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Land application of biosolids accounts for some 50% of the total biosolids generated in the USA. Current land application regulations concerning nutrient loads apply to nitrogen (N). Phosphorus (P)-management plans for biosolids application appear to be imminent and, if instituted, would further restrict biosolids loading. Biosolids P contents will most likely increase from their current values because nutrient removal wastewater treatment plants are becoming more widespread and both the chemical and the biological removal of P from wastewater conserves the P in the biosolids. Using literature data this paper shows that the leachability/availability of P in biosolids and biosolids/soil mixtures is a function of the ratio of P to aluminum (Al) and iron (Fe) i.e., to the molar ratio [P]/([Al] + [Fe]). When this molar ratio is <1,P is poorly available and leachable. This relationship applies to a wide range of biosolids and to inorganic fertilizer. These findings raise questions concerning the total environmental impact of P removed from wastewater. Enhanced biological P removal processes are being promoted on their ability to provide P removal without the addition of “chemicals”. This paper shows that the P removed biologically from wastewater is readily leachable from biosolids during land application but that its leachability can be decreased by adding the very “chemicals” that are used for P removal in wastewater treatment plants. This scenario begs the question “Why not just add the chemicals to remove P in the first place?”!

Document Type: Research Article


Publication date: 2000-01-01

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