habitat for bacteria to attach and grow to assimilate
the colloidal/soluble BOD
5 remaining in wastewater (Sooknah, 2000). The average removal
efficiency of BOD5 in the hydrilla unit (45-51%)
was lower than in the lotus unit (63-79%). This
occurrence might be the effect of higher suspended
solids (algae) in the hydrilla unit. Excessive amount
of algae, which is accepted as organic matter, could
contribute to the higher BOD5 in effluent (Kim and
Kim, 2000). BOD
5 removal efficiency was also a
function of hydraulic retention time. The longer
hydraulic retention time increased the interaction