Adaptation of biomass During the biomass adaptation in the batch reactor, the sludgebecame degranulated, as a consequence of the completely mixing of the reactor. Fig. 2a shows the behavior of the organicmatter expressed as COD and BOD concentrations in functionof time. In the first six days, the concentration profiles ofCOD and BOD followed a logarithmic trend; a second orderkinetics can be adjusted with an overall rate constant forCOD and BOD of 7.2 × 10−5and 3.37 × 10−4L mg−1day−1,respectively. This behavior is attributed to the high ability ofmicroorganisms to degrade carbohydrates and amino acidscontained in this type of wastewater; removal efficiencies ofCOD and BOD achieved 81% and 87%, in a period of 15 days.Accumulated volume of methane during the batch operationof the reactor was 2500 mL at operation conditions (T = 37◦C,Guadalajara (Mexico) atmospheric pressure = 0.84 atm).