Evaluation of a pilot microwave based reactor unit for faecal sludge treatment in emergency situations

This document presents the development of a research approach focused on the evaluation of the operational condition of a microwave (MW) based reactor unit for faecal sludge (FS) treatment in emergency situations. As a result of the negative impacts caused by natural and man-made disasters in the public health temporary sanitation solutions are mostly installed. It involves the rapid generation of FS that requires an effective treatment to minimize the potential risk of pandemics and diseases spread during the emergency situations. Later, in the emergency recovery phase other sludge types can be generated as septage and sewage sludge due to the extension of the onsite facilities. In any event, the treatment is necessary and prioritized. The need of FS treatment was addressed with the positive laboratory scale results using MW radiation to sanitize and reduce its volume. Hence, the MW properties were further investigated in this study by the design and production of a new pilot MW reactor unit with a maximum input power of 3.4 KW and an initial volumetric capacity of 200 L. The unit was subjected to a variety of test and improvements to find its optimal operational conditions, namely effective volume and mixing settings (continuous or pulsed recirculation) treating different media types. Experiments were divided into two phases. The first preliminary study included the evaluation of the mixing system using tap water and industrial wastewater. The second phase contemplated the analysis of a recirculation system by pumping and two internal reactor modifications (fixed plate and mechanical bar mixer). This stage was tested with raw wastewater; waste activated sludge (WAS), septic sludge and centrifuged waste activate sludge (C-WAS). The MW reactor was assessed regarding its efficiency in volume reduction, pathogen removal and organic matter stabilization in function of variables as contact time and temperature evolution. Subsequent, the feasibility of the unit was compared to other technologies regarding to energy consumption. Under experimental conditions, it was determined a successful operation of the MW reactor unit treating 60 L of C-WAS (10-12% water content) and a capacity of 100 L for samples with high water content (> 97% w.). Both results were achieved while being mixed by screw rotation and continues recirculation by pumping, respectively. The pilot MW reactor unit was also capable of inactivating faecal pathogens (E. coli and coliforms), and another studied organism (Staphylococci, Enterococci and Pseudomonas Aeruginosa) after 4 hours of contact time. Conversely, the unit accomplished a slim volumes reduction in samples with high water content and promising values for a reduction in more dehydrated trials (from 50 to 62 %). The VS/TS ratio kept stable through experiment and it was an increment of COD in the samples with more water content fleeing into the vapour phase. The energy demand rounded about 4-9 kWh per litre of evaporated water in the dewatered samples being considered high for a process aimed to dry. Finally, it was established that the MW reactor unit needs deeper studies with real FS media and further test with more resistant pathogen related. Moreover, for condition operation improvements a particular increment of the MW input power is necessary to achieve rapid temperature increment and shorter contact times. Also, the condensate requires the suitable system for the optimal heat exchange and better measurement production and analysis