The degradation of organic matter by anaerobic filters can be
associated with the removal of suspended solids (62 24 mg L1
)
and the reaction which takes place with nitrogenous compounds.
In the said research, the effluents from the anaerobic filter had a
concentration of 53.5 mg L1 of TKN (total Kjeldahl nitrogen). Out
of this amount, 95.1% were composed of ammoniacal nitrogen.
After the passage through the sand filters, a great removal of
organic matter could be spotted (Table 2). Even in the most critical
situation studied (800 L m2 day1
), an average BOD of 18 16 mg
L1 and an average COD of 68 49 mg O2 L1 were achieved. With
regard to both BOD and COD, the removal was always greater than
80% compared to the effluents from the anaerobic filter. In turn, the
overall removal of the combined anaerobic filter and sand filter
system reached at least 95%. Prochaska and Zouboulis (2003),
employing 1-meter deep sand columns fed with synthetic
wastewater, achieved efficiencies of COD that ranged from 70 to
80%.