Slurry Solids Research Articles

Wastewater as a resource: a unique approach to achieving energy sustainability

A wastewater-treatment flowsheet was developed to integrate uniquely designed biological processes with physical-chemical unit processes, allowing conversion of the organic carbon in the wastewater to methane, the removal and recovery of phosphorus and nitrogen from the wastewater, and the production of water suitable for reuse. In the flowsheet, energy is derived from the wastewater by first shunting a large fraction of the organic carbon in the wastewater to a solids slurry which is treated via anaerobic digestion. The anaerobic digestion system consists of focused pulsed (FP) pretreatment coupled to anaerobic membrane bioreactors (MBRs). Computer modelling and simulation results are used to optimize design of the system. Energy generation from the system is maximized and costs are reduced by using modest levels of recycle flow from the anaerobic MBRS to the FP pretreatment step.

Characterizing slurry hydrodynamic transport in a large overflow tubular ball mill by an improved mixing cell model based on tracer response data

Overflow tubular ball mills are depicted by an intrinsic pool of slurry at the toe of the ball charge, which facilitates the discharge of fine progenies (finished product) from the mill. To ensure that adequate slurry removal capacity is achieved while keeping the ball charge well saturated with slurry at all times (for efficient grinding), good knowledge of slurry transport inside the mill is essential. Most existing ball mill simulation models either inadequately account for the continuous exchange of slurry between the ball charge and the slurry pool or do not consider the realities such as back-mixing or bypasses in the system thereby leading to inaccurate prediction of slurry transport. To close that gap, a model is proposed here, in which both axial and radial flow parameters as well as a short-circuit component are incorporated as an improvement to the simple mixing cell model to correctly describe the inherent in-mill slurry transport dynamics. The model fits adequately to the experimental data for all conditions tested. Further, the model results show that the slurry axial back-mixing and the radial exchange rate are both affected by slurry solids concentration and ball load volume. Also, the model reveals that under conditions of low slurry solids concentration (< 37 vol.%), a part of the feed slurry may simply short-circuit to the exit. These results just serve as a priori indication that, having correct knowledge of in-mill slurry transport dynamics would enable mill operational variables to be appropriately tuned to achieve desirable mill behavior that corresponds to maximum milling and energy efficiencies.

Convenient storage of concentrated hydrogen peroxide as a CaO 2·2H 2O 2(s)/H 2O 2(aq) slurry for energy storage applications

Prior investigations have proposed, and successfully implemented, a stand-alone supply of aqueous hydrogen peroxide for use in fuel cells. An apparent obstacle for considering the use of aqueous hydrogen peroxide as an energy storage compound is the corrosive nature of the nominally required 50 wt.% maximum concentration. Here we propose storage of concentrated hydrogen peroxide in a high weight percent solid slurry, namely the equilibrium system of CaO 2·2H 2O 2(s)/H 2O 2(aq), that mitigates much of the risk associated with the storage of such high concentrations. We have prepared and studied surrogate slurries of calcium hydroxide/water that are assumed to resemble the peroxo compound slurries. These slurries have the consistency of a paste rather than a distinct two-phase (liquid plus solid) system. This paste-like property of the prepared surrogates enable them to be contained within a 200 lines-per-inch. (LPI) nickel mesh screen (33.6% open area) with no solids leakage, and only liquid transport driven by an adsorbent material is placed in physical contact on the exterior of the screen. This hydrogen peroxide slurry approach suggests a convenient and safe mechanism of storing hydrogen peroxide for use in, say, vehicle applications. This is because fuel cell design requires only aqueous hydrogen peroxide use, that can be achieved using the separation approach utilizing the screen material here. This proposed method of storage should mitigate hazards associated with unintentional spills and leakage issues arising from aqueous solution use.

Semi-solid processing of hypereutectic A390 alloys using novel rheoforming process

The feasibility of semi solid processing of hypereutectic A390 alloys using a novel rheoforming process was investigated. A combination of the swirl enthalpy equilibration device (SEED) process, isothermal holding using insulation and addition of solid alloy during swirling was introduced as a novel method to improve the processability of semi solid slurry. The effects of isothermal holding and the addition of solid alloy on the temperature gradient between the centre and the wall and on the formation of α(Al) particles were examined. In additional tests, phosphorus and strontium were added to the molten metal to refine the primary and eutectic silicon structure to facilitate semi solid processing. The results show that the combination of the SEED process with two additional processing steps can produce semi-solid A390 alloys that can be rheoprocessed. The microstructure reveals an adequate amount of non-dendritic α(Al) globules surrounded by liquid, which greatly improves the processability of semi-solid slurry.

Effects of organic additives on microstructure and mechanical properties of porous Si3N4 ceramics

Green bodies of porous Si3N4 ceramics were shaped by extrusion technique using different organic additives as binder during extrusion molding. Different porosity, microstructures and mechanical properties after the extrusion, drying, debinding and sintering stages were investigated. The solid slurry content of 70–75% and extrusion pressure of 0.5–1.0 MPa had played a decisive role in the smooth realization of extrusion molding. The porous Si3N4 ceramics were obtained with excellent properties using 4% hydroxypropyl methyl cellulose (HPMC) as binder and polyethylene glycol (PEG) of molecular weight, 1000, as plasticizer with a density of 1.91 g cm−3, porosity of 41.70%, three-point bending strength of 166.53 ± 20 MPa, fracture toughness of 2.45 ± 0.2 MPa m1/2 and Weibull modulus (m) of 20.75.

Implications of Aerated Stabilization Basin Dredging on Potential Effluent Toxicity to Fish

Benthal solids accumulated in aerated stabilization basins (ASBs) must be dredged to regain treatment capacity. While dredging restores treatment performance, it has been associated occasionally with the failure to meet regulatory effluent toxicity limits at the time of dredging. A first study of its kind was undertaken to investigate the implications of ASB dredging on potential effluent toxicity to fish. The study showed that benthal solid slurry removed from the quiescent zone of an ASB with a hydraulic dredge was toxic to rainbow trout with a 96-hour median lethal concentration (LC50) of 2.2%. The high ammonia concentration in the sample was the main cause of fish mortality. Hydrogen sulfide and resin and fatty acids also were present in the dredged material at concentrations that could cause fish mortality. These findings have led to best management practices that can be used to mitigate or eliminate fish toxicity issues during dredging operations.

Phosphorus Distribution in Untreated and Composted Solid Fractions from Slurry Separation

The distribution of phosphorus (P) (water-soluble inorganic P [P(i)], acid-soluble P(i), and residual P) was determined in 40 samples of solids from solid-liquid separated slurry. These were collected from separation plants using different technologies, separating by simple mechanical means, by flocculation as pre-treatment before mechanical separation or by anaerobic digestion followed by separation and centrifugation. Simple mechanical separation yielded a low solid TP content (8-9 g P kg(-1) dry matter [DM]) compared with separation by flocculation (26 g P kg(-1) DM) or by anaerobic digestion-centrifugation (33.4 g P kg(-1) DM). Acid-soluble P(i) predominated in the high P-yielding solids, whereas organic-bound or residual P was a minor component in all slurry solids. Acid-soluble P(i) and residual P were significantly correlated with total phosphorus (TP) content (R(2) = 0.855 and R(2) = 0.584), but water-soluble P(i) was uncorrelated (R(2) = 0.077). The relative distribution of P(i) to TP in the solids showed a high proportion of water-soluble P(i) in solids from simple mechanical separation, whereas the absolute concentrations were highest in solids from separation by flocculation and anaerobic digestion-centrifugation. Three solid fractions, representing the range of solids variability produced by the separation techniques, were composted for 30 d, and the P distribution was compared before and after composting. Total mass of P was conserved during composting, but water-soluble P(i) as a proportion of TP decreased in most cases. The most pronounced decrease in water-soluble P(i) was observed during composting of the solids separated using flocculation. However, changes in short- to medium-term bioavailability of P were modest, and thus the potential benefits of composting regarding storage and handling can presumably be realized without seriously compromising the P fertilization quality.

Erosion–corrosion performance of high-Cr cast iron alloys in flowing liquid–solid slurries

In many slurry transportation systems, such as in FGD (Flue Gas Desulphurization) and chemical processing applications, corrosion and erosion are the two main mechanisms of material degradation of the pump wet-end components including pump casing, impeller and liners. The performance of a selected material is mostly dependent upon its relative corrosion and erosion resistance to the service environment. In these cases erosion, corrosion and the related synergistic effects can be very complicated since they are affected by numerous factors including solid and slurry properties, chemical contents, hydraulic conditions and temperatures. In this experimental study, sliding Coriolis erosion testing has been performed with various corrosion factors such as pH value, chlorides content and temperature to evaluate the erosion–corrosion resistance of some high-alloyed white cast irons containing different levels of chromium and other elements. Optical microscope and SEM-EDS have also been used to examine microstructure and surface conditions of tested materials. Results indicated that material loss due to corrosion factors increased as acidity-chlorides and temperature increased. At relatively high corrosion intensity, the white cast irons with higher alloy content (especially chromium) clearly showed improved corrosion resistance and combined erosion–corrosion resistance over those with lower alloy content. Under certain corrosion and hydraulic conditions, particle size is perhaps the single most influential factor on erosion–corrosion rate of the high-Cr cast iron alloys. Relatively large particles are much more effective than small ones at removing both the corroded surface layer and the fresh material, causing substantially higher rate of material loss. Some other related factors have also been addressed.

Measurement of solid slurry flow via correlation of Electromagnetic Flow Meter, electrical resistance tomography and mechanistic modelling

The study presented here was carried out to obtain the actual solids flow rate by the combination of electrical resistance tomography and electromagnetic flow meter. A new in-situ measurement method based on measurements of the Electromagnetic Flow Meters (EFM) and Electrical Resistance Tomography (ERT) to study the flow rates of individual phases in a vertical flow was proposed. The study was based on laboratory experiments that were carried out with a 50 mm vertical flow rig for a number of sand concentrations and different mixture velocities. A range of sand slurries with median particle size from 212 μm to 355 μm was tested. The solid concentration by volume covered was 5% and 15%, and the corresponding density of 5% was 1078 kg/m 3 and of 15% was 1238 kg/m 3. The flow velocity was between 1.5 m/s and 3.0 m/s. A total of 6 experimental tests were conducted. The equivalent liquid model was adopted to validate in-situ volumetric solids fraction and calculate the slip velocity. The results show that the ERT technique can be used in conjunction with an electromagnetic flow meter as a way of measurement of slurry flow rate in a vertical pipe flow. However it should be emphasized that the EFM results must be treated with reservation when the flow pattern at the EFM mounting position is a non-homogenous flow. The flow rate obtained by the EFM should be corrected considering the slip velocity and the flow pattern.

Automotive storage of hydrogen in alane

Abstract Although alane (AlH 3 ) has many interesting properties as a hydrogen storage material, it cannot be regenerated on-board a vehicle. One way of overcoming this limitation is to formulate an alane slurry that can be easily loaded into a fuel tank and removed for off-board regeneration. In this paper, we analyze the performance of an on-board hydrogen storage system that uses alane slurry as the hydrogen carrier. A model for the on-board storage system was developed to analyze the AlH 3 decomposition kinetics, heat transfer requirements, stability, startup energy and time, H 2 buffer requirements, storage efficiency, and hydrogen storage capacities. The results from the model indicate that reactor temperatures higher than 200 °C are needed to decompose alane at reasonable liquid hourly space velocities, i.e., > 60 h −1 . At the system level, a gravimetric capacity of 4.2 wt% usable hydrogen and a volumetric capacity of 50 g H 2 /L may be achievable with a 70% solids slurry. Under optimum conditions, ∼80% of the H 2 stored in the slurry may be available for the fuel cell engine. The model indicates that H 2 loss is limited by the decomposition kinetics rather than by the rate of heat transfer from the ambient to the slurry tank.

Competitive biodegradation of dichlobenil and atrazine coexisting in soil amended with a char and citrate

The role of char nutrients in the biodegradation of coexisting dichlobenil and atrazine in a soil by their respective bacterial degraders, DDN and ADP, was evaluated. Under growing conditions, their degradation in soil extract was slow with <40% and <20% degraded within 64 h, respectively. The degradation in extracts and slurries of char-amended solids increased with increasing char content, due to nutritional stimulation on microbial activities. By supplementing soil extract with various major nutrients, the measured degradation demonstrated that P was the exclusive limiting nutrient. The reduction in the degradation of coexisting dichlobenil and atrazine resulted apparently from the competitive utilization of P by DDN and ADP. With a shorter lag phase, ADP commenced growing earlier than DDN with the advantage of utilizing P first in insufficient supply. This resulted in an inhibition on the growth of DDN and thus suppression on dichlobenil degradation.

An Evaluation of a Two-Stage Spiral Processing Fine Anthracite Refuse

Testing was conducted to evaluate the performance of a two-stage Multotec SX7 spiral concentrator treating fine anthracite refuse. Two sets of samples were collected from an anthracite cleaning plant located in eastern Pennsylvania. One sample consisted of the thickener feed slurry (nominal − 1.2 mm) and the other consisted of the thickener underflow slurry. A third sample was prepared by desliming the thickener feed using a 102-mm diameter Krebs cyclone to produce a nominal − 1.2 + 0.025 mm product. The effects of slurry flow rate and solids concentration on spiral performance were investigated. For the + 0.025 mm material, the feed ash value could be reduced from 71% to 21%, while producing a refuse with an ash value of 91%. Regardless of whether the feed slurry was deslimed or undeslimed, the + 0.025 mm material would separate. The separation occurred even with the thickener underflow, which had been treated with flocculant. The − 0.025 mm material split in approximately the same proportion as the water.

Efeito do arejamento no processo de compostagem da fracção sólida do chorume de pecuária leiteira

Manure surpluses in dairy farms can be reduced by separation of the solid fraction from slurry whereas composting allows the stabilization of the organic matter of the solid fraction. The solid fraction can be exported to other farms with a high demand for organic amendments after composting because this turns cattle slurry solids into a uniform, easily handled, organically stable, without pathogens or viable weed seeds that can be land applied and marketed as a soil amendment. However, when 60% moisture content of solids is exceeded, and this is the situation for most separated slurry solids, oxygen movement is somewhat restricted. Therefore, the effect of turning the compost pile must be researched since it provides oxygen for the decomposition process. Dairy cattle slurry solids from two different farms located at the NW Portugal (Vila do Conde), with 70% and 78% moisture contents, were removed from the tank using an auger encased in a perforated stainless steel screen, allowing removal of excess water. Twelve pile treatments of 15 m3 of freshly separated solids were placed in bare soil. The effects of using straw as a framework and of turning with a tractor-mounted front-end loader were evaluated through chemical analysis on pile samples collected over a 15 week period. Thermophilic temperatures were achieved soon after separation for 70% moisture solids, but these temperatures were attained for 78% moisture solids only once mixed with straw, indicating that differences in bedding material affects the temperature and oxygen concentration during composting. Moreover, solids with initial 70% moisture had a faster rate of composting and took shorter time to reach maturity than solids with 78% moisture. Although chemical evolution based on parameters such as pH, electrical conductivity and C/N ratio provided substantial evidence that agronomical suitable compost can be obtained, future challenges include optimizing the process to minimize the loss of nitrogen in the form of ammonia gas, given that pH ranged from 8 to 9 throughout the compost process.

Hydrodynamic and kinetic characterization of industrial columns in rougher circuit

In the present investigation the relationship between collection zone rate constant ( k c) and gas dispersion parameters, viz. bubble size ( d b), superficial gas velocity ( J g), gas hold-up ( ε g) and bubble surface area flux ( S b) was evaluated. Experiments were conducted in an industrial (4 m in diameter and 12 m high) and a pilot (0.1 m in diameter and 4 m high) flotation column in rougher circuit at Miduk copper concentrator in Iran. Gas hold-up was measured using pressure difference technique and mean bubble sizes were estimated from a drift flux analysis. It was found that the collection zone rate constant was not correlated with d b and J g solely but was linearly dependent on ε g and S b for the range of interest. Collection efficiency ( E k) and floatability factor ( P) in the industrial columns were quantified ( E k = 3.1%; P = 7.7 × 10 −3). The influence of operating parameters comprising superficial gas velocity, slurry solids% and frother dosage/type on S b and flotation kinetics was discussed. Analysis of available industrial data suggested that S b and ε g were related by S b = 4.46 ε g over the range 30 < S b < 60 s −1 and 7% < ε g < 14%.

A Scraped Surface Bioreactor for Enzymatic Saccharification of Pretreated Corn Stover Slurries

High solids processing of biomass slurries provides the following benefits: maximized product concentration in the fermentable sugar stream, reduced water usage, and reduced reactor size. However, high solids processing poses mixing and heat-transfer problems above about 15% for pretreated corn stover solids. High solids slurries exhibit high viscosities and require high power consumption in conventional stirred tanks because they must be run at high rotational speeds to maintain proper mixing. An 8 L scraped surface bioreactor (SSBR) is employed here for enzymatic saccharification experiments to handle high solids loading and as a means for scale-up from laboratory-scale shake flasks. The scraping action of the blades keeps the reactor surface clear, which improves the heat-transfer characteristics. The horizontal rotation of the shaft and blades provides mixing and prevents particle settling much more effectively than in conventional stirred tanks, even at very low rotational speeds. The reactor is desi...

An Evaluation of a Two-Stage Spiral Processing Ultrafine Bituminous Coal

Testing was conducted to evaluate the performance of a multistage Multotec SX7 spiral concentrator treating ultrafine bituminous coal. This spiral mimics a two-stage separation in that the refuse is removed after four turns, and the clean coal and middlings are repulped (without water addition) and then separated in the final three turns. Feed samples were collected from the spiral circuit of a coal cleaning plant located in southwestern Pennsylvania. The samples consisted of undeslimed cyclone feed (nominal − 0.15 mm) and deslimed spiral feed (nominal 0.15 × 0.053 mm). Testing was carried out to investigate the effects of slurry flow rate and solids concentration on spiral performance. Detailed size and ash analyses were performed on the spiral feed and product samples. For selected tests, float-sink and sulfur analyses were performed. In nearly all cases, ash reduction occurred down to approximately 0.025 mm, with some sulfur reduction occurring even in the − 0.025 mm interval. The separation of the + 0.025 mm material was not significantly affected by the presence of the − 0.025 mm material when treating the undeslimed feed. The − 0.025 mm material split in approximately the same ratio as the slurry, and the majority of the water traveled to the clean coal stream. This split ultimately increased the overall clean coal ash value. A statistical analysis determined that both flow rate and solids concentration affected the clean coal ash value and yield, though the flow rate had a greater effect on the separation.

Biomass production and nutrient accumulation in Sparganium emersum Rehm. after sediment treatment with mineral and organic fertilisers in three mesocosm experiments

The response of the aquatic plant Sparganium emersum to different sediment nutrient levels was studied in three mesocosm experiments. The aim was to assess plant growth parameters and nutrient accumulation in the plant tissue under conditions relevant for habitats with sediments affected by anthropogenic nutrient enrichment. The experimental treatments were produced by fertilisation of the rooting medium (washed river sand) with differing doses of either NPK mineral fertiliser or digested sludge from solid pig slurry waste. Growth inhibition by high nutrient levels was not observed in any treatment (highest nutrient concentrations in the sediment with mineral fertiliser: N 250 mg kg−1, P 50 mg kg−1; organic fertiliser: N 6300 mg kg−1, P 1800 mg kg−1), which confirms the tolerance of S. emersum to high nutrient loads. The sediment nutrient concentration was best reflected in shoot dry mass. Nutrient contents in plant tissues were similar for most nutrient concentrations in the rooting media; only N increased significantly with N levels in the sediment in belowground parts. Nutrient standing stocks in plants, however, generally corresponded to the nutrient supply, and reached highest values (max. N 3.7 g m−2, P 1.2 g m−2) in the richest treatments with organic fertiliser. The capability of S. emersum to use nutrients from high sediment concentrations and in organically polluted environments recommends this species for use in water quality management including tertiary wastewater treatment.

Rising and descending bubble size distributions in gas–liquid and gas–liquid–solid slurry bubble column reactor

Dual-tip conductivity probe is used to determine distributions of rising and descending bubble size in gas–liquid and gas–liquid–solid bubble column. The column is 100 mm in internal diameter and 1500 mm in height. The solid particles used are glass beads with average diameter of 17.82 μm representing typical particle size for catalytic slurry reactors. Bubbles are categorized to two size classes, small bubbles with chord length ( d c) less than 10 mm and large bubbles with chord length greater than 10 mm. The effects of superficial gas velocity (1.0 cm/s ≤ U g ≤ 6.4 cm/s), solid holdup (0% ≤ ɛ s ≤ 30%) and radial location ( r/R = 0, 0.4 and 0.7) on bubble size distributions are determined. A fundamental statistic test— χ 2-test is used to test whether the experimental rising and descending bubble size distributions follow the commonly used distributions. It is found that increasing U g and ɛ s can increase the size and quantity of large bubbles. The results indicate that most small rising bubble size distributions are well characterized by lognormal or gamma distributions at low solid holdup. The descending bubble size does not follow any often used distributions; the majority of them are less than 4 mm, and a few of large descending bubbles appear with the increasing of ɛ s and U g. Usually, the total bubble size distributions are not fit for the lognormal distributions except when the descending bubbles are few under the condition of U g = 1.0 cm/s and ɛ s = 0%.

High‐throughput microplate technique for enzymatic hydrolysis of lignocellulosic biomass

Several factors will influence the viability of a biochemical platform for manufacturing lignocellulosic based fuels and chemicals, for example, genetically engineering energy crops, reducing pre-treatment severity, and minimizing enzyme loading. Past research on biomass conversion has focused largely on acid based pre-treatment technologies that fractionate lignin and hemicellulose from cellulose. However, for alkaline based (e.g., AFEX) and other lower severity pre-treatments it becomes critical to co-hydrolyze cellulose and hemicellulose using an optimized enzyme cocktail. Lignocellulosics are appropriate substrates to assess hydrolytic activity of enzyme mixtures compared to conventional unrealistic substrates (e.g., filter paper, chromogenic, and fluorigenic compounds) for studying synergistic hydrolysis. However, there are few, if any, high-throughput lignocellulosic digestibility analytical platforms for optimizing biomass conversion. The 96-well Biomass Conversion Research Lab (BCRL) microplate method is a high-throughput assay to study digestibility of lignocellulosic biomass as a function of biomass composition, pre-treatment severity, and enzyme composition. The most suitable method for delivering milled biomass to the microplate was through multi-pipetting slurry suspensions. A rapid bio-enzymatic, spectrophotometric assay was used to determine fermentable sugars. The entire procedure was automated using a robotic pipetting workstation. Several parameters that affect hydrolysis in the microplate were studied and optimized (i.e., particle size reduction, slurry solids concentration, glucan loading, mass transfer issues, and time period for hydrolysis). The microplate method was optimized for crystalline cellulose (Avicel) and ammonia fiber expansion (AFEX) pre-treated corn stover.

Pilot Tests of Slurries for In Situ Remediation of Pyrite Weathering Products

The efficiency of three slurries was tested for treating of acidity caused by pyrite weathering. Slurries of BauxsolTM, powdered limestone, and brucite [Mg(OH)2] were sprayed onto 10-ton masses of pyritic aggregate, and the acidity and sulfate concentrations of outflows were monitored for 21.5 months. After addition in identical procedures, neutralization of the outflow to a pH of above 6 was achieved by Bauxsol for about 1 day, by limestone for 4 days, and by Mg(OH)2 for the 652 days of the testing. Limestone control of pH was limited by armoring of the CaCO3 by gypsum [CaSO4·2H2O] and by restricting of water flow to channels so that most of this slurry remained unreacted. Channels were not evident in the Mg(OH)2-treated aggregate. With the limestone and Mg(OH)2 slurries, sulfate concentrations were controlled by crystallization of gypsum, or at higher concentration of sulfate by hexahydrite [MgSO4⋅6H2O]. The limestone slurry limited sulfate concentration to approximately 25 percent less than that occurring with the Mg(OH)2 slurry. An ideal slurry might include Mg(OH)2 for neutralization, limestone for limiting sulfate concentration, and other components to alter rheological behavior. Thixotropic behavior that favors initial dispersion of the slurry solids yet reduces loss in outwash and also limits channelization of water flow is best.