A review on sludge dewatering indices

Abstract

Dewatering of sludge from sewage treatment plants is proving to be a significant challenge due to the large amounts of residual sludges generated annually. In recent years, research and development have focused on improving the dewatering process in order to reduce subsequent costs of sludge management and transport. To achieve this goal, it is necessary to establish reliable indices that reflect the efficiency of sludge dewatering. However, the evaluation of sludge dewaterability is not an easy task due to the highly complex nature of sewage sludge and variations in solid-liquid separation methods. Most traditional dewatering indices fail to predict the maximum cake solids content achievable during full-scale dewatering. This paper reviews the difficulties in assessing sludge dewatering performance, and the main techniques used to evaluate dewatering performance are compared and discussed in detail. Finally, the paper suggests a new dewatering index, namely the modified centrifugal index, which is demonstrated to be an appropriate indicator for estimating the final cake solids content as well as simulating the prototype dewatering process.

Removal of Nitrate in Simulated Water at Low Temperature by a Novel Psychrotrophic and Aerobic Bacterium, Pseudomonas taiwanensis Strain J

“…The World Health Organization (WHO) has recommended that the nitrate concentration in drinking water should be lower than 10 mg/L [ 5 ] and the same value was also proposed by China [ 6 ]. Unfortunately, the nitrate concentration was higher than 10 mg/L in numerous aquifers and even exceeded 30 mg/L in some groundwater in China [ 7 – 9 ]. The nitrate remediation, thereby, is a big challenge and has become a matter of great concern in the recent years.…”

Enhancing sludge dewaterability and phosphate removal through a novel chemical dosing strategy using ferric chloride and hydrogen peroxide

“…Thus, the necessity to explore the key factors affecting the conditioning and dewatering performance remains important. Dewaterability rate is the focal point of conventional dewatering indices, including specific resistance to filtration (SRF) and capillary suction time (CST) (Novak, 2006; To, Nguyen, Vigneswaran, & Ngo, 2016). Although SRF is able to predict the cake solid content for sludge with suspended solids concentration higher than 0.5%, its complexity and laborious nature hinder its widespread utilization (To et al, 2018).…”

Novel methodologies for determining a suitable polymer for effective sludge dewatering

“…It is believed that a reliable dewatering index should be established to simulate real water extraction process and estimate the maximum solids content of sludge cake achievable by that process [13]. Most traditional dewaterability measuring techniques, including Capillary Suction Time (CST) and Specific Resistance to Filtration (SRF), often measure the rate of filtration/water removal only.…”

“…Furthermore, it does not represent the full-scale dewatering process. The SRF test, which is quite similar to pressure filters and vacuum filters, can provide cake solids content, but it is time-consuming and complex [13]. Various attempts have been made to identify reliable indicators for sludge dewatering by centrifuge.…”