Volatile Fatty Acids (VFAs) Generated by Anaerobic Digestion Serve as Feedstock for Freshwater and Marine Oleaginous Microorganisms to Produce Biodiesel and Added-Value Compounds.

Alok Patel,Amir Mahboubi,Ilona Sárvári Horváth,Ulrika Rova,Mohammad J Taherzadeh,Leonidas Matsakas,Paul Christakopoulos

doi:10.3389/fmicb.2021.614612

Alok Patel, Amir Mahboubi + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2021.614612

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Abstract

Given an increasing focus on environmental sustainability, microbial oils have been suggested as an alternative to petroleum-based products. However, microbial oil production relies on the use of costly sugar-based feedstocks. Substrate limitation, elevated costs, and risk of contamination have sparked the search for alternatives to sugar-based platforms. Volatile fatty acids are generated during anaerobic digestion of organic waste and are considered a promising substrate for microbial oil production. In the present study, two freshwater and one marine microalga along with two thraustochytrids were evaluated for their potential to produce lipids when cultivated on volatile fatty acids generated from food waste via anaerobic digestion using a membrane bioreactor. Freshwater microalgae Auxenochlorella protothecoides and Chlorella sorokiniana synthesized lipids rich in palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), and linoleic acid (C18:2). This composition corresponds to that of soybean and jatropha oils, which are used as biodiesel feedstock. Production of added-value polyunsaturated fatty acids (PUFA) mainly omega-3 fatty acids was examined in three different marine strains: Aurantiochytrium sp. T66, Schizochytrium limacinum SR21, and Crypthecodinium cohnii. Only Aurantiochytrium sp. T66 seemed promising, generating 43.19% docosahexaenoic acid (DHA) and 13.56% docosapentaenoic acid (DPA) in total lipids. In summary, we show that A. protothecoides, C. sorokiniana, and Aurantiochytrium sp. T66 can be used for microbial oil production from food waste material.

Highlights

A green and sustainable bio-based economy has become a key element of long-term growth and well being
The effluent from anaerobically digested food waste in a membrane bioreactor served as the volatile fatty acids (VFAs) mixture and its composition was analyzed by high-performance liquid chromatography (HPLC) (Table 1)
The Auxenochlorella protothecoides SAG 211-13 (AP) cultivated on VFAs at C/N of 20 achieved 2.52 g/L of cell dry weight and 0.30 g/L of lipids, which corresponded to 12.08% w/w lipid content after consumption of almost all C2, C3, C5, and small amounts of C4 and C6 (Figure 2A)

Summary

INTRODUCTION

A green and sustainable bio-based economy has become a key element of long-term growth and well being. The high proportion of polyunsaturated fatty acids (PUFAs) in lipids derived from oleaginous microorganisms makes them unsuitable as biodiesel substrates because the presence of more than two double bonds promotes unwanted oxidation (Knothe, 2012; Patel et al, 2019a, 2018) Instead, these PUFAs could be used as an energy-rich dietary source of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) by humans, as we lack the desaturases and elongases required to synthesize them (de Jong et al, 2014; Lands, 2014; Zárate et al, 2017). Instead of using pure substrates in heterotrophic cultivation, the substrates obtained from low-cost non-edible lignocellulosic biomass, agricultural residues, and other waste substrates bring down the overall production cost (Patel et al, 2016) Enzymatic hydrolysis of these carbohydrate-rich waste substrates to generate feedstock for oleaginous microorganisms and for the generation of omega-3 fatty acids has been a promising way of valorizing such resources. Wastewater treatment plants provide the ability to divert vast volumes of food waste, one of the biggest waste sources currently going to landfills worldwide (Awasthi et al, 2020)

MATERIALS AND METHODS

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT