This study evaluated the impact of pig manure acidification on anaerobic treatment and composition of the fecal microbial
community. According to the di erent chemical oxygen demand (COD) in the anaerobic treatment processes, pig manure was diluted
4 times ( 4), 16 times ( 16), or 64 times ( 64) and subjected to acidification. During the acidification process, pH, soluble chemical
oxygen demand (SCOD), volatile fatty acids (VFAs), nitrogen (N), phosphorus (P) and potassium (K) were determined along with
microbial population dynamics. The pH of the three dilutions first declined, and then slowly increased. The total VFAs of 4 and
16 dilutions peaked on day 15 and 20, respectively. The content of acetic acid, propanoic acid, butanoic acid and valeric acid of
the 4 dilution were 23.6, 11.4, 8.8 and 0.6 g/L respectively, and that of the 16 dilution was 5.6, 2.3, 0.9 and 0.2 g/L respectively.
Only acetic acid was detected in the 64 dilution, and its level peaked on day 10. The results showed that the liquid pig manure was
more suitable to enter the anaerobic methanogenic bioreactors after two weeks of acidification. During the acidification process, total
P concentration increased during the first ten days, then dropped sharply, and rose again to a relatively high final concentration, while
total N concentration rose initially and then declined. Based on the analysis of denaturing gradient gel electrophoresis (DGGE) and 16S
rRNA gene clone library, we concluded that the acidification process reduced the number of pathogenic bacteria species in pig manure.