3.3. Effects of some selected heavy metals on biogas production
Table 2 shows the comparison of the results from this work with the reports from other authors. The anaerobic fermentation and microbial growth are dependent on the availability and/or optimal supply of nutrients [32]. Despite the importance of trace elements for process stability and the production of biogas, it is very clear that there is still no formula for optimum composition [33]. Several studies have also shown that the addition of trace elements can stimulate the biogas process and enable higher organic loadings (Table 2). In the present study, Ni2+ (100 ppm), Zn2+ (150 ppm) and Cu2+ (50 ppm) gave 279, 114 and 117 mL/day of biogas, respectively. Comparison of biogas yield Ni+ with Zn2+and Cu2+, showed that there was a significant difference in their performance (P < 5%).