Fig. 3: Effects of CaO2 pre-treatment on the cumulative methane production and physicochemical properties of sludge over time during MAD with CaO2 pre-treatment.

a The cumulative methane, b soluble chemical oxygen demand (SCOD), c soluble protein, d soluble polysaccharides, e pH, and f ammonia nitrogen. Black, red, blue, green, and purple represent the control group and CaO2 dosages of 0.08, 0.16, 0.24, and 0.32 g/g VSS, respectively.