Description of Challenge
At the same step that water scarcity is becoming a extremely serious theme, our society has been using drinking water to solve sanitation issues. Conventional toilets use from 6 to 20 liters of water every flush.
While dry toilets are a known solution for this challenge they are still considered a taboo for many people, motivated by the lack of confidence in the treatment of humanure, fear of insects, and contamination. Some companies offer products that are not accessible ($) for many people.
“The world is divided into two categories of people: those who shit in drinking water and those who don't.”
― Joseph C. Jenkins, The Humanure Handbook: A Guide to Composting Human Manure
This abstract was extracted from the Dissertation submitted to the Post-Graduate Program degree in Environmental Engineering from the Federal University of Santa Catarina for obtaining a Master’s Degree in Engineering Environmental, by Richard Eilers Smith.
Since water is a natural resource increasingly scarce, there is a need to develop technologies that can contribute to its conservation and sustainable use. This study evaluated a Urine Diverting Dry Toilet (UDDT) using technical-scientific criteria, and this evaluation was conducted through two main experiments. The first experiment was a comparative diagnosis, carried out with 14 dry toilets in Brazil. Aspects of the construction, operation and environmental perception of the users were considered. Among the results, the greatest difficulty for users of these 14 dry toilets is the control of insects, followed by lack of confidence in the treatment and acceptance of the technology. The main motivation for use is environmental and ecological and the most common treatment is composting. The second experiment consisted in monitoring a feces treatment process in the evaluated UDDT.
The proposed treatment was conducted using a segregating vessel that separates the feces from urine, treating excreta separately. After each defecation was added a powder material on top of the feces called additive. The composition of the additive used was agricultural limestone (CA), ash (CZ) and a small amount of urea (U) in the proportion (CA: CZ: U 1: 1: 0.02). The amount of additive tested was 300 g or 420 ml (after each defecation), which corresponds to 150% with respect to the wet weight of feces. Physical-chemical parameters were evaluated (pH, total solids, fixed and volatile organic carbon concentrations and nitrogen fractions), microbiological (Salmonella sp., Enterecoccus faecalis, total coliforms, Escherichia coli, somatic coliphages, bacteriophage RNA male-specific and adenovirus human type 2 HAdV) and also its composition to reuse.
The results confirmed the treatment efficiency of this additive by drying the feces, pH elevation, hydrolysis of urea, increasing the percentage of fixed solids and also the reduction of the 7 microorganisms analyzed, bacteriophages (somatic coliphages and RNA Male -específicos) those who had the highest resistance to treatment. The reduction of 1 log unit time (T90) was 5.6 days for total coliforms, 7.9 days for Escherichia coli, Enterococcus faecalis 11.3 days to 13.1 days for the human adenovirus type 2, 17.3 days for the bacteriophage RNA- male-specific and 34.8 days for somatic Coliphages. With regard to reuse, from the sanitary/health point of view, excreta meet 100% of the requirements of Brazilian Resolution CONAMA 375/2006 for the sludge classified as type A. According to the parameters of Normative Instruction 25/2009, treated feces attended most of the criteria for use as fertilizer, being viable for non-commercial use. From the results, it is proposed 3 to 4 months for treating the feces with the additive, enclosed in the storage container (bombona), varying according to the requirement of treatment intended use: 3 months for less restriction uses, such as restoration or landscape gardening and four months for more demanding uses such as agriculture of raw food. Urine, as previous research statements, needs 6 months in a closed container for safe reuse.
This research confirmed the urine-diverting dry toilet (UDDT) model potential, proving the efficiency of the treatment of feces, the possibility of a safe reuse of treated excreta and thus contributing to the conservation of water resources and soil fertility .
Keywords: Ecological sanitation, Urine Diverting Dry Toilet (UDDT);
Feces; Drying; Urea.