The effect of various carbonate sources on the survival of Escherichia coli in dairy cattle manure

Manure slurries (n = 3) prepared from the feces and urine of lactating dair y cattle (1 part urine, 2.2 parts feces, and 6.8 parts distilled water) had an initial pH of 8.6 +/- 0.1; dissolved carbonate concentrations of 48 +/- 4 mM, and Escherichia coli counts of 5.9 +/- 0.7 logs per mi slurry. The p H of untreated slurries declined to pH 7.0 +/- 0.1 by the 10th day of incub ation, and the E. coli count increased approximately 10-fold (P < 0.05). Wh en slurries were treated with Na2CO3, K2CO3, NaHCO3 or Na2CO3<bullet>NaHCO3 (0 to 16 g/kg slurry), the dissolved carbonates increased in a linear fash ion, but only Na2CO3 and K2CO3 (8 g/kg or greater) or Na2CO3. NaHCO3 (16 g/ kg) ensured an alkaline pH. Even relatively low concentrations of Na2CO3 of K2CO3 (8 or 12 g/kg) caused a decrease in E. coli viability (P ( 0.05), an d E. coli could not be detected if 16 g/kg was added (day 5 or 10 of incuba tion). Na2CO3. NaHCO3 also caused a decrease in E, coli viability, (P < 0.0 5), but some E. coli (approximately 10(4) cells per g) were detected on day 10 even if the concentration was 16 g/kg. NaHCO3 did not prevent the decre ase in pH or cause a decrease in E. coli numbers (P > 0.05). Calculations b ased on the Henderson-Hasselbalch equation (pH and dissolved carbonates) in dicated that little E. coli killing was noted until the dissolved carbonate anion concentrations (CO3-2) were greater than 1 mM, but bicarbonate anion (HCO3-) concentrations as high as 180 mM did not affect E. coli viability. These results are consistent with the idea that carbonate anion has antimi crobial properties and can kill E. coli in dairy cattle manure.