The survival of cefazolin-resistant bacteria in mesophilic co-digestion of dairy manure and waste milk

Abstract

The use of cefazolin to treat mastitic cows leads to cefazolin residues in milk and manure. This is responsible for the high occurrence of cefazolin resistant bacteria (CRB) in waste and the environment. Anaerobic digestion is considered to have the potential to reduce antibiotic-resistant bacteria present in waste that results from concentrated animal feeding operations. Thus, the objective of this study was to investigate the survival of CRB and the digester performance in mesophilic co-digestion of dairy manure and waste milk. The experiment was carried out using three digester compositions: 100% slurry (slurry), 50% slurry + 50% manure (manure mixture) and 50% slurry + 45% manure + 5% waste milk (milk mixture) in batch digesters of 1 l with a working volume of 800 ml in triplicate at 37°C for 34 days. The daily biogas production in each digester, and methane (CH4) and carbon dioxide compositions in the gas were determined. The population densities of total culturable bacteria (TCB) and CRB were determined by plate counts on agar media at day 0, 10, 20 and 34 of digestion. Milk mixture produced the highest (P < 0.05) daily and cumulative total and CH4 gas. The maximum percentage reductions of TCB and CRB in manure and milk mixture was observed at day 20, the values being 96.2%, 96.0% and 99.8% and 99.8% respectively. Final volatile fatty acids (VFA) and pH values of the digesters confirmed the digester stability. Based on the findings, mesophilic anaerobic digestion can be considered a potent method to avoid the dissemination of CRB in nature.

Evaluation of use of biogas plant digestate as fertilizer in alfalfa and winter wheat

“…Post-digestion liquid is produced as well, which can be used as a fertilizer in agriculture. It should not be discharged into sewers due to the hazard of bacterial infestation [26].…”

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

“…A study conducted by Beneragama et al, in 2012 has shown that a cefazolin concentration of 10 mg L -1 does not have an effect on the reduction level of multi drug resistant bacteria during anaerobic co-digestion of dairy manure and waste milk. Furthermore, it was clear from the results of a previous study (Beneragama et al, 2013) that mesophilic co-digestion of dairy manure and waste milk from cows treated with cefazolin for mastitis would give better performances, in both curtailing the cefazolin resistant bacteria and producing higher amount of methane, if the hydraulic retention time is set compromised in between 20 -25 days. Therefore, an environmentally feasible cefazolin concentration of 10 mg L -1 was tested to examine its influence on the thermophilic and mesophilic anaerobic co-digestion of dairy manure and waste milk separately in laboratory scale digesters.…”

“…Journal of the National Science Foundation of Sri Lanka 43 (4) Related studies conducted on this aspect are found in literature although not many. Fisher et al, in 1981 have found that the biological activity of the anaerobic digestion of pig slurry was reduced by the presence of lincomycin.…”

“…All gas measurements were expressed at 0 °C and a pressure of one atmosphere. Prior to measuring the volume of produced gas, the composition of gas (CH 4 and CO 2 ) was determined through gas chromatography (GC-14A, Shimadzu, Japan) equipped with a thermal conductivity detector. The operational temperatures of injector port, column and the detector were 220, 150 and 220 v°C, respectively.…”

“…It involves the degradation and stabilisation of organic materials under anaerobic conditions by microbial organisms and leads to the formation of biogas (a mixture of CO 2 and CH 4 ) and microbial biomass (Kelleher et al, 2000). In anaerobic digestion, acedogenic and methanogenic bacteria differ widely in terms of physiology, nutritional needs, growth kinetics, and sensitivity to environmental conditions (Pohland & Ghosh, 1971).…”