Biogas Recovery Research Articles

Effect of ozonation on biodegradability enhancement and biomethanation potential of pretreatment process wastewaters from 2G ethanol production

AbstractBACKGROUNDThe production of second‐generation (2G) ethanol from lignocellulosic biomass generates large quantities of high‐strength complex wastewaters from various stages of the process. An effective pretreatment is necessary in order to overcome the low biodegradability of these wastewaters for further biomethane recovery. The present study reports the effect of ozonation on the biodegradability enhancement and biomethanation potential of complex 2G ethanol pretreatment process wastewaters, from acid (H2SO4) and alkali (NaOH) pretreatment process.RESULTSOzonation (9.33 g m−3) was performed for both acid and alkali pretreatment wastewaters at a flow rate of 10 L min−1 for 1 h. Ozonation of both wastewaters increased biodegradability index (BI) up to 36% along with minimal chemical oxygen demand (COD; 7 ± 3%), color (10 ± 4%), and toxicity (22.5 ± 7.5%) reduction. Biomethane potential tests were carried out for the control and ozonated wastewaters having BI > 0.4. The acid‐pretreatment wastewater indicated poor biomethanation potential due to high presence of sulfates (COD/SO4 ~ 3.0). However, ozonation of alkali‐pretreatment wastewater facilitated up to twofold enhancement in the cumulative methane volume, while the enhancement in the rate of methane production was found to be up to 47%. Fourier transform infrared spectroscopic analysis of control and ozonated wastewaters revealed the breakdown of complex organic molecules and aromatics to readily biodegradable intermediates. The kinetics of methane generation could be predicted by the modified Gompertz model.CONCLUSIONThe study demonstrated the efficacy of ozonation as an effective pretreatment option to facilitate biodegradability enhancement of 2G ethanol pretreatment process wastewaters. The enhancement in biodegradability was observed to enable subsequent biogas recovery via anaerobic digestion along with COD removal. © 2023 Society of Chemical Industry (SCI).

Prioritization of Waste-to-Energy Technologies Associated with the Utilization of Food Waste

Taking advantage of the growing production of organic waste for its conversion to waste-to-energy (WtE) also contributes to mitigating the problems associated with its final disposal, which is a global trend of increasing application. This work presents an innovative approach for the identification and prioritization of WtE alternatives available from the use of food waste (FW) present in the municipal solid waste (MSW) of a Colombian municipality with source separation and selective collection: (i) a systematic literature review, which allows one to identify WtE alternatives; (ii) the prospective MIC-MAC method (Matrice d’Impacts Croisés Multiplication Appliqués à un Classement) allowed the selection of criteria and sub criteria; (iii) the analytical hierarchical process (AHP) and the technique of order of preference by similarity to the ideal solution (TOPSIS), allowed a ranking of selected alternatives considering the technical, environmental, and social aspects. The WtE technologies identified were anaerobic digestion, gasification, incineration, biogas recovery from landfills, and pyrolysis; this last was excluded due to its greater application potential with substrates such as plastic waste. The six sub-criteria identified and prioritized were social acceptability (36%), greenhouse gas emissions mitigated (16.17%), MSW reduction (15.83%), energy production (13.80%), technological maturity (12.95%), and electrical energy conversion efficiency (5.25%), with the decreasing order of preferences of anaerobic digestion (78.2%), gasification (47.5%), incineration (27.4%), and biogas recovery from landfills (6.6%); the latter was the least desirable alternative (lower social acceptance and CO2 tons mitigated in relation to the other options). The innovative nature of this study is the identification and consideration of the comprehensive management of this type of waste of a large number of criteria (120 environmental, 52 social, and 59 technical) and the validation of the results through a sensitivity analysis, which allowed us to confirm for this study, that anaerobic digestion is the most favorable technology for the treatment and energy use of FW.

Biorefinery of Sewage Sludge: Overview of Possible Value-Added Products and Applicable Process Technologies

The disposal of excess biological sewage sludge from wastewater treatment is a growing environmental issue due to the vast quantities generated worldwide. For many years, sludge disposal has been considered an inevitable “nuisance” linked to the main task of wastewater treatment; recently, the issues relating to the presence of emerging pollutants in sludge have contributed to severe limitations on traditional disposal routes and increased process costs. As a consequence of the water industry’s approach to sustainability and circular economy principles, the investigation into options for sludge-embedded resource recovery has been increasing over time. Among these, the definition of biorefinery encompasses many processes used to process sewage sludge for biofuel and/or resource recovery. In addition to the “conventional” recovery of biogas and nutrients, biopolymers (PHAs and EPS), proteins, enzymes, biopesticides, and biofuels are among the “new” sludge extraction products that are being studied. Not all of the proposed technologies are, however, mature for industrial exploitation as yet. This paper presents an overview of possible product recovery from sludge biorefinery, with emphasis on recent developments, and on the benefits and limitations of applicable technologies for ensuring sustainability and environmental efficiency, through an analysis of the current literature.

Development of ecological sanitation approaches for integrated recovery of biogas, nutrients and clean water from domestic wastewater

Access to adequate sanitation services and the treatment of domestic wastewater becomes a critical problem in developing countries. Domestic wastewater treatment based on conventional sanitation concept is the most common approach, which is neither ecological nor economical sound to realize sustainable sanitation solution. Therefore, there is a need to block the sanitation-linked concerns and limitations of the conventional systems through the development of an alternative sustainable sanitation systems. With the rising demand to improve the existing sanitation system for environmental protection and resources conservation (energy, nutrient, and water), ecological sanitation approach appealed the attention of scientific communities. This paper presents the comprehensive review of domestic wastewater characteristics, conventional sanitation systems and its sustainability challenges; ecological sanitation technologies, process conditions and their performances in terms of resource recovery efficiency (i.e. biogas, struvite-based nutrients and clean water). The outcome of these approaches are resource oriented and closed-loop systems, which promotes the sustainable sanitation by overwhelmed the limitations of conventional systems. Moreover, the application of these technologies to treat domestic wastewater also helps to improve public health by reducing the introduction of disease causing pathogens in to the water cycle and minimizes the negative environmental impacts. Accordingly, the applications of ecological sanitation technologies to treat domestic wastewater would be a viable option to solve the existing sanitation problems; and simultaneously promoting energy-food-water-health nexus, especially in developing country. • Eco-San approaches of DWW in biogas, struvite and clean water recovery is reviewed. • COD removal and biogas recovery potential of various technologies are reported. • Nutrients removal and struvite recovery efficiencies from DWW are described. • The water reuse is based on the stringent water quality standards. • Future research is needed for an integrated recovery of valuables from mixed DWW.

Hydrothermal carbonization of sewage sludge: Optimization of operating conditions using design of experiment approach and evaluation of resource recovery potential

Scientific disposal of sewage sludge (SS) is a tedious task worldwide. Landfilling of the SS after centrifugation may have serious adverse impacts on the environment. The present study investigated efficacy of hydrothermal carbonization (HTC) as pretreatment for the centrifuged sewage sludge with an aim to improve resource recovery. In this study, both solid and liquid fractions recovered after the HTC were subjected to the detailed analysis for examining the opportunities for recovery of value-added chemicals and biogas. The HTC conditions were optimized using design of experiments (DOE) approach. The runs were performed in a high-pressure reactor at 160–240 °C temperatures and total pressures of 6.1–34.2 kg/cm2 for 1–3 h duration without supply of air. The optimum HTC temperature and duration were found to be 200 °C and 1 h, respectively. Under these conditions, the dried hydrochar (HC) had higher heating value of ~13 MJ/kg. Its properties were found similar to that of the sub-bituminous coal based on the atomic ratio of elements. The HTC pretreatment resulted in substantial reduction in carbon and oxygen due to decarboxylation, dehydration and oxidation (due to oxygen present in reactor headspace) reactions. The process wastewater (PWW) recovered after HTC at the optimum conditions had high concentration of the recoverable value-added compounds such as humic acid (HA) and PO43--P (concentration = 20 g/l and ~0.5 g/l, respectively). Moreover, significant quantity of biogas could be generated from the PWW. Hence, hydrothermal pretreatment can be considered a potential option for SS valorization.

Economic performance of biogas production and use from residues co-digestion in integrated 1G2G sugarcane biorefineries: Better electricity or biomethane?

Recovering bioenergy through anaerobic digestion (AD) has become the most attractive waste management approach in modern industrial plants, because both the environmental adequacy and the provision of clean biogas-derived energy can be successfully met. Recent investigations have particularly shown the energetic benefits of residue co-digestion in sugarcane biorefineries, which significantly enhances biogas production compared to mono-digestion schemes. This work carried out an economic analysis to assess the feasibility of producing biogas from residues co-digestion in an integrated 1G2G (first and second generation) ethanol biorefinery and its application in electricity and biomethane (BioCH4) production. Scenarios considered the mono-digestion of 1G vinasse in the season (MD1-base scenario), the mono-digestion of 1G vinasse in the season followed by the mono-digestion of 2G vinasse in the off-season (MD2), the co-digestion of 1G vinasse, filter cake and deacetylation liquor in the season followed by the co-digestion of filter cake and deacetylation liquor in the off-season (CD1), and finally the co-digestion of 1G vinasse, filter cake and deacetylation liquor in the season followed by the mono-digestion of 2G vinasse in the off-season (CD2). The scenarios comparison aimed to investigate the potential to implement year-round biogas production in sugarcane processing plants. The results showed that co-digestion-based scenarios (CD1 and CD2) had the best performance for producing both electricity and BioCH4 from biogas, with the higher profitability related to the latter. Scenario MD1 scenario presented a negative net present value (NPV) for both electricity and BioCH4 production, whilst only BioCH4 production would be profitable in scenario MD2. The NPV for electricity production in scenario CD2 reached USD 9 million (4-fold higher than mono-digestion of 1G vinasse reported in the literature), whilst a peak of USD 45 million was calculated for BioCH4 production. In addition, the current bioelectricity production from bagasse burning showed to be much more economically unfavorable compared to biogas production and use. Biogas recovery from residue co-digestion has been increasingly confirmed as an attractive alternative for energy generation within 1G2G ethanol biorefineries, maintaining year-round production and consisting of a robust BioCH4 source, with great potential to be used both as a biofuel to supply the plant’s fleet and to replace natural gas via injection into the grid.

Assessing the environmental impact of resource recovery from dairy manure

Manure management is a major contributor to environmental impacts from large-scale dairy production. In this study, technologies for recovering energy, nutrients, and water from dairy manure were evaluated using life cycle assessment (LCA) and compared to conventional practices on California dairy farms. Six scenarios were evaluated: conventional manure management practices, anaerobic digestion (AD) for biogas recovery, and four scenarios for nutrients, energy, and water integrated recovery, called NEWIR. The NEWIR system consists of hydrothermal carbonization (HTC) for energy recovery via hydrochar, algae cultivation in the HTC aqueous product for nutrient recovery and production of protein-rich cattle feed, and water recovery from algae pond effluent via membrane distillation. Four NEWIR scenarios were evaluated, each with a different species of algae. Based on the results of the LCA, AD improves GHG emissions relative to conventional practices by 82%, but has similar eutrophication impacts, posing similar concerns for nutrient management as current practices. Results for the NEWIR system are highly dependent on the algae species used. Three of the four species evaluated (Chlamydomonas reinhardtii, Chlorella vulgaris, and Scenedesmus obliquus) improve GHG emissions by 420–500 kg CO2-eq. per functional unit, while net water consumption is increased by approximately 75% over AD and conventional practices Spirulina maxima requires more water and chemical inputs for cultivation than the other species, resulting in higher water use (21 times higher than baseline), though GHG emissions are still reduced by 85 kg CO2-eq. per functional unit relative to conventional practices. All NEWIR scenarios improve eutrophication impacts relative to AD and conventional practices by 16–46% for marine eutrophication and 18–99% for freshwater eutrophication, depending on the algae species used. The results suggest integrated resource recovery through NEWIR is a promising treatment method for manure to mitigate GHG emissions and improve nutrient management on large-scale farms. In addition, carbon and nutrient trading policies are discussed in relation to resource recovery technologies and their potential to incentivize producers to recover products from dairy manure.

Bioenergy potential of agricultural crop residues and municipal solid waste in Cameroon

<abstract> <p>Biomass has emerged as an important and promising energy source, particularly in developing countries, owing to continuous research for sustainable energy sources that do not interfere with food, water or land needs. This study introduces the surplus availability factor (SAF), minimum, average and maximum biogas production technique in the assessment of crop production data in 2020 to provide a more precise and current estimate of Cameroon's crop residue and municipal solid waste (MSW) bioenergy potential. Crop residues contributed roughly 96% while MSW contributed the remaining 4% of the total bioenergy potential of 606 PJ per year. The bioenergy potential was calculated using crop production statistics derived from the FAOSTAT database of the Food and Agriculture Organization, while the residue-to-product ratio (RPR) and surplus availability factors (SAF) were found from related studies. The study concludes that crop residues and MSW have significant energy potential capable of meeting the country's electricity, transport fuel and biogas demand while simultaneously mitigating climate change through the capture of about 1.6 billion kg of CO<sub>2</sub> through biogas recovery. It also highlights the lack of accurate and up-to-date data on the country's biomass potential and recommends ground data collection and geospatial mapping of areas with enormous potential for these resources to guide policymakers and investment plans.</p> </abstract>

Membrane reciprocation as energy-efficient fouling control with high biogas recovery in a pilot-scale anaerobic membrane bioreactor

Anaerobic membrane bioreactor (AnMBR) as a primary treatment has the benefit of energy recovery through biogas generation. However, high energy consumption for fouling control remains the bottleneck for its applications. To this end, this study investigated the energy outlook of using membrane reciprocation as fouling control method in a pilot-scale AnMBR treating domestic wastewater, as compared to using conventional biogas sparging. The carbon balance calculation was conducted during the AnMBR operation to identify the methane conversion from organic carbon, setting the basis for energy evaluation. Both fouling control strategies were investigated under different biogas sparging speeds and membrane reciprocation frequencies. Critical flux tests and energy calculations have shown membrane reciprocation to consume 0.59 kWh/m3 at 7 L/m2/h (LMH), 62% less energy contrasting biogas sparging (1.56 kWh/m3 at 6 LMH). With the high biogas recovery and energy-efficient fouling control, positive net energy balance (0.55–0.74 kWh/m3) was achieved in this AnMBR, highlighting the potential of AnMBR with membrane reciprocation as an energy-positive A-stage in domestic sewage treatment.

Biogas Recovery from Refinery Oily Sludge by Co-Digestion Followed by Sustainable Approach for Recycling the Residual Digestate in Concrete Mixes

Biogas Recovery from Refinery Oily Sludge by Co-Digestion Followed by Sustainable Approach for Recycling the Residual Digestate in Concrete Mixes

An integrated leachate bed reactor – anaerobic membrane bioreactor system (LBR-AnMBR) for food waste stabilization and biogas recovery

This study developed an integrated LBR – AnMBR system for efficient stabilization and biogas recovery from food waste (FW) at room temperatures (21–22 °C). First, the leachate recirculation rate (4.4–13.2 L/h) was optimized to maximize hydrolysis and acidification yields. The maximum hydrolysis yield of 551 gSCOD/kg VSadded was achieved at recirculation rate of 13.2 L/h. The VFA concentrations in the FW leachate was as high as 12.5–16.0 g/L, resulting in a high acidification of 468 g CODVFA/kg VS. The solubilized FW was further stabilized by feeding the leachate to AnMBR. Different hydraulic (HRT) and solids retention times (SRT) were tested to achieve high COD removal and methane yields. High COD removal of 86 ± 3% was obtained in the AnMBR at HRT of 13 and SRT of 75 days. High biogas recovery of about 850 kWh per ton FWtreated was achieved along with high quality of AnMBR permeates containing low COD concentration but advantageously high concentration of nutrients (NH4+-N 317–403 mg/L, total phosphate 23–213 mg/L) without any particulates, which can be reused for landscape or liquid fertilizer.

Relevance of sludge management practices and substance modeling in LCA for decision-making: A case study in Chile

Reducing the costs and environmental impacts of sludge management is currently one of the main challenges faced by the wastewater treatment sector. Anaerobic digestion followed by land application has been widely endorsed as a low-impact approach to sludge management, mainly due to the recovery of biogas and the valorization of digestate. However, the influence that the operational conditions of digestion and the management practices of land application can have over the environmental performance of this strategy has been scarcely studied. Furthermore, most of the previous studies dealing with the environmental assessment of this strategy use simplified methods for estimating emissions after land application of sludge, and the lack of systematic accounting of these environmental flows might significantly affect the validity and comparability of the results. Therefore, this work performed an assessment of the influence that 4 relevant practices can have over the environmental impacts of this approach in the context of south-central Chile, providing a mass-balanced inventory for nitrogen, phosphorus and heavy metals in soil based on the ad hoc implementation of models developed for agricultural Life Cycle Assessment (LCA). A total of 16 scenarios were defined and 10 impact categories were evaluated, with the results showing that the environmental impacts were greatly influenced by the variables under study. Overall, solids retention time and the inclusion of pre-treatment mainly influenced climate change, fossil resource depletion and terrestrial ecotoxicity potential, while sludge application rate influenced the eutrophication, water ecotoxicity and human toxicity categories. The type of crop in the receiving soil was a significant driver behind the differences observed in the human toxicity category, which showed the highest variation and relevance in the final weighted result. The results clearly highlight the relevance of using context specific data as well as of quantifying the fate of nutrients, metals and heavy metals during LCA of sludge management. Based on the results, some policy and decision-making recommendations are formulated to optimize the environmental performance of sludge digestion and land application.

Polymeric nanocomposite membranes for gas separation: Performance, applications, restrictions and future perspectives

In recent decades, anthropogenic industrial-based activities (i.e., energy production and its conveyance) has led to the emission of deleterious greenhouse gases such as CO 2 , H 2 S, and NO 2 as an important environmental concern. Membrane-based gas separation processes have been currently of paramount attention in critical industrial applications such as purification, biogas recovery, water treatment, gas processing and H 2 recovery. Polymeric nanocomposite membranes (PNM) have illustrated indisputable potential of utilization to mitigate the release of gaseous pollutants to the ecosystem and reduce their hazardous environmental effects. Incorporation of novel nanoparticles including activated carbon, nanofibers and carbon nanotubes have revolutionized the efficiency of polymeric membranes for gas separation. This review paper aims to present disparate applications of polymeric nanocomposite membranes for mitigating the emission of toxic/acidic gases to environment. Moreover, performance, applications and challenges towards the use of nanocomposite membranes are reviewed comprehensively and future perspectives towards their development in industrial applications are recommended. Finally, prevalent nanocomposite membranes for the separation of various gaseous mixtures are presented.

Digestate Management and Processing Practices: A Review

The implementation of sustainable agro-energy systems that integrate crop, livestock, and bioenergy production is attracting increasing interest from farmers. Livestock produces large amounts of animal manure which can serve as organic fertilizer for crops and pasture growth. However, the nutrients contained in manure can adversely affect air, water, and soil quality and pose a public health risk if not handled properly. Existing manure management practices vary widely on a global scale. Researchers are striving to identify appropriate manure management practices with the aim of environmental protection. Anaerobic digestion of manure and subsequent digestate (DG) processing technologies have been proposed to stabilize manure so that it can be safely used for land applications. DG, which represents digested substrate removed from the anaerobic reactor after recovery of biogas, is a rich source of N, P, K, and S, various micronutrients, and organic matter, the addition of which to the soil can stimulate soil microbial biomass metabolic activities thus improving soil ecosystem function. However, the optimal fertilization properties of DG can be lost if it is neither fully stabilized nor contains biodegradable materials. To overcome these problems, various processing technologies can be used to convert DG into value-added by-products. Composting has been proposed as one such preferred post-treatment that can convert DG into mature, stable, safe, humus- and nutrient-rich compost. Other processing technologies such as thermal drying, gasification, hydrothermal carbonization, pyrolysis, membrane filtration, struvite precipitation, ammonia stripping, and evaporation have also been proposed for DG processing and nutrient recovery from DG. The objective of this review paper was to provide an overview of the current state of the art in DG management regulations and practices and to provide an update on the various processes that have been developed to meet DG stabilization requirements, with a focus on composting as one of the preferred solutions.

Adopting the circular model: opportunities and challenges of transforming wastewater treatment plants into resource recovery factories in Saudi Arabia

Abstract With the ever-growing population, water, energy, and resources need to be used carefully, reused, and renewed. There is an increasing global interest in resource recovery from ‘waste’, which is driven by sustainability and environmental concerns and motivated by the potential for economic benefits. A new era in waste (water) management is being realized where wastewater treatment is becoming part of the circular economy by integrating the production of reusable water with energy and resource recovery. In this new perspective, wastewater is no longer seen as a waste to be treated with energy expenditure but rather as a valuable source of freshwater, energy, nutrients (nitrogen and phosphorous), and materials (e.g., bioplastics, cellulose fibres, and alginate). In this review paper, the conversion of wastewater treatment plants (WWTPs) into resource recovery factories (RRFs) is presented as one of the ways forward to achieve a circular economy in the water sector for the Kingdom of Saudi Arabia (KSA). The advanced technologies, some highlighted in the article, can be installed, integrated, or retrofitted into existing WWTPs to create RRFs enabling the recovery of freshwater, cellulose, alginate-like exopolymers (bio-ALE), and biogas from municipal wastewater achieving climate neutrality, decarbonization, and production of new and promising resources. The article highlights the need for modular, adaptive, and/or decentralized approaches using sustainable technologies such as aerobic granular sludge (AGS)-gravity-driven membrane (AGS-GDM), anaerobic electrochemical membrane bioreactor (AnEMBR), and anaerobic membrane bioreactor (AnMBR) for conducive localized water reuse. The increase in reuse will reduce the pressure on non-renewable water resources and decrease dependency on the energy-intensive desalination process. This article also outlines the water challenges that are arising in KSA and what are the major water research programmes/themes undertaken to address these major challenges.

Optimization of substrate mixing ratios for wet anaerobic digestion of selected organic waste streams for productive biogas systems

In order to realize the objective of productive biogas systems, which is to provide waste management and modern renewable energy services, sustainable biogas production is paramount. While there are several factors that affect sustainability, quality of substrate for biogas production is one key anaerobic digestion (AD) parameter that should be optimized for improved and sustainable biogas yield. Since heterogeneity is an inherent characteristic of biomass, it is important that before application of any given biomass material for AD, its key characteristics are first examined to guide further processing to meet standards for optimal biogas recovery. In this study, physical and chemical characteristics of selected feedstocks were examined with intent to develop optimal substrate mixing ratios to improve quality of substrate for optimal biogas yield. Mathematical modeling of the required substrate moisture concentration was done, which gave way to the determination of optimal substrate mixing ratios. Results indicate that characteristics of feedstock vary widely according to source and type, as well as their substrate mixing ratios. However, for chicken litter with rice hull, the substrate mixing ratio was statistically not different from that of chicken litter with coffee husks and wood shavings, and therefore can be used on all the three feedstocks without significant effects on biogas yield.

Silica extraction followed by biogas generation from rice straw: Investigating the impact of pretreatment on purity of silica, biogas yield and microbial diversity along with insights on techno-economic analysis

Valorisation of agriculture waste namely rice straw (RS) for the recovery of value-added products such as high purity silica and biogas has gained tremendous research interest. Presence of silica and lignin limits the utilization of these wastes as potential feedstock for biological treatment. Therefore, this study investigated the impact of alkali (NaOH) pre-treatment at varied concentration of 2%, 4%, 6%, 8%, and 10% (w/v)) on lignin and silica removal at 90 °C so that the silica can be recovered as a value-added product and the lignin free biomass can be utilized as feedstock to estimate the biogas generation at mesophilic temperature (35 ± 2 °C) for 45 days. The impact of pre-treatment was studied and supported by the SEM, FTIR for morphological, and compositional variations while the AD is supported by 16 s rRNA metagenomic sequencing. Results revealed that increasing the concentration of NaOH up to 8% improved silica extraction with a purity of 97.34% with simultaneous lignin removal by 50 – 70%. Pretreatment with 2% NaOH was more effective in facilitating the accessibility of cellulose and hemicellulose to microbes during AD. In summary, this study concludes 2% NaOH treatment is ideal for both silica and biogas recovery.

Municipal Solid Waste-to-Energy-Facility to Advance Circular Economy: A Case Study in the City of Spokane, Washington

The development of technologies for processing residual solid mixed waste has only become a focus of attention stimulated by the search for more efficient energy sources. The majority of municipal solid waste (MSW) is of biological origin (biogenic). Typically, half of the energy content in MSW is from biogenic material. Consequently, this energy is often considered renewable energy according to the waste input, and as a result, the energy yields and profit generated can be accounted for in the circular economy. Waste-to-Energy (WtE) processes can play a role in the transition to a “circular economy” provided that a country’s waste hierarchy is used as a guiding principle and that the choices made do encourage and reward higher levels of waste minimization, reuse, remanufacturing, refurbishing, and recycling. In conclusion, both Waste to Energy and landfill biogas recovery systems are credited for their respective recovered energy and revenue generation while managing MSW disposal using best management practices and in an environmentally sustainable manner.

Comparison of Bacterial and Archaeal Microbiome in Two Bioreactors Fed with Cattle Sewage and Corn Biomass

The bacterial and archaeal communities of two full-scale biogas producing plants (P1 and P2), associated with a 999 kW cogeneration unit, both located in North Italy, were analyzed at start up and fully operating phases, by means of various molecular approaches: (i) Automated Ribosomal Intergenic Spacer Analysis; (ii) cloning and sequencing of PCR amplicons of archaeal genes 16Srrna and mcrA; (iii) 16S rDNA high throughput next generation sequencing. P1 and P2 use the same technology and both were fed with cattle manure and corn silage. During the study of P1 also the post digester (fed with pig manure) was analyzed. The aim of this research was to characterize the bacterial and archaeal communities in two very similar plants to profile the core microbiota. The results of this analysis highlighted that the two plants (producing comparable quantities of volatile fatty acids, biogas, and energy) differed in anerobic microbiota (Bacteria and Archaea). Notably the methanogenic community of P1 was dominated by the strict acetoclastic Methanosaeta (Methanothrix) (up to 23.05%) and the unculturable Candidatus Methanofastidiosum (up to 32.70%), while P2 was dominated by the acetoclastic, but more substrate-versatile, Methanosarcina archaeal genus (49.19%). The data demonstrated that the performances of plants with identical design, in similar operating conditions, yielding comparable amount of biogas (average of 7237 m3 day−1 and 7916 m3 day−1 respectively for P1 and P2), VFA (1643 mg L−1 and 1634 mg L−1) and energy recovery (23.90–24 MWh day−1), depend on the stabilization of effective and functionally optimized methanogenic communities, but these communities are taxonomically different in the two biodigesters.

Deploying two-stage anaerobic process to co-digest greasy sludge and waste activated sludge for effective waste treatment and biogas recovery

High-strength waste activated sludge (WAS) and greasy sludge (GS) were largely generated from canned tuna processing. This study reports the performance of the two-stage anaerobic process for co-digesting WAS and GS. Various WAS:GS mixing ratios of 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:00 (volatile solids (VS) basis) were investigated in batch acidogenic stage at ambient (30 °C ± 3 °C), 55 °C, and 60 °C temperatures. Subsequently, the effluents from the first stage were used to produce methane in the second methanogenic stage at an ambient temperature. The highest methane yield of 609 mL CH4/g-VSadded was achieved using acidogenic effluents generated from a WAS:GS mixing ratio of 40:60 at an ambient temperature. The first-order kinetic constants (k) for the first (k1) and second (k2) stages were subsequently estimated to be 0.457 d−1 and 0.139 d−1, respectively. The obtained k constants were further used to predict the hydraulic retention time (HRT) for the two continuously stirred tank reactors (CSTR) in series. Consequently, the calculated 4-day HRT and 20-day HRT for 50-L CSTR1 and 250-L CSTR2, respectively, were used to operate the continuous two-stage process at an ambient temperature by feeding with a 40:60-WAS:GS mixing ratio. A satisfactory methane yield of 470-mL CH4/g-VS along with 75% chemical oxygen demand (COD) removal was generated. Furthermore, the predicted methane yield of 450-mL CH4/g-VS obtained from the simple kinetic CSTR model resembled the experimental yield with 96% accuracy. The obtained experimental results demonstrate that WAS and GS co-digestion could be successfully accomplished using a practical two-stage anaerobic process operated at an ambient temperature.