TABLE 1.

Physical and chemical properties of the fresh and mature sludges

ParameterResult for sludgea
FreshMature
Total solids (%)29.1 (1.0)27.1 (1.8)
Volatile solids (%)57.3 (2.2)54.8 (2.2)
pH at 1:5 (wt/vol)7.93 (0.05)8.65 (0.03)*
Electrical conductivity at 1:10 wt/vol (mS cm−1)3.97 (0.05)*3.75 (0.10)
C (%)30.07 (2.50)*24.72 (1.50)
N (%)2.00 (0.08)1.92 (0.11)
C/N ratio15.0 (0.5)*12.9 (0.2)
Acetate (mM)10.02 (1.01)*1.01 (0.20)
Propionate (mM)7.16 (0.73)6.69 (0.49)
Butyrate (mM)3.31 (0.40)*0.06 (0.04)
i-Valeriate (mM)1.03 (0.11)*0.52 (0.10)
i-Butyrate (mM)0.57 (0.03)*0.28 (0.03)
Valeriate (mM)0.37 (0.05)0.35 (0.24)
  • a Standard deviations are given in parentheses (n = 5). Asterisks indicate significant differences at P < 0.001 after Student's t test or multivariate one-way analysis of variance (for VFAs) with SPSS 15.0.