Tertiary treatment alternatives to achieve nitrogen and phosphorus removal from wastewaters

Many wastewater treatment plants in the UK will be required to achieve removal of both nitrogen and phosphorus in order to meet their consent obligations under the EC Freshwater Fisheries Directive and the Water Framework Directive. Where possible Water Companies will attempt to deliver these consent requirements using biological nutrient removal techniques. However wastewater in the UK is very weak and rarely contains adequate carbon to deliver both nitrogen and phosphorus removal by this mechanism. Indeed for many treatment plants there is inadequate carbon over the whole of the winter period and additionally during storm events over the summer period. Chemical dosing can be used either to supplement the available carbon (generally as acetate to achieve phosphorus removal or methanol for nitrogen removal) or as ferric to precipitate phosphorus. However both of these techniques are seen as unsustainable and thus more environmentally benign techniques are required. This paper will examine some of the more novel techniques currently being trialled in the UK at both laboratory and full-scale and these include the applications of recycled glass as a filter medium and a range of naturally occurring minerals that demonstrate phosphate adsorption properties.