Fig. 2. Volatile fatty acids (VFA) content and pH in columns with mixtures of feces, urine, and inoculum kept at 15 and 20°C, respectively. Open squares, cattle manure stored at 15°C; open circles, pig manure stored at 15°C; solid squares, cattle manure stored at 20°C; solid circles, pig manure stored at 20°C. Error bars represent the standard deviation.