Abstract
The Blue Diversion AUTARKY Toilet is a urine-diverting toilet with on-site treatment. The toilet is being developed to provide a safe and affordable sanitation technology for people who lack access to sewer-based sanitation. Water used for personal hygiene, hand washing, and flushing to rinse urine- and feces-collection bowls is treated, stored, and recycled for reuse to reduce reliance on external water supplies. The system provides an opportunity to investigate hygiene of water for reuse following treatment. Treatment in the toilet includes a Biologically Activated Membrane Bioreactor (BAMBi) followed by a secondary treatment technology. To identify effective secondary treatment, three options, including granular activated carbon (GAC) only, GAC+chlorine (sodium hypochlorite), and GAC+electrolysis are considered based on the bacterial inactivation and growth inhibition efficiency. Four different hygiene-relevant bacteria are tested: Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, and Salmonella typhimurium. Our evaluation demonstrates that—despite treatment of water with the BAMBi—E. coli, P aeruginosa, and S. typhimurium have the potential to grow during storage in the absence of microbial competition. Including the indigenous microbial community influences bacterial growth in different ways: E. coli growth decreases but P. aeruginosa growth increases relative to no competition. The addition of the secondary treatment options considerably improves water quality. A column of GAC after the BAMBi reduces E. coli growth potential by 2 log10, likely due to the reduction of carbon sources. Additional treatments including chlorination and electrolysis provide further safety margins, with more than 5 log-10 inactivation of E. coli. However, reactivation and/or regrowth of E. coli and P. aeruginosa occurs under in the absence of residual disinfectant. Treatment including the BAMBi, GAC, and electrolysis appear to be promising technologies to control bacterial growth during storage in water intended for reuse.
Highlights
Two-thirds of the world’s population suffer from water scarcity (United Nations, 2012; Global Water Institute, 2013; Mekonnen and Hoekstra, 2016)
Water treated with the biologically activated membrane bioreactor (BAMBi) had generally higher nutrient and metal ion concentrations than water treated with the BAMBi and granular activated carbon (GAC) (Table 1)
The indigenous microbial community, E. coli, and P. aeruginosa, grew in both waters during storage, whereas Ent. faecalis and S. typhimurium only grew in water after treated with BAMBi (Figure 1)
Summary
Two-thirds of the world’s population suffer from water scarcity (United Nations, 2012; Global Water Institute, 2013; Mekonnen and Hoekstra, 2016). Water recovery and reuse from diverse sources (i.e., graywater, wastewater, stormwater) can help to increase water efficiency and reduce impacts of scarcity. Disinfection reduces the concentration of pathogens in water and helps prevent pathogen growth during subsequent distribution and/or storage. Chlorine disinfection (1.4 mg L−1 with 30 min exposure, or 42 mg min L−1) was shown to be effective in inactivating fecal coliforms in treated graywater, with no regrowth (or growth following disinfection) (Friedler et al, 2006). Gilboa and Friedler (2008) report observing no regrowth of fecal coliforms, P. aeruginosa, or Staphylococcus aureus after exposure to UV disinfection (0–439 mJ cm−2, unreported water thickness) up to 6 h (Gilboa and Friedler, 2008).
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