Simulated Sludge Research Articles

Stabilization of nickel-laden sludge by a high-temperature NiCr 2O 4 synthesis process

The feasibility of stabilizing nickel-laden sludge by a high-temperature NiCr 2O 4 synthesis process was investigated with different sintering temperatures, salt contents, molar ratios, and reaction atmospheres. The crystalline phases of species were investigated by using an X-ray diffraction, and the surface characteristics of particles were observed by scanning electron microscopy. The leaching behavior of the stabilized sludge was evaluated by Toxicity Characteristic Leaching Procedure (TCLP) test. The results indicated that NiCr 2O 4 was formed at around 800 °C by transforming NiO and Cr 2O 3 into a spinel structure. Leaching concentrations of both nickel and chromium decreased with an increase in the sintering temperature. The existence of salt in the sludge disturbed the formation of spinel, but a moderate salt content contributed to stabilization efficiency. A Cr/Ni molar ratio >2 also contributed to the stabilization efficiency of heavy metals after the thermal process. NiCr 2O 4 was transformed from simulated sludge under both an N 2 and air atmosphere. The sintering strategy designed for nickel-laden sludge was proven to be beneficial in stabilizing nickel and chromium.

Modelling a full scale membrane bioreactor using Activated Sludge Model No.1: challenges and solutions

A full-scale membrane bioreactor (1,600 m(3) d(-1)) was monitored for modelling purposes during the summer of 2006. A complete calibration of the ASM1 model is presented, in which the key points were the wastewater characterisation, the oxygen transfer and the biomass kinetics. Total BOD tests were not able to correctly estimate the biodegradable fraction of the wastewater. Therefore the wastewater fractionation was identified by adjusting the simulated sludge production rate to the measured value. MLVSS and MLSS were accurately predicted during both calibration and validation periods (20 and 30 days). Because the membranes were immerged in the aeration tank, the coarse bubble and fine bubble diffusion systems coexisted in the same tank. This allowed five different aeration combinations, depending whether the 2 systems were operating separately or simultaneously, and at low speed or high speed. The aeration control maintained low DO concentrations, allowing simultaneous nitrification and denitrification. This made it difficult to calibrate the oxygen transfer. The nitrogen removal kinetics were determined using maximum nitrification rate tests and an 8-hour intensive sampling campaign. Despite the challenges encountered, a calibrated set of parameters was identified for ASM1 that gave very satisfactory results for the calibration period. Matching simulated and measured data became more difficult during the validation period, mainly because the dominant aeration configuration had changed. However, the merit of this study is to be the first effort to simulate a full-scale MBR plant.

Structural studies of iron in vitrified toxic wastes

Mossbauer spectroscopy and X-ray absorption spectroscopy (XAS) have been used to obtain information on the redox and coordination of iron in glasses made by the vitrification of simulated and actual sewage sludge combustion ashes. Mossbauer spectra have been deconvoluted using three extended Voigt-based profiles to allow quantitative analysis of multiple Fe3 + coordination environments. XAS Fe pre-K-edge absorption peaks have been analysed and fitted against reference standards to yield complementary analyses and provide validation of the Mossbauer results. Correlations are noted between the iron redox and the Fe3 + coordination. Tetrahedral Fe3 + is much more likely to take part in any redox reaction whilst octahedral Fe3 + appears to be more resistant to reduction to the ferrous state. Results from XAS also suggest that Fe2 + ions occupy both four- and six-fold coordination environments. Neither technique has provided any clear evidence for the existence of Fe2 + or Fe3 + in five-fold symmetry in the glasses studied.

Process Development for Permanganate Addition during Oxidative Leaching of Hanford Tank Sludge Simulants

In previous studies, we have examined using sodium permanganate for selectively oxidizing and removing chromium from washed Hanford tank sludges. The conclusion from the previous work was that contact with sodium permanganate in a minimally caustic solution, i.e., 0.1 to 0.25 M [OH–] initially, provided maximum Cr dissolution while minimizing concomitant Pu dissolution. This report describes work focused on developing simulants to be used in pilot scale oxidative leaching tests; developing methods for monitoring chromium oxidation by permanganate; and identifying the Cr and Mn materials formed during the oxidative leaching process. The impact of such variables as the Cr compound used, agitation rate, temperature, hydroxide concentration, and initial MnO4 −:Cr ratio on the rate and extent of chromate formation were examined.

EFFECT OF TEMPERATURE ON SOLIDS REDUCTIONS AND ON DEGRADATION KINETICS DURING THERMOPHILIC AEROBIC DIGESTION OF A SIMULATED SLUDGE

Laboratory‐scale experiments were conducted to determine the influence of higher thermophilic temperatures on thermophilic aerobic digestion treatment of a simulated sludge. The efficiency of the process was evaluated in respect of solids removal and degradation rate constants at four thermophilic temperatures. Batch runs were operated at a retention time of one day and temperatures of 65, 70, 72 and 75 °C. The results indicated that temperature increase did not impart any significant benefits to the digestion operation in terms of suspended solids and biochemichal oxygen demand reduction. The findings from this research also suggested that the treatment would not appear to benefit from temperatures higher than 65 °C, as classically suggested by Van’t Hoff‐Arrhenius. Therefore, increase of thermophilic temperature in the tested 65‐–75 °C range does not enhance the efficiency of thermophilic, aerobic sludge digestion treatment.

The National Nuclear Laboratory and Collaborative University Research in the UK

AbstractThe UK has recently established its first National Nuclear Laboratory (NNL). This has been formed out of the Nexia Solutions organisation, formally the Research and Technology subsidiary of BNFL. Over the next year the NNL will develop so that it can fulfil its mission, which will include the development and maintenance of key skills and undertaking strategic R&D programmes both in the UK and in international collaborations. A key role of the NNL will be to enhance its interactions with universities to facilitate skills transfer into the nuclear industry as well as support its R&D programmes. Over the past decade the NNL and its predecessor has already established close relationships with leading universities in the UK including Sheffield, Manchester, Leeds and Imperial College London. One of the key objectives of the NNL has been to work in an integrated way with university researchers with programmes spanning fundamental research through to applied R&D. This paper describes the future plans for working with universities as the NNL develops, building on the success to date. Joint R&D research programmes already cover many important areas for the nuclear industry. This includes support for the UK Pu disposition programme where R&D at the Immobilisation Science Laboratory, Sheffield has included investigating a range of ceramic and glass wasteforms which has allowed a number of ceramic wasteforms to be down selected for detailed evaluation. Cementation research has included understanding wasteform performance, for example long-term durability. This has involved work on determining free water and the implications for immobilisation of reactive wastes. Other work involving the NNL and Universities, in particular at Leeds and Manchester, has considered the characteristics and behaviour of intermediate and high level waste sludges. This has included determining the chemical speciation of actinides and fission products, and physical properties of active and simulated sludges using experimental and modelling techniques. A significant programme on environmental work has been undertaken by the NNL. In research applicable to low level waste disposal and contaminated land reactive transport modelling is utilised to apply experimental and field based research in environmental geochemistry and radiochemistry undertaken by university collaborators. This paper will describe a number of examples of R&D carried out by NNL in association with its university partners.

Bio-oxidation of tripropylene glycol under aerobic conditions

Aerobic biodegradation of tripropylene glycol (PG3) was investigated under the conditions of the OECD screening test 301E and the Continuous Flow Activated Sludge Simulation test (CFAS). A modified two-chamber facility with a denitrification stage was used for the CFAS test. Primary PG3 biodegradation was measured by the HPLC with fluorimetric detection and analyte derivatisation. Metabolites were identified by LC-MS with electrospray ionisation and GC-MS with electron impact ionisation, as well as semiquantitatively determined by the LC-MS technique. PG3 was found to be inherently biodegradable and it exhibits a strong poisonous effect on activated sludge after exceeding the threshold concentration (10 mg l(-1)). Metabolite accumulation onto the activated sludge is probably responsible for this poisonous effect. Probable biotransformation products of tripropylene glycol under the aerobic conditions include metabolites with a single terminal aldehyde or a ketone group and metabolites with two terminal aldehyde or ketone groups. Their concentration rises at the end of the OECD screening test.

Optimization of Nitrogen Removal for Alternating Intermittent Aeration-Type Activated Sludge System: A New Process Modification

A new activated sludge process modification was proposed for intermittent aeration process to achieve more stable nitrogen removal performance. A single completely mixed reactor was divided into two compartments in series and operated in intermittent aeration mode by using activated sludge simulation model. The new configuration provided competetive advantage on nitrification as well as denitrification capacity, compared to the intermittently aerated system with a single reactor. In addition, the dissolved oxygen set-point control during air-on periods was found to be an important parameter in terms of nitrogen removal.

Partitioning of U(VI) and Eu(III) between Acidic Aqueous Al(NO3)3 and Tributyl Phosphate in n‐Dodecane

The preferred approach to removing Al from Hanford tank sludges, based on aqueous alkaline leaching, often does not achieve complete success. Previous laboratory investigations on the treatment of Hanford tank sludge simulant samples indicate that an acidic scrub can enhance the dissolution of Al from various sludge matrices. If acidic leaching was deployed to enhance removal of tank waste residues, the resulting acidic Al(NO3)3 leachate solution could contain measurable amounts of solubilized transuranic elements and so would demand treatment prior to disposal. In this study, a liquid‐liquid extraction system for the decontamination of the HNO3/Al(NO3)3 aqueous leachate by contact with 60% v/v tributyl phosphate (TBP)/n‐dodecane organic solution has been examined. The partitioning of U and Eu between the TBP phase and solutions of varying [HNO3] and [Al(NO3)3] containing small amounts of Cr or ascorbic acid have been investigated.. The results indicate that >99% of both species could be removed from the aqueous phase using such a process.

The Dangers of Uncalibrated Activated Sludge Simulation Packages

The Dangers of Uncalibrated Activated Sludge Simulation Packages

Enhanced Selective Leaching of Chromium from Radioactive Sludges

An enhanced selective oxidative alkaline leaching (ESOAL) process has been developed for the removal of chromium from high level waste (HLW) tank sludges. Because of the adverse effect of excess chromium on the vitrification process, chromium removal becomes a critical factor in the pretreatment of underground storage tanks (USTs) containing nuclear waste. The ESOAL process described here uses a unique approach based on the innovative combination of an effective oxidant and sonochemical oxidation, achieving efficiencies and removal rates substantially better than either of the processes used independently. Results are shown here for the ESOAL treatment of a tank sludge simulant (Hanford tank S‐101). The effects of different variables (e.g., time, ultrasound power, temperature, sodium hydroxide concentration, and the use of an oxidant) on the amount of sludge dissolved are presented.

Oxidative Leaching of Plutonium from Simulated Hanford Tank‐Waste Sludges

The behavior of surface‐sorbed plutonium during leaching of four Hanford tank waste sludge simulants with alkaline permanganate solutions has been investigated. The sludge simulants are representative of materials created as a result of the operation of the Bismuth Phosphate (sludges B and M), PUREX (sludge P), and REDOX (sludge R) processes at Hanford. Leaching with oxidants under alkaline conditions has been proposed as a means of reducing the chromium content of actual sludge samples prior to their vitrification. With identical amounts of plutonium deposited on each sludge sample, the percentage of radiotracer Pu leached from the sludges increased in the order P≥R>B. This order is the reverse of the chromium content of the sludges. The percentage of plutonium leached was independent of its initial oxidation state. The reverse trends of chromium content and plutonium leaching can be understood in terms of Pu re‐adsorption onto the MnO2 generated as Cr(III) (and other substrates) are oxidized by permanganate/manganate. The effect of chelating agents that are known to be present in tank wastes (EDTA, gluconate, glycolate, oxalate, and citrate) on KMnO4 reduction/MnO2 production and redeposition of plutonium was also studied and found to have varied effects on the process of oxidative dissolution/Pu redeposition. Overall, it appears that the MnO2 produced as a byproduct of oxidation helps to control Pu concentrations in the leachate phase. Oxidation of Pu to the hexavalent state without concomitant production of MnO2 leads to greater plutonium content in the leachate. The results are discussed, emphasizing the potential impact of oxidative leaching on plutonium mobilization from actual tank‐waste sludge. Work performed under the auspices of the Environmental Management Science Program (EMSP) of the U.S. Department of Energy at Argonne National Laboratory under contract number W‐31‐109‐ENG‐38

Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Oxidative alkaline leaching has been proposed to pretreat the high‐level nuclear waste sludges to remove some of the problematic (e.g., Cr) and/or nonradioactive (e.g., Na, Al) constituents before vitrification. It is critical to understand the behavior of actinides, americium and plutonium in particular, in oxidative alkaline leaching. We have studied the leaching behavior of americium from four different sludge simulants (BiPO4, BiPO4 modified, Redox, PUREX) using potassium permanganate and potassium persulfate in alkaline solutions. Up to 60% of americium sorbed onto the simulants is leached from the sludges by alkaline persulfate and permanganate. The percentage of americium leached increases with [NaOH] (between 1.0 and 5.0 M). The initial rate of americium leaching by potassium persulfate increases in the order BiPO4 sludge<Redox sludge<PUREX sludge. The data are most consistent with oxidation of Am3+ in the sludge to either AmO2 + or AmO2 2+ in solution. Though neither of these species is expected to exhibit long‐term stability in solution, the potential for mobilization of americium from sludge samples would have to be accommodated in the design of any oxidative leaching process for real sludge samples. This work was supported by the Office of Science, Biological and Environmental Research, under U.S. Department of Energy Contract No. DE‐AC03‐76SF0098 at Lawrence Berkeley National Laboratory and Contract No. W‐31‐109‐ENG‐38 at Argonne National Laboratory.

Application of Activated Sludge Models in Traditionally Operated Treatment Plants—A Software Environment Overview

Abstract Activated sludge simulation modelling is considered an accepted tool in engineering practice. However, due to the complexity involved, these models are only extensively used within a limited scientific community. There is a true need to increase the use of these models among average plant operators to make them better understand the interactions of various factors of the process. A user-friendly software environment that enables an ordinary user to access and use these models to simulate a system without the need for either a complete understanding of underlying models or any special programming skills will help promote model applications. This paper defines the broad architecture of such an environment and identifies other applications that should be integrated into the simulator such as expert systems and database systems. It also discusses the steps necessary to develop a reliable site-independent activated sludge simulator. Finally, the paper points out that to introduce mathematical model simulations to traditionally operated treatment plants, a how-to protocol is needed to adjust routine operating data for model use.

A central fission pathway in alkylphenol ethoxylate biodegradation

A representative alkylphenol Triton X-100 (having 9.5 oxyethylene subunits) was treated over 40 days under the conditions of the continuous flow activated sludge simulation test in a plant with aeration and denitrification chambers. Treated sewage was separated by sequential extraction with ethyl acetate and chloroform. The extracts were analysed by high-performance liquid chromatography-electrospray ionisation-mass spectrometry (HPLC-ESI-MS). Single ion chromatograms of the chloroform extracts showed the presence of neutral, mono- and di-carboxylated poly(ethylene glycols). This is evidence of the central fission of alkylphenol ethoxylates (APE). Simultaneously, the APE having ω-carboxylated oxyethylene chains were identified. This is the evidence that apart from central fission, the ω-oxidation oxyethylene chain pathway also occurs.

Actinides in Alkaline Media: Dissolution, Mineral Associations, and Speciation in Hanford Waste Tank Sludge Simulants

We have investigated the leaching behavior of actinides from simulants of tank waste sludges derived from the BiPO4, Redox, and PUREX processes, the principal chemical separations processes that operated at the Hanford site during 40+ years of plutonium production. Fundamental investigations of the speciation of uranium and neptunium in solutions representative of proposed alkaline sludge washing liquors have also been completed. Correlation of the results from sludge leaching indicate that, while Am and Pu are generally not appreciably dissolved from the sludges into alkaline solutions in the absence of oxidants, Np and U can be mobilized during alkaline sludge washing. Leaching of sludges with acidic solutions and strong complexing agents indicate considerable association of all actinide ions with Cr, Fe, and Mn oxides in the sludge simulants. Electrochemical experiments conducted in strongly alkaline solutions have defined the formal potentials of Np in strong base and reveal that mononuclear hydrolysis products dominate the speciation of neptunium (and by analogy U and Pu) in concentrated alkali. The results of these observations are discussed in the context of alkaline sludge washing procedures associated with waste tank remediation.This work was supported by the Assistant Secretary for Environmental Management under U.S. Department of Energy Contract Numbers W-3M09-ENG-38 at Argonne National Laboratory and DE-AC03-76SF0098 at Lawrence Berkeley National Laboratory

Biodegradation of oxo-alcohol ethoxylates in the continuous flow activated sludge simulation test

Biodegradation of two α-methyl branched oxo-alcohol ethoxylates (OAE) of different polydispersity: LIAL 125/14 BRD (LIALB) (broad M.W. distribution) and LIAL 125/14 NRD (LIALN) (narrow M.W. distribution), both having an average of 14 oxyethylene subunits (EO) and a C 12–15 alkyl moiety were tested under the continuous flow activated sludge conditions of the classical Husmann plant. Primary biodegradation and concentration of metabolites: free oxo-alcohol fraction (FOA) and poly(ethylene glycols) (PEG), were measured. PEG were divided into two fractions: short-chained PEG (PEGshch) (1–4 EO) and long-chained PEG (PEGlch)(>4 EO). The indirect tensammetric technique combined with an adequate separation was used for analysis. Central fission was found to be a highly dominating pathway, as is the case with fatty alcohol ethoxylates. OAE are highly primarily biodegraded (above 95%). High concentrations of FOA and PEG are formed. Once formed the PEGlch are further fragmented into the PEGshch. Free alcohol fraction compounds are biodegraded sooner when alkyl moiety is shorter. OAE polydispersity has an influence on the kinetics of biodegradation; PEG formed from LIALN are biodegraded slower and to a lower degree than those from LIALB.

Foaming in simulated radioactive waste.

Radioactive waste treatment process usually involves concentration of radionuclides before waste can be immobilized by storing it in stable solid form. Foaming is observed at various stages of waste processing like SRAT (sludge receipt and adjustment tank) and melter operations. This kind of foaming greatly limits the process efficiency. The foam encountered can be characterized as a three-phase foam that incorporates finely divided solids (colloidal particles). The solid particles stabilize foaminess in two ways: by adsorption of biphilic particles at the surfaces of foam lamella and by layering of particles trapped inside the foam lamella. During bubble generation and rise, solid particles organize themselves into a layered structure due to confinement inside the foam lamella, and this structure provides a barrier against the coalescence of the bubbles, thereby causing foaming. Our novel capillary force balance apparatus was used to examine the particle-particle interactions, which affect particle layer formation in the foam lamella. Moreover, foaminess shows a maximum with increasing solid particle concentration. To explain the maximum in foaminess, a study was carried out on the simulated sludge, a non-radioactive simulant of the radioactive waste sludge at SRS, to identify the parameters that affect the foaming in a system characterized by the absence of surface-active agents. This three-phase foam does not show any foam stability unlike surfactant-stabilized foam. The parameters investigated were solid particle concentration, heating flux, and electrolyte concentration. The maximum in foaminess was found to be a net result of two countereffects that arise due to particle-particle interactions: structural stabilization and depletion destabilization. It was found that higher electrolyte concentration causes a reduction in foaminess and leads to a smaller bubble size. Higher heating fluxes lead to greater foaminess due to an increased rate of foam lamella generation in the sludge system.

PLUTONIUM MOBILIZATION AND MATRIX DISSOLUTION DURING EXPERIMENTAL SLUDGE WASHING OF BISMUTH PHOSPHATE, REDOX, AND PUREX WASTE SIMULANTS

Consecutive washing of simulant sludges from the BiPO4 (Cycle 3), Redox, and PUREX processes shows less than 4.5% of sorbed Pu(III/IV) or Pu(VI) is mobilized during CrO4 2− dissolution by the 0.01 M NaOH + 0.01 M NaNO2 sluice or 3.0 M NaOH leach solutions to be used for sludge pretreatment at Hanford. Experimental sludge washing with 2.0 M HNO3 results in 5.8-65.5% dissolution of Pu(III/IV) or Pu(VI) from all simulants and dissolution of Nd(III), Cr(III), and Fe(III) (where present) from BiPO4 simulants. The dissolution of Pu(III/IV) and Pu(VI) from BiPO4 sludge simulants by strongly chelating media is accompanied by dissolution and reduction of Mn(IV) to a Mn(III) complex. Details of radioanalytical and spectroscopic investigations of sludge simulant washing are discussed in the context of understanding actinide behavior during alkaline leaching of radioactive sludge wastes.

Biodegradability properties of sulfonamides in activated sludge

AbstractTwelve different sulfonamides were selected for a biodegradation study using a respirometric screening test and an activated sludge simulation test. A simple bacterial growth inhibition test was applied to show that the sulfonamides did not affect the bacteria at the concentration levels used. None of the compounds were degraded in the screening test, leading to the conclusion that sulfonamides cannot be classified as readily biodegradable. In the simulation test, primary degradation of mixtures of four compounds at concentration levels of 250 to 500 μg/L were tested and analyzed using high‐performance liquid chromatography. Biodegradation occurred after lag phases of 7 to 10 d at 20°C when nonadapted sludge was applied. Test compounds were degraded within a few days. At 6°C, degradation lag phases and degradation rates were three to four times longer. Degradation curves fit well to the logistic growth model, indicating growth of specific degraders in the test system. Sulfonamide adapted bacterial cultures were able to degrade either the same compounds as previously added or four other sulfonamides in a rapid and uniform way (t1/2 from 0.2 to 3 d). This finding shows that if capable of degrading one sulfonamide substance, these bacteria may also degrade many other sulfonamides. In practice, this implies that because the biodegradation rate is found to be identical for several sulfonamides in the sludge, the compounds may be assessed as a group by studying only a few compounds in applications such as environmental fate assessments. The mechanism for inducement of sulfonamide adaptation to the bacteria was not revealed in this study.