Production of lactic acid from paper sludge using acid-tolerant, thermophilic Bacillus coagulan strains

Photocatalytic conversion of biomass is considered an effective, clean, and environmentally friendly route to obtain high-valued chemicals and hydrogen. However, the limited conversion efficiency and poor selectivity are still the main bottlenecks for photocatalytic biomass conversion. Herein, we report the highly selective photocatalytic conversion of glucose solution on holo-symmetrically spherical three-dimensionally ordered macroporous TiO₂-CdSe heterojunction photonic crystal structure (s-TCS). The obtained s-TCS photocatalysts show excellent stability and strong light harvesting, uniform mass diffusion and exchange, and efficient photogenerated electrons/holes separation and utilization. The optimized s-TCS-4 photocatalyst displays the highest photocatalytic performance for glucose oxidation and hydrogen production. The glucose conversion, lactic acid selectivity, and yield on s-TCS-4 are about 95.9%, 94.3%, and 96.4%, respectively. The photocatalytic production of lactic acid for s-TCS-4 (18.5 g/L) is 2.3 times higher than the pure spherical TiO₂ photonic crystal without CdSe (s-TiO₂, 8.1 g/L), and the hydrogen production rate of s-TCS-4 is 9.4 times that of s-TiO₂. For the first time, we reveal that the photocatalytic conversion of glucose to lactic acid is a third-order and four-electron-involved reaction. This work could shed some new light on the efficient photocatalysis conversion of biomass to highly value-added products with high selectivity and yield, and simultaneously sustainable hydrogen evolution.

The continuous production of lactic acid from deproteinized whey by immobilized single and mixed culture of L. casei and L. lactis in Ca‐alginate beads has been investigated. A coimmobilized culture system gave better results than immobilized single cultures regarding lactic acid concentration, productivity, yield, and lactose utilization. Maximum lactic acid productivity of 7 g/lh was obtained at D=0.4 h−1 with a yield of 70% lactic acid and 50% lactose utilization. At a dilution rate of 0.1 h−1, a lactic acid productivity of 2.5 g/lh was obtained with a 55.5% lactic acid yield and 90% lactose utilization. The bioreactor system was operated at a constant dilution rate of 0.1 h−1 for 20 days without loss of original activity. In this case, the average lactic acid productivity, lactic acid yield and lactose utilization were 24 g/lh, 55% and 90%, respectively.

Rhizopus fungi is suitable for the production of lactic acid, which is the backbone material of polylactic acid used as green plastic from lignocellulosic biomass, since it can grow and ferment in simple medium with various carbon sources such as starch and cellulose. Although paper sludge (PS) contains a lot of cellulosic fibers and in general was incinerated for volume reduction and heat recovery, other efficient utilizations have hardly been developed. In effective production of lactic acid from PS, the research of the extraction of cellulosic fiber from raw PS to obtain effectively fermentable sugars by cellulase and the selection of lactic acid microorganism are necessary. In this study, the PS pretreatment method with NaOH and HCl and the optimization of cellulase reagent were achieved, and also a desirable thermotolerant Rhizopus was selected. Finally, the production of lactic acid from the treated PS at 40 °C by simultaneous saccharification and fermentation (SSF) with the strain and an optimized cellulase cocktail was investigated. Rhizopus oryzae NBRC 5384 was selected for thermotolerant lactic acid production from Rhizopus library because of its heat tolerance up to 40 °C and high lactic acid production of 80 g/L. The strain can ferment to lactic acid from hexose, pentose, sugar alcohol, disaccharide and starch. The soaking of raw PS in NaOH and HCl was able to reduce effectively inorganic materials and other reagents for repulping, and the content of Al and Ca per PS dry matter was mainly decreased from 32.9 and 30.8 to 14.1 and 1.66 %, respectively. SSF of the treated PS of 50 g/L with optimized cellulase cocktail and 5384 at 40 °C resulted in lactic acid production of 9.33 g/L for 96 h. The thermotolerant Rhizopus fungus was found based on its high performance in lactic acid production at high temperature from not only glucose, but also other various carbon sources including polysaccharides and the secretion of amylases and cellulases. The treatment of raw PS by NaOH and subsequent HCl was able to remove a large amount of inorganic materials with decrease of hydrophobicity. In SSF of the treated PS with the strain and the optimized cellulase cocktail, lactic acid was able to be produced. However, the increase of initial PS concentration in SSF led to the decrease of the yield with ethanol production, because of limited aeration due to increase of density. An appropriate oxygen supply to the strain is necessary to improve lactic acid production.

Lactic Acid as a platform chemical has broad application in various industries, especially in the production of Poly Lactic Acid (PLA) for biodegradable plastic. Empty fruit bunch (EFB), abundant by product from palm oil mill industry, is one of potential feedstock to be used in the production of lactic acid from lignocellulose biomass. EFB contains high cellulose and hemicellulose about 37– 59.7% w/w and 16–28% w/w, respectively. The aim of this paper is to study the effects of the operating conditions, such as temperature, reaction time, biomass loading, and catalyst concentration on the yield of lactic acid using barium hydroxide as alkaline catalyst. EFB pretreatment with steam explosion was applied to remove lignin content. The results showed that pretreatment reduced the lignin content from 22.66% to 9.69% w/w. Meanwhile, hemicellulose and cellulose increased from 14.40% to 16.40% w/w and 29.37% to 63.57% w/w, respectively. The highest yield of lactic acid was 21.57% C-mol, achieved by using 0.25 M Ba(OH)2 as the catalyst, with 5% w/v biomass loading, temperature 240°C, during 4 h reaction times. The yield was approximately equal to yield of lactic acid (~ 20%) compared with Pb2+ as the catalyst for EFB conversion although the later catalyst produced fewer by products during conversion.

In the current work, date wastes were used for lactic acid (LA) production under thermo-alkaline conditions to overcome some fermentation challenges. Amongst 27 bacterial isolates that produced LA from date juice, isolate D-218 exhibited better growth stability and LA production under various stressed conditions. This isolate was characterized as Bacillus coagulans D-218 using physiological and molecular identification methods. In batch fermentation mode, strain D-218 could not completely utilize 80 g/L of the total sugar and produced only 45.8 ± 2.8 g/L of LA at LA productivity of 0.214 g/L.h and high residual sugar (29.2 g/L) was unutilized in the fermentation media. Different repeated batch fermentations with different initial sugar concentrations and gradual increase in sugar concentrtions were conducted to maximize LA productivity. Starting with 60 g/L of total sugar, four runs of repeated batch fermentations were conducted that enhanced the LA productivity (70%) to 0.49 g/L.h. Another 9 runs were initiated with 40 g/L which further improved LA productivity that reached up to 0.77 g/L.h. Surprisingly, initiating fermentations with 20 g/L of total sugar successfully attained long-term fermentation (18 runs) with high LA yield and productivity without carbon loss of initiated startup sugar of date waste. In this process, strain D-218 could completely consume 80 g/L sugars with high LA production titer (72.9 ± 0.56 g/L), yield (0.92 g/g), and productivity (0.71 g/L.h). This study is the first to exploit date waste in a cost-effective system for high-titer lactic acid production under thermo-alkaline conditions (pH 9.0; 50 °C) and to report repeated batch fermentation for LA production from date wastes.

Continuous fermentation of clarified corn stover hydrolysate for the production of lactic acid at high yield and productivity

The present study investigated the synergistic effect of nutritional supplements (amino acid and Tween 80) on lactic acid production by Lactobacillus delbruckii utilizing a sugar refinery by product (cane molasses) in a submerged fermentation process. Initially, the effect of individual factors on lactic acid yield was studied by supplementing amino acids and their combinations, Tween 80 and cane molasses at varying concentrations in production medium. A combination of l-phenylalanine and l-lysine gave a maximum lactic acid yield of 47.89 ± 0.1 g/L on a dry cell weight basis at individual factor level. Similarly, maximum lactic acid yield was obtained by supplementing the production medium with 40.0 g/L and 2.0 g/L Tween 80 and cane molasses, respectively, at individual factor level. In order to further improve the lactic acid yield, nutritional supplements were optimized by central composite rotatable design (CCRD) using Minitab 15 software. Shake flask cultivation under optimized conditions, i.e., cane molasses (32.40 g/L), Tween 80 (2.0 g/L) and l-phenylalanine and l-lysine (34.0 mg/L) gave a lactic acid yield of 64.86 ± 0.2 g/L, corresponding to 95.0 % of the predicted yield of 67.78 ± 0.3 g/L. Batch cultivation performed in 7.5 L bioreactor (working volume: 3.0 L) under optimized conditions gave maximum lactic acid yield and productivity of 79.12 ± 0.2 g/L and 3.40 g/L·h, which is higher than previous studies with reduced fermentation time. Screening of lactic acid producing bacteria and characterization of lactic acid was also done.

Optimized feeding schemes of simultaneous saccharification and fermentation process for high lactic acid titer from sugarcane bagasse

Ethanol and lactic acid production as affected by sorghum genotype and location

Utilisation of microwave-NaOH pretreatment technology to improve performance and l-lactic acid yield from vinasse

In this research, I studied cellulose conversion into levulinic acid and lactic acid. Cellulose in biomass is considered as a renewable carbon source because of decreasing of fossil fuel in the world. I studied the effect of hot compressed water with carbon dioxide process on cellulose conversion into levulinic acid and I also studied the effect of metal oxides as a catalyst on cellulose conversion into lactic acid. Moreover, the optimum condition, amount of catalyst, the type of catalyst, and reusability of catalyst were investigated. The results are divided as three parts. First part, I reported that the use of hot compressed water with carbon dioxide could be directly converted cellulose to levulinic acid and that the yield of levulinic acid slightly differed when carbon dioxide is added into reaction. Thus, I concluded that the use of hot compressed water with carbon dioxide was not enough for cellulose conversion into levulinic acid. Second part, I studied the effect of metal oxides on cellulose conversion into lactic acid. The result showed that ZrO2 gave the high yield of lactic acid. I obtained 21.2% yield of lactic acid by using ZrO2 as a catalyst. The optimum condition for cellulose conversion was reaction temperature 473 K, reaction time 6 h. Many ZrO2 was characterized to understand correlation between the yield of lactic acid and properties of catalyst. I found that the amount of acid site and base site of catalyst played an important role for cellulose conversion into lactic acid. The result of reusability of catalyst showed that the yield of lactic acid slightly decreased after the first reaction. Third part, I studied the effect of mixed metal oxides on cellulose conversion into lactic acid. Various mixed metal oxide were used in reaction. The results showed that 10%ZrO2-Al2O3 gave the 25.3 % yield of lactic acid.

Lactic acid fermentations were conducted using water hyacinth. It is known that the pretreatment and enzyme hydrolysis process optimize the potential of water hyacinth. Lactic acid produced by using lactic acid bacteria. All cells were grown at <TEX>$37^{\circ}C$</TEX> and initial pH 5.5. Lactic acid production was measured by HPLC. All Lactobacillus strains could produce lactic acid from pretreated water hyacinth. The highest lactic acid was achieved when lactic acid fermentation was carried out by L. delbrueckii for D-form and L. helveticus for L-form lactic acid production. The lactic acid concentration was 10.70 g/L by L. delbrueckii and it converted glucose in the medium to lactic acid, almost perfectly. Lactic acid production became higher when fermentation was carried out at a controlled pH 5.5. Lactic acid yield and productivity were 0.52 g/g and 0.19 g/L/h for L. helveticus, while L. delbrueckii was 0.64 g/g and 0.27 g/L/h. This study showed that water hyacinth medium could be alternative medium which can replace the complex and expensive medium for growing Lactobacillus strains in production of lactic acid.

Bioconversion of waste office paper to l(+)-lactic acid by the filamentous fungus Rhizopus oryzae

Potential use of Lactobacillus casei TISTR 1500 for the bioconversion from palmyra sap and oil palm sap to lactic acid

Lactic acid fermentation from food waste with indigenous microbiota: Effects of pH, temperature and high OLR