The Problem of Human Waste Disposal in National Parks: A Solar Energy Experiment in Yosemite National Park, California, U.S.A.

Abstract

of California is one of the most used parks in the U.S.A. Within the Park are ten composting toilets open to the public at six different backcountry locations. Two of these toilets are used by over 70,000 people in the summer months alone. Approximately 5.8 metric tons of human excreta are removed from these toilets every year. Hitherto, all of this compost has been removed from these sites using either pack animals or helicopters and disposed of in a landfill outside of the boundary of the Park (Williamson, 1996). This report presents the results of a cooperative project by the U.S. Department of Agriculture, Forest Service, San Dimas Technology and Development Center, San Dimas, California, and the U.S. Department of Interior, Park Service, Yosemite National Park, California, to assess the development and operation of a passive solar insulated box (termed the Hot Box, or HB) to treat the endproduct from composting toilets used by hikers in the backcountry (Figure 1). The primary objective is to determine if the device can heat-treat the compost and reduce pathogen levels, producing a 'Class A sludge' as determined by the U.S. Environmental Protection Agency (EPA) regulation 40 Code of Federal Regulations (CFR) Part 503 (which will be referred to as 'Regulation 503'). Numerous studies have documented innovative passive solar devices used to cook food (Telkes, 1959; Malhotra et al., 1983; Vaishya et al., 1985; Khalifa et al., 1987; Mullick et al., 1987; Pande and Thanvi, 1987; Yadav and Tiwari, 1987; Olwi and Khalifa, 1988; Channiwala and Doshi, 1989; Grupp et al., 1991; Das et al, 1994; Habeebullah et al., 1995). The pasteurization of water using passive solar cookers has also been tested (Ciochetti and Metcalf, 1984). However, little is known of the effectiveness of using passive solar heat for treatment of sewerage and suchlike. T e end-product from backcountry composting toilets is often high in pathogens and does not meet the EPA 40 CFR 503 Regulation guidelines for beneficial reuse or land application. The reuse or surface application of the compost is restricted due to the potential contamination of surface or groundwater sources. Transporting the endproduct from backcountry sites can often be expensive, time-consuming, and unpleasant. If solar energy can be used to treat toilet end-product so that it complies with EPA regulations, then the heat-treated compost can be applied to the land in the area where it is generated. This would reduce the reliance on pack animals and/or helicopter resources to transport the end-product from a site, resulting in cost savings and providing an environmentally safe means of recycling human waste back into the land.