Integration of powdered activated carbon in tertiary disc filtration of wastewater

Abstract: This thesis investigates the feasibility of integrating Powdered Activated Carbon (PAC) in to chemical treatment in combination with disc filtration of tertiary wastewater. Jar and tube tests have been performed, where the suspension was filtered through a 10 μm disc filter from Hydrotech Veolia Water Technologies. The effluent has been analyzed for total phosphorus (TP), total suspended solids (TSS), number of particle per ml and turbidity to evaluate the efficiency of the experiments. The PAC can be used to adsorb micropollutants, which are small organic molecules derived from e.g. pharmaceuticals and hormones which are starting to impose problems in the aquatic environment as many of these are not treated in normal wastewater treatment plants (WWTPs) today. The chemical treatment of water is a two-step process where coagulant in the form of AlCl3 and flocculant as a cationic polymer is added to bind small particles in to bigger agglomer- ates. The PAC, coagulant and flocculant has been added in different orders and with two dif- ferent doses of PAC to examine how this affected the process and what was most benifical in terms of effluent quality. In addition to dosing and order of addition, the PAC’s effect on the wastewater without chemicals and its effect on disc filters were also investigated, showing that PAC itself adsorbs TP and has an accumulative effect on the filter cloth despite being thoroughly cleaned before each filtration. The results were very promising when using 20 mg/l of PAC added either first, after or at the same time as the coagulant, always followed by the flocculant last. Lowering the mixing speed after adding the flocculant also showed a good floc formation and a very clean effluent. The exact order of addition regarding PAC should be deciding after examining its ability to adsorb micropollutants, something that was not investigated in this study. The conclusion is therefore that it is feasible to integrate the addition of PAC in to chemical treatment in combination with Hydrotech’s disc filter, although further research and optimizing should be conducted when applying these experiments in a pilot plant regarding doses and where in the process to add PAC. Since it is shown that PAC can be integrated without disrupting coagulation and flocculation, the plan is to send samples based on experiments produced in thesis to Århus University for analyses on the reduction of micropollutants in the water.