Earnest F. Gloyna

EFFECTS OF pH AND OXIDATION STATE OF CHROMIUM ON THE BEHAVIOR OF CHROMIUM IN THE ACTIVATED SLUDGE PROCESS

Abstract The behavior of chromium (Cr) in the activated sludge process (ASP) was evaluated in laboratory-scale, fill-and-draw activated sludge experiments. Both pH and the oxidation state of chromium were confirmed as critical parameters in the ASP for evaluating the behavior of chromium. More than 55% of chromium was removed when trivalent chromium [Cr(III)] was introduced into the influent while less than 60% was removed when hexavalent chromium [Cr(VI)] was added over a pH range from 5 to 9. As pH was increased, the removal increased when Cr(III) was introduced but the reverse occurred with Cr(VI). Introduction of Cr(VI) into the influent resulted in less than 80% of chromium associated with solids; however, with Cr(III), more than 90% of chromium was bound with solids. These results suggest that the ASP is capable of controlling the transport of Cr(III) to the environment but such is not case for Cr(VI). Theoretical consideration based on thermodynamics predicted that no reduction of Cr(VI) into Cr(III) should occur and the only redox reaction should be the oxidation of Cr(III) into Cr(VI). However, no oxidation of Cr(III) into Cr(VI) was observed; some Cr(VI) was reduced into Cr(III). Kinetic constraints may have impeded the oxidation of Cr(III). Under the conditions of this study, Cr(III) may have been removed through adsorption rather than precipitation as Cr(OH)3. Cr(VI) might be adsorbed on the bacterial surface through specific adsorption.

Efficiency of H2O2 and O2 in supercritical water oxidation of 2,4-dichlorophenol and acetic acid

Abstract The efficiencies of hydrogen peroxide and oxygen as oxidants for the destruction of acetic acid and 2,4-dichlorophenol were compared under supercritical water conditions using a batch reactor system. The effects of temperature, water density, and oxidant concentration on the destruction of both compounds were studied. Diluted oxygen (21% O2 and 79% N2) and premixed hydrogen peroxide (32 % aqueous solution) were used as the oxidants. The reaction temperatures were 400, 450, and 500°C. Water densities were fixed at 0.15 g/mL and 0.35 g/mL. The destruction efficiency of hydrogen peroxide was significantly higher than that of oxygen. For acetic acid, the highest conversion of 97.7% was achieved with hydrogen peroxide at 500°C for a reaction time of 10 min. while 64.3% conversion was achieved with oxygen at the same temperature but for a reaction time of 30 min. For 2,4-dichlorophenol, conversions higher than 99.995% were obtained with hydrogen peroxide at 450°C for a reaction time of 2 min as compared to 87.6% conversion with oxygen at 500°C for the same reaction time. The change in supercritical water density from 0.15 g/mL to 0.35 g/mL at 400°C only slightly increased the conversion of both compounds. The conversion of acetic acid was enhanced by 10% at 450°C as hydrogen peroxide supply was increased from 100 to 200% of stoichiometric demand. However, concentration of hydrogen peroxide higher than 300% of stoichiometric demand did not yield higher conversions of acetic acid. The effect of excess oxygen was not conclusive.

Supercritical water oxidation: An engineering update

Abstract This paper reviews the need for innovative treatment technologies and describes a wastewater treatment system capable of completely destroying toxic organic substances and biological sludges. The basic concept of supercritical water oxidation (SCWO), associated engineering research, and technology development are examined. During the last few years a growing body of SCWO knowledge has been assembled. A number of universities, federal agencies, and private companies have participated in both engineering research and technology development. In general, engineering research has focused upon reaction kinetics and mechanisms, salt formation and solubility, mass and heat transfer, transformation product identification, catalysis, corrosion, and additive impacts. As research progressed, technology development has directed its attention to materials of construction, reactor design, heat exchange and recuperative heat recovery, solid-liquid separation, gas-liquid separation, control systems, emuent handling, ash disposal, safety requirements, and process integration. SCWO technology relies on the unique properties of supercritical water to create an excellent reaction medium. The system is capable of operating as a totally enclosed facility, providing complete destruction, and meeting all regulatory emuent requirements. As such, this new technology is an environmentally attractive option. Because of favorable treatability, safety, and economic considerations a growing number private and governmental entities are currently involved in the development of more effective SCWO facilities.

Supercritical water oxidation of acetic acid by potassium permanganate

Abstract Supercritical water oxidation (SCWO) of acetic acid by potassium permanganate (KMnO 4 ) was studied. The experiments were performed in a batch reactor at temperatures and pressures, respectively, ranging from 400 °C to 460 °C and from 275 bar to 350 bar. For comparison purposes, other oxidants, such as oxygen, hydrogen peroxide, CuH 2 O 2 , FeH 2 O 2 and MnSO 4 H 2 O 2 , were studied. Subcritical tests with potassium permanganate were also conducted at temperatures of 250°C, 300°C and 350°C. The order of acetic acid destruction effectiveness was found to be KMnO 4 > Cu-H 2 O 2 > FeH 2 O 2 > MnSO 4 H 2 O 2 > H 2 O 2 > O 2 at a temperature of 400°C, density of 0.3 g/ml and reaction time of less than 10 min. The acetic acid destruction efficiency by potassium permanganate was 77% at a temperature of 400°C, density of 0.3 g/ml and a reaction time of 2.5 min. Under similar conditions, only 40% of acetic acid was destroyed at 250°C. Potassium permanganate was demonstrated to be an effective oxidant for SCWO of acetic acid.

Statistical study of the liquefaction of used rubber tyre in supercritical water

The objectives of this study were to evaluate statistically the feasibility of oil recovery from spent automobile rubber tyres in supercritical water (SCW), to determine key process variables affecting the yield of this oil recovery, and to evaluate the destruction efficiency of rubber. Experiments were carried out using a two-level 24 factorial design. The qualitative variables were the initial gas phase composition and catalyst choice. The quantitative variables were temperature and contact time. The maximum conversion and oil yield of volatile matter for this rubber tyre were 89 and 68 wt% respectively. Based on the F-test, the variables of greatest significance for both oil yield and rubber conversion were temperature and gaseous atmosphere.

Effect of organic compounds on photosynthetic oxygenation—I. Chlorophyll destruction and suppression of photosynthetic oxygen production

Abstract This paper describes the inhibition of chlorophyll synthesis and the destruction of chlorophyll in Chlorella pyrenoldosa due to the presence of selected organic compounds. Emphasis in Part I is directed toward an explanation of laboratory techniques and an evaluation of changes in photosynthetic oxygen production due to the addition of selected compounds. In Part II, which will follow the influence of certain organic compounds on the design of waste stabilization ponds will be considered. Changes in extractable chlorophyll concentrations are presented in terms of exposure time and concentration of chemical additives. Selected algal cultures were grown for a test period of 72 hr in test tubes under constant temperature conditions, with continuous illumination, and under controlled nutrient supplies. Under such conditions the chlorophyll content decreases markedly in relation to the concentration of the organic additive. For the compounds evaluated, the chlorophyll reduction seems to be a function of the substituted groups and their relative positions. Also, a direct manometric technique is described for measurement of photosynthetic gas exchange. Results show that oxygen production is suppressed by chlorinated and nitrated phenols.

REACTOR FUEL WASTE DISPOSAL PROJECT DEVELOPMENT OF DESIGN PRINCIPLE FOR DISPOSAL OF REACTOR FUEL WASTE INTO UNDERGROUND SALT CAVITIES

Waste disposal in underground salt cavities is considered. Theoretical Investigations for spherical and cylindrical cavities included analysis of elastic stress, thermal stress, and stress redistribution due to the development of a plastic zone around the cavity. The problems of temperature distribution and accompanying thermal stress, due to heat emission from the waste, were also studied. The reduction of the cavity volume, the development of the plastic zone, and the resulting stress redistribution around the cavity are presented as functions of cavity depth, internal pressure of cavity, strenzth of salt, and cavity teraperature rise. It is shown that a salt cavity can be designed such that it is structurally stable as a storage container assuming a chemical equilibrium can be established between the liquid waste and salt. (W.D.M.)

Separation of metal oxides from supercritical water by crossflow microfiltration

Low-shear crossflow microfilters rated for 34.5 MPa and 455°C were evaluated for their ability to remove α-alumina particles from supercritical water. The crossflow microfilters were tested in conjunction with a 2.5 L/h bench-scale apparatus and a 150 L/h pilot plant. The filter elements were made of sintered Stainless Steel 316L tubes with a nominal pore size of 0.5 μm. Process variables included volumetric feed concentration, feed flow rate, temperature, and fluid density and viscosity. The mean particle diameter was about 1.6 μm. Filtration characteristics were similar at supercritical water conditions to those at ambient conditions: Increased shear rates and decreased fluid viscosity resulted in increased filtrate fluxes. Filtrate flow deterioration over time and the required transfilter pressure drop were about 40% less at supercritical water conditions as compared to the performance obtainable at ambient conditions. Higher shear rates delayed the establishment of steady state operating conditions. Filtrate flux could be augmented by pressure swings or periodic increases in the shear rate. Particle separation efficiencies typically exceeded 99.9%. A modified concentration polarization model for turbulent flow yielded steady state filtrate fluxes that were within a factor of two of the experimental results. Back diffusion was modeled as a process-in-series of molecular diffusion and eddy diffusion. The proposed model was consistent with findings of numerical diffusion studies and the theory of concentration polarization as recently presented in the literature. To save on energy costs it might be possible to achieve the benefits of filtration at supercritical conditions at near-critical subcritical conditions: viscosity and mass diffusion coefficients are similar but the density of subcritical water is 3 to 4 times higher than supercritical water thus increasing the filtrate mass flow rate by a factor of 3 to 4 for a given filter.

Separation of Inorganic Salts From Supercritical Water by Cross-Flow Microfiltration

Abstract A cross-flow microfilter capable of operating at elevated temperatures and pressures was evaluated for its ability to remove inorganic salts from supercritical water (SCW). The separation characteristics of molten sodium nitrate were investigated. The overall performance of the cross-flow microfilter and the effects of process variables on the separation efficiency were evaluated. Separation efficiencies up to 85% were observed. An empirical model was developed for the prediction of the filtrate salt concentration and the fluidized cake resistance as a function of the salt solubility and salt flux to the filter. Physical principles governing the separation process were defined.

Anionic and nonionic surfactant sorption and degradation by algae cultures.

Degradation of three surfactants has been determined by organic extraction procedures and infrared spectroscopy. Axenic cultures of five species of blue-green algae and three species of green algae which are common to waste stabilization ponds were test organisms. Analytical data are shown comparing the effects produced by the algae cultures and a heterogeneous microcosm. Linear alkyl sulfonate was the anionic surfactant compound tested. An alkyl polyethoxylate and an alkyl phenol polyethoxylate were the nonionic test surfactants. Sorption of the compounds by the algae usually was followed by release and degradation of up to 99% of some of the component parts of the surfactant molecule.