Two strategies for improving animal farm wastewater treatment in reed beds.

In this study, dewatered alum sludge cakes were used as substrate in a laboratory scale tidal vertical flow reed bed system treating animal farm wastewater. Tidal flow operation was employed to enhance oxygen transfer into the system while dewatered alum sludge cake was used to enhance phosphorus (P) removal through ligand exchange. Except for the removal of P which was consistently high throughout the experiment, the removal of organics (BOD5, COD) exhibited a trend of gradual and increasing removal and this highlights the benefits of using dewatered alum sludge cake in the reed bed. For the removal of organics, a mean removal percentage of 82.3 +/- 3.5% was obtained for BOD5 at a mean loading rate of 84.6 g/m2.d. The first-order kinetics constant for BOD5 removal (K(BOD), m/d) obtained was about 9 times the rate constant commonly obtained in conventional horizontal flow systems. The mean level of dissolved aluminium (Al) monitored in the effluent was 0.04 +/- 0.01 mg/1 and this is well below the discharge limit of 0.2 mg/l for Al discharge into all waters.