Abstract
Anaerobic fermentation is considered as a cost-effective way of biomass waste disposal. However, the compound heavy metals contained in the biomass may induce complex effects on anaerobic fermentation, which limit the utilization of metal-contaminated biowaste. In this study, the impacts of Cd and Zn addition on biogas properties, process stability, substrate biodegradation, enzyme activity, and microbial properties were studied. The results showed that the addition of Cd together with Zn (Cd+Zn) increased the maximum daily and cumulative biogas yields, and brought forward the gas production peak compared with the Cd-added group. Taking the whole fermentation process into account, the promotion effects of adding Zn into the Cd-containing fermentation system on biogas yields were mainly attributable to better process stability, higher average NH4+-N concentration in the later stage of fermentation, reduced COD (p < 0.05), and increased biodegradability of lignocelluloses (p < 0.01), especially cellulose (p < 0.05) and lignin (p < 0.01). Meanwhile, the addition of Zn promoted the coenzyme M activity (p < 0.05), and increased the absolute abundance of Methanothermobacter. The bacteria communities during the fermentation process were responsible for the degradation of lignocelluloses. The results demonstrated that the addition of appropriate Zn into the Cd-containing fermentation system enhanced the efficiency of anaerobic fermentation and utilization of biowaste.
Highlights
With the rapid development of industries such as metal plating facilities, mining operations, fertilizer industries, tanneries, batteries, paper industries, pesticides, etc., large areas of land and water are polluted by heavy metals
Lignocellulosic biomass containing heavy metals were utilized as raw materials for anaerobic fermentation [5,6], which expressed different degrading patterns compared with the single feedstock fermentation
This research studied the different effects of Cd and Cd together with Zn (Cd+Zn) addition on anaerobic fermentation with mixed corn stover and cow manure as feedstocks
Summary
With the rapid development of industries such as metal plating facilities, mining operations, fertilizer industries, tanneries, batteries, paper industries, pesticides, etc., large areas of land and water are polluted by heavy metals. During the process of phytoremediation, the rapid growth of plants produces a large amount of lignocellulosic biomass, which can be used as an energy resource by technologies, such as anaerobic fermentation [3,4]. Lignocellulosic biomass containing heavy metals were utilized as raw materials for anaerobic fermentation [5,6], which expressed different degrading patterns compared with the single feedstock fermentation. The fermentation process with animal manure as a single feedstock would express a one-phase decomposition [8,9]. The anaerobic fermentation process with mixed lignocellulosic biomass and animal manure and other inoculums was likely to show a diauxie
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