On-Site Fecal Sludge Treatment with the Anaerobic Digestion Pasteurization Latrine

Abstract

The Anaerobic Digestion Pasteurization Latrine (ADPL) is a self-contained and energy neutral on-site sanitation system using anaerobic digestion of fecal sludge to generate biogas and then uses the biogas to pasteurize the digester effluent at 65–75°C to produce a safe effluent that can be reused locally as a fertilizer. Two ADPL systems were installed on residential plots with 17 and 35 residents in a peri-urban area outside of Eldoret, Kenya. Each system comprised three toilets built above a floating dome digester and one heat pasteurization system to sanitize the digested effluent. ADPLs are simple systems, with no moving parts and relying on gravity-induced flows. Adoption at the two sites was successful, and residents reported that the systems had little to no odor or flies. ADPLs were monitored for biogas production and temperatures in the pasteurization system. ADPLs serving 17 and 35 residents produced on average 16 and 11 Lbiogas/person/day (maximum of 20 and 15 Lbiogas/p/d), respectively. The temperature in the sterilization system was greater than 65°C on 58% and 87% of sampling days during the most stable period of operation. Treated effluent was analyzed periodically for chemical oxygen demand (COD), biochemical oxygen demand (BOD), total ammonia nitrogen (TAN), pH, and fecal coliform (FC). On average, the effluent at the two locations contained 4,540 and 6,450 mg COD/L (an 85% or 89% reduction of the estimated input), 2,050 and 3,970 mg BOD/L, and 2,420 and 4,760 mg NH3-N, respectively, and greater than 5 log reductions of FC (nondetectable) in the sterilization tank. Results from this field study show that anaerobic digestion of minimally diluted fecal sludge can provide enough energy to pasteurize digester effluent and that the ADPL may be a suitable option for on-site fecal sludge treatment.

Is anaerobic digestion a reliable barrier for deactivation of pathogens in biosludge?

“…The abundance of pathogens in sewage sludge generally fluctuates with the process configuration and operation conditions. Temperature had been considered as the primary suppressive factor of pathogens in anaerobic digested sludge (Forbis-Stokes et al, 2016). In fact, lethal effect of high temperature could be primarily attributed to denaturation of inactivating enzymes or capsid protein (Pandey and Soupir, 2011).…”

“…The biotechnological development was less reported to integrate with AD compared to physiochemical technologies. One notable example is anaerobic digestion pasteurization latrine system developed by researchers in North Carolina of the Statesa self-contained and energy neutral on-site sanitation systemusing the biogas generated from the sludge to pasteurize the digestate at 65-75°C to produce a safe fertilizer (Forbis-Stokes et al, 2016). It was essentially the integrated AD with thermal treatment via technical modifications.…”

Nitrifying trickling filters and denitrifying bioreactors for nitrogen management of high-strength anaerobic digestion effluent

“…A desired outcome of this study was to inform a possible future implementation for effluent treatment of onsite sanitation systems such as those described by Forbis-Stokes et al. (2016) .…”

Locally produced lactic acid bacteria for pathogen inactivation and odor control in fecal sludge

“…Fresh human feces contains high amounts of pathogens, such as fecal coliforms, Helminth eggs, Escherichia coli, Salmonella spp, fecal streptococcus, and other bacteria, all of which are harmful to humans ( Gold et al., 2017 , Langergraber and Muellegger, 2005 , Yemaneh, 2015 ). The direct use of FS in agriculture results in unhygienic conditions ( Dold and Holland, 2011 , Forbis-Stokes et al., 2016 , Langergraber and Muellegger, 2005 ).…”