Evaluation of a microwave based reactor for the treatment of blackwater sludge

Abstract

A laboratory-scale microwave (MW) unit was applied to treat fresh blackwater sludge that represented fecal sludge (FS) produced at heavily used toilet facilities. The sludge was exposed to MW irradiation at different power levels and for various durations. Variables such as sludge volume and pathogen reduction were observed. The results demonstrated that the MW is a rapid and efficient technology that can reduce the sludge volume by over 70% in these experimental conditions. The concentration of bacterial pathogenic indicator E. coli also decreased to below the analytical detection levels. Furthermore, the results indicated that the MW operational conditions including radiation power and contact time can be varied to achieve the desired sludge volume and pathogen reduction. MW technology can be further explored for the potential scaling-up as an option for rapid treatment of FS from intensively used sanitation facilities such as in emergency situations.

Microwave treatment of faecal sludge from intensively used toilets in the slums of Nairobi, Kenya

“…in sludge drying beds), anaerobic co-digestion with organic solid waste, and co-treatment in wastewater treatment plants (Ingallinella et al., 2002, Katukiza et al., 2012, Ronteltap et al., 2014). However, they are mostly suited for regular sanitation contexts and have limitations such as slow treatment processes, large land space requirements, among others (Mawioo et al., 2016), which hinder their application to situations with unusually high rate of FS generation. Consequently, there is need to develop FS treatment technologies that are more appropriate for conditions such as those prevailing in slums and emergencies.…”

“…A microwave (MW) based technology can be a viable option for the treatment of fresh FS from intensively used toilet facilities as it has been shown being regarding the efficient pathogen inactivation and volume reduction (Mawioo et al., 2016). MW irradiation uses the MW energy (E MW ) with wavelengths between 1 mm and 1 m and frequencies between 300 MHz and 300 GHz in the electromagnetic spectrum (Haque, 1999, Remya and Lin, 2011, Tang et al., 2010).…”

“…The MW technology has been used in various applications, most of which involve the use of heat generation. In such applications, the heat is generated by the molecular motion in the target material resulting from the migration of ionic species and/or rotation of the dipolar species when they interact with the microwaves (Haque, 1999, Mawioo et al., 2016, Thostenson and Chou, 1999). Various benefits are associated with heating by MW (Haque, 1999, Mawioo et al., 2016).…”

“…sludge extracted from a blackwater stream generated in low flush toilets, TS = 12%) contain dipolar molecules (e.g. water and organic complexes) with high loss dielectric properties and have demonstrated a good response to the MW treatment (Mawioo et al., 2016, Yu et al., 2010). For instance, nearly complete bacterial removal was reported when sewage sludge (Hong et al., 2004, Hong et al., 2006) and blackwater sludge (Mawioo et al., 2016) were heated by MW to temperatures above 65 °C.…”

Continuously flow microwave pre-treatment for enhanced anaerobic biodegradability of dairy industry sludge

“…These effects led to intramolecular friction resulted in internal heat generation. The electromagnetic energy interact directly with the components of materials, the medium absorb the energy and convert it into heat (Mawioo et al, 2016). Considering the specific heat generation mechanisms of microwave irradiation, in real and complex medium, such as the wastewater, composition, dielectric properties of compounds, intermolecular interaction, chemical structure of molecules, physicochemical state, temperature, viscosity and density of continuous phase and their possible alteration during irradiation, furthermore the frequency of electromagnetic field has also effect on the thermal efficiency of heating (Holtze et al, 2006).…”