Moderately-rapid assessment of alkaline desiccation environmental systems

Abstract

A moderately-rapid assessment tool was developed to analyze the waterless desiccation compost toilet investigated in a rural Mexican setting. Over 100 social factors were identified along with the applicable technical factors that influenced the low acceptability of the toilets. A 4-point rating scale was developed to increase the ability and speed of analyzing both the social and technical data. The treatment process was an alkaline-desiccation process with mean pH values of 8.2 ± sd 1.1 and water content of 18.3% ± sd 9.9, which resulted in mean fecal coliform values of 15.0 MPN/g ± sd 31.8, drastically lower than the 1000 MPN/g United States Environmental Protection Agency (USEPA) limit. Alkalinity, not pH, was determined to be the limiting factor in some waste samples, resulting in the need to dilute the waste with local soils. Designs were developed to reduce the unnecessarily long detention times between 0.75 to 4.4 years and improve other features, especially additive use and waste handling. Solvita® test kits were used to assess compost characteristics. Modifications, made to kit procedures to enable their use, included adjusting pH values and extending the pre-test acclimation period. With low macro-nutrient concentrations, a mean carbon/nitrogen ratio of 14.0 ± sd 6.1, and a mean volatile solids value of 15.9 ± sd 6.9 indicative of low organic matter, the finished waste had limited agricultural value, however, the treatment process did efficiently remove nitrogen in many samples and eliminate the pathogens in all of them. Mean Specific Oxygen Uptake Rate (SOUR) values of 1.4 ± sd 1.1 mg O2 / gram total solids were substantially close with the USEPA standard of 1.5. The SOUR on a volatile solids basis was not applicable. A socially and technically useful ASH/VS (inorganic/organic solids) ratio was discovered with mean concentration values of 6.8 ± sd 4.2 with most values falling within an easily explainable socially-valuable ten-point scale. The introduction of two other dry batch composting toilets created a competitive situation in the community where comparative analysis was being performed with the preferred pour-flush water toilet. If water shortages continue, the desiccation toilet’s acceptability may increase again