• Acidification of slurry to reduce NH 3 and CH 4 emissions. • Slurry pH 5.5 increased TVC, Lactobacilli , TCC, and E. coli during 7-week storage. • Low influence of acid type on TCC and E. coli in dairy cattle slurry. • More TVC due to acidification with lactic acid instead of sulphuric acid. • Anaerobic storage of acidified slurry results in lower amounts of Lactobacilli. Acidification reduces ammonia and methane emissions during storage of slurry. However, pH reduction can lead to a shift in microbial composition of the slurry and might affect survival rates of pathogens. So far, the influence of different acids (lactic or sulphuric acid), target pH values or management strategies (addition of glucose for internal acidification, subsequent anaerobic storage) on aerobic total viable count (TVC), and different bacteria like Lactobacilli , total coliform count (TCC) and Escherichia coli ( E. coli ) is unknown. This pilot study with slurry from fattening pigs and dairy cattle showed that a one-time acidification process increases TVC during a storage period of 7 weeks (about 0.8 and up to 0.3 log 10 cfu mL −1 ). Only acidification to pH 3.0 resulted in lower TVC (− 1.7 log 10 cfu mL −1 ). Lactobacilli , TCC and E. coli also increased during storage due to a pH reduction to pH 5.5. The addition of glucose before acidification resulted in larger quantities of Lactobacilli compared to the addition of acid alone (+ 0.3 log 10 cfu mL −1 ). Anaerobic storage of the acidified slurry results not only in lower pH increase after acidification, but also in lower amounts of Lactobacilli (− 0.5 log 10 cfu mL −1 ). In the dairy cattle slurry acidified with lactic acid, there were slightly higher numbers of TVC and Lactobacilli present, while the influence of acid type on TCC and E. coli was less. Under the target pH conditions tested, acidification influenced microbial stability, but did not lead to noticeable reduction compared to the non-acidified variant.
Ebertz et al. (Sun,) studied this question.