Evaluating the performance of microwave sludge treatment : A comparison with conventional sludge treatment technologies

This document presents the results of a study for assessing the efficiency of a novel pilot-scale MW system, developed for the treatment of different types of sludges. The aim was to demonstrate if this technology can compete with those that are currently in high use in the 27-European countries. MW system is the main part of Shit killer®, a technology that has developed recently as a semi-centralized, mobile, and containerized technology for sewage, septic, and fecal sludge treatment and includes a set of highly advanced technologies for sludge treatment; mechanical pre-treatment, microwave irradiation, membrane separation, air treatment, solar energy conversion, and combustion of sludge. Pathogen removal in this technology is achieved by MW irradiation of sludge and so this technology is named Shit Killer®. The goal of this invention is to provide a robust technology for sanitizing and drying sludge in addition to producing highly treated, reusable permeate and condensate water in both on-site and off-site sanitation systems. For this purpose, the data for sludge treatment using the mentioned MW system were collected from the literature. Then 14 scenarios were defined in a way that results can be compared between the MW system performance and current technologies for sludge treatment. First, two sludge stabilization processes, anaerobic and aerobic sludge digestion, were defined for the treatment of three types of pre-thickened sewage sludges; primary, secondary, and a mixture of primary and secondary sludges. The quality of influent sludge was extracted from the reference books and literature and included COD, VS, TS, fecal coliforms, TN, NH4 content, and calorific value of sludge. The quantity of the influent sludge for each scenario was defined to be 1000 kg TS per day. The quality of the treated sludge with respect to heavy metals and fecal coliforms was not calculated but was collected from the literature. The consumed/produced energy for sludge digestion was calculated using the developed models in the literature. Reduction in the volatile and total solids of sludge, and also in COD were calculated using mass and energy balances by considering the factors and fractions extracted from literature. In some cases, assumptions were made. Then the results for centrifuge dewatering proses were calculated using specific gravities of volatile and fixed solids in sludges and mass balances. The energy consumption of centrifuge was extracted from literature. The required energy for sludge drying using a rotary drum dryer and MW system was calculated by mass and energy balances, thermodynamic tables, psychrometric charts, and calculating the volume of evaporated water. The next step involved making a comparison between different scenarios with respect to their energy consumptions per kg initial mass of sludge, sanitization performance, and the quality of traded sludge and produced condensate. The results showed that integrating an MW system to sludge treatment train makes it able to produce a class A biosolid with the expense of significantly lower energy than applying a conventional sludge dryer in train