The TSS removal exceeded the typical 50e65% removal for
conventional primary clarification (WEF, 2007). The TSS removal is
comparable to the highest removals observed with chemically
enhanced primary treatment when chemical addition, flocculation
and settling are employed, range of 60e90% (WEF, 2007), but does
not require chemical addition nor solids wasting. The TSS removal
in the ABR is comparable to the highest removals observed in large
pilot-scale UASB reactors (80e90%), shown in Table 1. The high TSS
removal occurred in systems with a range of HRT (3e54 h) that
received influent COD less than or equal to the ABR. The single and
hybrid UASB reactors with the lowest percent removal of TSS
(41e55%) were operated at influent COD concentrations two times
higher than for this study. The removal of greater than 80% of the