Alkaline pretreatment for enhancement of biogas production from banana stem and swine manure by anaerobic codigestion

Cellulose from the banana stem: optimization of extraction by response surface methodology (RSM) and charaterization

Cellulose was extracted from the banana stem by chemical method and the factors affecting the extraction process such as concentration of NaOH and H₂O₂, as well as the assisted microwave time were investigated. Design-Expert software with Response Surface Methodology was used in the modeling and optimization of the cellulose extraction process. The results of XRD, FT-IR, SEM were also used to determine the physicochemical properties of cellulose obtained from the banana stem. The results of the modeling and optimization process of cellulose extraction showed the efficiency of the process and the high applicability of cellulose from the banana stem to create valuable industrial products.

Impact of different pretreatments on the anaerobic digestion performance of cucumber vine

Copious amounts of cucumber vine (CV) derived from crop growing and harvesting are casually discarded in the field, posing severely negative impacts on public health and the ecological environment. Treating CV via anaerobic digestion (AD) could represent a promising approach while the recalcitrant lignocellulosic structure restricts its conversion efficiency, thus underscoring the importance of valid pretreatments. This study systematically investigated the effects of nine types of commonly applied chemical pretreatments involved H₂SO₄, HCl, H₃PO₄, NaOH, KOH, Ca(OH)₂, CaO, H₂O₂, and alkaline hydrogen peroxide (AHP) pretreatments on methane production of CV. Results showed that alkaline and AHP pretreatments were beneficial to the methane production of CV and obtained the considerable cumulative methane yield and biodegradability of 194.3-241.5 mL·g_VS^-1 and 47.59-59.15%, respectively, 36.83-70.07% higher than untreated. Analyses of lignocellulosic compositions and structural characterizations revealed that alkaline and AHP pretreatments well destroyed both hemicellulose and lignin, which commendably increased the accessibility of cellulose, facilitating the methane production. The findings of this study provide not only efficient pretreatment methods for the disposal and utilization of CV during AD process but also promising alternatives for enhancing methane production performance of similar vine residues, which would be greatly valuable for industrial applications in the future.

Evaluation of electro-oxidation and Fenton pretreatments on industrial fruit waste and municipal sewage sludge to enhance biogas production by anaerobic co-digestion

This study presents the effect of electro-oxidation and Fenton pre-treatment on anaerobic co-digestion (AnCoD) of fruit-juice industrial waste (FJW) and municipal sewage sludge (MSS). Biogas production increased from 767 mL to 857 mL and 918 mL after EO and Fenton pretreatment, respectively. The methane amount increased by 28% and 39% for EO and Fenton processes. The removal efficiencies of soluble COD, carbohydrate, and protein for the conditions with the highest biogas production as a result of the pretreatment process were 48%, 65%, 61% for the Fenton pre-treatment, and 37%, 52%, and 39% for the EO pre-treatment, respectively. Cumulative biogas production efficiency for all pre-treated mixtures was estimated with kinetic models. In addition, an evaluation has been made regarding cost, economic gain, and energy consumption of the pre-treatment processes.

Methane production of banana plant: Yield, kinetics and prediction models influenced by morphological parts, cultivars and ripening stages

Banana trees and fruits with three ripening stages, including green, ripe, and overripe, of two cultivars, namely Nam wa and Hom were separated into different morphological parts for biogas yield determination. Specific methane yields (SMY) were significant different among banana parts (p ≤ 0.05). High non-structural carbohydrates and high non-lignocellulosic residual in substrates promoted high SMY. Pseudostem showed the highest share of energy yields among farm wastes which Nam wa cultivar provided higher energy potential than Hom. Peel presented the major energy source from fruit wastes which ripening stages did not have a significant effect on its SMY. Modified Gompertz model presented the best fit for methane production of most substrates. The SMY prediction models based on chemical constituents were developed to obtain conveniently used methane estimating tool which showed that a combination of lignin, hemicellulose, non-lignocellulosic residual, and crude fiber contents presented the highest performance for banana substrates.

Banana Waste-to-Energy Valorization by Microbial Fuel Cell Coupled with Anaerobic Digestion

Banana is the most cultivated fruit plant in the world. It is produced in Latin America, Asia and Africa. India and China are the world’s largest banana producers, with almost 41% of the world’s production. This fruit reaches a total world production of 158.3 million tons per year. However, during their production cycle, the banana agroindustry produces large volumes of solid waste derived from overripe fruit. It contributes between 8–20 percent of the waste (around 100 kg of banana waste for every ton of banana produced). Therefore, the use of overripe banana waste represents a huge opportunity for bioenergy production. This work demonstrates that banana waste can be further used for power generation using a microbial fuel cell (MFC) coupled with anaerobic digestion (AD). First, the maximum methane production (MMP), methane production rate (MPR) and biochemical methane potential (BMP) were measured using an anaerobic batch bioreactor for 64 days of monitoring. Finally, the digestate generated from AD was used in the MFC to determine the polarization curve, maximum voltage, maximum power density (MPD), resistance and current. As a result, the AD generated an MMP of 320.3 mL, BMP of 373.3 mLCH4/gVS and MPR of 18.6 mLCH4/Lb⋅day. The MFC generated 286 mV (maximum voltage), 41.3 mW/m2 (MPD), 580.99 Ω (resistance) and 0.0002867 A (current). Both processes together produced a total bioenergy of 13.38 kJ/gVS. This coupled system showed a suitable and promising use of banana waste for ecofriendly bioenergy generation. Therefore, this feedstock could be taken advantage of for generating sustainable processes and developing a circular economy in the banana agroindustry.

Overview of pretreatment technologies on vegetable, fruit and flower market wastes disintegration and bioenergy potential: Indian scenario

Disposal of segregated organic fractions of centralized wholesale market wastes (i.e. vegetable, fruit and flower markets waste) in dumpsites/landfills are not only a serious issue but also underutilizes the huge potency of these organic wastes. Anaerobic digestion (AD) is a promising technology for converting organic wastes into methane, as a carbon-neutral alternative to conventional fuels. The major challenges related to the AD process are poor biodegradation of wastes and buffering capacity within the anaerobic digester that lowers the biogas yield. To accelerate biodegradation and to enhance the process efficacy of anaerobic digestion, several pretreatment technologies (mechanical, thermal, biological, chemical and combined pre-treatments) for organic wastes prior to the AD process were developed. This review article presents a comprehensive analysis of research updates in pretreatment techniques for vegetable, fruit and flower markets wastes for enhancing biogas yields during the AD process. The technological aspects of the pretreatment process are described and their efficiency comparison with the resultant process yields and environmental benefits are also discussed. The challenges and technical issues associated with each pretreatment and future research directions for overcoming the field implementation issues are also proposed.

Bio-packaging based on cellulose acetate from banana pseudostem and containing Butia catarinensis extracts

Banana (Musa acuminata) pseudostem cellulose was extracted and acetylated (CA) to prepare membranes with potential use as bio-packages. The CA membrane was embedded by Butia seed (CA-BS) or Butia pulp (CA-BP) extracts obtained from Butia catarinenses (Butia). The produced CA, CA-BS, and CA-BP membranes were evaluated for their physical-chemical, mechanical, thermal, and antibacterial properties. The process for obtaining the cellulose yielded a material with about 92.17% cellulose (DS = 2.85). The purity, cellulose degree acetylation, and the incorporation of Butia extracts into the membranes were confirmed by FTIR. The CA-BS and CA-BP membranes showed a smaller contact angle and higher swelling ratio than the CA membrane. Furthermore, Butia seed or pulp extracts reduced the elastic modulus and deformation at break compared to the CA membrane. The DSC analysis suggested the compatibility between sections and the CA matrix, whereas the TGA analysis confirmed the thermal stability of the membranes. Moreover, less than 1% of the Butia seed and pulp extracts were put into a food simulant media from the membrane. Finally, the CA-BS and CA-BP membranes could inhibit the growth of Staphylococcus aureus and Escherichia coli on their surface, confirming the potential use of these membranes as bio-packaging for food preservation.

Improving the biogas yield of manure: Effect of pretreatment on anaerobic digestion of the recalcitrant fraction of manure

Anaerobic digestion of animal manure show a maximum of ca. 50% conversion of volatile solids due to recalcitrance of lignin and crystalline cellulose under anaerobic conditions. The aim of this study is to evaluate different pretreatments on anaerobic digestion of manure fibers after anaerobic digestion. Physical, chemical, thermal, and thermal combined with alkaline pretreatments using sodium hydroxide were tested on manure fiber fraction separated out after anaerobic digestion of cow manure. The anaerobic digestion after pretreatment along with untreated controls were done in semi-continuous anaerobic bioreactors. All pretreatments showed positive effect and the highest increase in VS conversion (42.4%) and methane yield (ca. 127%) was found for 3% NaOH pretreated sample at 180 °C. Composition analysis showed that cellulose, hemicellulose and lignin in digested manure fibers were optimally reduced by 24.8, 29.1 and 9.5% respectively during pretreatment and 76.5% of cellulose and 84.9% of hemicellulose was converted to methane during AD.

A comprehensive review of the recent development and challenges of a solar-assisted biodigester system

The extensive use of fossil fuels and the environmental effect of their combustion products have attracted researchers to look into renewable energy sources. In addition, global mass production of waste has motivated communities to recycle and reuse the waste in a sustainable way to lower landfill waste and associated problems. The development of waste to energy (WtE) technology including the production of bioenergy, e.g. biogas produced from various waste through Anaerobic Digestion (AD), is considered one of the potential measures to achieve the sustainable development goals of the United Nations (UN). Therefore, this study reviews the most recent studies from relevant academic literature on WtE technology (particularly AD technology) for biogas production and the application of a solar-assisted biodigester (SAB) system aimed at improving performance. In addition, socio-economic factors, challenges, and perspectives have been reported. From the analysis of different technologies, further work on effective low-cost technologies is recommended, especially using SAB system upgrading and leveraging the opportunities of this system. The study found that the performance of the AD system is affected by a variety of factors and that different approaches can be applied to improve performance. It has also been found that solar energy systems efficiently raise the biogas digester temperature and through this, they maximize the biogas yield under optimum conditions. The study revealed that the solar-assisted AD system produces less pollution and improves performance compared to the conventional AD system.

Enhancing the production of biogas through anaerobic co-digestion of agricultural waste and chemical pre-treatments

Large amounts of agricultural solid wastes (ASWs) and animal dung are produced annually causing serious environmental problem that requires proper treatment. The present study proposes a strategy for optimizing the anaerobic co-digestion of ASWs and cow dung (CD), identifies the key factors governing the co-digestion performance and evaluates the effect of NaHCO₃ alkalinity treatment on improving the economy and performance of anaerobic digestion (AD). The results revealed that the highest cumulative methane production (CMP) of 297.99 NL/kgVS can be generated by co-digestion of ASWs and CD at a ratio of 60:40. Further improvement was achieved via alkalinity treatment with 1.0 g of NaHCO₃/gVS leading to decrease in lignin, cellulose, and hemicellulose contents of feedstock by 3.5%, 10.5% and 15.9%, respectively, converting them to soluble fractions and improving the CMP by 11.2-29.7% based on substrate quality. The improved CMP in the chemically treated substrates reflects a 19% increase in the generated revenue. The kinetics of the AD process was successfully fitted to modified Gompertz model with very low standard deviation residuals (SDR) ≤ 5.21 and R² ≥ 0.979. Results confirm that the proposed strategy is an effective method for producing biogas from co-digestion of ASWs and CD.

Pretreatment of Animal Manure Biomass to Improve Biogas Production: A Review

The objective of this research is to present a review of the current technologies and pretreatments used in the fermentation of cow, pig and poultry manure. Pretreatment techniques were classified into physical, chemical, physicochemical, and biological groups. Various aspects of these different pretreatment approaches are discussed in this review. The advantages and disadvantages of its applicability are highlighted since the effects of pretreatments are complex and generally depend on the characteristics of the animal manure and the operational parameters. Biological pretreatments were shown to improve methane production from animal manure by 74%, chemical pretreatments by 45%, heat pretreatments by 41% and physical pretreatments by 30%. In general, pretreatments improve anaerobic digestion of the lignocellulosic content of animal manure and, therefore, increase methane yield.

Evaluation of squeezing pretreatment for improving methane production from fresh banana pseudo-stems

Banana pseudo-stems (BPS) are an abundant and low-lignin-content lignocellulosic biomass for methane production. However, the high-water content in BPS increases the transport costs, and the resistant structure of BPS hinders methane production. In this study, squeezing of BPS as a pretreatment was evaluated for improving anaerobic digestion (AD). After 20-d digestion, methane production from squeezed BPS was 204.2 ± 6.2 mL/(g volatile solids (VS) of feedstock), which was 41.2% more than that from untreated BPS. This increase was mainly attributed to the improvement of physical properties (e.g. water absorbing capacity) and the change in the resistant structure of BPS after squeezing, which promoted good contact between microbes and substrate during AD. The measured methane production was described using a modified Gompertz model and the results showed that anaerobic process would take less time and occur faster when pretreated BPS was used as the substrate. The energy produced during AD of squeezed BPS, after deducting the energy used by the squeezer, resulted in an energy surplus of 26.2%.

Evaluation of Anaerobic Co-Digestion to Enhance the Efficiency of Livestock Manure Anaerobic Digestion

In this paper, the anaerobic co-digestion of three different organic wastes, including livestock manure, slaughterhouse waste, and agricultural by-products (ABs), was carried out to enhance the efficiency of mono-digestion of livestock manure. The characteristics of co-digestion were evaluated at different mixing ratios. The experiment was performed using the Batch test and was divided into two parts. The first experimental section (EXP. 1) was designed to evaluate the seasonal characteristics of ABs, which are the different ratios of fruits and vegetables, where the mixing ratio of spring (fruits:vegetables = 3:7) showed the highest biogas yield (0.24 m3/kg volatile solids). The second experiment (EXP. 2) was conducted by using ABs in the ratio that gave the highest biogas yield in EXP. 1 in combinations of three wastes livestock manure, slaughterhouse waste, and ABs. The highest CH4 yield was 0.84 m3/kg volatile solids (VS), which was obtained with a mixing ratio that had even amounts of the three feedstocks. In addition, the results of the second biochemical methane potential test, which assessed the digestive efficiency according to the mixing ratio of the three types of organic waste, showed that the CH4 production rate of the merged digestion was approximately 1.03–1.29 times higher than that of the mono-digestion of livestock manure. The results of our experiment were verified using the modified Gompertz model, the results of which were relatively similar to the experimental results.

A novel hydraulic biogas digester controlling the scum formation in batch and semi-continuous tests using banana stems

Scum formation is a widespread phenomenon and causes serious damage in straw biogas digesters. A 10-L novel hydraulic conical digester for controlling scum was developed in this work and compared with a hydraulic cylindrical digester that simulated the conventional digester. After 30 d of batch and 120 d of semi-continuous fermentations using banana stems, the scum volumes of in cylindrical digesters were 4.12 and 2.12 times that in the conical digesters, respectively. The conical digesters increased biogas production by 5.7% and 11.6% in batch and semi-continuous tests, respectively. The VS removal of feedstock in conical digesters were 5.6 and 7.2% greater than for the batch and semi-continuous cylindrical, respectively. The microbial diversity and evenness were higher in conical than cylindrical digesters. The results demonstrated that conical shape was an effective structure for controlling scum formation and improving biogas production.

Low-cost composited accelerants for anaerobic digestion of dairy manure: Focusing on methane yield, digestate utilization and energy evaluation

To improve the methane yield and digestate utilization of anaerobic digestion (AD), low-cost composited accelerants consisting of urea (0.2-0.5%), bentonite (0.5-0.8%), active carbon (0.6-0.9%), and plant ash (0.01-0.3%) were designed and tested in batch experiments. Total biogas yield (485.7-681.9 mL/g VS) and methane content (63.0-66.6%) were remarkably enhanced in AD systems by adding accelerants compared to those of control group (361.9 mL/g VS, 59.4%). Composited accelerant addition led to the highest methane yield (454.1 mL/g VS), more than double that of control group. The TS, VS, and CODt removal rates (29.7-55.3%, 50.9-63.0%, and 46.8-69.1%) for AD with accelerants were much higher than control group (26.2%, 37.1%, and 39.6%). The improved digestate stability and enhanced fertilizer nutrient content (4.95-5.66%) confirmed that the digestate of AD systems with composited accelerants could safely serve as a potential component of bioorganic fertilizer. These findings open innovative avenues in composited accelerant development and application.

Improvement of wheat straw anaerobic digestion through alkali pre-treatment: Carbohydrates bioavailability evaluation and economic feasibility

Lignocellulosic biomasses such as wheat straw are widely used as a feedstock for biogas production. However, these biomasses are mainly composed of a compact fibre structure and therefore, it is recommended to treat them prior to its usage for biogas production in order to improve their bioavailability. The aim of this work is to evaluate, in terms of performance stability, methane yield and economic feasibility, two different scenarios: a mesophilic codigestion of wheat straw and animal manure with or without a low-energy demand alkaline pre-treatment (0.08g_KOHg_TS^-1of wheat straw, for 24h and at 25°C). Besides this, said pre-treatment was also analysed based on the improvement of the bioavailable carbohydrate content in the untreated versus the pre-treated wheat straw. The results pointed out that pre-treated wheat straw prompted a more stable performance (in terms of pH and alkalinity) and an improved methane yield (128% increment) of the mesophilic codigestion process, in comparison to the "untreated" scenario. The pre-treatment increased the content of cellulose, hemicellulose and other compounds (waxes, pectin, oil, etc.) in the liquid fraction, from 5% to 60%, from 11.5% to 39.1% TS and from 57% to 79% of the TS in the liquid fraction for the untreated and pre-treated wheat straws, respectively. Finally, the pre-treated scenario gained an energy surplus of a factor 13.5 and achieved a positive net benefit of 90.4€t_VS-WS^-1d^-1, being a favourable case for an eventual scale-up of the combined process.

Appropriate conditions for applying NaOH-pretreated two-phase olive milling waste for codigestion with food waste to enhance biogas production

The high methane gas production potential of two phase olive milling waste (2POMW) makes its application to biogas plants in business an economical process to increase the productivity of the plants. The objective of this study was to investigate the appropriate conditions for the codigestion of NaOH-pretreated 2POMW with food waste. NaOH pretreatment can increase the methane production by increasing the soluble chemical oxygen demand (sCOD), but it may cause inhibition because of higher levels of alkalinity, sodium ion, volatile fatty acids and long chain fatty acids (LCFAs). Therefore, the first experimental phase of this study aimed to investigate the effect of different mixing ratios of 2POMW to food waste. A continuous stirred tank reactor experiment with different mixing ratios of 3%, 4.3%, 5.7% and 8.3% (2POMW: food waste) was conducted. NaOH pretreatment in the range of 6-20% was used. A mixing ratio up to 4.3%, when 10% NaOH pretreatment was used, caused no inhibition and increased methane production by 445.9mL/g-VS(2POMW). For this mixing ratio an additional experimental phase was conducted with the 20% NaOH pretreatment as the 20% NaOH pretreatment had the highest sCOD. The methane gas production was increased by 503.6mL/g-VS(2POMW). However, pH adjustment was required for applying this concentration of the high alkalinity 20% NaOH-pretreated 2POMW. Therefore, we consider using 10% NaOH pretreatment in a mixing ratio of 4.3% to be more applicable. The increase in methane gas production was correlated to the oleic acid concentration inside the reactors. The high oleic acid concentration of 61.8mg/L for the 8.3% mixing ratio was responsible for the strong inhibition. This study showed that adjusting the appropriate mixing ratio of the NaOH-pretreated 2POMW could increase the electricity production of a reactor that regularly receives food waste.

Thermophilic bio-hydrogen production from corn-bran residue pretreated by calcined-lime mud from papermaking process

This study investigated the use of calcined-lime mud from papermaking process (CLMP) pretreatment to improve fermentative hydrogen yields from corn-bran residue (CBR). CBR samples were pretreated with different concentrations (0-15 g/L) of CLMP at 55°C for 48 h, prior to the thermophilic fermentation with heat-treated anaerobic sludge inoculum. The maximum hydrogen yield (MHY) of 338.91 ml/g-VS was produced from the CBR pretreated with 10 g/L CLMP, with the corresponding lag-phase time of 8.24h. Hydrogen yield increments increased from 27.76% to 48.07%, compared to the control. The CLMP hydrolyzed more cellulose, which provided adequate substrates for hydrogen production.

Scope of algae as third generation biofuels

An initiative has been taken to develop different solid, liquid, and gaseous biofuels as the alternative energy resources. The current research and technology based on the third generation biofuels derived from algal biomass have been considered as the best alternative bioresource that avoids the disadvantages of first and second generation biofuels. Algal biomass has been investigated for the implementation of economic conversion processes producing different biofuels such as biodiesel, bioethanol, biogas, biohydrogen, and other valuable co-products. In the present review, the recent findings and advance developments in algal biomass for improved biofuel production have been explored. This review discusses about the importance of the algal cell contents, various strategies for product formation through various conversion technologies, and its future scope as an energy security.

Asparagus stem as a new lignocellulosic biomass feedstock for anaerobic digestion: increasing hydrolysis rate, methane production and biodegradability by alkaline pretreatment

Recently, anaerobic digestion of lignocellulosic biomass for methane production has attracted considerable attention. However, there is little information regarding methane production from asparagus stem, a typical lignocellulosic biomass, by anaerobic digestion. In this study, alkaline pretreatment of asparagus stem was investigated for its ability to increase hydrolysis rate and methane production and to improve biodegradability (BD). The hydrolysis rate increased with increasing NaOH dose, due to higher removal rates of lignin and hemicelluloses. However, the optimal NaOH dose was 6% (w/w) according to the specific methane production (SMP). Under this condition, the SMP and the technical digestion time of the NaOH-treated asparagus stem were 242.3 mL/g VS and 18 days, which were 38.4% higher and 51.4% shorter than those of the untreated sample, respectively. The BD was improved from 40.1% to 55.4%. These results indicate that alkaline pretreatment could be an efficient method for increasing methane production from asparagus stem.