Nitrogen removal in maturation waste stabilisation ponds via biological uptake and sedimentation of dead biomass

摘要

In this work a set of experiments was undertaken in a pilot-scale WSP system to determinenthe importance of organic nitrogen sedimentation on ammonium and total nitrogen removalsnin maturation ponds and its seasonal variation under British weather conditions, from Septembern2004 to May 2007. The nitrogen content in collected sediment samples varied from 4.17% ton6.78% (dry weight) and calculated nitrogen sedimentation rates ranged from 273 to 2868 g N/ha d.nHigh ammonium removals were observed together with high concentrations of chlorophyll-a innthe pond effluent. Moreover, chlorophyll-a had a very good correlation with the correspondingnincrement of VSS (algal biomass) and suspended organic nitrogen (biological nitrogen uptake)nin the maturation pond effluents. Therefore, when ammonium removal reached its maximum,ntotal nitrogen removal was very poor as most of the ammonia taken up by algae was washednout in the pond effluent in the form of suspended solids. After sedimentation of the dead algalnbiomass, it was clear that algal-cell nitrogen was recycled from the sludge layer into the pondnwater column. Recycled nitrogen can either be taken up by algae or washed out in the pondneffluent. Biological (mainly algal) uptake of inorganic nitrogen species and further sedimentationnof dead biomass (together with its subsequent mineralization) is one of the major mechanismsncontrolling in-pond nitrogen recycling in maturation WSP, particularly when environmental andnoperational conditions are favourable for algal growth.