Lactic Acid Fermentation of Human Feces: A Process-Oriented Evaluation of Key Operational Parameters for Practical Implementation as a Treatment Technology

Authors:
Open Access
Publisher website
Google Scholar
Abstract
Lactic acid fermentation (LAF) is a promising low-tech approach for the stabilization and hygienization of human feces from dry toilets. However, practical implementation remains limited due to a lack of application-relevant knowledge. This study systematically evaluated the influence of a series of practical process parameters on the performance of LAF under standardized laboratory conditions. Feces obtained from different types of dry toilets were physicochemically characterized and subsequently fermented under varying process conditions, using pH and lactic acid production as key indicators of fermentation performance. The results indicate that LAF is feasible across a broad range of process conditions, including temperatures between 8 and 30 °C, and is largely independent of carbon source type, air intrusion, and extended storage periods (>1 year), provided that a sufficient carbon supply is ensured. The investigated parameters exhibited varying degrees of influence on process performance, with carbon source dosage (≥10 w/w-% sugar beet molasses equivalent) and feces type emerging as the most influential factors. While ferrous iron addition (≤5 w/w-%) enhanced pH reduction, biochar, bentonite, and rock flour (≤10 w/w-%) showed negligible effects. Maximum lactic acid production was limited to ≤4.5 w/w-%, irrespective of carbon source dosage, resulting in minimum pH values ranging from 4.1 to 5.2. These values varied primarily with fecal type, suggesting a strong influence of intrinsic buffering capacity. Under conditions supporting stable LAF, i.e., rapid acidification followed by sustained low pH, E. coli was consistently reduced below the detection limit in the investigated samples. Overall, the findings suggest that LAF is a comparatively robust treatment approach and highlight operational parameters that are likely to be important for its practical implementation as a sanitation technology.
Funding Information
  • Deutsche Bundesstiftung Umwelt (AZ 37541/01)

This publication has 25 references indexed in Scilit: