Table 4 illustrates the average concentration and removal
efficiency of nutrients (N and P) in grey water treatment in the
UASB reactor. The results indicated that the grey water had a
limited amount of nitrogen, which was mainly in particulate
form (80–90%), while in the black water and domestic wastewater
most of the nitrogen is soluble as NH4. The concentration
of phosphorous in grey water was almost similar to that
in the domestic wastewater (6.8–8.6 mg total-PO4-P/L for
Dutch municipal wastewater, Elmitwalli et al., 2002a, b). The
UASB reactor removed only the particulate nutrients by
sedimentation and filtration and, therefore, it had relatively
low removal of nutrients (Aiyuk et al., 2004). At the longest
HRT (16 h), the NH4 and ortho-P had a negative removal due to
hydrolysis of particulate N and P, respectively