discussed. Experimental results showed that methanogen residuals were still observed in the last three compartments under HRT of 24 h and COD(Chemical oxygen demand) concentration of 8000 mg/L. Meanwhile, the first three compartments presented an ethanol fermentation type. The characteristics of butyric acid fermentation in Compartment IV were also enhanced. The average removal efficiency of COD was reduced to 15.4%. The average rates of biohydrogen production and specific biohydrogen production were 12.85 and 360.22 L/kg COD, respectively. The extension of HRT was beneficial to enrich hydrogen-producing acetogens and could increase the production rate of biohydrogen by a factor of 1.65. However, with the decrease in the bioactivity of acidogenic fermentation bacteria, the biohydrogen production efficiency of ABR was significantly reduced when HRT was longer than 30 h. The specific biogas production rate decreased from 191 to 92 L/(kg MLVSS·d). The specific biohydrogen production rate also decreased from 24.34 to 2.7 L/(kg MLVSS·d).
Highlights
With the rapid development of the modern food industry, the wastewater produced with high organic matter is gradually increasing
The increase in influent COD led to the transformation of fermentation type and metabolism characteristics of anaerobic-activated sludge (AnAS)
The first three compartments showed the characteristics of an ethanol fermentation type, while the last compartment presented as a butyric acid fermentation type
Summary
With the rapid development of the modern food industry, the wastewater produced with high organic matter is gradually increasing. A huge amount of organic wastewater is directly discharged to receiving water. Normal molasses wastewater is a typical high-strength organic wastewater, which is the by-product of sugar refinement. Gokcek et al found that COD removal increased along with the increase of organic loading rate, while the biogas yield decreased [1]. In order to reduce the environmental risks, enhanced biogas and lipid production are well developed. By the Processes 2020, 8, 339; doi:10.3390/pr8030339 www.mdpi.com/journal/processes
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