Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands; Department of Water Supply, Sanitation and Environmental Engineering, IHE-Delft Institute for Water Education, Westvest 7, 2611 AX Delft, the Netherlands; Tehnobiro d.o.o., Heroja Nandeta 37, 2000 Maribor, Slovenia.
Department of Water Supply, Sanitation and Environmental Engineering, IHE-Delft Institute for Water Education, Westvest 7, 2611 AX Delft, the Netherlands.
Sci Total Environ. 2020 Nov 10;742:140541. doi: 10.1016/j.scitotenv.2020.140541. Epub 2020 Jun 27.
Sewage sludge management and treatment can represent up to approximately 30% of the overall operational costs of a wastewater treatment plant. Microwave (MW) drying has been recognized as a feasible technology for sludge treatment. However, MW drying systems exhibit high energy expenditures due to: (i) unnecessary heating of the cavity and other components of the system, (ii) ineffective extraction of the condensate from the irradiation cavity, and (iii) an inefficient use of the microwave energy, among others issues. This study investigated the performance of a novel pilot-scale MW system for sludge drying, specifically designed addressing the shortcomings previously described. The performance of the system was assessed drying municipal centrifuged wasted activated sludge at MW output powers from 1 to 6 kW and evaluating the system's drying rates and exposure times, specific energy outputs, MW generation efficiencies, overall energy efficiencies, and specific energy consumption. The results indicated that MW drying significantly extends the duration of the constant rate drying period associated with the evaporation of the unbound sludge water, a phase associated with low energy input requirement for evaporating water. Moreover, the higher the MW output power, the higher the sludge power absorption density, and the MW generation efficiency. MW generation efficiencies of up to 70% were reported. The higher the power absorption density, the lower the chances for energy losses in the form of reflected power and/or energy dissipated into the MW system. Specific energy consumptions as low as 2.6 MJ L (0.74 kWh L) could be achieved, well in the range of conventional thermal dryers. The results obtained in this research provide sufficient evidence to conclude that the modifications introduced to the novel pilot-scale MW system mitigated the shortcomings of existing MW systems, and that the technology has great potential to effectively and efficiently drying municipal sewage sludge.
污水污泥管理和处理的费用约占污水处理厂总运营成本的 30%。微波（MW）干燥已被认为是一种可行的污泥处理技术。然而，MW 干燥系统由于以下原因表现出高能耗：（i）腔室和系统其他部件的不必要加热，（ii）从照射腔室中提取冷凝水的效率低下，以及（iii）微波能量的使用效率低下等问题。本研究调查了一种新型中试规模 MW 系统用于污泥干燥的性能，该系统是专门为解决前面描述的缺点而设计的。评估了该系统在 MW 输出功率为 1 至 6kW 时的市政离心废活性污泥的干燥性能，评估了系统的干燥速率和暴露时间、比能输出、MW 产生效率、整体能源效率和比能消耗。结果表明，MW 干燥显著延长了与非结合水蒸发相关的恒速干燥期的持续时间，这一阶段与蒸发水所需的低能量输入要求有关。此外，MW 输出功率越高，污泥的功率吸收密度越高，MW 产生效率越高。报道的 MW 产生效率高达 70%。功率吸收密度越高，以反射功率和/或能量耗散到 MW 系统的形式损失能量的机会就越低。可实现低至 2.6MJ L（0.74kWh L）的比能消耗，远低于传统热干燥器的范围。本研究获得的结果提供了充分的证据，可以得出结论，新型中试规模 MW 系统的改进减轻了现有 MW 系统的缺点，并且该技术具有有效和高效干燥市政污水污泥的巨大潜力。
