When comparing the chemical properties of wastewater
from the last tank so-called post-biogas on biogas farms
and at the last pond on non-biogas farms, before it is
released to the public groundwater, it was found that the
coliform and BOD levels in biogas farm samples were
significantly lower than in non-biogas swine farm samples.
E. coli and COD levels in biogas farm samples were
lower than in non-biogas farms, but the differences were
not significant. This finding strongly suggests that biogas
farms have lower environmental impacts. However, the
levels of Zn, Cu and Pb in wastewater from biogas farms
were higher than those for non-biogas farms. The levels
of E. coli in wastewater from biogas farms were lower
than those for non-biogas farms but, unfortunately, these
differences were not significant at p < 0.05 (Table 3), but
they should be considered for future evaluations.