Effects of percolate impounding. Based on the experimental results during Phase 2b to 3b (Table 4),
it can be noticed that the percolate impounding in CW units could achieve significant effect on N
removal, rather than the removals of solid and organic matters. The low NO3 concentrations were
observed in the impounded percolates than in the non-impounded ones (Table 4). Impounding could
likely lead to anaerobic conditions in the percolate and, hence, possibly allows denitrification
reactions in the CW units. Impounding for for12 days resulted in the highest TKN and NH3
removals (amounting to 94% and 92%, respectively), as well as in the lowest percolate NO3
concentrations. Nevertheless, a 12-day impoundment is not compatible with a once-a-week septage
loading practice. Therefore, a percolate impounding period of 6 days was finally chosen as the
appropriate operation, still guaranteeing satisfactory removal efficiencies (TKN: 91% and NH3:
85%). Moreover, average NO3 concentrations in the CW percolate at the impounding period of 6
days was only 36 mg/L, as compared to 50 and 106 mg/L for the beds subjected to 2 and 0 days of
impoundment, respectively. Percolate impounding had insignificant effects on TS and TCOD
removal efficiencies, probably because the filtering capacity of the CWs remained unaffected and
biodegradation of organic constituents was modest anyway. The effluent SS concentrations of the
CW units at impounding periods of 6 and 12 days were slightly lower than those obtained from a 0
or 2-day impounding, likely due to the better settleability of suspended particles within the filter
media.
Effects of percolate impounding. Based on the experimental results during Phase 2b to 3b (Table 4),it can be noticed that the percolate impounding in CW units could achieve significant effect on Nremoval, rather than the removals of solid and organic matters. The low NO3 concentrations wereobserved in the impounded percolates than in the non-impounded ones (Table 4). Impounding couldlikely lead to anaerobic conditions in the percolate and, hence, possibly allows denitrificationreactions in the CW units. Impounding for for12 days resulted in the highest TKN and NH3removals (amounting to 94% and 92%, respectively), as well as in the lowest percolate NO3concentrations. Nevertheless, a 12-day impoundment is not compatible with a once-a-week septageloading practice. Therefore, a percolate impounding period of 6 days was finally chosen as theappropriate operation, still guaranteeing satisfactory removal efficiencies (TKN: 91% and NH3:85%). Moreover, average NO3 concentrations in the CW percolate at the impounding period of 6days was only 36 mg/L, as compared to 50 and 106 mg/L for the beds subjected to 2 and 0 days ofimpoundment, respectively. Percolate impounding had insignificant effects on TS and TCODremoval efficiencies, probably because the filtering capacity of the CWs remained unaffected andbiodegradation of organic constituents was modest anyway. The effluent SS concentrations of theCW units at impounding periods of 6 and 12 days were slightly lower than those obtained from a 0or 2-day impounding, likely due to the better settleability of suspended particles within the filtermedia.
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