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, Ni2þ (100 ppm),
Zn2þ (150 ppm) and Cu2þ (50 ppm) gave 279, 114 and 117 mL/day
of biogas, respectively. Comparison of biogas yield Niþ with
Zn2þand Cu2þ, showed that there was a significant difference in
their performance (P < 5%).