Anaerobic fluidized bed reactor has better mass transfercharacteristics when compared with the fixed biofilm reactor.Additionally, AFBR has high amount of attached biomass whichis rich in microbial diversity and it recoveries rapidly after insta-bility conditions changed [80,85]. Reported operational conditionsand performance comparisons of AFBRs for the treatment of dairywastewater are given in Table 3. Toldra et al. [86] studied the effectsof temperature and HRT on the treatment of low-strength dairywastewater (0.2–0.5 g COD L−1) in an AFBR. They reported thatreducing temperature from 35◦C to 20◦C decreased COD removalefficiency between 10 and 25%; however, the reactor performancegradually increased with the increasing of HRT from 0.083 to0.33 d. Borja and Banks [23] changed pH, temperature and OLRand monitored the AFBR performance for the treatment of ice-cream wastewater at constant HRT of 0.33 d. Increasing of organicloading by stepwise increment of influent COD concentration short-ened start-up duration while changes in operational parametersdecreased pH and alkalinity. Reduction in pH decreased removal ofsuspended solids and COD, and biogas production; however, reac-tor recovered within 0.25–0.67 d upon restoring normal conditions.The reactor achieved the highest COD removal of 94.4% at OLR of15.6 kg COD m−3d−1.