Enhanced fermentative lactic acid production from source-sorted organic household waste: Focusing on low-pH microbial adaptation and bio-augmentation strategy

Zengshuai Zhang,Panagiotis Tsapekos,Merlin Alvarado-Morales,Xinyu Zhu,Athanasios Zervas,Carsten S Jacobsen,Irini Angelidaki

doi:10.1016/j.scitotenv.2021.152129

Zengshuai Zhang, Panagiotis Tsapekos + Show 5 more

Open Access

https://doi.org/10.1016/j.scitotenv.2021.152129

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Abstract

Lactic acid (LA) production at low pH could significantly reduce the need for neutralizing agents, leading to reduction of operational costs. In the present study, LA production at acidic conditions was investigated using source-sorted organic household waste (SSOHW). Controlling the pH at low value (i.e. 5.0) and bio-augmenting with Pediococcus acidilactici led to a concentration of 39.3 ± 0.5 g-LA/L with a yield of 0.75 ± 0.02 g-LA/g-sugar. In contrast, secondary fermentation at higher pH level (i.e. 5.5 and 6.0) resulted in complete LA degradation. Subsequently, consecutive batch fermentations were conducted to adapt P. acidilactici to SSOHW and improve the LA production. Results showed that P. acidilactici could successively adapt in the SSOHW reaching a relative abundance above 2.8% at adaptation process. The added P. acidilactici ensured a high concentration of LA at three consecutive generations, achieving an increment above 18% compared to control test (abiotic augmentation). Moreover, adaptation processes (i.e. maintaining pH at 4.0 or stepwise decreasing the pH from 5.0 to 4.0) significantly improved LA concentration and productivity at the pH of 4.0. Overall, the results provide a promising method to reduce the LA production costs using residual resources.

Highlights

As an important and versatile platform molecule, lactic acid (LA) has been widely applied in chemical, medical, pharmaceutical as well as food industry (Eş et al, 2018)
A set of comparative experiments with addition of P. acidilactici were conducted to elucidate the effect of pH on fermentative LA process
lactic acid bacteria (LAB) have higher acid tolerance compared to other acidogens (e.g. Acetobacter spp.) that are favored at neutral conditions and so, LA production is normally more competitive at acidic condition (Ahmad et al, 2020a; Lee et al, 2014)

Summary

Introduction

As an important and versatile platform molecule, lactic acid (LA) has been widely applied in chemical, medical, pharmaceutical as well as food industry (Eş et al, 2018). Food feedstocks (e.g. corn) are commonly used as the substrate, increasing the production cost (Abdel-Rahman et al, 2013). SSOHW is considered as a potential substrate for LA production, offering several advantages; as for example, high abundance, low cost, high polysaccharide content and non-seasonality (Eş et al, 2018; López-Gómez et al, 2019; Mak et al, 2021). With respect to economic and environmental concerns, fermentation of SSOHW for LA production could be an attractive waste management approach, converting residual resources to the useful platform chemical and at the same time minimizing the pollution

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