Phosphorus removal in laboratory-scale unvegetated vertical subsurface flow constructed wetland systems using alum sludge as main substrate

摘要

This research has two eventual goals: (1) To optimize performance of subsurface constructednwetlands for removal of phosphorus (P) (2) To demonstrate that dewatered alum sludgen(a by-product), can be reused as a constructed wetland substrate. To achieve these, alum sludgenfrom a water treatment plant was characterized and used as main substrate in four experimentalnvertical sub-surface flow constructed wetland systems treating dairy farm wastewater. Resultsnshow that the alum sludge has suitable hydraulic characteristics (uniformity coefficient ¼ 3.6) fornuse as a substrate, and in the batch studies, up to 48.6mg-P was removed by 1 g of the alumnsludge at a P concentration of 360mg-P/l and a dosage of 5 g/l. Results from the experimentalnsystems highlight the significant P removal ability of the alum sludge. However, the inclusion ofnpea gravel at the infiltrative surface of some of the systems had a negative effect on thenP removal performance. Sequential P-fractionation results show that there was no significantnincrease in the easily extractable P, but for total P, there was significant increase, althoughnthis was found to decrease with depth. This study shows that the novel use of dewaterednalum sludge can bring about high P removal in vertical subsurface flow constructednwetland systems.