Control of phosphorus discharges: present situation and trends

Abstract

The dominating sources of phosphorus in municipal wastewaters are excreta, 1.4 g P/(cap.d) and detergents, 0.6 -2 g P/(cap.d). Detergent phosphorus can ba substituted by nitrilotriacetic acid or zeolites, but if a substantial reduction of phosphorus in municipal waters is to be achieved, modifying the treatment process is necessary. Primary, treatment by sedimentation removes only 10-15x and secondary biological treatment 20-30 y0 of the phosphorus in waste water. If chemicals are added to the primary or secondary treatment stage or to a separate chemical stage, phosphorus can be efficiently removed. An effluent level of 0.8-1.5 g P me3 is easily achieved and with a filtration step it is possible to maintain 0.2 g P m-3 in the effluent. Different process configurations are discussed. As precipitants, ferrous and ferric salts, alum and lime are widely used. By introducing anaerobic zones in the activated sludge process, it is possible to promote the growth of bacteria which enhance biological phosphorus uptake. This makes it possible to achieve high phosphorus removal without or, al least, with very small chemical additions. Several emerging physical, chemical and biological phosphorus removal processes are discussed. The removal of phosphorus to a level of 0.8-1.5 g P m-3 increases cost lo-20% compared with conventional primary secondary treatment. Higher removal efficiencies will rapidly increase the marginal cost per marginal kg P removed.

Exploring global nitrogen and phosphorus flows in urban wastes during the twentieth century

“…[2] Although urban areas cover only a fraction of the global land area, urban activities dramatically alter regional and global nitrogen (N) and phosphorus (P) cycles [Svirejeva-Hopkins et al, 2011;Van Drecht et al, 2009]. Urban wastewater is emitted as point sources with large nutrient loads from excreta from humans and animals, P-based detergents, and waste generated by industries [Balmer and Hultman, 1988;Billen et al, 1999;Billen et al, 2012;Li et al, 2012;Nyenje et al, 2010;Quynh et al, 2005]. Since preindustrial times, river N export to the North Atlantic Ocean increased by a factor 2 to 20 [Howarth et al, 1996] as a result of increasing diffuse agricultural [Howarth et al, 1996;Liu et al, 2012;Némery et al, 2005;Quynh et al, 2010] and urban pointsource emissions [Barles and Lestel, 2007;Billen et al, 1999;Van Drecht et al, 2009].…”

“…[5] As opposed to diffuse agricultural nutrient emissions, nutrients can be partly removed from urban wastewaters if sewer connection and adequate treatment facilities are present [Balmer and Hultman, 1988;Rabalais et al, 2010]. However, currently, only few countries have adequate treatment facilities [UNEP, 2010], and negative effects of surface water eutrophication increased during the last few decades, especially in densely populated areas [Hallegraeff, 2003;Lewitus et al, 2012;Zhang et al, 2010].…”