Using Chain Elongation of Carboxylic Acids to Inactivate Ascaris Eggs and Provide New Methods for Sanitation Waste Treatment

Abstract

Improving global coverage of sustainable and safely managed sanitation requires innovative solutions for safely treating waste while saving and recovering resources, and pathogen inactivation is an important component of these solutions. In this dissertation, I present four studies that demonstrated the feasibility of biologically producing carboxylic acids within human fecal material (HFM) as a means of inactivating pathogens. In all studies I use eggs from the Ascaris suum roundworm as indicators of pathogen inactivation because Ascaris eggs are widely believed to be the most resistant pathogens to sanitation waste treatment processes. I found that HFM is a suitable substrate for carboxylic acid production and chain elongation, and I demonstrated that the microbial community naturally residing in HFM is capable of performing this fermentation. I also found that carbohydrate-rich food waste can be co-fermented with HFM to further increase carboxylic acid concentrations, reduce pH, and promote faster inactivation of Ascaris eggs. In addition, I conducted several studies to better understand the parameters that control Ascaris inactivation in this system. I demonstrated that only the undissociated form of carboxylic acids is effective for inactivating Ascaris eggs, and pH is critical for controlling the fraction of carboxylic acids that are in the undissociated form. However, pH does not directly affect Ascaris inactivation on its own. Small changes in mesophilic temperatures and the presence of oxygen also have a strong impact on inactivation rates. In a study testing the effect of temperature without the presence of carboxylic acids, I showed that current guidelines for thermal inactivation of Ascaris eggs are overly conservative, particularly under aerobic conditions, and I developed a new time-temperature relationship for Ascaris inactivation at temperatures between 34°C-45°C. In a separate study, I developed a logistic regression model to predict Ascaris inactivation as a function of n-butyric acid concentration, n-valeric acid concentration, n-caproic acid concentration, exposure time, and temperature. This model can be used to provide preliminary predictions for operating conditions required in sanitation waste treatment systems.