Characterisation of Particulate Matter in Municipal Wastewater

摘要

In the 'average' wastewater fractionation, the percentage of oxygen consuming components related to the theoretically determined settleable particle fraction is low, with a maximum of 21% for COD. A major part of BOD (44%), COD (38%) and phosphorous (35%) is present in suspended and supra-colloidal particle fractions with particle diameters between 1.2 and 63μm. For nitrogen, only 4% can be related to settleable particles and 13% to colloidal and suspended fractions; that leaves 83% of the nitrogen present in soluble form. By means of wastewater fractionation, the effect and applicability of a certain physical-chemical particle removal technique, the so-called 'pre-treatment potential' of a specific wastewater, can be derived. In addition, energy and cost calculations show the importance of particle removal in the pre-treatment down to approximately 5 to 1μm, depending on the wastewater, to save energy and costs in the total wastewater treatment system. From wastewater fractionation experiments, the primary effluent composition and the amount and composition of the produced primary sludge for a specific wastewater could be derived. The specific coagulant or flocculant dosage to gain the most efficient particle removal in the pre-treatment can be determined by wastewater fractionation based on particle size and could be controlled by turbidity-related dosing of organic polymers and online particle size counting. The applied testing procedure was promising and should be carried out on a broader scale. More advanced (online) sampling, separation, fractionation and analysing techniques should be implemented to optimise the fractionation and characterisation tests.