NaOH Pretreatment Research Articles

Influences of straw alkaline pretreatment on biogas production and digestate characteristics: artificial neural network and multivariate statistical techniques.

Anaerobic digestion is one of the best options for producing valuable end products (biogas and biofertilizer). The aim of this study was to investigate the influences of thermoalkaline pretreatment of wheat straw on biogas production and digestate characteristics from codigestion with waste-activated sludge. Different alkaline conditions (NaOH, KOH and Na2CO3) and pretreatment durations (1, 3 and 5 h) were used for straw pretreatment. Batch anaerobic codigestion of sludge and pretreated straw was conducted under different pretreatment conditions. A feedforward neural network (FFNN) model, logistic model and statistical analysis were applied to the experimental data to predict biogas and investigate the significance and relationships among the variables. NaOH pretreatment for 5 h showed the best treatment conditions: biogas yield was 6.59 times higher than that without treatment. Moreover, the proportions of total solids, total volatile solids, chemical oxygen demand and microbial count removed reached 63.52%, 74.60%, 78.15% and 82.22%, respectively. The methane content was 67.50%, indicating that the biogas had a high quality. The thermoalkaline pretreatment significantly affected biogas production and digestate characteristics, allowing it to be used as a biofertilizer. Experimental data were successfully modelled for predicting biogas production using the applied models. The R2 values reached 0.985 and 0.999 for the logistic and FFNN models, respectively.

Holistic biorefinery approach for biogas and hydrogen production: Integration of anaerobic digestion with hydrothermal carbonization and steam gasification

Recently, the integration of biochemical and thermochemical processes is recognized as a promising strategy for the valorization of lignocellulosic biomass into renewable energy production. In this study, different routes for the valorization of hemp hurd for biohydrogen and biomethane production were proposed, including anaerobic digestion (AD), hydrothermal carbonization, and steam gasification. AD results revealed that NaOH pre-treatment of hemp hurd improved biomethane production yield by 164%. Comparing hydrochars from raw hemp, digestate derived hydrochars had higher mass yield due to changes in composition during AD as well as high ash content of digestates. It was found that high ash content of digestates originated from inorganic compounds in inoculum that accumulated over hemp hurd during anaerobic digestion process. Among feedstocks (hydrochars and raw hemp hurd), hemp hurd derived hydrochar at 200 °C showed the best performance in terms of H2 yield (1278 mL/g) whereas carbon efficiency reached % 92 in case of digestate derived hydrochar at 200 °C. HTC improved the steam gasification performance of hemp hurd whereas hydrochars from NaOH pretreated digestate yielded lowest hydrogen production due to the high content of inorganics, particularly phosphorus (P) and aluminum (Al). According to BMP test, spent liquor obtained at the lowest HTC temperature (200 °C) exhibited the highest BMP, reaching 213 mL CH4/g COD. Considering the overall gas products of four different routes, it is concluded that HTC as a post-treatment exhibits slightly better performance than HTC as pre-treatment. Although alkali pretreatment enhanced the anaerobic digestion performance, the resulting hydrochars exhibited low gasification activity.

Optimisation of mechanical behaviour of Calotropis gigantea and Prosopis juliflora natural fibre-based hybrid composites by using Taguchi-Grey relational analysis

The properties of organic fibre-based hybrid materials are influenced by a variety of factors and even minor changes in these variables can outcome in substantial discrepancies in strength. In this regard, the current study aims to optimise various influencing parameters such as weight percentage, alkaline treatment concentration, and fabrication parameters (compression moulding pressure, and temperature), with the goal of enhancing the overall strength of the composite. Calotropis gigantea-stem and Prosopis juliflora-bark fibres were used in varying weight percentages to create epoxy-based hybrid composites. After fabrication the mechanical characterisation like tensile, flexural, and impact properties of the composites were tested. Taguchi experimental design was applied, and the results were analysed using a hybrid Taguchi-grey relational investigation method. It was observed that a combination of 20 wt.% Calotropis gigantea/20 wt.% Prosopis juliflora/6 % NaOH pretreatment/100 °C temperature with 14 MPa pressure and had the most desirable mechanical properties in the fabricated composites. Calotropis gigantea ranks first in enhancing the composite strength, followed by Prosopis Juliflora, NaOH pretreatment%, compression moulding temperature and pressure. This work highlights the significant role of Calotropis gigantea and Prosopis Juliflora fibres in enhancing composite strength and provides valuable insights for future research in the field of hybrid composite development.

Optimizing Sustainability of Concrete Structures Using Tire-Derived Aggregates: A Performance Improvement Study

Tire-derived aggregate concrete (TDAC), or rubberized concrete, is gaining ground as an eco-friendly option in civil engineering. By substituting traditional coarse aggregates with recycled rubber tires, TDAC offers a greener choice with excellent energy absorption capabilities. This leads to robust structures and reduced upkeep expenses. Nonetheless, TDAC’s lower strength than regular concrete requires a delicate balance between energy absorption and strength. This study investigates two enhancements to TDAC performance: (a) the impact of sodium hydroxide (NaOH) solution pretreatment and SikaLatex bonding agent addition on TDAC’s compressive strength, and (b) the use of varying water–cement ratios and superplasticizer to enhance TDAC’s mechanical properties. This study involves concrete cylinder compression tests and the creation of strength estimation equations. Results show that NaOH-treated tire-derived aggregate (TDA) boosts workability, increasing slump by 4.45 cm (1.75 in), yet does not significantly enhance compressive strength, causing a 34% reduction. Conversely, combining NaOH pretreatment with Sikalatex bonding agent enhances workability by 28% and boosts compressive strength by 21% at the same water-cement ratio. To optimize performance, it is advised to employ modified TDA concrete with a water–cement ratio under 0.34 and superplasticizer. These findings highlight the potential of modified TDA concrete in sustainable and seismic-resistant designs.

Effect of Chemically Pretreated Water Hyacinth Co-Digested with Poultry Litter in Anaerobic Digestion

This study focuses on the biogas production from water hyacinth (WH) while co-digested with poultry litter (PL) through bio methanation. The high content of hemicelluloses and cellulose present in the water hyacinth demands the need for pretreatment to enable the rapid anaerobic decomposition of the organic matter and resulting in improved process rate and biogas yield. Water Hyacinth is chemically pretreated using NaOH and lime to achieve partial disintegration of very long unbranched fibrils composed exclusively of glucose, with hydrogen bonding. The chemical disintegration of hemicellulose is achieved initially by hydrating the chopped WH in the ratio of 1:1. The hydrated WH is added with 1% by weight of NaOH and lime separately in batches. The digestion was performed in four fixed dome batch type digesters namely with raw WH, Lime pretreated WH+PL, and NaOH pretreated WH+PL and co-digestion of WH with PL. The digestion was carried out at mesophilic anaerobic condition and the pH is maintained at near neutral range for a hydraulic retention time of 21 days. As a result, it is observed that there is an increment of 51.57 % in biogas yield while codigesting with lime and more interestingly the digester with NaOH pretreatment results in 51.57% incremental biogas yield compared to the raw WH.

Transformations of bamboo into bioethanol through biorefinery.

The increasing demand for energy has prompted scholars to research alternative energy sources. Bamboo is a species of woody perennial grass that belongs to the Gramineae family and the Bambuseae subfamily. It could be considered a possible lignocellulosic substrate for the production of bioethanol due to its favourable environmental effects and increased yearly biomass yield. Non-renewable fossil fuels cannot provide enough energy to meet the needs of contemporary societies. Among the various alternative energy sources, bioethanol has drawn a lot of attention from people all around the world. This paper reviews the cost and process parameters for the synthesis of bioethanol from bamboo. This review aims to increase the effectiveness of the entire ethanol production process by focusing on pretreatment, enzymatic hydrolysis, and fermentation. The emphasis of this review is on the efficient process for producing bioethanol while maintaining environmental sustainability. When compared to other NaOH pretreatment techniques, bamboo substrates prepared with NaOH and ultra-high-pressure explosion (UHPE) exhibit higher enzymatic hydrolyzability when processed under optimal conditions, such as 100MPa, 121°C, and 70rpm for 2h, yielding 89.7-95.1% ethanol after 24h. The article lists the bamboo species responsible for creating each product, making it straightforward for producers to study and select the species based on whatever value-added product they wish to produce bioethanol with different parameters.

STATISTICAL OPTIMIZATION OF NaOH PRETREATMENT OF PINE NEEDLES USING BOX-BEHNKEN DESIGN FOR BIOETHANOL PRODUCTION

In this study, pine needles were exploited for bioethanol production. Pretreatment is the first and foremost step towards better yield of bioethanol from lignocellulosic biomass. In this study, NaOH pretreatment of pine needles was optimized by the Box Behnken design. Substrate characterization was done by using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Maximum cellulose (90%) and total phenolic compounds (51.03 ± 0.002 mM) were recorded under optimized conditions, and structural analysis also revealed the significance of the pretreatment. High F and R2 values and low P values indicated the accuracy and validity of the model. Pretreated biomass was further subjected to saccharification using commercial, as well as indigenous cellulase. Maximum saccharification (49.2%) was observed with commercial cellulase, which led to a 7% ethanol yield employing Saccharomyces cerevisiae. Maximum ethanol yield (7%) was observed in NaOH pretreated biomass. Results proposed that Pinus spp. needles could be potential cellulosic biomass for bioethanol production.

Pengaruh Pre-Treatment Kimia dan Biologi Terhadap Produksi Biogas dari Kulit Kopi

Coffee, as a major commodity in Indonesia, produces a huge number of byproducts and residues during the processing process. Coffee wastes and byproducts produced during coffee berry processing are a major source of contamination and represent significant environmental challenges in the coffee production process. One promising alternative in utilizing coffee wastes is converting into energy source i.e, of biogas from coffee pulp. Coffee pulp has toxic components that act as a methane inhibitor; these type of biomass have a problem with the lignin degradation process, which binds cellulose and hemicellulose. The use of cow's rumen fluid for methane production from coffee pulp is still rare, particularly for rumen fluid. Chemical pretreatment was carried out using alkali-peroxide followed by rumen fluid pretreatment. The performance of biogas produced from coffee pulp (with and without pretreatment) using rumen fluid as an inoculum has been investigated. Biogas was produced in a semi-batch reactor with a working volume of 2 liters for 30 days. Removal lignin, SS, VFA, and biogas yield were measured. This study aims to determine the biogas production from coffee pulp using variation HRT 20 and 30 days. It can be concluded that chemical pretreatment of NaOH - H2O2 combination can reduce lignin up to 75.02%. The volume of biogas produced increased with chemical pretreatment and rumen fluid as compared to the substrate with only rumen pretreatment According to Gas Chromatography analysis, the methane gas obtained from chemical pretreatment and rumen with HRT 30 days is 47.93%, while the methane obtained from rumen pretreatment with HRT 30 days is 34.28%.

Hydrothermal modification of calcined diatomite with CaO: Effect of NaOH pretreatment

The development and application of high-adsorptive calcined diatomite (C-D) can provide a cost-effective solution for the filter aid industry, which remains a challenge in this field. Herein, an alkali (NaOH) pretreatment was introduced before the calcium oxide (CaO)-mediated hydrothermal activation of C-D. The adsorption performance of the alkali-modified samples (modified calcined diatomite: M-D) was significantly improved. The methylene blue trihydrate (MB) adsorption capacity of the optimal M-D sample reached 45.76 mg/g, which was 2.73 times higher than that of the sample prepared without the alkali treatment. The substantial enhancement in adsorption performance of M-D was mainly attributed to the abundant SiO32− species which was primarily generated during the NaOH pretreatment. SiO32− species are helpful for generating silicate substances with a larger specific surface area. By regulating the amount of NaOH, it was feasible to control the morphology/nanostructure and composition of the final materials. Well-developed flower-like nanoclusters was synthesized on the surface of C-D, resulting in higher specific surface area and adsorption capacity. This work paves the way to the value-added application of natural diatomite resources via providing an efficient modification method to optimize the properties of C-D.

Effect of thermal and NaOH pretreatment on water hyacinth to enhance the biogas production.

Water hyacinth (WH) is used as the substrate for biogas production due to its high lignocellulosic composition and natural abundance. The present study used thermal and chemical (alkali) pretreatment techniques to enhance biogas production from water hyacinth used as a substrate by anaerobic digestion. Thermal pretreatment was done using an autoclave at 121 °C and 15 lb (2 bar) pressure and alkali pretreatment by NaOH at two concentrations (2% and 5% w/v). The inoculum:substrate ratio for biogas production was 2:1, where cow dung was used as inoculum. Results indicated that the pretreatments increased biomass degradability and improved biogas production. Water hyacinth pretreated with 5% NaOH produced the highest amount of biogas (142.61 L/Kg VS) with a maximum methane content of 64.59%. The present study found that alkali pretreatment can modify the chemical structure and enhance WH hydrolysis, leading to enhanced energy production.

Random forest and Shapley additive explanation for compressive strength prediction of NaOH-pretreated crumb rubber concrete

The compressive strength (CS) of crumb rubber concrete (CRC) can be improved through a chemical pretreatment involving immersion of the crumb rubber particles in a NaOH solution. Despite the potential benefits of this treatment, accurately estimating the CS value of NaOH-pretreated CRC remains challenging. To address this issue, a comprehensive database encompassing 118 entries on the fundamental mixtures of CRC along with NaOH concentration and pretreatment duration has been meticulously compiled for machine learning analysis. The random forest (RF) algorithm is employed to predict the 28-day CS value of NaOH-pretreated CRC. The model hyperparameters are optimized using a random search technique with 10-fold cross-validation. The findings reveal that the optimized RF attains acceptable predictive performance, yielding RMSE, MAE, and R2 values of 3.83 MPa, 2.84 MPa, and 0.85, respectively, on the testing dataset. Additionally, the model is interpreted using multiple techniques, including permutation importance, RF model-based feature importance, and Shapley additive explanation from global or local perspectives. The feature importance analyses consistently highlight the crucial role of crumb rubber content in determining the 28-day CS value of NaOH-pretreated CRC, and the influence of NaOH concentration and pretreatment time appear relatively inconsequential compared to features associated with the CRC mixture. This research contributes to a deeper understanding and better mixture design of CS for NaOH-pretreated CRC.

Effect of NaOH Pretreatment on Permeability and Surface Properties of Three Wood Species

Effect of NaOH Pretreatment on Permeability and Surface Properties of Three Wood Species

Effect of alkaline and steam pre-treatment on saccharification of corn cob and production of cellullase from fungal consortium

Lignocellulosic biomass as fossil fuel alternative comes with its challenges such as its inherent stability and recalcitrance. The use of commercial cellulase in the removal of lignin comes with high cost. This research seeks to answer questions on how alkaline and steam pre-treatment improve cellulose/glucose liberation from lignocellulosic biomass (corn cobs) using a consortium of <i>pichia kudriavzevii</i> and <i>cyberlindnera fabianii.</i><br /> In the current study, the effectiveness of steam and sodium hydroxide (NaOH) pre-treatment for reducing corn cob structure was examined, and the pre-treated biomass afterwards was exposed to the hydrolyzing activity of a consortium enzyme cocktail that was custom-formulated. The results of an analysis of composition showed that while alkaline pre-treated corn cob (APC) had 1.2% lignin, 75.8% cellulose, and 10.9% hemicellulose, steam pre-treated corn cob (SPC) had 2.5% lignin, 67.2% cellulose, and 25% hemicellulose. Lignin was eliminated from the biomass of corn cobs using both steam and NaOH pre-treatment. The hydrolyzing effect of the holocellulolytic enzyme cocktail, prepared with two multifunctional enzymes, was applied to the alkaline and steam pre-treated samples. This hydrolyzed SPCs more effectively than APC feedstocks, revealing that steam was a more effective pre-treatment attaining a remarkable 8.33 U/mg endoglucanase, 5.56 U/mg exoglycanase and 8.97U/mg beta-glucosidase levels (event 1) and glucose peak concentration of 0.433 mol/mL at 48 hours (event 2); according to a thorough examination of cellulase capacity and glucose levels.<br /> Overall, the consortium enzyme cocktail effectively hydrolyzed agricultural feedstocks that had undergone alkaline pre-treatment, making it a desirable option for usage in the bioconversion procedure in the biorefinery sector. This study demonstrates an effective technique for turning agricultural waste (corn cob) into high-value products through effective and practical chemical pre-processing.

Crystal violet adsorption onto modified biosorbent prepared from agricultural waste: kinetics, isotherm and thermodynamic studies

The present study investigated crystal violet removal by modifying the chestnut shell with a chemical activation method. For this purpose, H2SO4 and NaOH pretreatments were applied to the chestnut shell and the pretreatment method that gave the best performance under the same conditions was determined. The best adsorption efficiency was achieved with the NaOH pretreatment (99.06%) and the crystal violet adsorption reached equilibrium within 60 min. After selecting the best chemical activation method, the modified chestnut shell was characterized before and after adsorption (FTIR and SEM). Furthermore, the effects of parameters such as pH, initial crystal violet concentration, adsorbent dosage, temperature, and contact time were observed. Moreover, isotherm, kinetics and thermodynamics of the adsorption process were researched in detail. The best results were obtained with the Langmuir isotherm model (R2=0.99) and the pseudo-second-order kinetic model (R2=0.99). Thermodynamic parameters showed that the adsorption process is spontaneous, endothermic and feasible.

Integrated Production of Xylitol, Ethanol, and Enzymes from Oil Palm Empty Fruit Bunch through Bioprocessing as an Application of the Biorefinery Concept

Oil palm empty fruit bunch (OPEFB), an abundant source of lignocellulosic biomass waste, is rich in hemicellulose and is converted into xylose for xylitol production. The remaining cellulose-rich residue can be efficiently hydrolyzed into glucose, which serves as a substrate for bioethanol and enzymes. This process aligns with an integrated biorefinery model aimed at optimizing the utilization of OPEFB. This study optimizes a two-stage enzymatic hydrolysis fermentation for OPEFB conversion into value-added products. Using a 4% NaOH pretreatment, lignin was degraded while preserving hemicellulose and cellulose. This hydrolysis yielded 12.27 g/L of xylose and 36.86 g/L of glucose. Ethanol production, using varied fermentation media, achieved maximum concentrations of 0.043 g/L for xylitol and 21.35 g/L for ethanol, with substrate-to-product yields of 0.005 g/g and 0.374 g/g, respectively. Furthermore, enzyme production by Aspergillus niger was assessed on multiple parameters, recording a peak cellulase activity of 55.16 ± 20.24 U/mL and enzyme weight of 42.748 kDa. The OPEFB substrate yielded the highest protein content of 0.00942 ± 0.00010 mg/mL. These findings demonstrate the feasibility and efficiency of the two-stage enzymatic hydrolysis strategy in facilitating integrated biorefinery processes for efficient and sustainable OPEFB utilization.

Exploring the impact of NaOH pre-treatment for H2 and CO2 adsorption on clinoptilolite

The present investigation involved the treatment of natural clinoptilolite with varying concentrations of NaOH solutions followed by calcination. The samples' composition and structure were characterized and their performance was investigated in the context of hydrogen (H2) and carbon dioxide (CO2) adsorption. While a decreasing SiO2/Al2O3 ratio was observed in the NaOH-treated samples, the morphological structure obtained from SEM images and the increase in surface area according to BET results exhibited more pronounced alterations, particularly within the 0.5–1 M NaOH concentration range. The alkali treatment resulted in notable peak sharpening, with the most prominent changes observed in the (020), (100), and (101) lattice planes at the same concentration. However, there were no significant alterations in peak intensities. Although H2 adsorption (4.0192–26.4726 cm3/g) could reach higher values, higher amounts of CO2 adsorption (5.2308–20.2700 cm3/g) occurred as the concentration of NaOH increased. This phenomenon was attributed to structural modifications in clinoptilolites.

Enhancing Aqueous Carbonation of Calcium Silicate through Acid and Base Pretreatments with Implications for Efficient Carbon Mineralization.

Carbon dioxide (CO2) mineralization based on aqueous carbonation of alkaline earth silicate minerals is a promising route toward large-scale carbon removal. Traditional aqueous carbonation methods largely adopt acidification-based approaches, e.g., using concentrated/pressurized CO2 or acidic media, to accelerate mineral dissolution and carbonation. In this study, we designed and tested three distinctive routes to evaluate the effect of pretreatments under different pH conditions on aqueous carbonation, using amorphous calcium silicate (CS) as an example system. Pretreating CS with high concentrations (100 mM) of HCl (Route I) or NaOH (Route II and III) enhanced their carbonation degrees. However, NaOH pretreatment overall yielded higher carbonation degrees than the HCl pretreatment, with the highest carbonation degree achieved through Route III, where an extra step is taken after the NaOH pretreatment to remove the solution containing dissolved silica prior to carbonation. The HCl and NaOH pretreatments formed different intermediate silica products on the CS surface. Silica precipitated from the HCl pretreatment had a minimal effect on the carbonation degree. The high Ca/Si ratio intermediate phases formed from the NaOH, on the other hand, can be readily carbonated. In contrast to commonly utilized acidification-based approaches, basification offers a more promising route to accelerate aqueous carbonation as it can mitigate the need for costly pH swing and high-concentration/pressurized CO2. The key to aqueous carbonation under basic conditions, as suggested by this study, is the control of aqueous silica species that have a suppressing effect on carbonation. Overall, this study highlights the critical needs for investigations of aqueous mineral carbonation in a broader pH region.

The Effect of Different Sludge Pretreatment Methods on Microalgae Performance and the Release of Pollutants in Hydrolysis Acidification Solutions

Waste-activated sludge disposal has now become a serious global problem. After pretreatment, sludge was hydrolyzed and acidified to release nutrients. The effects of different sludge pretreatments on microalgal growth and contaminants in a hydrolysis acidification solution were compared. Alkalinization (NaOH), ultrasound (US), and combined pretreatment techniques (US-NaOH) all promoted contaminants’ release from the sludge by triggering microbial cell wall rupture and extracellular polymer dissolution. The organics released from the pretreated sludge were more readily and rapidly consumed due the presence of abundant microorganisms. The US group was more capable of releasing contaminants than the NaOH group, while the US-NaOH group overrode both. The growth characteristics, photosynthetic performance, and effluent treatment properties of Chlorella were observed in all group. In the untreated group, Chlorella exhibited higher algal density, maximum photochemical quantum yield, and effluent treatment capacity. The results demonstrated that sludge pretreatment could facilitate the release and rapid consumption of pollutants. Additionally, the NaOH pretreatment could remove the refractory organics to a higher degree, and could also accumulate more photosynthetic pigments. This study demonstrated the feasibility of Chlorella being used in practical scenarios such as hydrolytic acidification solutions for different sludge treatment methods, providing data for wastewater treatment and resource utilization.

Utilization of Festuca arundinacea Schreb. Biomass with Different Salt Contents for Bioethanol and Biocomposite Production

Soil salinity is one of the particularly important environmental factors, which limits the growth and development of plants, reduces the amount of crops and causes serious economic damage. The study found that Festuca arundinacea can be successfully used for the management and bioremediation of saline habitats, and it is characterized by a very well-developed root system and an average high biomass production of approx. 14.8 Mg∙ha−1, which can be used for industrial applications. Tall fescue biomass from soils with different levels of salinity was used to obtain bioethanol using 1.5% NaOH pretreatment and for the process of simultaneous enzymatic hydrolysis and ethanol fermentation (SSF). It was found that the content of Na+ ions in the tall fescue biomass had no significant effect on the amount of ethanol obtained (the average 19.32 g∙100 g−1 of raw material). F. arundinacea biomass was also used as a natural filler to obtain green composites using a biodegradable polylactide (PLA) matrix. It has been shown that tall fescue biomass with the lowest sodium content in biomass (approx. 2.5 mg∙g−1) from an area with high saline (above 6 g NaCl∙L−1) has the smallest effect on reducing the tensile and flexural strength of composites. Moreover, the highest value of bioethanol concentration (21.2 g∙100 g−1 of raw material) for this biomass sample was obtained.

Bioenergy production from pretreated rice straw in Nigeria: An analysis of novel three-stage anaerobic digestion for hydrogen and methane co-generation

The response to Nigeria's energy inadequacies and waste management issues is projected in this research to be achieved with hydrogen and methane co-produced from pretreated (PT) rice straw (RS) in a three-stage digestion process. This study also demonstrated a novel pretreatment (PTM) agent to improve biological energy recovery from RS. The objectives were accomplished using acidogenic and methanogenic procedures in batch, semi-continuous and continuous systems after pretreating RS with chemical/potash extract (PE) followed by a biological agent. At the same time, the energy assessments were done using data from the laboratory study and the literature. The research findings indicated that at the acidogenesis stage, specific hydrogen yield was insignificant when chemical agents and PE were employed alone. However, the daily H2 production increased when the PT RS residues were enzymatically hydrolysed with NaOH-PT (114 NmL H2 g−1 TS d−1) and PE-PT (103 NmL H2 g−1 TS d−1) RS substrates having the highest values at steady states and raw RS producing the least (30 NmL H2 g−1 TS d−1). In the methanogenesis phase, chemical/ PE PTM followed by enzymatic hydrolysis of RS improved the daily specific methane production by 18%, 31.7% and 41.5% for HCl, PE and NaOH-PT RS residues. The methane production efficiency was 80% for NaOH, 75% for PE, and 68% for HCl RS PT samples, while the raw RS was 48%. The total output energy expressed in electricity and thermal production using combined cooling, heat, and power (CCHP) showed that NaOH and PE-PT RS digesters gave the highest electricity (892.43 and 852.00 KWhelect. tonne-1 TS) and thermal (1194.10 and 1140 KWhtherm. tonne-1 TS) yield respectively. Similarly, the cooling fluid in KWhcool produced per tonne of TS RS was 835.57, 798.00 and 741.66 for NaOH, PE and HCl PT RS samples. Finally, whereas the Firmicutes, especially the Clostridium, Ruminococcus and Thermoanaerobacterium, were the dominant microbial community in acidogenic digestates, the Euryarchaeota typified by Methanobacterium, Methanosarcina and Methanosaeta were the principal phyla for most methanogenic reactors.