Methods for Evaluating Dewatering Properties of Sewage Sludge

Abstract: After the sewage wastewater is collected from different households and directed to the treatment plants, it goes through several processes, which are physical, chemical and biological. The different processes remove the contaminant, and produce a semi-solid material named sludge. Sludge has a huge amount of liquid. Disposing this sludge with no further treatment is a very costly procedure and presents an environmental hazard. Further treatment of the sludge reduces the liquid volume, and furthermore reduce the transportation cost. However, different techniques are evolving nowadays in large scale, but further investigation is needed of the sludge dewatering properties on the small scale. These laboratory scale methods reliability compared to full scale is a milestone due to lack of knowledge in this area. In this thesis work, attempts were applied to find methods for dewatering the sludge on lab scale, and then evaluate these different methods based on different criteria. The thesis was divided into two part: literature reviewing and laboratory work. From the literature, seven sludge dewatering methods were found: electro-dewatering, dewatering by osmosis, network strength, ultra-high-pressure filtration (UPF), capillary suction time (CST), centrifuge and lastly pressure filtration test. The first four methods were evaluated based on the information found in the literature. The criteria used for evaluating the methods were: time required and how comparable the obtained results are to large scale. The network strength method required around 24 hours until obtaining the results. The method concept was new and gave abundant data about the sludge dewatering properties. For this reason, network strength is considered an interesting method for further studies. The lab work included three methods found in the literature, which were CST, centrifuge and pressure filtration test (PFT). The sludge was firstly conditioned using two type of polymers from Kemira. Then lab-scale dewatering methods were applied. The results were obtained from both CST and centrifuge. The pressure filtration test (PFT) faced some technical difficulties regarding filtrating the sludge sample. The three methods were evaluated based on certain criteria. The criteria used for evaluating the methods used in the lab were: time required, space requirement, simplicity, and the reliability of the results. Based on the evaluation, CST test had a very simple methodology compared with others and consumed less time (few minutes). However, the centrifugation studied the solid content in the supernatant and dry solid content in the obtained sludge cake. These two are important parameters in studying efficiency of the sludge dewaterability. At last, the aim of this thesis work was accomplished. The different methods were evaluated based on certain criteria. The CST test could be recommended due to its simplicity, short time required to conduct the test, easiness and direct obtaining of the results.