Abstract
This study compared the dewatering properties of aerobic granular and activated sludge from full-scale wastewater treatment plants, and determined how polymer dose and type affect granular sludge dewatering efficiency. At the same dose, granular sludge filtration cake had about 4% lower humidity than activated sludge cake. Aerobic stabilization improved only activated sludge dewatering. The granular sludge reactor had over 1.5 times more extracellular polymeric substances (1.8 times more alginate) per reactor volume than the activated sludge reactor, but the high polymer content did not decrease granular sludge dewatering. Granular sludge dewatered best with FLOPAM EM 840MEB, due to its composition (n-alkanes, isoalkanes, cyclic/aromatic hydrocarbons). With this polymer, sludge cake moisture was lowest (84.7 ± 0.4%) at 1.6 g polymer/kg MLSS. With all tested polymers, the lowest dose (0.2 g/kg MLSS) ensured low cake humidities; this dose was far lower than typical doses for activated sludge dewatering. Upgrading from activated to granular sludge technology significantly facilitates excess sludge management.
Highlights
Dewatering of excess sludge has attracted much attention because it substantially affects the final volume of sludge before storage and transportation, and it diminishes the amount of bulking agents that are added during composting or energy usage for drying or incineration of sludge
granular sludge (GS) is a consortium of microorganisms aggregated in compact spherical shapes, while activated sludge (AS) consists of loosely connected clusters of bacteria
During dewatering of raw AS, the specific resistance to filtration (SRF) was an order of magnitude higher than during dewatering of raw GS this difference was smaller with aerobically stabilized sludge
Summary
Dewatering of excess sludge has attracted much attention because it substantially affects the final volume of sludge before storage and transportation, and it diminishes the amount of bulking agents that are added during composting or energy usage for drying or incineration of sludge. The low dewaterability of excess sludge means that capital and operating costs may account for up to 60% of the total costs of wastewater treatment (Wang et al 2017). The most commonly used type of biomass in sewage treatment systems is activated sludge (AS), but this is being. Extracellular polymeric substances (EPS) secreted by bacteria play an important role in building the skeleton and ensuring the integrity of the granules (Adav et al 2008), and determine sludge properties such as surface charge or hydrophobicity (Ruiz-Hernando et al 2013). EPS in biomass can be separated into two main fractions: soluble EPS (SOLEPS) and bound EPS (Yu et al 2008). SOL-EPS can move freely between the flocs and the surrounding solution, while bound EPS form a separate layer coating the biomass. Bound EPS can be further divided into loosely bound (LB-EPS)
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