Fraction Of Municipal Solid Waste Research Articles

Application of life cycle assessment to high quality-soil conditioner production from biowaste

The recent large-scale urbanization and industrialization resulted in an impressive growth of solid waste generation worldwide. Organic fraction generally constitutes a large fraction of municipal solid waste and its peculiar chemical properties open to various valorization strategies. On this purpose, life cycle assessment is applied to an innovative industrial system that processes 18 kt/y of agricultural and livestock waste into a high-quality soil conditioner. The high-quality soil conditioner production system consists of a series of processes, including anaerobic digestion and vermicomposting, allowing the generation of a peat-like material with high carbon content, porosity, and water-holding capacity. The presence of a photovoltaic plant and a cogeneration plant, fed with the biogas produced in the anaerobic digestion, makes the system entirely self-sufficient from the national grid and generating a surplus of electricity of 1177MWh/y. The high-quality soil conditioner showed better environmental performances in 15 out of 18 impact categories when compared to alternative scenarios. In particular, the high-quality soil conditioner and the related biowaste management resulted in a carbon saving of around 397 kg CO2 eq/ton compared with a scenario involving the employment of peat in place of the high-quality soil conditioner and a traditional biowaste management, and 165 kg CO2 eq/ton compared with a scenario where cogeneration is replaced by biomethane upgrading. This study demonstrates the possibility of using organic waste as an environmentally sustainable and renewable source for energy and carbon to soil conditioning.

Biochar from Digestate Pyrolysis as a Filler for Biopolymer Blends: Effect of Blend Composition

Abstract This study investigates the effect of biochar (BC) as a filler for biopolymer blends, with a focus on the effect of the biopolymer weight ratio on the final BC-added blends. The blends studied in this work were obtained by varying the weight ratio of poly-butylene adipate-co-terephthalate (PBAT) and polylactic acid (PLA) due to their great importance in packaging and agricultural fields. BC has been produced in our laboratories by the slow pyrolysis of the digestate obtained from the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). After pyrolysis, digestate-derived biochar has been milled and sieved to produce a powdery form with diameter of less than 45 μm. In order to better investigate the filler/polymer interactions, biochar particles were dimensionally, morphologically and chemically characterised. The inhomogeneity of the feedstock is responsible for content and high diversity of inorganics in biochar surface. The effect of BC on PBAT and PLA biopolymer matrices is different, and for the blend compositions the relative weight ratio between PBAT and PLA plays an important role. Furthermore, the biocomposite blend has been fully characterised: rheological, morphological, mechanical and dynamic-mechanical characterisations have been carried out, highlighting how the properties results strongly influenced by the presence of BC in the blend. In addition, a study of the viscous molar mass of the two polymer matrices when processed in the presence or absence of BC particless highlighting that a strong chemical interaction occurs between PLA and BC particles, unlike PBAT and BC. Graphical Abstract

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.

Process optimization for saccharification and fermentation of the Organic Fraction of Municipal Solid Waste (OFMSW) to maximize ethanol production performance

The Organic Fraction of Municipal Solid Waste (OFMSW) contains paper and cardboard, an attractive cellulosic feedstock for bioethanol production. Waste paper/cardboard (WPC) was subjected to mild acid treatment in solids loadings from 20 to 27.5 %. Different doses of commercial enzyme cocktail and various adjuvants facilitating enzymatic saccharification were tested. Enzyme dosing of 3.75 FPU/g fiber with very slow fed-batch saccharification of 27.5 % (w/v) solids from model lignin-free paper pulp resulted in 12.6 % (w/v) total sugar after 74 h. Use of cheap non-catalytic waste protein adjuvants including Soymeal, Protisyr, Feather meal strongly improved enzymatic saccharification and reduced the overall process cost by reducing commercial enzyme dosing. After fermentation with the industrial yeast strain BMD44 (Cellusec® 1.0) an ethanol titer of 5.77 % (v/v) was obtained using a reduced enzyme loading of 2.5 FPU/g of actual industrial WPC fiber. These results show the potential of economically profitable second-generation bioethanol production with WPC fiber.

Environmental life cycle assessment of polyhydroxyalkanoates production by purple phototrophic bacteria mixed cultures

Bioplastics offer a promising sustainable alternative to petroleum-based plastics due to their biodegradability as well as favourable thermal and mechanical properties. Among different types of biobased polymers, the production of polyhydroxyalkanoates (PHA) using purple phototrophic bacteria (PPB) and low-value substrates has gained increasing interest. Despite the momentum, challenges regarding the scalability and environmental feasibility of this biopolymer production pathway remain. In response, this study employs an exploratory LCA approach to quantitatively assesses the potential environmental implications of PHA production in powder form and the joint management of the organic fraction of municipal solid waste (OFMSW) through a novel photobiorefinery system that uses PPB mixed cultures. Environmental impacts were tested under multiple improvement scenarios and benchmarked against the production of conventional fossil-based granulate or unprocessed plastics, including low density polyethylene (LDPE), polyethylene terephthalate (PET) and polyurethane (PU). The photobiorefinery stage was found to have the greatest contribution to the impact categories, particularly due to direct emissions, consumption of electricity and production of extractive chemical agents used. These factors accounted for over 70% of the photobiorefinery impact in all cases. Avoided impacts provided net favourable outcomes in terms of carbon footprint and fossil resources when comparing PHA production to conventional plastics, especially PET and PU, with impact reductions ranging from 30% to 60%, respectively. However, when considering other impact categories like eutrophication, this situation was less favourable. The exploration of alternative scenarios offered significant impact reductions, especially when renewable electricity or an environmentally friendly extraction agent is used. Moreover, minimizing methane losses or co-producing hydrogen in the photobiorefinery had a notably positive effect on the carbon footprint, reducing the impact by more than 2 t of CO2 eq per t of PHA powder compared to the base case. Therefore, the implementation of feasible improvement measures in the short term can position PHA produced by mixed cultures as a sustainable alternative to petroleum-based plastics.

Pollutant Emissions from Municipal Biowaste Composting: Comparative Analysis and Contribution of N-Containing Organic Compounds

The disposal of municipal biowaste is associated with the formation of malodorous and frequently hazardous volatile compounds. The composition of volatile pollutants formed during composting of mechanically sorted organic fraction of municipal solid waste (ms-OFMSW), sewage sludge (SS), food waste (FW), and wood waste (WC) during 28 days in a laboratory setup was analysed using electrochemical measurements, gas chromatography, and solid phase microextraction. Despite the close biodegradation intensity of SS+WC, ms-OFMSW, and FW+WC, the average temperature values were 57.0, 51.7, and 50.6 °C. The emission of volatile substances per day were: CO2 0.64, 0.68, and 0.64 g/kg, NH3 22.3, 93.1, and 4.9 µg/kg, CH4 5.3, 1.5 and 8.7 mg/kg, H2S 5.0, 3.3 and 1.8 µg/kg organic matter. The ratios of emission from SS+FW, ms-OFMSW and FW+WC for inorganic substances were 1.0, 1.1, and 1.0, and for organic compounds (VOC) were 1, 24, and 123. A total of 121 VOC was identified. The 12 N-containing compounds detected at the beginning of composting, some of which are highly toxic, ranged from 3.2 to 21.0% of the total VOC and belonged to amines with a very low olfactory thresholds and heterocyclic compounds. The results of this research help to optimise the systems used to remove pollutants from exhaust air.

Sorption and economic viability of peat, compost and biochar for zinc-contaminated site

The growing demand for low-cost sorbents, which guarantee eco-efficiency in removing contaminants, has led to numerous studies in recent decades. In this sense, sorbents derived from organic residues have shown promising options; however, the organic fraction of municipal solid waste (OFMSW) has received little attention to date. This study compares the zinc (Zn) sorption performance of a traditional sorbent (peat) with that of materials derived from OFMSW (compost and biochar). According to the Langmuir model, biochar showed the highest sorption capacity (53.494 mg/g), followed by compost (37.569 mg/g) and peat (5.842 mg/g). Although the maximum sorption capacities adjusted by linear and non-linear regressions were close, the values were relevant only when they would have reached the saturation plateau. The cost estimate of the studied sorbents validated their economic viability with that of commercially available ones. The findings provide a theoretical basis for a better understanding of sorption experiments, from the choice of initial concentrations to the isothermal modelling of the results, for comparative evaluation of potential sorbents for the remediation of soils and waters contaminated with potentially toxic metals, such as zinc.

Changes in the prokaryotic communities occurring along a two-stage anaerobic digestion system treating the organic fraction of solid waste

Two-stage anaerobic digestion is useful for recycling of the organic fraction of municipal solid waste and wastewater; the prokaryotic communities involved in this process were characterized using massive sequencing of 16S rRNA gene amplicons. During the 60-day study the prokaryotic communities were stable in time but were affected by their position in the system. The first stage of solid waste digestion was operated in an anaerobic-hydrolytic leach bead reactor with high organic solids content, the microbial communities were dominated by members of the orders Bacteroidales (62%), Selenomonadales (15%), Lactobacillales (13%), Clostridiales (4%) and Rhodospirillales (1%). At this stage, a vertical stratification acted as a transition zone from aerobic to anaerobic environments modifying significantly the composition and structure of bacterial communities.The second stage occurred in an up-flow anaerobic sludge bed reactor specialized in acidogenesis-methanogenesis, where the leachate of the first stage was co-fed with municipal wastewater. In this stage, the bacterial community was dominated by members of the orders Pseudomonadales, Clostridiales, Burkholderiales, Bacteroidales and Syntrophobacterales (accounting for 52%), while the most abundant orders of the archaeal community corresponded to Methanosarcinales (72%) and Methanobacteriales (13%), both of them with methanogenic capacity.

The development of data-intensive techno-economic models for the comparison of renewable natural gas production from six different biomass feedstocks for the decarbonization of energy demand sectors

Renewable natural gas (RNG) from biomass can be used as an alternative to natural gas. However, there is limited understanding of the economic viability of RNG production from a wide range of feedstocks. In this study, a comprehensive comparative techno-economic assessment of RNG production via gasification from six biomass feedstocks with a wide range of moisture contents and characteristics was conducted. The feedstocks studied are corn stover (CS), wheat straw (WS), whole forest (WF), forest residues (FR), cow manure (CM), and the organic fraction of municipal solid waste (OFMSW). The RNG production plants were simulated and the simulation results were used to develop techno-economic models for each feedstock to estimate the production cost of RNG. The pathways were compared in terms of RNG yield, RNG production quantity, electricity generation, as well as RNG production costs and cost components. Sensitivity analyses were conducted on a wide range of factors and effect of including cardon credit on the production cost were studied. RNG production costs from the gasification of the OFMSW and CS were lower than those of other feedstocks at 6.28 $/GJ and 6.32 $/GJ, respectively. If the avoided cost (as a source of revenue) of landfilling of the OFMSW or carbon credit (minimum 90 $/t CO2) is considered, the RNG production cost can be competitive with natural gas price (1.4 $/GJ). The information developed in study is critical for decision makers in policy formulation and investment decisions.

Life Cycle Assessment of sewage sludge mono-digestion and co-digestion with the organic fraction of municipal solid waste at a wastewater treatment plant

Wastewater treatment plants (WWTPs) aim to increase energy independence by intensifying biogas production. The study involved Life Cycle Assessment (LCA) comparing sewage sludge (SS) anaerobic co-digestion (AcD) with the organic fraction of municipal solid waste (OFMSW) at WWTP against SS anaerobic mono-digestion (AD). The LCA was based on the authors' research showing that methane production related to wet mass in AcD was higher than in AD by 86.4, 225.8, and 354.3 % for SS:OFMSW mixing ratios of 75:25, 50:50, and 25:75, respectively. The LCA was conducted for 1 kWh of biogas energy produced at a WWTP and included two subsystems: energy production (AD/AcD and CHP) and associated digestate management (drying, incineration with energy reuse, residual landfilling). CML-IA baseline 2013 and Recipe 2016 Midpoint (H) LCIA methodologies indicated the environmental impacts on abiotic depletion - fossil fuels (fossil resource scarcity), global warming, human toxicity (non-carcinogenic), freshwater, and marine aquatic ecotoxicity. AD of SS in all categories was characterized by the highest impact. The impact decreased with an increase in the OFMSW rate. Both methodologies showed a significant impact of AD and AcD on global warming, which indicated the need for the determination of the carbon footprint (CF) of 1kWh biogas energy production (gCO2 kWh−1) at WWTP, using IPCC 2021 GWP100 (incl. CO2 uptake). The CF was the highest for biogas energy production in SS AD (1509 gCO2 kWh−1) and it decreased with the increase of OFMSW content in AcD (872–481 gCO2 kWh−1). This was also observed for the management of associated digestate. CF changed from 1508 gCO2 kWh−1 for SS AD to 396 gCO2 kWh−1 for SS: OFMSW mixing ratio of 25: 75 in AcD. The environmental burdens associated with biogas energy production and digestate management were equally significant. Finally, the formula for economic and ecological comparison of SS AD and AcD with OFMSW was proposed.

Operational performance of organic fraction of municipal solid waste discarded from communities, using an in-vessel hyperthermophilic composting technology

There is a great need of in-situ Organic Fraction of Municipal Solid Waste (OFMSW) disposal inside community in most countries due to less transportation cost and secondary environmental while a shorter maturation period and less odor is required. In-vessel hyperthermophilic composting could probably address these issues. In this work, we reported the physicochemical parameters and corresponding microbial dynamics of a pilot-scale in-vessel Thermophilic Compost (HTC) and compared with Traditional Compost (TC). Results demonstrated that HTC effectively accelerated the maturation period of composting compared to TC, which shorten the whole compost cycle to 25 days. And the hyperthermophilic and thermophilic phases maintained more than one third of the whole period of HTC, which exhibiting superior or comparable key evaluation indexes than TC. Besides, the maximum N2O emission rate for TC is 10.2 times that of HTC. It was obviously due to extreme temperature as a result of inhibition of denitrifying bacteria for the HTC. Results of microbials analysis showed that during the thermophilic and hyperthermophilic period, mainly six strains of thermophilic bacteria including Bacillus (39.88%), Calditerricola (8.92%), Lactobacillus (8.76%), Oceanobacillus (5.4%), Planifilum (4.83%), and Ureibacillus (4.42%) were observed in HTC. It has been revealed that physico-chemical parameters can be regulated to optimize microbial composition for the purpose of enhancing hyperthermophilic composting, promoting organic matter degradation, and facilitating the recombination of middle-hyperthermophilic community OFMSW composting.

Residual waste management in London, England: a reality check

Residual waste is a key fraction of municipal solid waste generated, yet its management is poorly understood and has gained little attention over the past years. Using London as a case study, the present study analyses the amount of residual waste collected and managed to check on how well ahead the UK is in making progress on achieving the circular economy principles. The study found that 5 Mt of residual waste is reported to be managed in London, of which 3.5 Mt is managed via recovery operations and 1.59 Mt is managed via disposal operations. For the latter, landfills are the principal disposal option taking in 0.82 Mt of residual waste each year. Amongst the recovery options, incineration with energy recovery, is the most prevalent, accounting for the management of 1.44 Mt of residual waste. This highlights the presence of an important technological lock-in that could jeopardise UK’s ability to achieve its net zero carbon ambition. It is worth noting that the data collated and analysed depicts the movements of residual waste rather than its final treatment, pointing to blind spots in the final fate of residual waste as well as potential double counting; both of which prevent decision- and policy-making. Therefore, the need for transparency in data recording and monitoring and the creation of a level playing field for all stakeholders involved in residual waste management are of paramount importance in gradually breaking reliance on destructive treatment processes. This could empower improved segregation of waste at source, and in turn, enable the better management of residual waste. The study underlines that residual waste has a significant role to play in making the transition to a circular economy and therefore is imperative to pave the way for future policy direction on residual waste management.

Use of a biogas-specific e-nose with machine learning to identify biogas pattern changes linked to hydraulic retention times in an anaerobic digester: A case study

Anaerobic digestion via biogas digesters is the most environmentally friendly solution to recycling degradable organic waste into organic fertilizer and energy. The organic fraction of municipal solid waste (OFMSW) is one of the main organic waste sources for biogas plants. The variations in characteristics of OFMSW as a main challenge lead to fluctuating organic loading rates and hydraulic retention time (HRT), which can adversely affect the performance of biogas plants. This study focused on the gaseous headspace of a biogas digester to assess a reliable monitoring method. An e-nose was applied to extract biogas patterns from a mesophilic digester, which operated at HRT of 30, 25, 20, and 15 days to treat OFMSW. The biogas samples were significantly classified based on their HRTs by the support vectors machine (SVM) and the random forest (RF). Finally, the results presented a promising method for monitoring the performance of the biogas digester.

Techno-economic analysis of H2@Scale production from organic municipal solid waste

Environmental sustainability entails alleviating a multitude of challenges including the minimization of waste and associated carbon emissions. The emergence of Green Hydrogen (H2) utilization is considered a promising groundbreaking initiative for the transition toward a low-carbon economy. While the concept of energy recovery from waste is not novel, its practical implementation remains questionable at times. This study examines the technical and economic viability of scaled H2 production from the organic fraction of municipal solid waste, through an in-depth techno-economic and cost-benefit analysis. The results demonstrate that the H2 yield obtained exclusively from plastic waste exceeds that from mixed-feed waste by ∼ 24.5 %. Equally significant, the LCOH stands at ∼$4.96/kg-H2, inclusive of CO2 capture and storage charges, while decreasing to $4.10/kg-H2 when excluding such charges. The integration of previously overlooked key macro and micro-economic and financial parameters has facilitated a more nuanced and practical evaluation of the levelized cost of H2, allowing for a fair comparison with the current market cost of blue H2.These findings are of significance for investors and decision-makers operating within the realm of ecological sustainability and energy transition, while concurrently serving as an indispensable benchmark for the formulation of sensible waste management policies.

Biodegradation of high cellulose-lignin content agricultural wastes in bioreactors

The bioreactor landfill is a solid waste disposal method that provides rapid degradation of solid waste and acquisition of methane. Bioreactors in which leachate circulation is carried out are generally operated anaerobically. The biodegradation of wastes with high lignin and cellulose content is very difficult. Especially under anaerobic conditions (moreover, if there is a lack of moisture), such wastes almost never decompose. In this study, the degradation of waste sunflower stalks that are difficult to biodegrade and have a high lignin-cellulose content and the production of methane gas in semi-aerobic bioreactors have been investigated. Sunflower stalks were loaded into the bioreactors in different proportions and mixed with the organic fraction of municipal solid waste (OFSWM). The bioreactors have been operated under different operating conditions. The contents of cellulose, hemicellulose, lignin, and initial and final organic matter in the wastes loaded into the bioreactors were examined. Parameters such as pH, COD, BOD5, TKN, NH4-N in leachate were analysed and the amounts of total and methane gas were measured. Initially, all bioreactors have been operated anaerobically. In the decomposition of the sunflower stalk, while 43% of the organic matter removal was achieved in the anaerobic bioreactor, 60% of the organic matter removal was realized in the semi-aerobic/anaerobic bioreactor. The other agricultural wastes were then subjected to decomposition under semi-aerobic/anaerobic operating conditions. As a result of the study, it can be said that semi-aerobic pretreatment accelerates the decomposition of agricultural waste with a high lignin and cellulose content, decreases the COD values of leachate, and increases the amount of methane.

Effect of forest-based biochar on maturity indices and bio-availability of heavy metals during the composting process of organic fraction of municipal solid waste (OFMSW)

The main objective of this study was to investigate the effect of biochar on the composting process of the organic fraction of municipal solid waste (OFMSW) under real conditions. Different doses of biochar (1%, 3%, and 5%) were mixed with compost piles to evaluate the variation of temperature, moisture content (MC), organic matter (OM), carbon (C), nitrogen (N), C/N ratio, and heavy metal (HM) contents in comparison with the control treatment (with 0% biochar addition). The results of this study showed that the compost piles combined with different doses of biochar had higher MC. The use of biochar as an additive, even at low doses (1%), was able to increase the compost quality through the reduction of N losses during the composting process. The highest reduction of OM during the composting process was observed in the control pile (without biochar addition) by 48.06%, whereas biochar affected the biodegradability of OM and prevented the reduction of nutrients during the composting process under real conditions. The contents of HMs (Pb, Zn, Ni, Cd, and Cu) showed a significant reduction in all of the compost piles combined with biochar in comparison with the control treatment. Considering that in terms of all compost quality indicators, the piles combined with biochar can regarded as high standard product, the composts obtained from combining the OFMSW with different biochar doses have desirable features to be used as an amendment agent to improve agricultural soil quality.

Implementation of anaerobic digestion for valorizing the organic fraction of municipal solid waste in developing countries: Technical insights from a systematic review

Anaerobic digestion (AD) as a waste management strategy for the organic fraction of municipal waste (OFMSW) has received attention in developed countries for several decades, leading to the development of large-scale plants. In contrast, AD of OFMSW has only recently drawn attention in developing countries. This systematic review was carried out to investigate the implementation of AD to treat the OFMSW in developing countries, focusing on assessing pilot and full-scale AD plants reported in the last ten years. Studies that met the selection criteria were analyzed and data regarding operating parameters, feedstock characteristics, and biogas, digestate, and energy production were extracted. As outlined in this systematic review, AD plants located in developing countries are mostly one-stage mesophilic systems that treat OFMSW via mono-digestion, almost exclusively with the aim of producing electrical energy. Based on the analysis done throughout this systematic review, it was noted that there is a large difference in the maturity level of AD systems between developing and developed countries, mainly due to the economic capacity of developed countries to invest in sustainable waste management systems. However, the number of AD plants reported in scientific papers is significantly lower than the number of installed AD systems. Research articles regarding large-scale implementation of AD to treat OFMSW in developed countries were analyzed and compared with developing countries. This comparison identified practices used in plants in developed countries that could be utilized in the large-scale implementation and success of AD in developing countries. These practices include exploiting potential products with high market-values, forming partnerships with local industries to use industrial wastes as co-substrates, and exploring different biological and physical pretreatment technologies. Additionally, the analysis of capital and operational costs of AD plants showed that costs tend to be higher for developing countries due to their need to import of materials and equipment from developed countries. Technical, economical, and political challenges for the implementation of AD at a large-scale in developing countries are highlighted.

Achieving Discharge Limits in Single-Stage Domestic Wastewater Treatment by Combining Urban Waste Sources and Phototrophic Mixed Cultures.

This work shows the potential of a new way of co-treatment of domestic wastewater (DWW) and a liquid stream coming from the thermal hydrolysis of the organic fraction of municipal solid waste (OFMSW) mediated by a mixed culture of purple phototrophic bacteria (PPB) capable of assimilating carbon and nutrients from the medium. The biological system is an open single-step process operated under microaerophilic conditions at an oxidative reduction potential (ORP) < 0 mV with a photoperiod of 12/24 h and fed during the light stage only so the results can be extrapolated to outdoor open pond operations by monitoring the ORP. The effluent mostly complies with the discharge values of the Spanish legislation in COD and p-values (<125 mg/L; <2 mg/L), respectively, and punctually on values in N (<15 mg/L). Applying an HRT of 3 d and a ratio of 100:7 (COD:N), the presence of PPB in the mixed culture surpassed 50% of 16S rRNA gene copies, removing 78% of COD, 53% of N, and 66% of P. Furthermore, by increasing the HRT to 5 d, removal efficiencies of 83% of COD, 65% of N, and 91% of P were achieved. In addition, the reactors were further operated in a membrane bioreactor, thus separating the HRT from the SRT to increase the specific loading rate. Very satisfactory removal efficiencies were achieved by applying an HRT and SRT of 2.3 and 3 d, respectively: 84% of COD, 49% of N, and 93% of P despite the low presence of PPB due to more oxidative conditions, which step-by-step re-colonized the mixed culture until reaching >20% of 16S rRNA gene copies after 49 d of operation. These results open the door to scaling up the process in open photobioreactors capable of treating urban wastewater and municipal solid waste in a single stage and under microaerophilic conditions by controlling the ORP of the system.

Mass Transfer Enhancement in High-Solids Anaerobic Digestion of Organic Fraction of Municipal Solid Wastes: A Review.

The increasing global population and urbanization have led to a pressing need for effective solutions to manage the organic fraction of municipal solid waste (OFMSW). High-solids anaerobic digestion (HS-AD) has garnered attention as a sustainable technology that offers reduced water demand and energy consumption, and an increased biogas production rate. However, challenges such as rheology complexities and slow mass transfer hinder its widespread application. To address these limitations, this review emphasizes the importance of process optimization and the mass transfer enhancement of HS-AD, and summarizes various strategies for enhancing mass transfer in the field of HS-AD for the OFMSW, including substrate pretreatments, mixing strategies, and the addition of biochar. Additionally, the incorporation of innovative reactor designs, substrate pretreatment, the use of advanced modeling and simulation techniques, and the novel conductive materials need to be investigated in future studies to promote a better coupling between mass transfer and methane production. This review provides support and guidance to promote HS-AD technology as a more viable solution for sustainable waste management and resource recovery.

Low-dosage enzymatic hydrolysis of organic municipal waste for sugar and ethanol production

AbstractEnzymatic hydrolysis (EH) of the organic fraction of municipal solid waste (OFMSW) is challenging due to its complexity and heterogeneous character. This study investigated the effects of OFMSW compositional characteristics and pretreatment techniques on the efficiency of EH. The experiments involved varying enzymatic dosages and pretreatment methods, including heat pretreatment and anaerobic incubation of raw OFMSW. Remarkably, after thermal pretreatment, a saccharification yield exceeding 50% was achieved with only 1 filter paper unit (FPU) of Cellic® Ctec3 and 0.5 glucoamylase unit (AGU) of AMG® 300 L BrewQ per g of dry OFMSW. This resulted in the recovery of 239 g of sugar per kilogram of dry OFMSW. The study revealed that the decomposition of OFMSW by enzymes is limited after reaching about 50% of the sugar recovery yield, and high concentrations of inhibitors such as organic acids, alcohols, and potentially other organics and inorganics may contribute to this limitation. These compounds, however, serve as excellent preservatives, achieving contamination control during biological conversion. Sugar-rich hydrolysates were subjected to ethanol fermentation using Saccharomyces cerevisiae, leading to the conversion of most hexose sugars into ethanol, reaching 331 g of ethanol per kilogram of dry OFMSW, and indicating that the limitation of OFMSW saccharification was not due to product inhibition. These findings highlight the need for further investigation of the saccharification process of biowaste to overcome inhibitory effects and subsequently achieve higher efficiency of the following bioprocesses.