Pretreatment For Anaerobic Digestion Research Articles

Magnetic iron oxide nanoparticle enhanced microwave pretreatment for anaerobic digestion of meat industry sludge

Our study investigates the effects of iron oxide (Fe3O4) nanoparticles combined microwave pretreatment on the anaerobic digestibility and soluble chemical oxygen demand (SCOD) of meat industry sludge. One of our main objectives was to see whether the different microwave-based pretreatment procedures can enhance biogas production by improving the biological availability of organic compounds. Results demonstrated that combining microwave irradiation with magnetic iron oxide nanoparticles considerably increased SCOD (enhancement ratio was above 1.5), the rate of specific biogas production, and the total cumulative specific biogas volume (more than a threefold increment), while having no negative effect on the biomethane content. Furthermore, the assessment of the sludge samples’ dielectric properties (dielectric constant and loss factor measured at the frequency of 500 MHz) showed a strong correlation with SCOD changes (r = 0.9942, R2 = 0.99), offering a novel method to evaluate pretreatment efficiency.

Energy Integration of Thermal Pretreatment in Anaerobic Digestion of Wheat Straw

Cereal straw stands out as one of the most abundant and globally distributed agricultural residues. Traditional applications cope with a limited amount of production, leaving the remainder in the field for natural decomposition. Managing cereal straw through controlled biological transformation under anaerobic conditions holds the potential to generate added value in the form of bioenergy. However, the lignocellulosic composition of these substrates poses challenges for organic degradation, often requiring energy-intensive pretreatments. A detailed study with a comprehensive calculation of the overall energy balance of the integrated process is proposed, aiming to provide real added value and replicability. Three scenarios for wheat straw transformation were investigated, incorporating two preliminary pre-treatment stages—mechanical milling and physicochemical steam explosion. Three conditions of pretreatment were essayed, varying the time exposure of the steam explosion. The subsequent energy integration analysis revealed that the process was optimized by up to 15% in the final energy balance when the steam explosion was set to 10 min. The macromolecular composition determination revealed that the thermal pretreatment reduced the lag phase of the hydrolysis step through hemicellulose breakdown.

Valorising lignocellulosic biomass to high-performance electrocatalysts via anaerobic digestion pretreatment

AbstractAnaerobic digestion (AD) was initially evaluated as a potential preprocessing method for preparing biomass-based carbon electrocatalysts in this study. The AD pretreatment succeeded in the structural depolymerization and nitrogen enrichment of Hybrid Pennisetum, which provided favorable conditions to achieve efficient and homogeneous nitrogen introduction due to microorganism community enrichment and provided a porous structure by degradation of the biodegradable components. The resulted biochar exhibited improved physiochemical properties including higher specific surface areas, nitrogen content and graphitization degree than that obtained from pyrolyzing raw biomass. These improvements were positively correlated with the AD time and showed to have enhanced the performance in oxygen reduction reaction and practical microbial fuel cell applications. Amongst the investigated samples, the obtained biochar pretreated by AD for 15 days exhibited the most excellent performance with an onset potential of 0.17 V (VS. saturated calomel electrode) and the maximal power density of 543.2 mW cm−2 assembled in microbial fuel cells. This study suggested applying AD as a new biological pretreatment in the preparation of biomass-based electrocatalysts, and provided a unique pathway for fabricating high-performance biochar-based catalysts by structure optimization and N-containing active sites construction via gentle biological method, thereby providing a cost-effective method to fabricate metal-free catalysts for oxygen reduction reaction. Graphical Abstract

Experimental Investigations on the Effect of Pretreatment in Anaerobic Digestion of Coir Pith Agro Waste

The coir industry in India’s southern coastal regions, especially in the state of Kerala, is becoming increasingly concerned about the environmental impact of the accumulation and incremental increase of coir pith each year. The objective of this study was to assess the effect of pretreatment on the anaerobic digestion of coir pith. The characterization study of coir pith shows high organic content, which can be anaerobically digested to produce biogas. But, the high lignin content (30.91%) makes the process slow. To overcome this, a biological pretreatment method was tried using two microbial cultures belonging to fungal genera known to be lignin decomposers, viz., Trichoderma and Pleurotus. By using Trichoderma, lignin content was reduced by 3.7%, and the maximum gas production was obtained in a shorter time (19 days) in comparison with the sample without any pretreatment (24 days). When Pleurotus was used for lignin degradation, the lignin content was reduced by 6.78%, and the maximum gas production was obtained in a much shorter time period (14 days) in comparison with the former two methods. The gas produced comprises 74 ppm of methane, which has fuel value. The sludge after digestion was tested, which indicated a marginal increase in NPK value and hence can be used as fertilizer. The results of the study appear to be quite promising in the transition towards green energy by providing scope for the process of biomethanation, with the conclusion that further research can transform coir pith into a good renewable energy resource.

Nitrite acts as the key “switch” governing the free nitrous acid pretreatment in anaerobic digestion: A comprehensive mechanism of abiotic, bioinformatics and bioenergetics effects

Free nitrous acid (FNA) pretreatment has been an effective and environmentally-friendly strategy to improve anaerobic digestion (AD) performance, and the mechanism was generally ascribed to the abiotic role of enhancing substrate solubilization. However, a comprehensive understanding of FNA is lack considering the different biotic roles on various steps, microbes and functional genes, as well as the variation of thermodynamic conditions. Herein, FNA pretreatment significantly enhanced the AD performance of food waste (FW), and the maximum increment of methane yield (36.45 %) was observed for FNA level of 1.42 mg HNO2 − N/L. Nevertheless, FNA exhibited an inhibition-to-enhancement effects as the AD process proceeds, and the introduced nitrite was the key “switch”. Initially, the abiotic effects of FNA reduced the molecular weight of components in FW, benefiting the solubilization and formation of available organics (glucose and amino acid). The individual steps experiment confirmed that residual nitrite severely inhibited methanogenesis rather than hydrolysis and acidogenesis, which resulted in the decrement of methane yield and accumulation of VFAs. Meanwhile, the methanogens (Methanothrix and Methanobacterium) and genes involved in methanogenesis metabolisms (aceticlastic and hydrogenotrophic pathways) were downregulated. However, with the elimination of nitrite, the microbial activities and gene expressions restored and were even enhanced, and Gibbs-energy-based analysis suggested that accumulated VFAs provided favorable thermodynamic conditions for subsequent methanogenesis. This study firstly proved that the abiotic breakdown of macromolecule components, selective and reversible inhibition on microbes and functional genes induced by nitrite and varying thermodynamic conditions together governed the FNA affecting the AD process of FW.

Effect of anaerobic digestion pretreatment on pyrolysis of distillers’ grain: Product distribution, kinetics and thermodynamics analysis

To systematically examine the effects of anaerobic digestion (AD) pretreatment on product distribution and kinetics of distillers’ grains (DG) and its digestates collected at different AD durations, Py-GC/MS and TG analyses were conducted. Py-GC/MS analysis revealed a reduction in the proportion of oxygenated and nitrogenous compounds in all digestates and increase the share of hydrocarbons: 46.72% (SD-2), 65.53% (SD-4), 43.20% (SD-6) and 50.05% (SD-8) than DG (38.61%). To assess activation energy, Friedman, Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa models were employed with average values ranging from 159.54 to 170.96 kJ mol−1 for DG, 156.59–165.42 kJ mol−1 for SD-2, 15.67–166.47 kJ mol−1 for SD-4, 153.28-159-45 kJ mol−1 for SD-6, and 156.02–167.37 kJ mol−1 for SD-8, which were lowered than DG. Thermodynamic studies showed positive ΔH and ΔG values, suggesting that the pyrolysis of DG and digestates is non-spontaneous. The negative ΔS values implied that the degree of disorder in products resulting from bond dissociation was lower than initial reactants. These findings provide valuable insight into the potential of AD as a pretreatment method and offer an understanding of the pyrolysis behavior of digestates. This study not only offers practical guidance but also contributes to the theoretical framework for utilizing AD as a pretreatment method for pyrolysis.

Enhancing Biomethane Production from OFMSW: The Role of Moderate Temperature Thermal Pretreatment in Anaerobic Digestion

Enhancing Biomethane Production from OFMSW: The Role of Moderate Temperature Thermal Pretreatment in Anaerobic Digestion

Enhancement of methane production by electrohydrolysis pretreatment for anaerobic digestion of OFMSW

Hydrolysis is the most critical rate-limiting step in the anaerobic digestion (AD) process for most types of substrates. The organic fraction of municipal solid waste (OFMSW) is a rich source for the AD process because of its high degradability. In this study, electrohydrolysis pretreatment was investigated for the OFMSW to overcome the rate-limiting step of hydrolysis. Electrohydrolysis pretreatment was applied to the OFMSW for 30 and 60 min in a custom-made reactor. In the untreated, 30-min. treated, and 60-min. treated OFMSW average methane production was observed as 225 ± 2 mL CH4/g VSadded, 231 ± 4 mL CH4/g VSadded, and 248 ± 7 mL CH4/g VSadded, respectively. By increasing the treatment time, the lag phase, during which hydrolysis occurs, was reduced by 40–43%. 3–10% more methane was produced by applying electrohydrolysis pretreatment. These results suggest that electrohydrolysis pretreatment is a promising method to improve the efficiency of AD for the OFMSW by reducing the time required for hydrolysis and increasing methane production. More investigation is required to better comprehend the effects of electrohydrolysis on the OFMSW.

Conversion of Materials and Energy in Anaerobic Digestion of Sewage Sludge with High-Pressure Homogenization Pretreatment

High pressure homogenization (HPH) pretreatment can improve sludge anaerobic digestion; however, the relationship among the material, energy conversion, and gas production efficiency was unclear under different operating conditions in sludge anaerobic digestion by HPH pretreatment. In this study, the performance of HPH pretreatment before sludge anaerobic digestion was investigated, and the relationship among the material, energy conversion, and gas production efficiency was explored. HPH pretreatment induced organic solubilization, and a maximum soluble chemical oxygen demand (SCOD)/total chemical oxygen demand (TCOD) of about 30% was achieved. Results showed that HPH pretreatment significantly improved the biogas production of sludge anaerobic digestion; the maximum increase in CH4 yield was 57%; and the anaerobic digestion period was shortened by about 10 days. The ratio of CH4 yield increment to volatile dissolved solids (VDS) increment was 0.21 mL/mg. The CH4 yield increment of 1 L/g volatile solid (VS) required a specific energy of 0.10 MJ/kg total solid (TS) by increasing the pressure with one cycle and 0.72 MJ/kg TS by increasing the cycle at 60 MPa. The minimum additive energy consumption of HPH pretreatment was 125 J/mL CH4 yield increment at 20 MPa with one cycle. Considering CH4 yield improvement and energy conservation, HPH pretreatment should maintain a pressure of no more than 60 MPa in one cycle. This study provides a theoretical reference for the practical application of HPH pretreatment in anaerobic digestion. HPH holds promise as a potential strategy for sewage sludge pretreatment to produce CH4 in anaerobic digestion.

Impact of sequential hybrid pretreatment in anaerobic digestion of food waste and garden waste co-digestion on waste characteristics and biogas production

Impact of sequential hybrid pretreatment in anaerobic digestion of food waste and garden waste co-digestion on waste characteristics and biogas production

Application of Ammoniation Pretreatment in Anaerobic Digestion of Straw

Straw is a widely available and highly renewable biomass resource with good utilization value. However, its dense structure is not conducive to methane production during anaerobic fermentation and requires pretreatment. To achieve high-value conversion, pretreatment technologies can effectively destroy the rank structure of straw and increase gas production. Ammoniation pretreatment has unique advantages in pretreating straws. This article reviews the ammoniation pretreatment mechanism, the impact of ammoniation pretreatment parameters on anaerobic fermentation, and ammoniation pretreatment technology, providing a reference for the ammoniation pretreatment of straw.

Ultrasonication as anaerobic digestion pretreatment to improve sewage sludge methane production: Performance and microbial characterization

A large amount of sludge is inevitably produced during sewage treatment. Ultrasonication (US) as anaerobic digestion (AD) pretreatment was implemented on different sludges and its effects on batch and semi-continuous AD performance were investigated. US was effective in sludge SCOD increase, size decrease, and CH4 production in the subsequent AD, and these effects were enhanced with an elevated specific energy input. As indicated by semi-continuous AD experiments, the mean daily CH4 production of US-pretreated A2O-, A2O-MBR-, and AO-AO-sludge were 176.9, 119.8, and 141.7 NmL/g-VSadded, which were 35.1%, 32.1% and 78.2% higher than methane production of their respective raw sludge. The US of A2O-sludge achieved preferable US effects and CH4 production due to its high organic content and weak sludge structure stability. In response to US-pretreated sludge, a more diverse microbial community was observed in AD. The US-AD system showed negative net energy; however, it exhibited other positive effects, e.g., lower required sludge retention time and less residual total solids for disposal. US is a feasible option prior to AD to improve anaerobic bioconversion and CH4 yield although further studies are necessary to advance it in practice.

Urine pretreatment significantly promotes methane production in anaerobic waste activated sludge digestion

Methane production of waste activated sludge (WAS) in anaerobic digestion is hindered due to the rate-limited hydrolysis process and the low methane potential of WAS. Pretreatment of WAS is a common and appealing strategy to improve methane production in anaerobic digestion. In this study, we proposed to use urine, an easily obtained human waste with high ammonium concentration and pH, as a novel pretreatment strategy for anaerobic WAS digestion. Urine pretreatment at levels of 5–30 % (Vurine/Vurine+WAS) could substantially enhance methane production by 5–35 % in biochemical methane potential (BMP) tests, with the highest methane production of 179.6 ± 3.3 mL/g volatile solids (VS) achieved under the highest level of urine (i.e. 30 % urine addition). Based on the model analysis, the biochemical methane potential (B0) and hydrolysis rate of WAS (k) rose from 131.9 mL/g VS and 0.19 d−1 in the control without pretreatment to 136.3–178.2 mL/g VS and 0.22–0.30 d−1, respectively, after the urine pretreatment (5–30 % addition). Urine pretreatment with 5–30 % addition also improved the degradation extent (Y) of WAS by 3–35 %. The promising results indicate that urine pretreatment in anaerobic digestion is a promising technology to improve the efficiency of anaerobic digestion with environmental and economic benefits.

Effects of anaerobic digestion pretreatment on the pyrolysis of Sargassum: Investigation by TG-FTIR and Py-GC/MS

Anaerobic digestion was tentatively used as a pretreatment to change the pyrolysis characteristics of Sargassum in this study. The physicochemical properties of Sargassum with different anaerobic digestion durations were investigated. With the increasing the anaerobic digestion duration from 0 to 21 days, the content of extract and cellulose decreased from 37.5 wt% and 12.63 wt% to 27.82 wt% and 4.73 wt%, respectively. While the content of lignin increased from 9.99 wt% to 14.69 wt%. The apparent structure of Sargassum was altered due to changes in chemical composition, which increased the fiber crystallinity and specific surface area. In addition, the effects of anaerobic digestion durations on the gaseous and liquid products of pyrolysis were analyzed by TG-FTIR and Py-GC/MS, respectively. The thermal stability of Sargassum was enhanced due to the consumption of organic matter during anaerobic digestion. The temperatures of weight loss peak for P1-P4 were 326.83, 335.92, 328.80 and 322.75 °C in the devolatilization step, and the final residual mass percentages of Sargassum digestate (digested for 0, 7, 14 and 21 days) were 37.39, 44.61, 48.89 and 49.29%, respectively. Due to the consumption of biodegradable fractions, the structure of Sargassum was loosened. Thus, mild anaerobic digestion pretreatment facilitated the release of functional groups and gases, whereas excessive consumption of some biodegradable fractions might reduce the corresponding gaseous product. The selectivity of bio-oils composition was also altered by anaerobic digestion pretreatment. The relative content of N-compounds and hydrocarbons was enhanced, and the formation of O-compounds was inhibited with anaerobic digestion pretreatment. This study proved that anaerobic digestion pretreatment could alter the composition and structure of the biomass, which varied the thermal-stability and thus influenced the quality of the pyrolytic products. This new attempt is expected to provide an alternative pretreatment for pyrolysis process.

Methods of Pretreating Raw Materials Containing Organic Compounds before Anaerobic Digestion

Introduction. The volume of accumulated organ-containing non-recyclable waste products in Russia is increasing. Existing technologies make it possible to recycle these waste products through using anaerobic digestion to produce biogas and fertilizers. The organic portions of waste consist mostly of hard-to-degrade lignin, cellulose, and extracellular polymers, which make anaerobic digestion difficult. Pretreating is necessary to make the raw materials available to microorganisms for bioavailability and deeper degradation. There are many different types of pretreating with their own specific effects on the raw materials. To improve understanding the process of pretreating organic raw materials prior to anaerobic digestion, and to improve the quality of the decisions made, pretreatment methods need to be identified and systematized. Materials and Methods. The subject of the study is the relationship between the effects of methods, techniques and specific operations of pretreatment for anaerobic digestion. The main method of this study is the analysis of data on the application of different methods to increase the bioavailability and degree of decomposition of organic matter of waste products during anaerobic digestion. Results. The scheme of preparatory operations and methods for pre-treatment of organic waste products before anaerobic digestion is developed. It is revealed that each method (mechanical, thermal, electromagnetic, chemical, biological and combined) contains many practices, which are divided into particular techniques. The mechanisms of influence that improve further processing are described. Discussion and Conclusion. The choice methods of pretreatment depends on the purpose and tasks performed, the physical and chemical composition of raw materials, access to energy, biological and chemical resources. Advantages and disadvantages of various methods should be studied in more detail and ranked into private methods according to energy costs and the effect they produce. The comparison of the research results reveals disadvantages and difficulties.

Effect of microaeration combined with ferric chloride pretreatment on anaerobic digestion of corn stalk

ABSTRACT In this study, microaeration combined with ferric chloride pretreatment was used to improve the methanogenic performance for thermophilic dry anaerobic digestion. Parameter optimization and mechanism analysis were explored for combined pretreatment in anaerobic digestion by response surface methodology and microbial diversity and community. The results showed that both microaeration and ferric chloride had significant effects on the cumulative methane production, and the effect of microaeration was greater than that of ferric chloride. The optimal pretreatment parameters were predicted at oxygen loading rate of 0.76 mL/g VS and ferric chloride addition rate of 4.04 mg/g VS. The methane production of anaerobic digestion was 114.05 mL/g VS with the optimal pretreatment parameters, which was 17.78% higher than that without pretreatment. In addition, microbial community analysis showed that combined pretreatment enhanced methanogenesis by enhancing the hydrogenotrophic pathway.

Anaerobic Biodegradation of Wheat Straw Lignin: The Influence of Wet Explosion Pretreatment

Large amounts of lignin residue is expected in the future when biorefineries for producing biofuels and bio-products will increase in numbers. It is, therefore, valuable to find solutions for using this resource for the sustained production of useful bioenergy or bio-products. Anaerobic digestion could potentially be an option for converting the biorefinery lignin into a valuable energy product. However, lignin is recalcitrant to biodegradation under anaerobic conditions unless the structure is modified. Wet oxidation followed by steam explosion (wet explosion) was previously found to make significant changes to the lignin structure allowing for biodegradation under anaerobic conditions. In this study, we examine the effect of wet explosion pretreatment for anaerobic digestion of wheat straw lignin under mesophilic (37 °C) conditions. Besides the biorefinery lignin produced from wheat straw, untreated lignin was further tested as feed material for anaerobic digestion. Our results showed that wet exploded lignin pretreated with 2% NaOH showed the highest lignin degradation (41.8%) as well as the highest methane potential of 157.3 ± 9.9 mL/g VS. The untreated lignin with no pretreatment showed the lowest methane yield of 65.8 ± 4.8 and only 3.5% of the lignin was degraded. Overall, increased severity of the pretreatment was found to enhance anaerobic degradation of lignin.

Enhancement of sludge dewaterability via the thermal hydrolysis anaerobic digestion mechanism based on moisture and organic matter interactions

It is known that sludge dewaterability improves during the thermal hydrolysis process (THP); however, the effect of thermal hydrolysis and anaerobic digestion (THP-AD) on sludge dewaterability is unclear. Further, the difference between thermal hydrolysis as pre-treatment for anaerobic digestion (pre-THP-AD) and as post-treatment (post-THP-AD) is also unclear. Based on the evolution of the interaction between organic matter and moisture, the mechanism of pre-THP-AD and post-THP-AD improving the sludge dewaterability was explored. The capillary suction time values of pre-THP-AD and post-THP-AD increased by 58% and 59%, respectively, and the proportion of free moisture increased by 10.44% and 10.59%, respectively, compared with the conventional anaerobic digestion (CAD) process. The cell structure was destroyed and most organic matter was converted into dissolved form through THP, organic matter degraded during AD, the interaction between moisture and organic matter declined, and the mechanically bound moisture transformed into free moisture. Additionally, the intensity of hydrophilic functional groups, such as amide I decreased and amide II disappeared after (pre- and post-) THP-AD. The surface hydrophobicity of sludge samples was enhanced and sludge dewaterability improved. The mechanism of pre-/post-THP-AD enhanced sludge dewaterability based on the interaction between moisture and organic matter; additionally, this will provide a reference for optimised moisture-sludge separation processes and guidance for the optimisation of engineering operation parameters.

Free ammonia pretreatment enhances the removal of antibiotic resistance genes in anaerobic sludge digestion

Sludge has been recognized as a reservoir of antibiotic resistance genes (ARGs) in the wastewater treatment plants. Our previous study has demonstrated that free ammonia (FA, i.e., NH3–N) pretreatment is an effective method for enhancing anaerobic digestion of sludge. However, the effects of FA pretreatment on the removal of ARGs in the anaerobic sludge digestion is still unknown. In this study, several ARGs representing various antibiotic classes and integrase gene (intI1) which is crucial for horizontal transfer of ARGs were chosen. This study demonstrated that combined FA pretreatment (420 mg NH3–N/L for 24 h, under which the highest anaerobic sludge biodegradability was achieved in our previous study) and anaerobic digestion could enhance the removal of aac(6′)-Ib-cr, blaTEM, sul2, tetA, tetB and tetX from sludge by 17–74% compared with anaerobic digestion without FA pretreatment, resulting in a lower ARGs abundance in the anaerobically digested sludge. This is caused by the removal of tested ARGs during FA pretreatment and the reduced abundance of potential microbial hosts of ARGs due to FA pretreatment during anaerobic digestion. The removal of IntI1 was not significantly affected by FA pretreatment and intI1 did not play a large role in the fate of the tested ARGs in this study. This study indicated that FA pretreatment for anaerobic digestion could potentially reduce the spread of ARGs from the sludge to the natural environment during sludge disposal or reuse.

Effects of alkali, autoclaving, and Fe+ autoclaving pretreatment on anaerobic digestion performance of coking sludge from the perspective of sludge extracts and methane production.

Pretreatment of activated sludge is an important step in increasing the reaction speed during anaerobic digestion by accelerating the hydrolysis process. It is necessary not only to analyze the changes in the general properties of the sludge before and after pretreatment but also to further analyze and evaluate the sludge structure and extracellular polymeric substances (EPS). In this study, the changes in coking sludge extracts after pretreatments with alkali, autoclaving, and Fe+ autoclaving were analyzed and compared using EPS heat extraction method. Moreover, the methane production potential of the pretreated coking sludge was investigated via biochemical methane potential (BMP) test. The results showed that after alkali, autoclaving, and Fe+ autoclaving, the concentration of protein and polysaccharide in the bound sludge extract accounted for approximately 40% and 28%, 62% and 51%, and 66% and 83% of the total protein and polysaccharide extracted from the sludge, respectively. In the experiment without pretreatment, there is no phenomenon of gas production from coking sludge. According to the BMP test results, Fe+ autoclaving pretreatment showed the highest methane production of 257mL/gVSS. This study revealed that the analysis of sludge extracts was necessary in assessing the effects of anaerobic digestion pretreatment and methanogenic potential. Moreover, coking sludge showed higher methanogenic potential after Fe+ autoclaving pretreatment.