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NASA NTRS1992

Running SINDA '85/FLUINT interactive on the VAX

Computer software as engineering tools are typically run in three modes: Batch, Demand, and Interactive. The first two are the most popular in the SINDA world. The third one is not so popular, due probably to the users inaccessibility to the command procedure files for running SINDA '85, or lack of familiarity with the SINDA '85 execution processes (pre-processor, processor, compilation, linking, execution and all of the file assignment, creation, deletions and de-assignments). Interactive is the mode that makes thermal analysis with SINDA '85 a real-time design tool. This paper explains a command procedure sufficient (the minimum modifications required in an existing demand command procedure) to run SINDA '85 on the VAX in an interactive mode. To exercise the procedure a sample problem is presented exemplifying the mode, plus additional programming capabilities available in SINDA '85. Following the same guidelines the process can be extended to other SINDA '85 residence computer platforms.

Simmonds, Boris↗

DOE OSTI2019

Assessing Impact of Reactor Scaling on Carbohydrate and Lipid Yields from Saline and Fresh Water Algae

Effective deconstruction of algal biomass is a major challenge associated with algal biofuels/bioproduct production. Improving biomass conversion requires understanding how reaction parameters affect the scale-up of bench scale processes to move to cost-effective conversion. Pretreatment of both aquatic and terrestrial feedstocks, using similar reaction conditions, identical feedstock and pretreatment chemistries have reported wide ranges in total sugar yields. This has been attributed to differences in reactor size or scale, type of operation (batch vs continuous), method of heating, reactor geometry and solids loading (w/w). These factors can impact both mass and heat transfer affecting both yield and reaction kinetics. To understand how total sugar yields in algal biomass are affected by different dilute acid pretreatment configurations we evaluated total sugar and lipid release at three reactor scales ranging from 4 ml to 300 ml, operated under mixed and non-mixed regimes.

09 BIOMASS FUELS↗

DOE OSTI2017

Full-Scale Vessel Testing of the Standard High-Solids Vessel for the Hanford Waste Treatment Plant Pretreatment Facility - 17282

Concerns over the mixing performance of the planned pulse-jet mixed (PJM) vessels for high solids applications in the Hanford Waste Treatment and Immobilization Plant (WTP) Pretreatment (PT) Facility, led to the development of a standard high-solids vessel (SHSV) design and full-scale vessel testing. The SHSV is intended as a potential replacement for several high-level waste feed receipt and lag storage vessels, ultrafiltration feed preparation vessels, and plant wash vessels. The SHSV design concept uses multiple smaller vessels (60 500 to 79 500 liters nominal batch size) to replace larger vessels, providing redundancy, improved mixing (PJM design and spargers), monitoring (multi-level bubblers), reduced material at risk, and improved structural features. The SHSV also requires qualification of a single vessel design for high solids Newtonian and non-Newtonian slurry processing, rather than earlier multiple vessel designs. Qualification of the SHSV design for mixing will be achieved through full-scale vessel testing (FSVT) with a prototypic SHSV under a set of most adverse design conditions in conjunction with additional engineering analyses. An Integrated Technical Team consisting of the U.S. Department of Energy (DOE), Bechtel National, Inc. (BNI), and independent experts was established to accelerate and provide oversight and direction to the test program and SHSV qualification. This paper will present an overview of the SHSV, full-scale vessel test and qualification program, and the management program to achieve closure of technical issues associated with PJM vessel mixing and control systems. (authors)

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DOE OSTI2017

Solvent hold tank sample results for MCU-17-150-152 (July 2017) and MCU-17-153-155 (August 2017): Quarterly report

A trend summary that includes the last two Solvent Hold Tank (SHT) monthly samples is shown; MCU- 17-150-152 (July SHT) and MCU-17-153-155 (August SHT). Since the last SHT sample sent for analysis was the August sample the chemical state of the solvent is best approximated by the chemical analysis of the August SHT sample (MCU-17-153-155). This report mainly focused on the chemical analysis of the August SHT sample. The analysis data from the July SHT sample are presented in the “trend” plots of this report. Analysis of the August SHT sample (MCU-17-153-155) indicated that the modifier (CS-7SB) was 2% below but the extractant (MaxCalix) concentration was at its nominal recommended level (169,000 mg/L and 46,400 mg/L respectively). The suppressor (TiDG) level has decreased since the last measurement taken while the Modular Caustic-Side Solvent Extraction unit (MCU) was operating in January 2017, but has remained steady in the range of 666 (observed in April) to 715 mg/L (observed in the August 2017 sample) since February 2017, well above the minimum recommended level (479 mg/L), but below the nominal level. The “flat” trends observed in the TiDG, MaxCalix, modifier, and Gamma measurement are consistent with the solvent being idle since January 10, 2017. A strong correlation between density and modifier concentration in the solvent continues to be observed in the SHT samples. This analysis confirms the Isopar™L addition to the solvent in January 2017. This analysis also indicates the solvent did not require further additions. Based on the current monthly sample, the levels of TiDG, Isopar™L, MaxCalix, and modifier are sufficient for continuing operation but are expected to decrease with time if the Modular Caustic-Side Solvent Extraction Unit (MCU) returns to processing radioactive liquid waste. Otherwise, the levels of these components will remain steady. A future Isopar™L trimming addition to the solvent is recommended when MCU resumes processing waste. Two unknown impurities related to the modifier (but not sec-butyl phenol: a modifier degradation product observed before) at the 290 and 110 mg/L levels were observed in the August SHT sample by the Gas - Chromatography-Mass Spectrometry (GC-MS) method. They were observed in a second GC-MS re-run with a new column. Their identification can’t be ascertained at this time. No impurities were observed in the Hydrogen Nuclear Magnetic Resonance (HNMR). Another impurity observed in the samples was mercury. Based on the August SHT sample, up to 23 ± 5 micrograms of mercury per mL of solvent was detected (the average of the Cold Vapor-Atomic Adsorption [CV-AA] and X-Ray Fluorescence [XRF] methods). The higher mercury concentration in the solvent (as determined in the last three-monthly samples) is possibly due to either a higher mercury concentration in Salt Batches 8 and 9 (Tank 49H) . The gamma level (~ 2.0E4 dpm/mL) measured in the August SHT samples was one order of magnitude lower than the gamma levels observed in the December 2016 and January 2017 SHT samples. A similar level was observed in the July SHT sample (MCU-SHT-150-152). The gamma level has remained consistently steady since January 10, 2017 when MCU stopped processing radioactive liquid waste. The laboratory will continue to monitor the quality of the solvent in particularly for any new impurities or degradation of the solvent components.

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DOE OSTI2026

Lignin Extraction and Condensation as a Function of Temperature, Residence Time, and Solvent System in Flow-through Reactors

Solvolytic extraction of lignin from biomass is a critical step in lignin-first biorefining, including the reductive catalytic fractionation (RCF) process. Key to optimal RCF processing is the ability to rapidly extract lignin from biomass at high delignification extents and transfer the lignin molecules to a catalyst surface in a time frame that minimizes lignin condensation reactions. Here, we use a flow-through reactor to study the effects of temperature (175–250 °C), residence time (9 to 36 min), and solvent composition (methanol and methanol–water) on lignin extraction and condensation. We evaluated three metrics at each condition: total delignification, delignification rate, and extent of condensation, the latter measured by a decrease in monomer yield for batch hydrogenolysis reactions of solvolysis liquor compared to batch RCF reactions. We observe that delignification is predominantly determined by temperature, while residence time dictates the lignin condensation extent. Moreover, the extent of both extraction and condensation increased in the methanol–water solvent system compared to that in the methanol system. Lignin extracted in methanol is stable up to 18-min residence times at or below 225 °C, while a majority of the lignin extracted in methanol–water is condensed with a 9-min residence time at 200 °C. These results can inform reactor designs and solvent selection for lignin-first biorefining processes that aim to physically separate the biomass and catalyst.

biorefining↗

DOE OSTI2016

Investigation of a Wedge Adhesion Test for Edge Seals

Many photovoltaic (PV) technologies have been found to be sensitive to moisture that diffuses into a PV package. Even with the use of impermeable frontsheets and backsheets, moisture can penetrate from the edges of a module. To limit this moisture ingress pathway from occurring, manufacturers often use a low permeability polyisobutylene (PIB) based edge seal filled with desiccant to further restrict moisture ingress. Moisture ingress studies have shown that these materials are capable of blocking moisture for the 25-year life of a module; but to do so, they must remain well-adhered and free of cracks. This work focuses on adapting the Boeing Wedge test for use with edge seals laminated using glass substrates as part of a strategy to assess the long-term durability of edge seals. The advantage of this method is that it duplicates the residual stresses and strains that a glass/glass module may have when the lamination process results in some residual glass bending that puts the perimeter in tension. Additionally, this method allows one to simultaneously expose the material to thermal stress, humidity, mechanical stress, and ultraviolet radiation. The disadvantage of this method generally is that we are limited by the fracture toughness of the glass substrates that the edge seal is adhered to. However, the low toughness of typical uncrosslinked or sparsely crosslinked PIB makes them suitable for this technique. We present data obtained during the development of the wedge test for use with PV edge seal materials. This includes development of the measuring techniques and evaluation of the test method with relevant materials. We find consistent data within a given experiment, along with the theoretical independence of fracture toughness measurements with wedge thickness. This indicates that the test methodology is reproducible. However, even though individual experimental sets are consistent, the reproducibility between experimental sets is poor. We believe this may be due to inconsistencies in sample history, sample batch, or small changes in sample preparation/assembly from one month to the next. Because the fracture strength of typical edge seal materials is so low, they cannot be relied upon for mechanical strength. A small stress or strain on the edge seal is capable of promoting delamination or tearing causing the edge seal to fail. Because of this, edge seals are very dependent on the processing and construction parameters in the full size PV module such that any long term evaluation of their durability must be conducted on full size modules to be accurate.

14 SOLAR ENERGY↗

DOE OSTI2014

Experimental investigation of wood combustion in a fixed bed with hot air

Highlights: • Upward combustion is a new combustion concept with ignition by hot primary air. • Upward combustion has three stages: short drying, rapid devolatilization and char combustion. • Variation of fuel moisture and inert content have little influence on the combustion. • Experimental comparison between conventional and upward combustion is presented. - Abstract: Waste combustion on a grate with energy recovery is an important pillar of municipal solid waste (MSW) management in the Netherlands. In MSW incinerators fresh waste stacked on a grate enters the combustion chamber, heats up by radiation from the flame above the layer and ignition occurs. Typically, the reaction zone starts at the top of the waste layer and propagates downwards, producing heat for drying and devolatilization of the fresh waste below it until the ignition front reaches the grate. The control of this process is mainly based on empiricism. MSW is a highly inhomogeneous fuel with continuous fluctuating moisture content, heating value and chemical composition. The resulting process fluctuations may cause process control difficulties, fouling and corrosion issues, extra maintenance, and unplanned stops. In the new concept the fuel layer is ignited by means of preheated air (T > 220 °C) from below without any external ignition source. As a result a combustion front will be formed close to the grate and will propagate upwards. That is why this approach is denoted by upward combustion. Experimental research has been carried out in a batch reactor with height of 4.55 m, an inner diameter of 200 mm and a fuel layer height up to 1 m. Due to a high quality two-layer insulation adiabatic conditions can be assumed. The primary air can be preheated up to 350 °C, and the secondary air is distributed via nozzles above the waste layer. During the experiments, temperatures along the height of the reactor, gas composition and total weight decrease are continuously monitored. The influence of the primary air speed, fuel moisture and inert content on the combustion characteristics (ignition rate, combustion rate, ignition front speed and temperature of the reaction zone) is evaluated. The upward combustion concept decouples the drying, devolatilization and burnout phase. In this way the moisture and inert content of the waste have almost no influence on the combustion process. In this paper an experimental comparison between conventional and reversed combustion is presented.

09 BIOMASS FUELS↗

DOE OSTI2016

Sample Results From Routine Salt Batch 7 Samples

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DOE OSTI2016

Analytical Results from Routine DSSHT and SEHT Monthly Samples

Strip Effluent Hold Tank (SEHT) and Decontaminated Salt Solution Hold Tank (DSSHT) samples from several of the “microbatches” of Integrated Salt Disposition Project (ISDP) Salt Batch (“Macrobatch”) 8B have been analyzed for 238 Pu, 90 Sr, 137 Cs, cations (Inductively Coupled Plasma Emission Spectroscopy - ICPES), and anions (Ion Chromatography Anions - IC-A). The analytical results from the current microbatch samples are similar to those from previous macrobatch samples. The Actinide Removal Process (ARP) and the Modular Caustic-Side Solvent Extraction Unit (MCU) continue to show more than adequate Pu and Sr removal for times when monosodium titanate (MST) is used. Even with no MST strike being performed there exists some small Pu and Sr removal, likely from filtration of fines containing these elements. The Cs removal continues to be excellent, with decontamination factors (DF) averaging 16,400. The bulk chemistry of the DSSHT and SEHT samples do not show any signs of unusual behavior. SRNL recommends that a sample of the strip feed be analyzed for cation and anion content if a further decline in boron concentration is noted in future SEHT samples.

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DOE OSTI2023

Preliminary Report on Compositional Specification for Printed 316SS

The Advanced Materials and Manufacturing Technologies Program is focused on accelerating the development and deployment of advanced materials and components fabricated via additive manufacturing (AM). A key challenge for the widespread adoption of AM is the variability in material properties, which can originate from powder feedstock, process parameters, geometry, and the machine. AM powder feedstock compositions are based on those developed for conventional manufacturing. However, the smaller melt pools combined with multiple melt cycles over the course of a build can have substantial effects on the local phase selection resulting from minor batch-to-batch feedstock variability. Therefore, this report focuses on coupling CALPHAD calculations with data mining and visualization to aid the development of compositional specifications for stainless steel 316, an important alloy for nuclear applications and suitable for AM. This work reports that δ-ferrite formation has a stronger dependence on the amount of nickel in the alloy despite nickel being an austenite stabilizer. These findings show the need for exercising a tighter control on the amount of nickel in the alloy compared with the amount of chromium, which is a ferrite stabilizer.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Lignin Extraction and Condensation as a Function of Temperature, Residence Time, and Solvent System in Flow-through Reactors

Solvolytic extraction of lignin from biomass is a critical step in lignin-first biorefining, including the reductive catalytic fractionation (RCF) process. Key to optimal RCF processing is the ability to rapidly extract lignin from biomass at high delignification extents and transfer the lignin molecules to a catalyst surface in a time frame that minimizes lignin condensation reactions. Here, we use a flow-through reactor to study the effects of temperature (175-250 °C), residence time (9 to 36 min), and solvent composition (methanol and methanol-water) on lignin extraction and condensation. We evaluated three metrics at each condition: total delignification, delignification rate, and extent of condensation, the latter measured by a decrease in monomer yield for batch hydrogenolysis reactions of solvolysis liquor compared to batch RCF reactions. We observe that delignification is predominantly determined by temperature, while residence time dictates the lignin condensation extent. Moreover, the extent of both extraction and condensation increased in the methanol-water solvent system compared to that in the methanol system. Lignin extracted in methanol is stable up to 18-min residence times at or below 225 °C, while a majority of the lignin extracted in methanol-water is condensed with a 9-min residence time at 200 °C. These results can inform reactor designs and solvent selection for lignin-first biorefining processes that aim to physically separate the biomass and catalyst.

09 BIOMASS FUELS↗

DOE OSTI2019

Radionuclide Inventory Calculations for the Calcined Solid Storage Facility Performance Assessment - 19292

Originally named the Idaho Chemical Processing Plant when it was constructed in the early 1950's, the Idaho Nuclear Technology and Engineering Center reprocessed SNF to recover highly enriched uranium and other nuclear-related products for the U.S. DOE. Reprocessing SNF generated millions of gallons of aqueous radioactive waste. Calcination was a process developed at the INL Site to convert liquid waste into a solid, granular form from 1963 to 2000. The calcination process produced a safer product for storage while reducing the volume of stored liquid waste by an average factor of seven. Calcine is currently stored in the Calcined Solids Storage Facility (CSSF). The CSSFs are often called 'bin sets' because each CSSF (CSSFs 1 through 6) contains several stainless-steel storage bins housed in a concrete vault. The CSSF is an interim waste storage facility. In the future, calcine will be retrieved, treated (if necessary), and sent to an off-Site facility for storage or disposal. To close the CSSF, the bulk of the calcine will be removed and stored or disposed of elsewhere. The bins and vaults will then be placed in a configuration that is protective of human health and the environment. For purposes of the performance assessment, the depth of the residual calcine at closure was assumed to be 5-cm in each bin. The 5-cm of residual calcine in each bin is assumed to be mixed in grout during closure. The activities of the residual radionuclides are the inventory used for the dose assessment calculations for the CSSF performance assessment. The objective of this analysis was to calculate the radionuclide activity in the residual calcine remaining in the CSSF after closure. The purpose of this paper is to present the approach used to calculate the radionuclide inventory of the calcine currently stored in CSSF and the residual calcine in the CSSF after closure using data from the calcined waste Historical Processing Model (HPM). Limited sampling and analysis of the calcine in the CSSF bins was conducted in the past. Future similar calcine sampling and analysis efforts would be costly, generate additional mixed waste, and may not provide the desired detailed calcine composition data. However, during the later years of calcining, an alternative to calcine sampling and analysis was developed and the information was captured in the HPM. The HPM uses multiple sources to provide definitive calcine volume, mass, and composition, including: compositions and volumes of the liquid wastes that were calcined, ORIGEN2 - and ORIGEN-ARP-based radioactivity calculations, calciner and CSSF operating data, and process knowledge of INTEC fuel and waste-processing systems. HPM calcine composition was used to develop an inventory of radionuclides for use in the performance assessment evaluation for closure of CSSF. There are 43 bins that contain calcine, with six to twelve segments in each bin for a total of 337 bin segments for which the HPM calculates the average calcine composition. The HPM calculates the composition of each of the nearly 7,000 batches of material (startup bed, nonradioactive material, and radioactive waste) charged to the calciners. The calculations use the CSSF dimensions, including the CSSF number of bins, heights, outside diameters, annular air space diameter (if necessary), and volume of calcine currently in the bins. For each of the CSSFs, for a 5-cm residual, the percent of total calcine was calculated along with the residual activity for the radionuclides. Residual activity was estimated for 148 different radionuclides. (authors)

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NASA NTRS2017

Batch Sequential Estimation with Non-Uniform Measurements and Non-Stationary Noise

Sequential estimation using the traditional discrete Kalman filter typically assumes the measurement time and state update time are coincident. This is often a poor assumption in realistic measurement scenarios where the data can be received from multiple sources at differing times. This paper develops the necessary algorithm adjustments needed for the Kalman filter to readily process measurement data that arrive at varying times and with non-stationary noise. The algorithm is applied to a relevant problem of orbit determination using one-way uplink radiometric tracking of a spacecraft (in the present case a Mars orbiter).

Seubert, Jill↗

DOE OSTI2022

Conversion kinetics during melting of simulated nuclear waste glass feeds measured by dissolution of silica

In this work, we experimentally investigated the batch-to-glass conversion kinetics of two low-activity and two high-level nuclear waste melter feeds that represent widely different behavior during melting; tests comprised thermogravimetric analysis, the feed expansion test, evolved gas analysis, and x-ray diffraction. Our study indicates that the conversion processes, which include gas-evolving reactions, dissolution of crystalline phases, and primary foam expansion and collapse, are interconnected and influenced by the feed’s thermal history. The fraction of dissolved silica was adopted as a measure of the extent of conversion inside the cold cap—the floating layer of feed material on the top surface of the melt in an electric melter. The interface between the cold cap and the free-flowing melt below was associated with a constant fraction of dissolved silica. The estimated viscosity of glass-forming melt at this interface lies within a narrow range for the feeds studied.

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DOE OSTI2023

Data for Tolerance of Engineered Rhodosporidium toruloides to Sorghum Hydrolysates During Batch and Fed-Batch Lipid Production

Oleaginous yeasts are a promising candidate for the sustainable conversion of lignocellulosic feedstocks into fuels and chemicals, but their growth on these substrates can be inhibited as a result of upstream pretreatment and enzymatic hydrolysis conditions. Previous studies indicate a high citrate buffer concentration during hydrolysis inhibits downstream cell growth and ethanol fermentation in Saccharomyces cerevisiae . In this study, an engineered Rhodosporidium toruloides strain with enhanced lipid accumulation was grown on sorghum hydrolysate with high and low citrate buffer concentrations. Both hydrolysis conditions resulted in similar sugar recovery rates and concentrations. No significant differences in cell growth, sugar utilization rates, or lipid production rates were observed between the two citrate buffer conditions during batch fermentation of R. toruloides . Under fed-batch growth on low-citrate hydrolysate a lipid titer of 16.7 g/L was obtained. Citrate buffer was not found to inhibit growth or lipid production in this engineered R. toruloides strain, nor did reducing the citrate buffer concentration negatively affect sugar yields in the hydrolysate. As this process is scaled-up, $131 per ton of hydrothermally pretreated biomass can be saved by use of the lower citrate buffer concentration during enzymatic hydrolysis.

Conversion↗

DOE OSTI2014

Organic Separation Test Results

Separable organics have been defined as “those organic compounds of very limited solubility in the bulk waste and that can form a separate liquid phase or layer” (Smalley and Nguyen 2013), and result from three main solvent extraction processes: U Plant Uranium Recovery Process, B Plant Waste Fractionation Process, and Plutonium Uranium Extraction (PUREX) Process. The primary organic solvents associated with tank solids are TBP, D2EHPA, and NPH. There is concern that, while this organic material is bound to the sludge particles as it is stored in the tanks, waste feed delivery activities, specifically transfer pump and mixer pump operations, could cause the organics to form a separated layer in the tank farms feed tank. Therefore, Washington River Protection Solutions (WRPS) is experimentally evaluating the potential of organic solvents separating from the tank solids (sludge) during waste feed delivery activities, specifically the waste mixing and transfer processes. Given the Hanford Tank Waste Treatment and Immobilization Plant (WTP) waste acceptance criteria per the Waste Feed Acceptance Criteria document (24590-WTP-RPT-MGT-11-014) that there is to be “no visible layer” of separable organics in the waste feed, this would result in the batch being unacceptable to transfer to WTP. This study is of particular importance to WRPS because of these WTP requirements.

complexants↗

DOE OSTI2015

Sample Results from Routine Salt Batch 7 Samples

Strip Effluent Hold Tank (SEHT) and Decontaminated Salt Solution Hold Tank (DSSHT) samples from several of the “microbatches” of Integrated Salt Disposition Project (ISDP) Salt Batch (“Macrobatch”) 7B have been analyzed for 238 Pu, 90 Sr, 137 Cs, Inductively Coupled Plasma Emission Spectroscopy (ICPES), and Ion Chromatography Anions (IC-A). The results from the current microbatch samples are similar to those from earlier samples from this and previous macrobatches. The Actinide Removal Process (ARP) and the Modular Caustic-Side Solvent Extraction Unit (MCU) continue to show more than adequate Pu and Sr removal, and there is a distinct positive trend in Cs removal, due to the use of the Next Generation Solvent (NGS). The Savannah River National Laboratory (SRNL) notes that historically, most measured Concentration Factor (CF) values during salt processing have been in the 12-14 range. However, recent processing gives CF values closer to 11. This observation does not indicate that the solvent performance is suffering, as the Decontamination Factor (DF) has still maintained consistently high values. Nevertheless, SRNL will continue to monitor for indications of process upsets. The bulk chemistry of the DSSHT and SEHT samples do not show any signs of unusual behavior.

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DOE OSTI2020

Fiscal Year 2020 Filtration of Hanford Tank Waste 241-AP-105

Bench-scale filtration testing of 15 liters of 241-AP-105 supernatant was conducted using a Mott inline filter Model 6610 (media grade 5) backpulsed dead-end filter (BDEF) in the hot cells of the Radiochemical Processing Laboratory at Pacific Northwest National Laboratory. The as-received samples were diluted with raw water from the Hanford Site to assess the propensity for solids to form upon dilution and to assess the impact those solids have on filtration performance. The feed was split into two batches. The first batch was settled and decanted as planned in Tank Side Cesium Removal operations. The BDEF was used to filter this AP-105 feed at a targeted flux of 0.065 gpm/ft 2 and exhibited no measurable pressure increase during filtration. The second batch was fed to the BDEF with solids resuspended. This was also operated at the targeted flux of 0.065 gpm/ft 2 . In this case, the target pressure differential of 2 psid (resistance of 6.24 × 10 10 m -1 ) was reached in slightly more than 12 h. A backpulse restored the filter flux; however, the time to the next backpulse was slightly shorter. These tests indicate that after the addition of raw water, settle and decant effectively removed solids from the feed. It is not possible to assess the time required for these solids to settle based on the result from these tests. However, if sufficient time is allowed for the solids to settle, no measurable filter fouling was observed in current testing. In contrast, if insufficient time is allowed for solids to settle, filter fouling will occur relatively quickly and will likely require backpulses more frequently than every 12 hours (1.91 m 3 /m 2 volume filtered). Solids concentrated from backpulse solutions displayed large variability in composition with Al-silicates and mixed chromium-aluminum oxide phases. Amounts of Mg, Fe, and Ca were also found in the presence of Na and O. These solids could be grouped in three categories: (1) soluble Na-salts that formed large block-like particles but were made up of fibrous materials, (2) amorphous Al-phases, and (3) colloidal iron oxides with an average particle diameter of 4.2 µm.

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