This licentiate thesis addressesphosphorus release from sewage sludge, which is the first stepin phosphorus recovery. The concept ofphosphorus recovery maybe seen as a part of sustainable sludge handling in that it isa means of recycling resources without supplying harmfulsubstances to humans or the environment. Independent of whichdirection the future development in the water and wastewatersector turns, phosphorus recovery as a part of the wholewastewater system is presumably to be included.
In order to obtain moreinformation about different ways of phosphorus release fromsewage sludge experiments have been carried out. The results ofthe experiments on phosphorus release using acid and base arepresented. Fractionation of sludge is an important step torelease different components from the sludge, includingphosphorus. With the addition of acid, a large fraction of theinorganic material can be dissolved, and thereby also sludgebound phosphorus compounds. In particular, fractionation byusing acid treatment on digested sludge releases a considerableamount of phosphorus.
The method of phosphorus removalin a conventional wastewater treatment plant has an impact onthe chemicals required for phosphorus recovery. A comparison oftechnology for the phosphorus recovery systems is highlydependent on the composition of the sludge, which is the rawmaterial for recovery of phosphorus, and different localconditions.
The results of the performedexperiments concerning chemical demand for phosphorus releaseare compared with calculations based on a study of chemicaldemand of different technology systems for phosphorus recoveryat present operational conditions at Henriksdal wastewatertreatment plant. Overall, experiment and theory seem to be ingood agreement. Thermal technology and addition of acid torelease phosphorus lead to high chemical demand. The essentialfactor is the incoming iron content of the sludge, as given asthe quotient iron/phosphorus.
Another possible method torelease phosphorus may be to use supercritical water oxidation,followed by phosphorus recovery. Studies of the Aqua Reciprocess, which uses this principle, have recently begun and theprocess is under development. Experiments have been performedto give information about recovery of phosphorus from sewagesludge, with application to digested sludge from biologicaltreatment and chemical precipitation with iron. Experimentsperformed on sludge residue from supercritical water oxidationare presented in this thesis.
The results show that phosphatewas leached out more easily with acid (hydrochloric acid) atroom temperature than with base (sodium hydroxide), howeverheavy metals show slightly higher leaching percentage with acidthan with base at room temperature. Also, the leachingexperiment showed that the phosphate is leached out before theiron, in both cases. The iron content seems to be leached outto a somewhat greater degree with acid than with base. This maydisturb the further process to obtain a valuable purephosphorus product. The results also indicate that phosphorusis more easily leached out with acid from the sludge residuefrom supercritical water oxidation than from ash viaco-incineration with sewage sludge and household wastes.Supercritical water oxidation followed by phosphorus recoverymay be seen as an option to incineration of sludge andphosphorus recovery from ash.
Keywords:Chemical demand, phosphorus recovery, sludgefractionation, supercritical water oxidation, sustainablesludge handling
Stockholm: Kemiteknik , 2002. , viii, 103 p.
Electrokinetic soil remediation, bentonite, copper, adsorption, electromigration, electroosmosis, pH, potential