Dry Batch Research Articles

Hydrocarbons, Hydrogen, and Organic Acids Generation by Ball Milling and Batch Incubation of Sedimentary Rocks

Pulverized rock samples are widely used in laboratory experiments, e.g., to assess microbial or abiotic processes in batch incubation tests. However, it is unclear if ball-milled samples accurately reflect in-situ conditions and if observed processes are affected by by-products artificially generated during the sample preparation procedure. As such, this study examined the effects of dry ball milling on the release of gases, which include C1-C4 hydrocarbons, carbon dioxide (CO2), hydrogen (H2), and low molecular weight organic acids (LMWOAs) from different sedimentary rocks. The experiments involved pulverization using a gas-tight zirconium oxide planetary ball mill followed by wet and dry batch incubation and thermal desorption up to 200 o C. During milling, all sedimentary rocks, except a low organic carbon sandstone sample, yielded methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), H2, CO2, and unsaturated hydrocarbons, e.g., ethene (C2H4). Sandstones only yielded H2, CH4, and CO2. Stable carbon isotope signatures of these products are similar to thermogenic gases. The gases were also detected in subsequent wet incubation experiments (after gases from milling had been removed). Additionally, formate, acetate, and citrate, were detected in all samples except for sandstone. Pyruvate, malate, and succinate were also detected in some samples. Thermal desorption products of powdered limestone, shale, and pyrite concretion samples included organic acids, such as acetate and formate, which were higher in milled samples than in crushed particles (∼1 mm). The original geological thermal maturity of the studied sedimentary rock samples was low (below “oil window”) and, thus, considerably below “gas window”, suggesting that most of the detected gases were generated during ball milling. H2 generated during ball milling may be derived from the reduction of water from fluid inclusion or phyllosilicates, involving the formation of reactive mineral surfaces or radicals. Notably, the concentrations of gaseous hydrocarbons derived from milling are relatively high and comparable to “wet” gases. At the same time, these data indicate that substantial amounts of gases and LWMOAs might be artificially generated during laboratory batch experiments with milled samples. Hence, ball milled rock samples must be used with caution if assessing (bio-)geochemical processes for natural environments.

From grass to gas and beyond: Anaerobic digestion as a key enabling technology for a residual grass biorefinery

Roadside grass clippings hold potential as a sustainable source of bioenergy as they do not compete with crops for land use, and are only partially utilized for low-value applications. In this study, we proposed using roadside grass as a sole feedstock for anaerobic digestion (AD) in three different settings, and assessed the potential of producing biomaterials and fertilizers from grass-based digestate. Wet continuous digestion at pilot scale and dry batch digestion at pilot and large scales resulted in biogas yields up to 700 Nm3.t−1 DOM with a methane content of 49–55 %. Despite promising results, wet AD had operational problems such as clogging and poor mixing; once upscaled, the dry digestion initially also presented an operational problem with acidification, which was overcome by the second trial. Digested grass fibers from the pilot dry AD were processed into biomaterials and performed similarly or better than the undigested fibers, while around 20 % performance reduction was observed when compared to reference wood fibers. A mass balance indicated reduced fiber recovery when higher biogas production was obtained. The liquid fraction from the pilot dry AD was characterized for its nutrient content and used as a biofertilizer in another study. In contrast, the leachate collected from the large-scale dry AD had a low nitrogen content and high chloride content that could hinder its further use. Finally, a regional market analysis was conducted showing that the biocomposites produced with the available grass fibers could substitute at least half of the current European market based on our results.

Scale-up of Vertical Wet Stirred Media Mill (HIGmill) via Signature Plots, Stress Analyses and Energy Equations

HIGmill, which is a type of vertical wet operated stirred media mill, has found applications in mineral industry requiring fine grinding stage. As the technology has recently been developed, knowledge regarding to its operation is scarce. This study aims to fulfill this gap with its focus on scale-up of the mill from laboratory scale tests. Within the scope of the work, a HIGmill operated at copper regrind circuit was sampled at different operating conditions, i.e., tip speeds, solids contents and media filling. In parallel, laboratory scale tests using the identical HIGmill feed were run in a dry batch operated vertical stirred mill and ball mill. The two results were initially calibrated by changing the operating parameters of the laboratory mills. Afterwards, the feed samples were processed with the optimal condition of stirred mill and the results of both scales were compared. In this study, the applicability of three different scale-up methodologies, signature plot, energy equations and stress analyses were examined. The investigations showed that the procedures can be utilized to predict both the required energy and volume required for the milling application. The developed methodologies may be helpful for basic engineering purposes requiring sizing the mill.

Material characterization and conditioning of cattle feedlot manure as feedstock for dry batch anaerobic digestion

The focus of the study was to determine the suitability of cattle feedlot manure originating from clay-pack feedlots as a possible feedstock material for dry batch anaerobic digestion. Oedometer tests were carried out that measure the permeability and compressibility of the feedstock under practical conditions experienced in large-scale dry batch anaerobic digestion plants. Material characterization tests showed that feedlot manure was impermeable under compression and therefore unsuitable for percolation. Mixtures of feedlot manure, wood chips (3 %ww) and wheat straw (6 %ww) showed superior permeability under compression compared to feedlot manure alone with an 56% increased permeability. Further practical tests showed that dry digestion of feedlot manure mixtures led to methane yields of 99 mL/g VS which equals 86% of the material biochemical methane potential (BMP). High percolation rate and low inoculum recycle led to the highest specific methane yield (SMY) and digester productivity with implications on process design to reduce capital investment costs.

Use of Inoculum, Water and Percolate as Strategy to Avoid Inhibition on Dry-Batch Anaerobic Digestion of Organic Fraction of Municipal Solid Waste

The impact of inoculum to substrate ratio (I:S) and the addition of water and percolate on stopping inhibition in dry batch anaerobic digestion of organic fraction municipal solid waste (OFMSW) was investigated. In particular, ratios of I:S from 1:2 to 1:16 and total solid contents from 40 to 25% with water and percolate addition were analysed. Tested I:S did not avoid acidification of the anaerobic digesters (ADs), and the highest biogas and methane production (16.2 and 1.7 L/kg VSadded, respectively) was achieved with the 1:4 ratio. Water addition was also insufficient to avoid acidification, and while biogas increased as TS decreased, 40.9 L/kg VSadded for 25% TS, methane yield remained low at 1.2 L/kg VSadded due to the inhibition of methanogenic archaea. Percolate addition proved a suitable strategy to increase pH buffering, with an increased methane production of 199.4 L/kg VSadded at similar TS ranges (27%). Impact on kinetics of methane formation was assessed by kinetic modelling with logistic model identified as the better fit for most of the ADs. Shorter lag phases were observed as TS were reduced, regardless of the acidification, as mass transfer limitations were reduced at the beginning of the batch, but an increase was observed when percolate was used instead of water. Increases of the maximum methane rate (Rmax) was also achieved with TS reduction, but only when acidification was avoided. This study has highlighted the need to profile percolate composition during batch digestion in order to balance recirculation of nutrients, microbial communities and toxic compounds.Graphic

The Preferential Comminution of Binary Mixtures

dability of limestone in their mixtures. This behavior may be attributed to the Representative samples of limestone, ilmenite, and quartz, were dry batch ground separately and in binary mixtures of limestone – ilmenite and limestone-quartz in different compositions in the ball mill. The study aimed to investigate the effect of the mixture composition on the mill product characteristics as reflected on each of the two components. The results indicated that quartz affects as a hard component more than the ilmenite as a heavy component on the grinability of quartz to transfer the kinetic energy of the grinding media to limestone component more than ilmenite, which increases the preferential comminution of limestone by quartz more than that by ilmenite.

Material Characterization and Substrate Suitability Assessment of Chicken Manure for Dry Batch Anaerobic Digestion Processes.

Chicken manure is an agricultural residue material with a high biomass potential. The energetical utilization of this feedstock via anaerobic digestion is an interesting waste treatment option. One waste treatment technology most appropriate for the treatment of stackable (non-free-flowing) dry organic waste materials is the dry batch anaerobic digestion process. The aim of this study was to evaluate the substrate suitability of chicken manure from various sources as feedstock for percolation processes. Chicken manure samples from different housing forms were investigated for their chemical and physical material properties, such as feedstock composition, permeability under compaction and material compressibility. The permeability under compaction of chicken manure ranged from impermeable to sufficiently permeable depending on the type of chicken housing, manure age and bedding material used. Porous materials, such as straw and woodchips, were successfully tested as substrate additives with the ability to enhance material mixture properties to yield superior permeability and allow sufficient percolation. In dry anaerobic batch digestion trials at lab scale, the biogas generation of chicken manure with and without any structure material addition was investigated. Digestion trials were carried out without solid inoculum addition and secondary methanization of volatile components. The specific methane yield of dry chicken manure was measured and found to be 120 to 145 mL/g volatile solids (VS) and 70 to 75 mL/g fresh matter (FM), which represents approximately 70% of the methane potential based on fresh mass of common energy crops, such as corn silage.

Comparison of anaerobic digestion technologies: An Italian case study

The present study focused on a comparison of two technologies applied in the mesophilic anaerobic digestion, namely a conventional wet one and a dry batch one. The considered substrate was the source sorted organic fraction of municipal solid waste (SS-OFMSW) and the input flow rate, for the study case, was 35,000 Mg/year. The analysed systems included the pre-treatment of the SS-OFMSW, anaerobic digestion, upgrading of biogas to biomethane and aerobic post-treatment for the purpose of obtaining compost. The comparison was made by the calculation of three indicators: net present value, total primary energy and CO2 equivalent emissions, with the aim of providing elements for choosing the most appropriate technology for the specific case. The results obtained demonstrated the finding of worse values by the total primary energy indicator for the dry batch technology, providing a saving of approx. 21% lower compared to the wet one. In terms of CO2 equivalent emissions, the dry batch anaerobic digestion technology provided a better indicator than the wet anaerobic digestion system. Sensitivity analysis revealed the finding of an opposite result only when high specific gas production values were assumed for wet anaerobic digestion, and low specific gas production values for the dry batch technology.From an economic perspective, the results indicated a preference for the dry batch technology due to a higher net present value and a shorter period of return of the investment. This finding was also confirmed by a Monte Carlo uncertainty analysis, showing how the dry batch system featured a 90% of possibility of achieving a higher economically sustainability versus the wet technology.

Dry batch anaerobic digestion of food waste in a box-type reactor system: Inoculum preparation and reactor performance

Abstract A box-type reactor system with liquid inoculum has been studied for the dry anaerobic digestion of food waste. The food waste was processed without any pre-treatment to remove physical impurities, neither water addition to dilute and slurry the feedstock. The experiment was carried out with inoculum to substrate ratios of 1:1 (w/w) and 0.08:1 (VS basis). Previous acclimation of liquid inoculum enhanced the process, assuring a fast start up of the box digester and preventing from process failure by volatile fatty acids accumulation. The percolate recirculation strategy was shown to have a relevant effect on the progress of the process. The results suggest that the process can be optimized by providing low percolate recirculation rate during the start-up of the box digester followed by an increase in the percolate recirculation rate when volatile fatty acids decrease and methane content in the biogas increases. The methane yield obtained in the box digester from the food waste was in the range 460–477 L CH4 kg−1 VS, being the VS removal efficiency between 91.1 and 91.4%. Globally, the process operated at an organic loading rate of 2.5 kg VS m−3 d−1 and yielded a volumetric methane production rate of 1.0 m3 CH4 m3 d−1. These results show the high potential of food waste for its conversion in renewable energy by using the dry batch anaerobic technology.

Insights into advanced ball mill modelling through discrete element simulations

Important advances have been made in understanding ball milling during the last 25 years or so, a great part of it owing to the widespread application of the discrete element method (DEM), which is now an integral part of several advanced ball mill models. These models, however, must rely on assumptions regarding the mill mechanical environment that can help make the problem more manageable. The paper analyzes the validity of some assumptions that have been the basis of several advanced ball mill models by conducting DEM simulations of dry batch mills including both grinding media and particles. The validity of the assumption of perfect mixing of grinding media and particles, as well as of simulating exclusively the grinding media in order to collect the collision energy information for prediction of breakage and, thus, saving computational effort, are analyzed in great detail. It is concluded that the assumption of perfect mixing in the radial direction is generally valid, except for mill frequencies that are unusually high and exceedingly large ratios of mean ball and particle sizes being ground. It is also observed that a fraction of the number of collisions inside the mill do not involve particles, so that an empirical expression that is based on the ratio of surface areas of the ball and particle charge is proposed to estimate such proportion of unsuccessful collisions. Finally, a model from the authorś laboratory, that assumes that each collision in the mill will involve a monolayer bed of particles, is tested, demonstrating reasonable agreement when compared to simulations.

Assessment of Solute Transfer Between Static and Dynamic Water During Percolation Through a Solid Leach Bed in Dry Batch Anaerobic Digestion Processes

The aim of this work was to characterize solute transfer between static and dynamic water during percolation through a solid leach bed reactor. A new experimental procedure was set up to measure the solute exchange rate between macro-and micro-porosity. Tracer tests were performed in closed-circuit recirculation experiments. The water behavior was modeled by a multiphase flow model in a double porosity medium using a previously published methodology. The solute exchange rate between static and dynamic water was described by first-order kinetics. The methodology was applied to wheat straw and solid cow manure beds. The solute exchange rate (hs was 0.054 and 0.324 h−1) for wheat straw and solid cow manure, respectively. The measured data was used to improve the prediction capacity of a CFD tool. The results of this work could be used to develop appropriate leachate recirculation strategies to optimize full-scale dry batch anaerobic digestion processes.

Techno-economic evaluation of a tandem dry batch, garage-style digestion-compost process for remote work camp environments

The extraction of natural resources often involves housing workers in remote work camps far from population centres. These camps are prevalent in northern Alberta where they house approximately 40,000 workers involved in oil sands processing. The central, full-service cafeterias at these camps produce a significant quantity of food and cardboard waste. Due to their remote nature, these camps face high waste disposal costs associated with trucking waste long distances to the landfill. In this study, we investigated the techno-economic feasibility of on-site treatment of food and cardboard waste in a tandem dry batch, garage-style anaerobic digestion-compost process in which the waste material is converted into renewable energy used to heat the camp water supply and a nutrient-rich soil amendment for local land reclamation projects. Dry batch digestion and windrow composting pilot trials were performed on a simulated work camp waste in order to assess technical performance. The quality of the final compost was found to meet regulatory standards. A complete mass balance was then developed for a facility treating 3000 tonnes food waste and 435 tonnes waste cardboard annually. An economic assessment of such a facility was performed and, depending on the level of capital support and recognition of carbon credits for landfill methane mitigation, would require waste disposal costs to be between $115 and $195 CAD per tonne to meet financial criteria for project selection in Alberta’s oil and gas industry.

Application of the product related stress model for product dispersity control in dry stirred media milling

Ground ultrafine and nano- materials are mainly produced by wet stirred media milling. The product related stress model can be used for the optimization of such grinding processes; the operational parameters can be related to the particle size or specific surface of the product. At the same time, for many materials dry grinding is required. During dry stirred media milling different problems arise, such as aggregation, agglomeration and particles sticking on the mill liners and on the grinding media. Consequently, the processes taking place in the mill and the effects of the operational parameters on the product properties are not as thoroughly known as in the case of wet stirred milling. In the present paper the application of the product related stress model for product dispersity control in dry batch stirred media milling is presented. Modifications of the models' main parameters such as stress intensity and stress number are introduced. The applications of the modified main parameters are presented for the optimization of the material and grinding media filling ratio, as well as functions for the characterization of the effect of the stress number and stress intensity on the product. With the introduced modifications, the product related stress model proved to be suitable for the characterization of dry batch stirred media milling.

An experimental study on foaming of linear low-density polyethylene/high-density polyethylene blends

In this research work, foaming behavior of selected polyethylene blends was studied in a solid-state batch process, using CO2 as the blowing agent. Special emphasis was paid towards finding a relationship between foamability and thermal and rheological properties of blends. Pure high-density polyethylene, linear low-density polyethylene, and their blends with two weight fraction levels of high-density polyethylene (10 and 25%wt.) were examined. The dry blended batches were mixed using an internal mixer in a molten state, and then the disk-shaped specimens, 1.8 mm in thickness, were produced for foaming purposes. The foaming step was conducted over a wide range of temperatures (120–170℃), and the overall expansion and cellular morphology were evaluated via density measurements and captured SEM micrographs, respectively. Three-dimensional structural images were also captured using a high resolution X-ray micro CT for different foamed samples and were compared. Rheological and DSC tests for the virgin and blends were also performed to seek for a possible correlation with the formability. Based on the results, blended polyethylene foams exhibited remarkable expansion and highly enhanced cell structure compared to pure polymers. Bulk density, as low as 0.33 g/cm3, was obtained for blends, while for the virgin high-density polyethylene and linear low-density polyethylene, bulk density lower than 0.5 g/cm3 was not attainable. The lowest density was observed at a foaming temperature of 10–20℃ above the melting (peak) temperature obtained via DSC test. Rheological characteristics, including storage modulus and cross-over frequency value, were also found to be the indicators for the materials foaming behavior. Moreover, blends with 25% wt. of high-density polyethylene exhibited the highest expansion values over a wider range of temperature compared with 90% linear low-density polyethylene/10% high-density polyethylene.

Methane production improvement by modulation of solid phase immersion in dry batch anaerobic digestion process: Dynamic of methanogen populations

Several 60L dry batch anaerobic digestion (AD) reactors were implemented with or without liquid reserve on cattle manure. The immersed part modulation of cattle manure increased the methane flow of about 13%. The quantitative real time PCR and the optimized DNA extraction were implemented and validated to characterize and quantify the methanogen dynamic in dry batch AD process. Final quantities of methanogens converged toward the same level in several inocula at the end of AD. Methanogen dynamic was shown by dominance of Methanosarcinaceae for acetotrophic methanogens and Methanobacteriales for the hydrogenotrophic methanogens. Overall, methanogens populations were stabilized in liquid phase, except Methanosaetaceae. Solid phase was colonized by Methanomicrobiales and Methanosarcinaceae populations giving a support to biofilm development. The methane increase could be explained by a raise of Methanosarcinaceae population in presence of a total contact between solid and liquid phases. Methanosarcinaceae was a bio-indicator of the methane production.

Electrical resistivity tomography to quantify in situ liquid content in a full-scale dry anaerobic digestion reactor

The electrical resistivity tomography (ERT) method is a non-intrusive method widely used in landfills to detect and locate liquid content. An experimental set-up was performed on a dry batch anaerobic digestion reactor to investigate liquid repartition in process and to map spatial distribution of inoculum. Two array electrodes were used: pole–dipole and gradient arrays. A technical adaptation of ERT method was necessary. Measured resistivity data were inverted and modeled by RES2DINV software to get resistivity sections. Continuous calibration along resistivity section was necessary to understand data involving sampling and physicochemical analysis. Samples were analyzed performing both biochemical methane potential and fiber quantification. Correlations were established between the protocol of reactor preparation, resistivity values, liquid content, methane potential and fiber content representing liquid repartition, high methane potential zones and degradations zones. ERT method showed a strong relevance to monitor and to optimize the dry batch anaerobic digestion process.

Impact of Inoculums of Dry Batch Type Digesters on Resultant Compost Quality

Anaerobic digestion (AD) of municipal solid waste is significant in terms of energy and material recovery. The resultant sludge from AD is 100% organic and used as a fertiliser. The batch type biogas digesters established by National Engineering Research and Development Center in Dikowita in Wattala is one of the waste to energy projects established in the Western Province in Sri Lanka. Pre-sorted market and green waste in the area are used as the substrate while three cow dung layers (as top, middle and bottom) are applied as inoculums in the digesters. However, continuous supply of cow dung to the plant has become a challenge at present. Hence, the top cow dung layer is replaced by one month old previously generated sludge by the plant. After generating biogas, sludge is composted by means of windrow composting and sent to the market. The aim of the present study was to assess the quality of resultant compost due to the replacement of top inoculum layer by previously generated sludge. Nine laboratory digester tanks were set up and filled representing three treatments (with three replicates), in which Treatment-1, Treatment-2 and control had cow dung, previously generated sludge and organic waste respectively as top inoculum layer. After completion of AD process, resultant organic sludge samples were air dried. The resultant compost samples from digesters were sieved through 4.75 mm aperture (mesh no.4). Physical, chemical and biological parameters of resultant compost were analysed. The results were subjected to One-Way ANOVA followed by Tukey‟s test to see whether there were significant differences among three treatments and compared with Sri Lanka Standard 1246:2003. The results revealed that, the potassium contents (K2O%) in the samples were insufficient (<1.0%). The moisture of Treatment-1, Treatment-2 and Control were 44.42%, 47.34% and 51.83% respectively and significantly different from each other (p≤0.05; ANOVA). However, the colour, odour, particle size, sand content, pH, organic carbon, total nitrogen, phosphorous, C/N ratio and viable weed seeds were comparable to Sri Lanka Standard 1246:2003, suggesting that the resultant compost could be used as a soil amendment. Keywords: Biogas, Compost, Digestion, Waste, Cow dung layer

Thermophilic anaerobic digestion of the screened solid fraction of dairy manure in a solid-phase percolating reactor system

An increase in volatile solids (VS) content from solid fraction of dairy manure would reduce the size of biogas on-farm facilities and could be of greater interest to farmers than manure slurry biogas plants. This study examined the technical feasibility of a solid-phase batch thermophilic anaerobic digestion system for the screened solid fraction (SF) of dairy manure using the digested liquid fraction of dairy manure as inoculum. Inoculum to substrate ratio (I/S) and percolate recirculation strategy were the parameters studied. The manure slurry separation process resulted in a solid fraction that represented 16.8% of total manure mass; this aforementioned fraction showed an ultimate methane yield of 61.5 L CH4 kg−1 SF (265 L CH4 kg−1 VS) which represented 48% of methane potential from raw manure slurry. Five comparative experiments with 40 kg SF and different I/S ratios and percolate recirculation rates revealed that higher I/S ratios provide more security against inhibition states due to high VFA levels and low pH in percolate. The results of the present work have shown that increasing the percolate recirculation rate in intermittent and short recirculation operations improves the stability and speed of the process. Under this percolate recirculation strategy dry batch operation was possible with a I/S ratio of 0.6 obtaining methane yields of 145, 175, 204 and 220 L CH4 kg−1 VS after 15, 20, 30 and 60 days of operation.

Assessment of percolation through a solid leach bed in dry batch anaerobic digestion processes

This work aimed at assessing water percolation through a solid cow manure leach bed in dry batch AD processes. A laboratory-scale percolation column and an experimental methodology were set up. Water behaviour was modelled by a double porosity medium approach. An experimental procedure was proposed to determine the main hydrodynamic parameters of the multiphase flow model: the porosity, the permeability and the term for water exchange from macro- to micro-porosity. Micro- and macro-porosity values ranged from 0.42 to 0.70m3m−3 and 0.18 to 0.50m3m−3. Intrinsic permeability values for solid cow manure ranged from 5.55·10−11 to 4.75·10−9m2. The term for water exchange was computed using a 2nd order model. The CFD tool developed was used to simulate successive percolation and drainage operations. These results will be used to design leachate recirculation strategies and predict biogas production in full-scale dry AD batch processes.

Influence of batch properties and the final coking temperature on the coke yield

At PAO Zaporozhkoks, the coke yield is determined experimentally as a function of the batch properties and the final coking temperature, in box coking. An empirical formula for the coke yield is obtained. With increase in the yield of volatiles from dry batch by 1%, the coke yield falls by 0.71%. With increase in the final coking temperature by 50°C, the coke yield falls by 0.35%.