Search

Biomass gasification has been considered as an important renewable energy alternative to deal with the environmental problems originating from fossil fuels and climate change effects. Olive pomace as a by-product of the olive oil production process is a significant biomass source. Although gasification technology is accepted as an environmentally friendly power system, the studies to determine its environmental impact via Life Cycle Assessment (LCA) are very limited. LCA is a key tool to evaluate all environmental impacts from the beginning to the end of the process. The aim of this study is to assess the overall environmental impacts of the olive pomace gasification for electricity generation and evaluation of its solid by-products namely biochar and tar. Four scenarios were compared to estimate the environmental impacts of gasification by-products with a LCA approach, following to the cradle-to-grave approach. The production of olive, olive pomace generation during its processing for olive oil production, gasification of olive pomace, construction of the gasifier, gas cleaning system and syngas composition have been included in the evaluations. It is clear from the analysis results that the scenarios have very low impact values in the case of beneficial usage of biochar in different industries. In terms of ozone layer depletion potential (2.74 × 10 −6 kg CFC11 eq) and global warming potential (36.99 GWP100a), the paramount scenario from an environmental viewpoint is the scenario having the biochar and tar usage as a resource in another industry.

Gasification process is considered as one of the best routes of energy recovery from biomass by producing syngas mostly including H2, CO, and CH4. Biomass as the main renewable energy resources has great advantages regarding its diversity, availability, and sustainability for supplying energy needs in heat, electricity production, biofuel production for transportation, etc. Various gasifiers based on the gasifying process and agents have been examined. This paper reviewed the theory of biomass gasification by comparing and analyzing different gasification models-designs and configurations, also different operational conditions. It aimed to bringa holistic approach for hydrogen rich syngas production based on the present technologies, techno-economic analysis, and industrial/commercialization pathways. The biomass gasification technologies need to be improved for hydrogen production regarding the global environmental and economic issues. The review provided better insights into the enhancement of syngas production from biomass. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Integration of solid oxide fuel cell (SOFC) and biomass gasification system is a promising way to obtain electricity and thermal energy with high thermal efficiency and low environmental impact from biomass. These technologies can be integrated with various ways to obtain useful products, such as electricity and thermal energy for heating and cooling. Many researchers have proposed configurations that include other technologies, such as organic Rankine cycle, gas turbine, and electrolysis, to these systems to further enhance their performance. This review study summarizes different proposed and demonstrated system layouts including SOFC, biomass gasifiers, and other technologies, and discusses modeling and optimization techniques for the main components as well as the integrated system. In addition, the methods used for the performance, cost, and environmental impact analyses of these systems are discussed and compared. These comparisons show that among the different configurations of SOFC and biomass gasifier-based integrated systems, the system consisting of a biomass gasifier, a SOFC, and a micro-scale gas turbine was found to be highly efficient (energy efficiency of 88%). Among the studies reviewed, the levelized unit electricity cost for the integrated system consisting of a biomass gasifier, a SOFC, a gas turbine, and an organic Rankine cycle was found to be lower than other systems with the value of 0.086 $/kWh. In addition, the integrated system consisting of a biomass gasifier, a SOFC, a gas turbine, a steam turbine, an absorption chiller, and an ORC yielded a lower specific CO2 emission (141.2 kg/MWh). It is also shown that exergo-economic analysis and life cycle assessment give the most comprehensive results in terms of economic and environmental analyses, respectively. Important achievements in this field are also summarized and recommendations and suggestions for future work are given.

This study presents research results on electricity production from waste activated sludge using MFCs during stabilization process. Different MFC configurations equipped with various electrodes were used. Voltage measurements were continuously done during 35 days of MFC operation. Experimental results showed that bioelectricity generation was linked to volatile solids (VS) and protein reductions as a fraction of extracellular polymeric substances (EPS). Double chamber MFC reactor equipped with graphite electrodes had better power and current densities as 312.98 mW/m(2) and 39.07 mu A/cm(2) while single chamber MFC equipped with titanium electrodes revealed better power and current densities as 97.60 mW/m(2) and 17.63 mu A/cm(2), respectively. Molecular results indicated that power outputs of MFCs effected by diverse microbial communities in anode biofilms. Although organic matter degradation is reported as 35%-55% VS reduction for digesters, this research provided a promising approach for sludge stabilization with enhanced degrading of organic matters up to 75% by using MFCs. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

This study aimed to investigate the gasification potential of municipal green waste in different fixed-bed gasifier configurations as updraft and downdraft. Both reactor systems were constructed from stainless-steel with a cyclone separator to increase synthesis gas yield and reduce tar production. Green waste collected from parks and gardens by Manisa Metropolitan Municipality, Turkey, was used in the experiments. After full-characterization of green waste, gasification experiments were performed above 700 ? to produce syngas with more than 40% (volumetric) H-2 and heating value around 12.54 MJ/ Nm(3). Dry air (DA) and pure oxygen (PO) were used as gasification agents. DA was applied with the flow-rates ranged between 0.4 and 0.05 L/min while the flow-rate of PO was 0.01 L/min. The maximum H-2 production as 45 vol% was obtained in downdraft reactor while it was about 51 vol% in updraft system. CH4 production was obtained as higher value (app. 19 vol%) in downdraft reactor than that (13 vol%) in the updraft one. In the experiments with DA above 700 ?, the H-2/CO ratio varied between 1 and 3, and in the experiments with PO, it increased up to a maximum value of 4. The study has found a suitable set of gasification process parameters for two reactor systems. Therefore, the findings have been compared and discussed in detail. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Microbial C1 gas conversion technologies have developed into a potentially promising technology for converting waste gases (CO2, CO) into chemicals, fuels, and other materials. However, the mass transfer constraint of these poorly soluble substrates to microorganisms is an important challenge to maximize the efficiencies of the processes. These technologies have attracted significant scientific interest in recent years, and many reactor designs have been explored. Syngas fermentation and hydrogenotrophic methanation use molecular hydrogen as an electron donor. Furthermore, the sequestration of CO2 and the generation of valuable chemicals through the application of a biocathode in bioelectrochemical cells have been evaluated for their great potential to contribute to sustainability. Through a process termed microbial chain elongation, the product portfolio from C1 gas conversion may be expanded further by carefully driving microorganisms to perform acetogenesis, solventogenesis, and reverse -oxidation. The purpose of this review is to provide an overview of the various kinds of bioreactors that are employed in these microbial C1 conversion processes., This study was conducted in collaboration with researchers from four different institu tions (Dokuz Eylul University, Turkey; University of Minho, Portugal; Izmir Democracy University, Turkey, and University of A Coruña, Spain), who were supported by the following funding bodies: A.A. [Dokuz Eylul University, Scientific Research Foundation (DEU-BAP) (#2011.KB.FEN.046) and TUBİTAK (#119R029)]; L.P. [Portuguese Foundation for Science and Technology (FCT) (UIDB/04469/2020), and FCT and European Social Fund (POPH-QREN) (POCI-01-0145-FEDER 031377)]; T.K. [TUBİTAK-CAYDAG (118Y305)]; and H.N.A. [Xunta de Galicia (ED431C 2021/55)]., A.A. acknowledges the support by Dokuz Eylul University, Scientific Research Foundation (DEU-BAP), Turkey, for the award on (#2011.KB.FEN.046) “Direct Electricity Generation from Treatment Plant Sludges by using MFCs” research project. A.A. acknowledges TUBİTAK for the support on #119R029 “Sustainable Energy Recovery from Treatment plant sludge, green waste and olive pomace via gasification process: Investigation of beneficial usage alternatives of gasification by-products”. L.P. acknowledges the Portuguese Foundation for Science and Technol ogy (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit. Also, the financial sup port from Portuguese Foundation for Science and Technology (FCT) and European Social Fund (POPH-QREN) through the project INNOVsyn - Innovative strategies for syngas fermentation (POCI-01-0145-FEDER-031377) are gratefully acknowledged. T.K. acknowledges the support from The Scientific and Technological Research Council of Turkey (TUBITAK-CAYDAG) (project no: 118Y305). H.N.A. thanks the Xunta de Galicia (Spain) for his postdoctoral fellowship (ED481D 2019/033). H.N.A., belonging to the BIOENGIN group of the UDC, also acknowledges Xunta de Galicia for recognizing the group as a competitive Reference Research Group (GRC) (ED431C 2021/55)., info:eu-repo/semantics/publishedVersion

This study presents the research results acquired from conducting municipal sludge gasification in a downdraft type gasifier at pilot scale. The assessment of the results was not only focused on syngas characteristics, but also on the gasification residues: char ash and glassy material. The gasification temperature was varied from 1000 to 1150 degrees C during the gasification trials. The produced high quality syngas was transferred to the engine to generate the electricity. About 1 kWh electrical power was achieved for approximately 1.2 kg municipal sludge gasified. Most of the heavy metals available in the sludge was found as fixed form in the glassy material. The gasification residues evaluated as valuable materials regarding their characteristics have reuse potential for different beneficial usage alternatives. Based on the costs for the investment and operation and incomes, the return on the investment for this pilot scale system was roughly found as 3.3 years. This study showed that the municipal sludge had an important fuel merit and the energy recovery from the sludge was possible via the gasification application. In this paper, the research results were discussed in detail to make better insight to full-scale applications as a promising alternative for sludge disposal. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Simultaneous pollutant removal and electricity production using microbial fuel cells is a promising environmental sustainable technology that contributes to the circular economy. Numerous studies have been conducted previously using exogenously adding easily degradable sugars for electricity generation in microbial fuel cells (MFCs). However, in real-world applications involving wastewater, the performance of the process varies according on the source, the microorganisms presented and the electrodes employed. The simulta-neous treatment of baker's yeast industrial effluents and electricity generation is investi-gated in various MFCs using titanium and graphite electrodes. Reduced chemical oxygen demand (COD) is reported to be between 73% and 92% depending on the MFC configuration and electrodes employed. The two-chamber MFC with titanium electrodes and inoculum sludge from upflow anaerobic sludge blanket reactors (UASB) perform better, reaching 51.02 mW/m2 and 12.74 mA/cm2 power and current densities, respectively. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

An accurate estimation of sludge rheological properties has proved to be of great interest for the design of treatment facilities, including storage and transportation systems. Further, rheological measurements allow us to quantitatively estimate the physical consistency of sludge, which also affects almost all treatment, utilization, and disposal operations. However, sludge is a complex mixture and it appears quite difficult to determine a priori the rheological behavior by simply using global macroscopic parameters such as the solids content, which often remains the main standard to distinguish different materials. Indeed, sludge continuously evolves due to microbiological activity and, from a physical point of view, presents a three-dimensional gel-like biofilm matrix. Thus, due to the complexity of sludge rheological behavior, the measurement of rheological properties requires the development of well-controlled procedures to allow reliable results. Procedures must also be simple to operate and applicable on the field, when necessary.

Sludges produced in biological wastewater treatment plants have rich organic materials in their characteristics. Recent research studies have focused on the energy recovery from sludge due to its high organic content. The gasification process is a thermal conversion technology transforming the chemical energy contained in a solid fuel into thermal energy and electricity. The produced syngas as a mixture of CO, CH4, H2 and other gases can be used to generate electrical energy. The gasification of yeast industry sludge has been experimentally evaluated in a pilot scale downdraft-type gasifier as a route towards the energy recovery. The gasifier has 20 kg biomass/h fuel capacity. During gasification, the temperature achieved was more than 1,000°C in the gasifier, and then the syngas was transferred to the gas engine to yield the electricity. A load was connected to the grid box and approximately 1 kWh electrical power generation for 1 kg dry sludge was determined. The characteristics of residuals – ash, glassy material – were also analyzed. It was found that most of the heavy metals were fixed in the glassy material. Experimental results showed that the yeast industry sludge was an appropriate material for gasification studies and remarkable energy recovery was obtained in terms of power production by using syngas.

The present experimental investigation examined the applicability of fry-drying technology for municipal dewatered sludge by using waste engine oil for frying. The process was studied in a 100180 degrees C temperature range for 2 to 20min frying times. The cakes were shaped in a diameter range of 1 to 3cm with 3-cm-length prior to the frying. Experimental points were determined by the BoxWilson experimental method. Statistical analysis was employed for determining the response function coefficients for variables. The response functions were as dry solids content (DS), volatile solids content (VS), and low heating value (LHV). Experimental and predicted results indicated good agreement with high correlation coefficients. The results showed that fry-drying is an alternative, fast process for sludge drying. In addition, it makes fry-dried sludge as a product with noteworthy LHV. This study provides further insight into the fry-drying of municipal dewatered sludges.

Thermal drying of dewatered municipal sludge was studied in the temperature range 50-180 degrees C for different times from 10 to 120 min. The Box-Wilson response surface experimental method was used to investigate the effects of temperature and time on sludge drying. Statistical analysis using the methodology was employed to determine the response function coefficients for each variable: temperature and time. The response functions of the study were dry solids (DS) content, volatile solids (VS) content, and low heating value (LHV). Experimental and predicted results from the model indicated excellent agreements. Higher drying temperatures and time led to higher DS content. Higher temperatures increase the drying kinetics and longer drying times allow more time for water to evaporate. The elevated temperatures and time did not drastically change the VS content values. Only small-scale changes were observed regarding the increases in temperature and time. Higher shrinkage percentages were achieved via increased temperature and time. The drying kinetics exhibited increased drying rates depending on the decrease in water content. This study showed that the response surface methodology could be used as a tool for drying process optimization.

Hydrolytic enzymes such as glucosidases, lipases, and proteases have an imperative function at the hydrolysis stage of complex organic structures in the degradation of biodegradable particulate organic matter. As a key factor, extracellular polymeric substances (EPS) control the extracellular hydrolytic enzymes in this degradation mechanism. A flocculated matrix of EPS bridging with bacteria holds back the dewaterability properties of the bioprocessed sludges. Disruption of the flocculated matrix leads to improved solubilization of sludge solids by attacking the hydrolytic enzymes to polymeric substances forming enzyme-substrate complexes. To determine the floc disintegration mechanisms by enzymes during aerobic and anaerobic bioprocessing of sludges, experimental data obtained from three aerobic digesters and three anaerobic digesters were evaluated. As part of a broader project examining the overall fate and effects of hydrolytic enzymes in biological sludge stabilization, this paper compares the performances of aerobic and anaerobic reactors used in this study and reports significant improvements in enzymatic treatment of activated sludge.

The management of sludge produced during water/wastewater treatment processes is one of the most important environmental problems to be solved in all over the world. Recently, the need to achieve a...

Conditioning of either wastewater biosolids or water treatment residuals conventionally utilizes a single polymer to improve subsequent dewatering. The sequential addition of two polymers has been reported to enhance biosolids dewaterability, but comparable benefits have not been demonstrated for water treatment residuals. This paper evaluated the use of cationic and nonionic polymers, singly and in combination (dual), to investigate whether dual polymer conditioning of residuals offers any advantages, and to determine whether the results could be accommodated by current mechanistic understandings. For this purpose, lab-scale tests used capillary suction time (CST), supernatant viscosity, zeta potential, streaming current, turbidity, floc size, and rheometric analyses. Comparisons of CST and viscosity results for single and dual polymer additions indicated that dual polymer use gave moderately improved dewaterability, possibly due to the increased mixing utilized for dual polymer addition. Using a cationic polymer produced a less turbid supernatant. Zeta potential and streaming current were not good indicators of conditioning efficacy when a nonionic polymer was used. Rheometric analyses were only meaningful in one selected method for treatment of the data: the area under the rheogram up to a shear rate of 30 inverse s. Overall, implementation of dual polymer use does not appear warranted.

This paper reports on the ability of an enzymatic pre-treatment to significantly improve the conditioning of wastewater sludges (biosolids) significantly using by a polymeric flocculant. Experiments used anaerobically digested biosolids samples from two different municipal wastewater treatment facilities, and a formulation containing several different hydrolytic enzymes. Samples were incubated at 35 degrees C for 16 h then conditioned with the cationic polymer solution. A laboratory scale mechanical dewatering unit, which simulates full-scale belt filter presses, was used in dewatering of,the biosolids. Dewaterability was evaluated using capillary suction time (CST), solid content of final cake product, filtrate turbidity, and suspended solids analysis. The enzyme additions enhanced dewaterability of the polymer conditioned samples in terms of CST and solids content of final product, demonstrating the possibility of significant volume reductions using enzymatic treatment at full-scale. The biosolids structures with the additions of enzyme, polymer, and both additives were determined using field emission scanning electron microscopy. (c) 2004 Elsevier Ltd. All rights reserved.

Sludge produced by municipal wastewater treatment plants (WWTPs) amounts to only a few percent by volume of the processed wastewater, but its handling accounts for up to 50% of total operating costs. Moreover, the need to achieve a sustainable sludge management strategy has become of great concern. It follows that as conventional and more traditional options, such as land spreading for agricultural purposes, are progressively restricted, and often legally banned, the development of innovative systems to maximize the recovery of useful materials and/or energy is required. A change toward more sustainable procedures can be promoted through an integrated approach, including the assessment of management routes capable of maximizing the recycle/recovery benefits, through low energy impact systems, and the development of operational systems appropriate to local circumstances. Based on the above considerations, an integrated system is proposed in this paper. It includes Anaerobic digestion, Dewatering/Drying, and Pyrolysis/Gasification processes which are efficiently coupled for the recovery of products for material reuse and/or energy purposes. Such an integrated system should also allow the recovery of one or more materials, depending on the combination of processes which best fit specific local situations.

An immobilization cell was successfully coupled to a controlled stress rheometer to quantify rheological properties of a sludge during its dewatering. An anaerobically digested sludge and a synthetic sludge were analyzed and conditioned at various doses with a cationic flocculant. Direct strain-controlled oscillatory analyses could not be performed due to rapid dewatering, but controlled shear rate analysis quantified the increases in sludge viscosity as the solid's concentration increased. Immobilization times determined by these experiments-viscosity versus dewatering time-agree with capillary suction times, since both indicate the time required for water removal (r(2) from 0.81 to 0.99). However, capillary suction time tests were more strongly influenced by filtrate viscosity at high polymer doses. The immobilization cell allowed quantified amounts of shear to be imposed during dewatering, with greater shearing found to provide more rapid immobilization. This finding is consistent with the design of belt filtration dewatering devices, but demonstrates that current models do not account for a critical aspect of this process.

Materials known as complex fluids exhibit a transitional behaviour between their solid and liquid states. Sludges produced at different treatment stages of wastewater treatment are examples of these materials, since they exhibit solid behaviour within shorter time frames and liquid behaviour over longer durations. These sludges can also change from solid-like to liquid-like, or vice versa, when subjected to even a slight deformation; this stems from their complex makeup, which includes both particulate materials and polymeric gels, including both biopolymers and the synthetic polymers used in conditioning them. This paper focuses on two means of quantifying dynamic rheological test results: (1) the linear viscoelastic behaviour (LVE) of sludge samples, as measured by the strain sweep analysis storage (G′) and loss moduli (G″); and (2) the flow curve, which presents the relationship between the shear viscosity and shear rate and determines the yield stress values of samples using the strain sweep test mode. With these methods, sludges can be more accurately characterised, allowing better prediction of their behaviour in treatment and transport processes.

One of the most crucial processes in biosolids management is stabilisation, which is typically accomplished using either anaerobic or aerobic digestion processes. Although there are many advantages to both of these methods – such as reduction of volatile organic matter, pathogen content, and offensive odours – one common disadvantage is that digested biosolids exhibit poor dewaterability characteristics. The deterioration in dewaterability of digested biosolids leads to increases in polymer requirements, connoting higher conditioning costs. Many studies have examined this phenomenon based on conventional filterability tests such as capillary suction time and specific resistance to filtration. However, these test methods are limited in their ability to predict full-scale dewatering behaviour (particularly in centrifugation), and do not regard handling properties as being important for sludge transport. For this purpose, new rheometric methods may assist in predicting sludge behaviour, potentially allowing optimisation of stabilisation and conditioning processes relative to the desired sludge properties. This paper investigates the possible utility of these methods. Classical methods for characterising biosolids, such as filtration tests, are compared with yield stress values and other rheological properties as determined using the steady-shear rate sweep test. The rheological behaviours are compared for different sludge types, including raw and polymer conditioned thermophilic anaerobically, mesophilic anaerobically, and mesophilic aerobically digested biosolids. The paper demonstrates the determination of specific energy values associated with breakdown of the flocculated matrix. Robust modelling approaches are employed to optimise the conditioning of the digested samples, and to shed light on commonly used rheological models such as Bingham, Herschel-Bulkley, and Ostwald equations.

In this paper, we demonstrate that the rheological behavior of pasty sewage sludges, regardless of origin, treatment or composition, follows a Herschel-Bulkley model. The yield stress and solid volume fraction are found to be the only two distinctive rheological characteristics of these materials. By scaling the shear rate and the shear stress with two parameters depending only on the yield stress and the solid fraction, the flow curves of 48 pasty sludges all fall along a unique dimensionless master curve. This result may be used in practice to determine, from simple, independent measurements, the rheological behavior of any pasty sludge: the yield stress can be measured with the help of the, slump test' and the solid concentration determined from the organic and mineral matter contents. The results obtained with this technique are in very good agreement with those obtained by direct rheometry. (C) 2004 Elsevier Ltd. All rights reserved.

The efficient and economic management of waste activated sludge (WAS) requires a proper understanding of the sludge's material properties. Though there has been much study of WAS, an adequate linkage between its physical and chemical properties has been elusive. In particular, the conditioning and dewatering of WAS are expensive operations, and the addition of polymer to WAS leads to even more complex material behavior that is difficult to optimize. This paper reports on an extensive characterization of WAS, both with and without polymer conditioning. We combined the classical “jar test” approach with less conventional rheometric and electrokinetic measurements. In addition to the use of sampled WAS, a synthetic surrogate sludge was formulated, attempting to duplicate properties of WAS and allow more extensive characterization of a reproducible surrogate to WAS. Results with both the synthetic surrogate and WAS indicated that the traditional, electrokinetic, and rheological properties were related. However, the dose optima by rheometry were somewhat higher in both cases.