The conversion of waste water from food processing facilities to chemicals by adapting anaerobic digestion

Anaerobic digestion (AD) is an attractive bioenergy waste, and wastewater treatment technology. The comparative advantages of AD, when compared to other systems, include production of a useable fuel (biogas/methane); higher organic loads; reduced carbon footprint; lower quantities of sludge generation; and suitability for integration into a wide variety of process configurations and scales.  To date, AD has been mainly applied for biogas production and treatment of high-strength industrial wastes, sewage sludge and increasingly the organic fraction of municipal solid waste. AD is a mixed microbial community process, which proceeds in four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. As a result of hydrolysis, complex organic matter (e.g., carbohydrates, proteins) and particulates are converted to monomers (e.g., sugars, amino acids). Subsequently, acidogenesis converts these monomers into volatile fatty acids (VFA) and Medium-Chain Carboxylic Acids (MCCA), ketones, alcohols, and hydrogen.  Acetogenesis converts the products of acidogenesis into acetic acid and hydrogen, which are the substrates for methanogenic Archaea. We propose a two-phase AD process where hydrolysis and acidification take place in one reactor (producing VFAs and MCCAs via chain elongation) while methanogenesis occurs in the other.  Such systems open the possibility of a mixed community fermentation process with recovery of high-value VFA/MCCA (e.g. butyrate, caproate, caprylate) in the first stage, and biogas production in the second from the remaining syntrophic and methanogenic substrates.

The AD platform thus offers the potential as a core biorefinery technology not only for the generation of biogas, but also for the production of a variety of products from sustainably derived organic waste feedstocks.

Aims: To optimise a mixed-community process for production of volatile fatty acids (VFA) and Medium-Chain Carboxylic Acids (MCCA) through hydrolysis and directed fermentation. 

Objectives: The specific objectives are to: (i) Optimise the performance of mixed microbial species fermentation at bench-scale for VFA/MCCA production through the short circuiting of the normal biogas production system, (ii) identify the microbial functions important for production of key VFAs, butyric and hexanoic acid, in mixed species fermentation and (iii) pilot the optimised butyric and hexanoic acid production and recovery system.