Large volumes of sludge are produced from onsite sanitation systems in densely populated areas (e.g. slums and emergency settlements) and wastewater treatment facilities that contain high amounts of pathogens. There is a need for technological options which can effectively treat the rapidly accumulating sludge under these conditions. This study explored a pilot-scale microwave (MW) based reactor as a possible alternative for rapid sludge treatment. The reactor performance was examined by conducting a series of batch tests using centrifuged waste activated sludge (C-WAS), non-centrifuged waste activated sludge (WAS), faecal sludge (FS), and septic tank sludge (SS). Four kilograms of each sludge type were subjected to MW treatment at a power of 3.4 kW for various time durations ranging from 30 to 240 min. During the treatment the temperature change, bacteria inactivation (E. coli, coliforms, Staphylococcus aureus, and enterococcus faecalis) and sludge weight/volume reduction were measured. Calorific values (CV) of the dried sludge and the nutrient content (total nitrogen (TN) and total phosphorus (TP)) in both the dried sludge and the condensate were also determined. It was found that MW treatment was successful to achieve a complete bacterial inactivation and a sludge weight/volume reduction above 60%. Besides, the dried sludge and condensate had high energy (≥ 16 MJ/kg) and nutrient contents (solids; TN ≥ 28 mg/g TS and TP ≥ 15 mg/g TS; condensate TN ≥ 49 mg/L TS and TP ≥ 0.2 mg/L), having the potential to be used as biofuel, soil conditioner, fertilizer, etc. The MW reactor can be applied for the rapid treatment of sludge in areas such as slums and emergency settlements.@en

Management of sludge is one of the most pressing issues in sanitation provision. The situation is especially complex when large quantities of fresh sludge containing various contaminants are generated in onsite sanitation systems in urban slums, emergency settlements and wastewater treatment facilities that require proper disposal of the sludge. The application of fast and efficient sludge management methods is important under these conditions. This study focuses on addressing the existing challenges and gaps in sludge management, particularly the management of faecal sludge that is generated in the densely populated areas, through innovative concepts and technological development. To assess the current status of decentralized management of faecal sludge, a review of the existent (emergency) sanitation practices and technologies was conducted. In the study, the gaps and opportunities in technological developments for sanitation management in complex situations was identified. The need for an innovative sludge management system led to the development of the “emergency sanitation operation system, eSOS”. This concept proposed and demonstrated the application of modern innovative sanitation solutions and existing information technologies for sludge management. In addition, as a component of the eSOS concept, a sludge treatment system based on microwave irradiation technology, which forms the core of this research, was developed and tested. The microwave technology study was carried out in two stages. The first stage involved preliminary and validation tests at laboratory scale using a domestic microwave unit to assess the applicability of the microwave technology for sludge treatment. Two sludge types, namely blackwater sludge, extracted from highly concentrated raw blackwater stream, and faecal sludge, obtained from urine diverting dry toilets, were tested. The results demonstrated the capability of the microwave technology to rapidly and efficiently reduce the sludge volume by over 70% and decrease the concentration of bacterial pathogenic indicator E. coli and Ascaris lumbricoides eggs to below the analytical detection levels. Basing on these results, a pilot-scale microwave reactor unit was designed, produced and evaluated using waste activated sludge, faecal sludge, and septic sludge, which formed the second stage of the study. The results demonstrated that microwave treatment was successful to achieve a complete bacterial inactivation like in the laboratory tests (i.e. E. coli, coliforms, staphylococcus aureus, and enterococcus faecalis) and a sludge weight/volume reduction above 60%. Furthermore, the dried sludge and condensate had a high energy (≥ 16 MJ/kg) and nutrient contents (solids; TN ≥ 28 mg/g TS and TP ≥ 15 mg/g TS; condensate TN ≥ 49 mg/L TS and TP ≥ 0.2 mg/L), having the potential to be used as biofuel, soil conditioner, fertilizer, etc. Overall, in this study the existence of a wide range of regular onsite and offsite sanitation options was revealed that have the potential to be applied for sludge management in the emergencies. Situations with more or less similar characteristics to emergencies such as urban slums can also benefit from these technologies. In addition, the shortfalls experienced in the many current emergency sanitation responses were associated with the often used conventional fragmented approach that does not capture the entire sanitation chain, but rather looks at the individual components separately with emphasis on the containment facilities. An innovative emergency Sanitation Operation System (eSOS) concept was thus introduced in this study that uses and promotes a systems approach integrating all components of an emergency sanitation chain. Furthermore, the study demonstrated that a microwave technology based reactor can be applied for the rapid treatment of sludge in the areas where large volumes of sludge are generated such as slums and emergency settlements. @en