Evaluation of using fine grain size Polonite® as sorbent for retaining phosphorus from wastewater.
Abstract: To avoid eutrofication and excessive algal bloms it is necessary to reduce the phosphorus contents in wastewater. Previous wastewater treatment systems often have a good process for phosphorus reduction but in general not the ability to recycle the material and phosphorus for further utilisation after its use in wastewater treatment. Polonite® is a material with large content of calciumoxide which makes it very reactive and an effective sorbent of phosphorus. It has also been stated that when loaded with nutrients like phosphorus, Polonite® can be used as fertilizer for plants. In this thesis a prototype developed by Bioptech AB was tested to see if it can remove phosphorus from wastewater with fine grain size Polonite® as sorbent and then retain the phosphorus loaded Polonite® for further use, for example as fertilizer in agriculture. Unlike previous wastewater treatment systems the used material och retained phosphorus would then be recycled. If this can be achieved it would complete the environmental cycle for phosphorus which is important for a sustainable and healthy ecosystem. The prototype was setup at the wastewater treatment plant in Skokloster, north of Stockholm. The prototype is developed so that it first can create the right circumstances for Polonite® to come in contact with the wastewater and reduce fosfor contents. Then it can retain the used material for further use by separating it from the solution. Separation is made with a drumfilter and sedimentationtank. The wastewater was taken from after the mechanical and biological treatment since tests in the laboratory indicated that the process could be interfered and less effective with high BOD and organic matter. As expected high pH was necessary to get a succesful reduction of phosphorus. When pH is over 10, the reduction of phosphorus is more then 95% after 5 minutes. 4kg Polonite®/m3 had to be added for these results. The sorption capacity for this amount is more than sufficient. The process needs to be more effective, to much material is needed to get good reduction of phosphorus besides the fertilizer potential can probably not be guaranteed with so little phosphorus attached to the Polonite®. The outgoing water was checked for Polonite® material and the retention was assumed to be over 90%. Even better retention could be achieved with a larger sedimentation tank and smoother outlet of the water stream.
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