Abstract
Pretreating lignocellulosic biomass is an energy and time consuming process. This study presents an alternative pretreatment technique, which explores a synergistic approach between ozonolysis and cellulolytic microorganism-Pseudomonas putida at room temperature. Ozone is a strong oxidative agent that reacts with lignin by attacking the carbon-carbon double bonds, while P. putida preferentially hydrolyses the exposed cellulolytic parts of the biomass to simple sugars. The results from SEM and FTIR show a significant reduction in lignin and cellulose contents, leading to relatively high sugar recovery. The glucose concentration increases coincidentally with the ozonation duration and After 24 h however, the concentration reached 1.1 mg/ml, a 323% increase compared with results after 2 h. Increasing the ozonation time to 24 h reduced the biological pretreatment time by 50% but crucially, increases microbial biomass. This approach has potentially high ramifications particularly for industries exploiting lignocellulosic biomass as a feedstock for bioethanol production.
Highlights
Lignin present in lignocellulosic biomass is a major barrier to widespread utilization of their carbohydrate content [1]
There was no observable difference in performance between microbubble mediated ozonolysis pretreatment (MMO) and mediated ozonolysis and microbial pretreatment (MMO-M) pretreatments. pH is a system parameter that significantly affects the release and yield of radicals as well as their reaction rate during the ozonation process [20]
The glucose concentration produced reached ~0.25 mg/ml at the end 6 h MMO pretreatment (Fig. 5a), five times higher than the glucose produced after 2 h MMO pretreatment (Table 1)
Summary
Lignin present in lignocellulosic biomass is a major barrier to widespread utilization of their carbohydrate content [1]. Ozonation has been proven as an efficient technique in degrading the lignin polymer, and helps to oxide carbohydrates concurrently the rate of reaction with the latter is slower [3]. The mechanism for carbon-carbon double bond cleavage follows the Criegee mechanism, which predicts the ozonolysis for alkene compounds (C1⁄4C) progresses in three different steps [5]. These reactions are fast, and this was proven by observing both the high initial rates of ozone consumption and rapid lignin degradation [1,6]. The other benefit of the process is that the resulting solution is void of the degradation by-products, which interfere with the downstream processing such as enzymatic hydrolysis with Pseudomonas putida and fermentation processing with Zymomonas mobilis [7]
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