Abstract
Anaerobic sludge digestion is an important tool for converting sludge into a renewable fuel - biogas. However, digested sludge can also be used as a fuel, and a fundamental parameter determining the energy value of digested sludge is as effective as possible dewatering. The main aim of the presented study was to evaluate how the anaerobic digestion (AD) technology and post-treatment technology can affect sludge dewaterability. Two technological alternatives of AD were evaluated: mesophilic (MAD) and thermophilic (TAD). In addition, also the effect of postaeration of digested was evaluated. The dewaterability was assessed using two methods based on centrifugation and filter pressing. Finally, the sludge cake concentration of total suspended solids (TSS) was compared. The results showed the difference in sludge dewaterability for the tested sludges: The sludge cake concentration was similar or slightly higher for MAD compared to TAD sludge. Post-aeration of digested sludge increased sludge cake concentration.
Highlights
The importance of sludge dewaterability as a crucial qualitative parameter of stabilized sludge is growing simultaneously with growing application of thermal processes such as drying, incineration, pyrolysis etc. in the sludge management of wastewater treatment plants
Thermophilic anaerobic digestion (TAD) In the first period of experiments, the standard condition of the centrifugation dewatering method was examined in more detail
Sludges were collected at different WWTPs with both mesophilic and thermophilic anaerobic stabilization
Summary
The importance of sludge dewaterability as a crucial qualitative parameter of stabilized sludge is growing simultaneously with growing application of thermal processes such as drying, incineration, pyrolysis etc. in the sludge management of wastewater treatment plants. The importance of sludge dewaterability as a crucial qualitative parameter of stabilized sludge is growing simultaneously with growing application of thermal processes such as drying, incineration, pyrolysis etc. From practical point of view it is important that the dewaterability brings an information about extent of water removable from sludge by mechanical processes because the energy requirements related to water removal by thermal processes (water evaporation) are much higher in comparison with mechanical processes (pressing, centrifugation, etc.). Any improvement of sludge dewaterability can have big effect on energy balance of the sludge management. Temperature is often reported parameter affecting properties of the sludge as regards dewaterability the conclusions are sometimes contradictory [8-10]. Some papers even shown that temperature and thermal history of sludge can affect irreversibly the rheological properties of sludge [11]
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