Inactivation kinetics of indicator microorganisms during urea treatment for sanitizing finished compost from composting toilet

Abstract

This study aimed at estimating the sanitizing effectiveness of urea treatment by studying the inactivation kinetics of selected indicator microorganisms. Finished composts from a composting toilet were inoculated with indicator microorganisms and subjected to different urea concentrations (0.5–2% w/w) and temperatures (22, 32 and 42°C). The inactivation kinetics parameters were determined in relation to pH, ammonia content and temperature during treatment time. The results show that urea addition to compost enhanced inactivation of microorganisms. The decline in number of E. coli and Enterococus followed a linear reduction, while that of Ascaris lumbricoides eggs followed a linear reduction plus shoulder. The inactivation rate constants of all microorganisms tested were positively correlated to the increase of NH3(aq) concentration and temperature. The relationship between the inactivation rate of microorganisms, ammonia through urea concentration and temperature were established. Therefore, the best decimal decay of E. coli, Enterococus and A. lumbricoides eggs occurred with 2% w/w urea concentration at 42°C within 0.9, 1.1 and 1.4 days, respectively. E. coli was the most sensitive microorganism to urea treatment, while Enterococcus and A. lumbricoides eggs showed resistance, especially at lower temperatures. Urea treatment has proved to be an efficient option for safe reuse of compost from composting toilets.

Sanitation By-Products Used for Lettuce (<i>Lactuca sativa</i> L.) Production: Quantitative Microbial Risk Assessment

“…The infection risks from soil ingestion and lettuce consumption are very close to one another Lettuce Consumption (n = 52 days) 6.20 × 10 −3 7.24 × 10 −3 for the toilet compost reuse. The mitigation measures could be adopted, such as improved composting process (Urea treatment), limitation in the use of toilet compost (application control), use of personal protection equipment (mask, face shields, shoes, gloves) and behavioral change for farmers (personal hygiene) and consumers (improve washing of produce) along the toilet compost-reuse chain (Strunz et al, 2014;Sossou et al, 2016;Butte et al, 2021). In this order, Butte et al (2021) have reported that these possible mitigation strategies for workers and farmers showed a reduction in monthly risk of 30% -70% from fecal sludge reuse.…”

Using indicators to assess microbial treatment and disinfection efficacy

“…The effectiveness of chlorination is a function of dose, contact time, pH and temperature (Carvajal et al, 2017) Chlorination can be placed at any position during the treatment process; however, it is important to note that organisms entrapped in particles may be shielded from the action of the chemicals. For over 100 years now, chlorination has shown to be more effective in inactivating indicator or model organisms and vanquished the outbreaks of cholera, typhoid, and other waterborne diseases in the developed world by the 1940s (Sossou et al, 2016).…”

“…Chlorine -Chlorine extensively damages the cell membrane by disrupting cell permeability to inactivate microbes, (Sossou et al, 2016). Membrane damage is not the only key event in the inactivation of bacteria by chlorine, by uncoupling of the electron chain or enzyme inactivation either in the membrane or in the cell interior, damage of nucleic acids and repression of gene transcription are also involved in the bactericidal mechanism of chlorine (Virto et al, 2005;Bitton, 2014).…”

Ecological Sanitation Opportunities in Rural Panamá: Effectiveness and Social Implications of Intrinsic Ammonia-Based Treatment for Pathogen Inactivation and Incorporation of Ferrocement Technology

“…The NH 3 molecule has the freedom to travel between this membrane and alkaline properties might raise the internal pH and cause this cell disintegration. This has an added benefit to biosolids or compost in that the process does not consume ammonia, but rather increases its nutrient potential (Sossou, 2016;Fidjeland, 2015;Nordin, 2009).…”