Enhanced valorization of food waste to VFAs as an external carbon source for the denitrification process

Abstract

Anaerobic digestion (AD) has been known as a promising technology for food waste treatment since it not only accommodates high impurity and moisture substrates, but also produces a valuable renewable energy source. However, this technology still has some challenges such as volatile fatty acid accumulation, process instability, long operating time as well as high investment and transportation. Overcoming rigorous requests in operating process and improving biogas quality including design innovation, additives, or the control of foam in AD have been therefore studied. Even though the accumulation of VFAs during AD is considered to be a barrier as they cause inhibition on methanogens and thus impede methane formation, Their applications are extremely wide in industrial field

moreover, they are one of the energy sources to generate electricity in microbial fuel cells, carbon sources for the production of biopolymers, and a good external carbon source for biological nutrient removal at urban and industrial wastewater treatment plants. With the aim of not only alleviating the burden of AD due to the accumulation of VFAs, but also extracting a valuable source which can be applied to various fields. In this study, we aspire to maximize the production of VFAs by combining favorable conditions for the production of VFAs and carbon nanotube structures in batch and continuous experiments. In addition, an evaluation of the potential application of VFAs produced from food waste for the denitrification process was carried out from artificial VFAs sources. In chapter 1, the research background and objectives are summarized. In chapter 2, the value of VFAs and strategies for producing VFAs from food waste was presented in general. In chapter 3, together with favorable conditions for the VFAs production, the efficiency of VFAs production was improved by 16% and the rate of acidogenesis was increased by 22%, but the produced VFAs composition remained unchanged in the presence of carbon nanotube structure (CNS). In Chapter 4, similar to batch experiments, VFAs production were improved by adding CNS to continuous reactors, and the potential for recovery of VFA by ED was achieved by 84% at an acceptable energy consumption, 0.041 kWh/kgVFAs for 80 minutes. In chapter 5, as an external carbon source, the VFAs produced from food waste showed a denitrification rate not inferior to the current source (methanol) or single VFAs (acetic acid, propionic acid, butyric acid) at 3.2 mgNO$_3$$^-$-N/g-MLVSS/h In summary, this study not only fulfilled the expectation of a solution to one of the significant challenges of AD operation, but also provided a valuable source for the denitrification process instead of current non-renewable sources, which were concluded in Chapter 6.