Pretreatment of rice straw using microwave assisted FeCl3-H3PO4 system for ethanol and oligosaccharides generation

Conventional and microwave-assisted acid pretreatment of tea waste powder: analysis of functional groups using FTIR

Tea waste powder (TWP) is one of the potential biomass waste to recover valuable chemicals and materials. The prime objective of this work is to investigate the role of acid pretreatment on TWP. Diluted acids (HCl, H3PO4, CH3COOH, and H2SO4) were used to soak the TWP to understand the role of acids on bond cleavage and chemicals formation. One gram of TWP was soaked in 100 mL of diluted acids for 24 h. The soaked samples were further subjected to a hot air oven (temperature: 80 °C, duration: 6 h), orbital shaking (shaking speed: 80-100 rpm, duration: 6 h), and microwave irradiation (microwave power: 100 W, duration: 10 min) to understand the synergistic effects of acids and mode of exposure. The pretreated solid samples and liquid samples were analyzed using FTIR to understand the presence of functional groups. The mass loss of TWP after treatment significantly varied with the type of acid and exposure mode used. In the orbital shaker, the mass loss was varied in the following order: H2SO4 (36%) > CH3COOH (32%) > H3PO4 (22%) > HCl (15%). In hot air oven, high mass loss was observed compared to orbital shaking [HCl (48%) > CH3COOH (37%) > H2SO4 (35%) > H3PO4 (33%)]. The mass loss in microwave irradiation is lower (19 to 25%) with all acids compared to orbital shaking. In the solid samples, O-H stretching, C-H stretching, C=O stretching, C=C stretching, -C-O-, and -C-OH- functional groups were noticed. Similarly, C=O and C=C peaks and C-O and -C-OH peaks were noticed in liquid samples. Interestingly, microwave irradiation showed promising results in 10 min of pretreatment, whereas orbital shaking and hot air oven pretreatments require 6 h to achieve the same result.

Life-cycle analysis of biohydrogen production via dark-photo fermentation from wheat straw

This study presents a life-cycle analysis using energy conversion characteristics as an evaluation index to assess the feasibility of this production method. The results indicate that for a system processing 1000 kg/h of wheat straw, the addition of 12000 kg/h of 2 wt% H2SO4 and 120 kg/h of CH3COONa yields 340,000 L/h of H2 and 348.6 kW of electricity. The energy conversion efficiency from the feedstock to the product is 21.4 %, while the efficiency from the hydrolysate to the product is 62.2 %. The total CO2 emission is 27.1 kg/h. Variations in the hydrolysate have the most significant impact on energy conversion efficiency. This study explores the feasibility of industrial-scale biohydrogen production via dark-photo fermentation from wheat straw and analyzes the energy characteristic indices and the sensitivity of these indices to key parameters.

Environment friendly emerging techniques for the treatment of waste biomass: a focus on microwave and ultrasonication processes

In the recent past, an increasing interest is mostly observed in using microwave and ultrasonic irradiation to aid the biological conversion of waste materials into value-added products. This study is focused on various individual impacts of microwaves and ultrasonic waves for the treatment of biomass before the synthesis of value-added products. Following, a comprehensive review of the mechanisms governing microwaves and ultrasonication as the treatment methods, their effects on biomass disruption, solubilization of organic matter, modification of the crystalline structure, enzymatic hydrolysis and production of reducing sugars was performed. However, based on the lab-scale experiments evaluated, microwaves and ultrasonication were studied to be economically and energetically ineffective despite their beneficial effects on the waste biomass. This article reviews some of the difficulties associated with using microwaves and ultrasonic irradiation for the efficient processing of waste biomasses and identified some potential directions for future study.

A review on the environment-friendly emerging techniques for pretreatment of lignocellulosic biomass: Mechanistic insight and advancements

The process of pretreatment is considered as an indispensable unit operation in the field of lignocellulosic conversion. The traditional pretreatment operations of lignocellulosic biomass are observed as inefficient to meet the demand for an industrial adaptation. In view of that, numerous investigations are reported on various conventional pretreatment methods but very limited information's are available on the advanced technologies. The present review article provides an exclusive discussion on various emerging and environment-friendly pretreatment methods applied on a number of different feedstock materials. Further, an insight on the reaction mechanism involved with each of the technologies such as microwave, ultrasound, deep eutectic solvent, irradiation, and high force assisted pretreatment methods are elucidated for an effective valorization of lignocellulosic biomass. Hence, in a single article, the readers of this paper will get to know all important aspects of the emerging pretreatment techniques of lignocellulosic biomass including the advancements, and the mechanistic insight which will be highly beneficial towards the selection of an efficient pretreatment method for large scale of commercial implementation in a lignocellulosic biorefinery.

Waste-to-energy nexus for circular economy and environmental protection: Recent trends in hydrogen energy

The energy demand has increased exponentially worldwide owing to the continuously growing population and urbanization. The conventional fossil fuels are unable to satiate this requirement causing price inflation and significant environmental damage due to unrestrained emission of greenhouse gases. The focus now has shifted towards alternative, economical, renewable and green sources of energy such as hydrogen to deal with this bottle-neck. Hydrogen is a clean energy-source having high energy content (122 kJ/g). Recently, biological methods for the hydrogen production have attracted much attention because traditional methods are expensive, energy-exhaustive and not eco-friendly. The employment of biological methods promises utilization of waste or low-value materials for producing energy and building waste-to-energy nexus. Around 94% of the waste is discarded precariously in India and waste generation is growing at an alarming rate of 1.3% per year. The "waste-to-energy" techniques follow 'Reuse, Reduce, Recycle, Recovery and Reclamation' system solving three subjects at once; waste-management, energy-demand and environmental concern. Moreover, these methods have easy operability, cost-effectiveness and they help to shift from linear to circular model of economy for sustainable development. Biological processing of waste materials like agricultural discard (lignocellulosic biomass), food-waste and industrial discharge can be used for biohydrogen production. Dark and photo fermentation are the chief biological processes for the transformation of organic substrates to hydrogen. Dark fermentation is the acidogenic fermentation of carbohydrate-rich materials without light and oxygen. Clostridia, Enterobacter and Bacillus spp. are appropriate heterotrophic bacteria for dark fermentation. Various pretreatment methods like heat treatment, acid or base treatment, ultrasonication, aeration, electroporation, etc., can be applied on inoculums to increase H₂ producing bacteria eventually improving the hydrogen yield. However, only around 33% of COD in organic materials is transformed to H₂ by this method. Photofermentation by the photosynthetic non-sulfur bacteria (PNS) converts organic substrate to H₂ and CO₂ in the presence of nitrogenase enzyme in ammonium-limited and anoxygenic conditions. Rhodobacter or Rhodopseudomonas strains have been widely examined in this regard. But these methods are only able to produce H₂ with a poor yield. Combining dark and photofermentation is a noteworthy alternative for procuring enhanced hydrogen yields. Two-stage sequential method utilizes volatile fatty acids accumulated as byproducts after dark fermentation (in the first stage) for photofermentation by suitable bacteria (in the second stage). A proper investigation of the dark fermenter effluents is required before using them as a substrate for photo-fermentation. In a single-stage dark and photofermentation, co-culture of anaerobic and PNS bacteria in a single reactor is carried out for obtaining improved yield. The single stage system is comparatively inexpensive and less laborious; moreover, a limited requirement for an intermediate dilution stage is necessary. Economic analysis of hydrogen production showed that H₂ production by the present methods, save pyrolysis, is reasonably higher than the conventional approaches of fuel production. Probable routes to make H₂ production more cost-effective are reducing the cost of photobioreactor, installing proper storage system, etc. A constructive effort in the area of research and development of biological approaches of H₂ production technologies is vital. The commercial viability of biohydrogen production is imperative for accomplishment of circular economy system and sustainable development.