In contrast to the findings of all these authors, Yu et al. [101] report that Ca2+ concentrations
upto only 300 mg/l enhanced granulation in a UASB reactor (operated on a 4000 mg/l COD wastewater) and 500 mg/l or higher inputs of Ca2+ were detrimental to this cause. In UASB reactors set to
generate hydrogen, even 300 mg/l of Ca2+ were found to be ‘overly high’ by Chang et al.