PHOSPHORUS AVAILABLE FOR PLANT UPTAKE IN SEWAGE SLUDGE - A LITERATURE SURVEY / Växttillgänglig fosfor i avloppsslam - en litteraturstudie
Re-use options for sewage sludge are being developed since the disposal of sludge is becoming an increasing problem. The spreading of sewage sludge on agricultural fields as a phosphorus (P) fertiliser is one such option given that it fulfils the requirements for limitation values for metals/toxic substances. The plant availability of P in sludge has therefore been in focus in different ways. Different analysis techniques (chemical extraction methods, isotope exchange methods and pot/field experiments) have been used to determine P in sludge. These analysis techniques were found to be one reason for considerably differences in the fertilizing value of sludge compared to commercial P-fertilisers. Other factors causing this difference were differences in sludge origin and
sludge treatment in the wastewater treatment plant (choice of precipitation chemical, stabilisation and de- watering methods). It was concluded that fresh sludge appeared to have higher concentrations of plant available P than dried sludge and that chemically Ca-precipitated sludge had a higher value than Al- or Fe-precipitated sludge. Factors such as soil pH and presence of mycorrhiza were also concluded to affect the amount of P
assimilated by plants. Finally, it was concluded that many people agree that sewage sludge is a valuable source of P.