The effect of cefazolin on biogas production from thermophilic and mesophilic anaerobic co-digestion of dairy manure and waste milk

Abstract

Antibiotic residues in animal waste from concentrated
animal feeding operations are of considerable concern because
of the potential development of antibiotic resistant bacteria
in the environment and the effect of these residues on manure
treatment systems. The objective of this study was to determine
the effect of cefazolin (10 mg L-1
) during thermophilic and
mesophilic anaerobic co-digestion of manure and waste milk
from cows treated with cefazolin for mastitis. The collected
antibiotic free manure samples were mixed with slurry and
milk obtained from a healthy cow accordingly to form manure
mixture (slurry 50 % and manure 50 %) and milk mixture (slurry
50 %, manure 45 % and milk 5 %), each of which was further
separated as the control and cefazolin spiked (10 mg L
-1
), loaded
into triplicate 1 L batch digesters and anaerobically digested at
37 °C and 55 °C for 22 days separately. Control and cefazolin
spiked milk mixtures always produced significantly (p < 0.05)
higher total and methane gas yields compared to the respective
manure mixtures. Compared to the control in both digester types,
no significant (p > 0.05) differences in total and methane gas
yields were observed in the respective cefazolin spiked digesters
despite the temperature at which the digestion was carried out.
Volatile fatty acid (VFA) accumulation and reduction of pH
were not observed in any digester of both substrates at both
temperatures at the end of the experiment, which confirmed the
process stability. However, further investigations are necessary
to analyse the effects of increased concentrations of cefazolin in
the substrates on digester stability.