Detoxification of acidic biorefinery waste liquor for production of high value amino acid

Comparison of the solid-state and submerged fermentation derived secretomes of hyper-cellulolytic Penicillium janthinellum NCIM 1366 reveals the changes responsible for differences in hydrolytic performance

Solid-state fermentation (SSF) and submerged fermentation (SmF) have often been compared for production of biomass hydrolyzing enzymes highlighting the superiority of the SSF produced enzymes, but the reasons for the performance differences are under-explored. Penicillium janthinellum NCIM 1366 culture extracts from SSF had better hydrolytic performance along with a higher initial rate of reaction. Secretome analyses of the SSF and SmF enzymes using LC/MS-MS, indicated that while the type of proteins secreted were similar in both modes, the abundance of specific beta glucosidases, lytic polysaccharide monooxygenases and hemicellulolytic enzymes were very high in SSF resulting in efficient initiation, low accumulation of cellobiose and high initial reaction rates. Key enzymes that catalyse lignocellulose breakdown under SSF and SmF are therefore different and the fungus may be speculated to have regulation mechanisms that aid differential expression under different cultivation modes.

Sequential mild acid and alkali pretreatment of rice straw to improve enzymatic saccharification for bioethanol production

Sequential pretreatment using different NaOH concentrations (0.5%, 1.0%, 1.5%, w/w) and 1% H₂SO₄ (w/w) was evaluated as a strategy for effective hydrolysis of rice straw. The efficiency of sequential NaOH and H₂SO₄ (SNA) pretreatment against sequential H₂SO₄ and NaOH (SH) was assessed. SH pretreated biomass attained more sugar yield compared to SNA pretreated biomass. The sugar yields from pretreated biomass improved with increasing NaOH concentration in both SH and SNA treatments. The maximum sugar release of 40.6 mg/ml (83.2% efficiency) was obtained from SH pretreated biomass when the stage 2 alkali treatment was performed at 1.5% w/w NaOH. The non-detoxified hydrolysate from this biomass was fermented with 96.8% efficiency.

Detoxification of fermentable broth with activated biocarbon resulting from pyrolysis of agroforestry residues

Carbon-like materials from pyrolysis (<500°C) of agricultural leftovers (rice husks, eucalyptus sawdust and peach stones) were submitted to steam activation and the expected adsorbent properties evaluated by means of a chemical method (methylene blue) and physically characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and surface area (BET). Batch experiments were carried out to check the pH effect on the adsorption of methylene blue, by evaluating the respective equilibrium isotherms (Langmuir, Freundlich and Temkin). The steam-activated biocarbons showed significant adsorbent capacity, which increased along with pH. The best performance was achieved by the activated biocarbon from peach stones, which showed adsorptive properties similar to activated carbon market. The suitable detoxification efficiency of untreated broths with activated biocarbon, and an increase in the required fermentability, supports the potential use of these adsorptive bioproducts from agricultural leftovers. The profitable use of agricultural waste materials is actually a welcome strategy for consolidating the biorefinery concept as well as ensuring planetary sustainability. PRACTITIONER POINTS: Use of biomass residues for detoxification of fermentable broth. The activated biocarbons showed significant adsorbent capacity similar to activated carbon market. The results revealed the potential of the biomass residues as a promising source within bio-refineries.

New insight into continuous recirculation-process for treating arsenate using bacterial biosorbent

In this study, a new recirculation column reactor system for arsenate removal using a polyethylenimine coated bacterial biosorbent was developed. Solution pH was the most important factor in process design and operation. In order to control and optimize solution pH favorable for arsenate removal, a pH control and recirculation system was added to a column reactor. The effects of recycle ratio, initial arsenate concentration, and flow rate on the arsenate removal performance of the developed process were examined. Thomas and Yoon-Nelson models were used to interpret the breakthrough curve of arsenate removal. The maximum arsenate adsorption amount of the new reactor was determined to be 50.86 mg/g by the Thomas model. Importantly, the new reactor showed unimpeded adsorption performance compared with that in the batch experiments. The desorption study also showed excellent reusability. The results indicated that the newly developed process could be a promising application prospect for removing arsenate.

A review on commercial-scale high-value products that can be produced alongside cellulosic ethanol

The demand for fossil derivate fuels and chemicals has increased, augmenting concerns on climate change, global economic stability, and sustainability on fossil resources. Therefore, the production of fuels and chemicals from alternative and renewable resources has attracted considerable and growing attention. Ethanol is a promising biofuel that can reduce the consumption of gasoline in the transportation sector and related greenhouse gas (GHG) emissions. Lignocellulosic biomass is a promising feedstock to produce bioethanol (cellulosic ethanol) because of its abundance and low cost. Since the conversion of lignocellulose to ethanol is complex and expensive, the cellulosic ethanol price cannot compete with those of the fossil derivate fuels. A promising strategy to lower the production cost of cellulosic ethanol is developing a biorefinery which produces ethanol and other high-value chemicals from lignocellulose. The selection of such chemicals is difficult because there are hundreds of products that can be produced from lignocellulose. Multiple reviews and reports have described a small group of lignocellulose derivate compounds that have the potential to be commercialized. Some of these products are in the bench scale and require extensive research and time before they can be industrially produced. This review examines chemicals and materials with a Technology Readiness Level (TRL) of at least 8, which have reached a commercial scale and could be shortly or immediately integrated into a cellulosic ethanol process.

Evaluation of a wet processing strategy for mixed phumdi biomass conversion to bioethanol

Biorefineries typically use dry feedstock due to technical and logistic issues, but in unique cases where climatic conditions are unfavorable and where the biomass has to be processed without a holding time, wet processing might be advantageous. The present study evaluated the possibility of using the fresh (non-dried) mixed biomass harvested from Phumdis; which are floating vegetation unique to Loktak lake in Manipur, India, for bioethanol production. Pretreatment with dilute alkali (1.5% at 120 °C for 60 min) resulted in 36% lignin removal and an enhancement of cellulose content to 48% from 37%, and enzymatic hydrolysis released 25 g/L glucose. Fermentation of the hydrolysates was highly efficient at 95%, attained in 36 h and 80% in just 12 h. The new wet processing strategy could help in value addition of mixed phumdi biomass.

A preliminary study on l-lysine fermentation from lignocellulose feedstock and techno-economic evaluation

l-Lysine is a commodity amino acid produced from starch feedstock. Various alternative feedstocks had been used for l-lysine production, but the yield was very low. This study took the first preliminary investigation on l-lysine production from lignocellulose for the replacement of food-crop starch. Corn stover was dry acid pretreated and biodetoxified, then used for enzymatic hydrolysis and l-lysine fermentation by an industrial Corynebacterium glutamicum strain. Various fermentation parameters, nutrient additions, and operation variables were applied and finally 33.8 g/L of l-lysine was obtained. This l-lysine titer is still below that of starch based fermentation, but already 3-5 folds greater than that of other alternative feedstocks based fermentation. A techno-economic analysis was conducted and the minimum selling price of l-lysine (hydrochloride form) was calculated to be $2.445 per kg. The cost reduction by the future improvement could fill the technical and economic gap between the cellulosic and starch based l-lysine production.

Bioconversion of pentose sugars to value added chemicals and fuels: Recent trends, challenges and possibilities

Most of the crop plants contain about 30% of hemicelluloses comprising D-xylose and D-arabinose. One of the major limitation for the use of pentose sugars is that high purity grade D-xylose and D-arabinose are yet to be produced as commodity chemicals. Research and developmental activities are going on in this direction for their use as platform intermediates through economically viable strategies. During chemical pretreatment of biomass, the pentose sugars were generated in the liquid stream along with other compounds. This contains glucose, proteins, phenolic compounds, minerals and acids other than pentose sugars. Arabinose is present in small amounts, which can be used for the economic production of value added compound, xylitol. The present review discusses the recent trends and developments as well as challenges and opportunities in the utilization of pentose sugars generated from lignocellulosic biomass for the production of value added compounds.

Current status on metabolic engineering for the production of l-aspartate family amino acids and derivatives

The l-aspartate amino acids (AFAAs) are constituted of l-aspartate, l-lysine, l-methionine, l-threonine and l-isoleucine. Except for l-aspartate, AFAAs are essential amino acids that cannot be synthesized by humans and most farm animals, and thus possess wide applications in food, animal feed, pharmaceutical and cosmetics industries. To date, a number of amino acids, including AFAAs have been industrially produced by microbial fermentation. However, the overall metabolic and regulatory mechanisms of the synthesis of AFAAs and the recent progress on strain construction have rarely been reviewed. Aiming to promote the establishment of strains of Corynebacterium glutamicum and Escherichia coli, the two industrial amino acids producing bacteria, that are capable of producing high titers of AFAAs and derivatives, this paper systematically summarizes the current progress on metabolic engineering manipulations in both central metabolic pathways and AFAA synthesis pathways based on the category of the five-word strain breeding strategies: enter, flow, moderate, block and exit.

A biorefinery-based approach for the production of ethanol from enzymatically hydrolysed cotton stalks

Cotton post-harvest residue/cotton stalk (CS) - a major agro-residue in south asian countries was evaluated as a feed stock for bioethanol production. The common thermochemical pretreatment strategies based on dilute acid and alkali and different combinations of biomass hydrolyzing enzymes were evaluated for saccharification of CS biomass. A hydrolytic efficiency of 80% was achieved for alkali treated biomass using cellulase supplemented with beta glucosidase. Recycling of undigested/residual biomass and/or enzyme supported same final sugar concentration as for fresh hydrolytic experiments. Fermentation was carried out using a novel, inhibitor-resistant strain of Saccharomyces cerevisiae where 76% of theoretical maximum efficiency was attained. Material balances were derived for the entire process from biomass pre-processing to hydrolysis.

Physico-Chemical Alternatives in Lignocellulosic Materials in Relation to the Kind of Component for Fermenting Purposes

The complete bioconversion of the carbohydrate fraction is of great importance for a lignocellulosic-based biorefinery. However, due to the structure of the lignocellulosic materials, and depending basically on the main parameters within the pretreatment steps, numerous byproducts are generated and they act as inhibitors in the fermentation operations. In this sense, the impact of inhibitory compounds derived from lignocellulosic materials is one of the major challenges for a sustainable biomass-to-biofuel and -bioproduct industry. In order to minimise the negative effects of these compounds, numerous methodologies have been tested including physical, chemical, and biological processes. The main physical and chemical treatments have been studied in this work in relation to the lignocellulosic material and the inhibitor in order to point out the best mechanisms for fermenting purposes. In addition, special attention has been made in the case of lignocellulosic hydrolysates obtained by chemical processes with SO₂, due to the complex matrix of these materials and the increase in these methodologies in future biorefinery markets. Recommendations of different detoxification methods have been given.