Cadmium Addition Effects on Anaerobic Digestion with Elevated Temperatures

Abstract

Anaerobic fermentation with biogas as an energy source is influenced by the presence of heavy metals. However, the availability of the heavy metals is dependent on the digestion temperature. In this study, the impacts of Cd on the characteristics of biogas, substrate biodegradation, and enzyme activity during anaerobic co-digestion were investigated under varying digestion temperatures. The results showed that 1 mg/L initial Cd concentration improved cumulative biogas yields by 404.96%, 16.93%, and 5.56% at 55 • C, 45 • C, and 35 • C, respectively. In contrast, at low temperatures (25 • C), the yield decreased by 0.77%. In the 55 • C group, Cd addition improved the activity of cellulase (p < 0.05) and coenzyme F 420 (p < 0.01). The total chemical oxygen demand (COD) during the peak period and the transformation of hydrolytic organic components into volatile fatty acids (VFAs) influenced the CH 4 and biogas yields. There were no significant differences in cellulase, dehydrogenase, and coenzyme F 420 activities with or without Cd addition when the digestion temperature was 45 • C, 35 • C, and 25 • C. Therefore, thermophilic digestion is recommended for the efficient degradation of Cd-contaminated biowaste. Moreover, the impact of metals on the performance of anaerobic digestion should be considered together with temperature conditions in future research and practice.there is still lack of information about the role of Cd in biodegradation, particularly on the modification of the methanogenic pathway.The concentration of the available Cd in the reactor is greatly influenced by temperature changes. Under thermophilic conditions (55.0 ± 1.0 • C), Cd concentrations less than 1.0 mg/L were shown to be non-inhibitory to the anaerobic digestion process [14]. However, to the best of our knowledge, most of the previous research on the impacts of temperature was carried out without considering the presence of heavy metals in the reactors.The aim of this study was to examine the effect of elevated temperatures combined with the addition of Cd on the anaerobic digestion of lignocellulosic biomass. The impacts of Cd on the biogas properties, substrate biodegradation, and enzyme activity were investigated by comparing with a control that had no Cd added. Data from this study demonstrate the impact of temperatures on the performance and biodegradability of anaerobic fermentation and provide information for biogas production practice from metal-contaminated lignocellulosic biomass. Materials and Methods Experimental MaterialsA corn stover, a representation of lignocellulosic biomass, collected from farmland in Shandong Province, China was used as the feedstock. Prior to grinding into powder and passing through a 10-mesh sieve, the corn stover was air-dried. The stover was then pretreated with 6% phosphoric acid for 24 h at room temperature to destroy the lignocellulosic structure and enhance fermentation efficiency. After pretreatment, the corn stover was washed with deionized water 5-8 times. Fresh cow dung collected from the Yan...

Anaerobic digestion characteristics and key microorganisms associated with low-temperature rapeseed cake and sheep manure fermentation

“…Low temperatures affect the development of the biogas industry in Qinghai, resulting in biogas utilization e ciency being far lower in this area compared to low altitude areas. Thus, numerous agricultural biogas digesters have been abandoned in the area and these wasted resources represent a serious problem (Tian et al 2019;Yang et al 2020;Han et al 2020). However, the selection of easily degradable raw materials (Li et al 2020), the fermentation of mixed substrate components (Shi et al 2021) and fermentations with high solid contents (Elmitwalli et al 2004) can adequately reduce environmental condition requirements for fermentation.…”