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.

Popular Abstract

Wastewater is collected from different household then channeled to the treatment plant where it goes through physical, biological and chemical treatment. Then a by-product is produced from these different process called sludge, which requires further treatment before final disposal.
The sludge undergoes thickening, conditioning and dewatering processes before the final disposal. In the thickening stage, the solids of the sludge are concentrated and the water volume is reduced. The conditioning phase is a process of breaking out the jelly-like layer in the sludge by using chemicals (polymers) or various means. The following step is the dewatering of the sludge.
Sludge dewatering is basically separating the solid and liquid components to minimize the waste. It is important to note that sludge dewatering does not treat the sludge, it only separate the two states for further separate treatment and easier final disposal. Besides that, reducing the volume of sludge corresponds to a reduction of transportation and final disposal costs.
Different technologies are used nowadays for sludge dewatering but to maximize and increase the dewatering efficiency, it is imperative to have more researches studying the composed sludge dewatering properties and evaluate the used method in a small scale. Furthermore, compare this used methods with the results obtained from large scale.
The methodology used for this work are both literature reviewing and conducted experiments in the laboratory. From the literature reviewing, four methods were found which are Electro-dewatering, Osmosis pressure for dewatering, Ultra high pressure and Network strength methods. These methods were then evaluated using different criteria : the time used to conduct the experiment and how comparable the obtained results with the full scale results. The evaluation was based on the available data found in the scientific reports of these methods.
The laboratory work consisted of conducting three methods which are Capillary Suction Time (CST), Centrifuge and Pressure filtration test (PFT). The Capillary suction time method is not a sludge dewatering method but it provides information regarding the ease of separating the water portion from the solid one in the sludge. The Centrifuge performance on the other hand depends on different parameters; intensity, time, type of sludge and the used polymer. The pressure filtration test (PFT) principle is applying pressure on the sludge sample to extract the water from the sludge.
The capillary suction time was measured for the different doses for the two polymers type. As for the centrifuge, different time durations were used with a constant speed to study the effect of the centrifugation timing on the sludge dewaterability. The method were then evaluated based on simplicity of implementation, time required to conduct the experiment, area used in the laboratory and how comparable the results are to the large scale results.
The results and conclusions achieved in this study are tangible proof and indicator to conduct more research in this area. A better understanding of this will lead to improve the way we handle the sludge today and the waste management.

• author: Abdalla, Nadia
• supervisor: Åsa Davidsson
• organization: Chemical Engineering (M.Sc.Eng.)
• course: VVAM01 20181
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: sludge dewatering, sewage sludge, laboratory scale sludge treatment, dewatering sludge, dewatering sewage sludge, CST, capillary suction time test, centrifuge, lab-centrifuge, rheology, polymers conditioning, sludge conditioning, centrifuge on lab scale, evaluation of lab experiments, CST evaluation, mechanical de-watering evaluation, sludge dewatering at lab, lab scale dewatering process, sludge dewatering methods at lab, Chemical engineering, Lab centrifuge, Capillary Suction Time (CST), Mechanical sludge dewatering evaluation, Polymers conditioning of sludge, sewage sludge dewatering, methods for sludge dewatering at lab, water engineering, environmental engineering, vattenförsörjningsteknik, avloppsteknik
• report number: 2019-01
• language: English
• additional info: This thesis study discusses several methods used for sludge dewatering at lab scale and evaluating these different methods. Further work is recommended for more in-depth understanding on this subject.
• id: 8969709
• date added to LUP: 2019-02-22 15:13:21
• date last changed: 2019-02-22 15:13:21