Treatment of agricultural wastewater in a pilot-scale tidal flow reed bed system

Tidal flow reed bed treatment is a process consisting of alternately fillin g and draining the bed matrix with wastewater. During the draining process, air is positively drawn from the atmosphere into the bed so the aeration o f the system is significantly improved A pilot-scale tidal flow reed bed sy stem was studied for the treatment of agricultural wastewater, which was pr epared by diluting pig slurry. At an average influent BOD5 of 649 mg l(-1) and ammoniacal-nitrogen of 333 mg l(-1), the BOD5, COD, SS and PO4-P levels were reduced by 71.0, 58.3, 65.2 and 38.7%, respectively. The removals of BOD5 COD, SS and PO4-P increased with their influent strengths in straight line correlations. The NH4-N was reduced by only 13.3% through the system; 69.0% of this removal resulted from nitrification into NO2-N and NO3-N, whe reas 31% of the removal was due to other processes. The average oxygen cons umption rate in this tidal flow system reached 203 gO(2) m(-2) d(-1), signi ficantly higher than the rates obtainable in horizontal flow and downflow r eed beds. The rhythmical air and water movement in the tidal flow system en hances the oxygenation ability of the beds and improves the efficacy of uti lisation of the available bed volume. Accordingly, tidal flow reed beds app ear to have much potential as initial treatment stages for small amounts of strong waste effluents where the bulk of the BOD5 removal can take place.