An integrated system for hydrogen and methane production during landfill leachate treatment

The patent-pending integrated waste-to-energy system comprises both a novel biohydrogen reactor with a gravity settler (Biohydrogenator), followed by a second stage conventional anaerobic digester for the production of methane gas. This chemical-free process has been tested with a synthetic wastewater/leachate solution, and was operated at 37 °C for 45 d. The biohydrogenator (system (A), stage 1) steadily produced hydrogen with no methane during the experimental period. The maximum hydrogen yield was 400 mL H₂/g glucose with an average of 345 mL H₂/g glucose, as compared to 141 and 118 mL H₂/g glucose for two consecutive runs done in parallel using a conventional continuously stirred tank reactor (CSTR, System (B)). Decoupling of the solids retention time (SRT) from the hydraulic retention time (HRT) using the gravity settler showed a marked improvement in performance, with the maximum and average hydrogen production rates in system (A) of 22 and 19 L H₂/d, as compared with 2–7 L H₂/d in the CSTR resulting in a maximum yield of 2.8 mol H₂/mol glucose much higher than the 1.1–1.3 mol H₂/mol glucose observed in the CSTR. Furthermore, while the CSTR collapsed in 10–15 d due to biomass washout, the biohydrogenator continued stable operation for the 45 d reported here and beyond. The methane yield for the second stage in system (A) approached a maximum value of 426 mL CH₄/gCOD removed, while an overall chemical oxygen demand (COD) removal efficiency of 94% was achieved in system (A).     

Effect of organic loading on a novel hydrogen bioreactor

This study investigated the impact of six organic loading rates (OLR) ranging from 6.5 gCOD/L-d to 206 gCOD/L-d on the performance of a novel integrated biohydrogen reactor clarifier systems (IBRCSs) comprised a continuously stirred reactor (CSTR) for biological hydrogen production, followed by an uncovered gravity settler for decoupling of solids retention time (SRT) from hydraulic retention time (HRT). The system was able to maintain a high molar hydrogen yield of 2.8 mol H₂/mol glucose at OLR ranging from 6.5 to 103 gCOD/L-d, but dropped precipitously to approximately 1.2 and 1.1 mol H₂/mol glucose for the OLRs of 154 and 206 gCOD/L-d, respectively. The optimum OLR at HRT of 8 h for maximizing both hydrogen molar yield and volumetric hydrogen production was 103 gCOD/L-d. A positive statistical correlation was observed between the molar hydrogen production and the molar acetate-to-butyrate ratio. Biomass yield correlated negatively with hydrogen yield, although not linearly. Analyzing the food-to-microorganisms (F/M) data in this study and others revealed that, both molar hydrogen yields and biomass specific hydrogen rates peaked at 2.8 mol H₂/mol glucose and 2.3 L/gVSS-d at F/M ratios ranging from 4.4 to 6.4 gCOD/gVSS-d. Microbial community analysis for OLRs of 6.5 and 25.7 gCOD/L-d showed the predominance of hydrogen producers such as Clostridium acetobutyricum, Klebsiella pneumonia, Clostridium butyricum, Clostridium pasteurianum. While at extremely high OLRs of 154 and 206 gCOD/L-d, a microbial shift was clearly evident due to the coexistence of the non-hydrogen producers such as Lactococcus sp. and Pseudomonas sp.     

Anodic dissolution of nickel in acidic chloride solutions

The anodic dissolution of nickel was studied galvanostatically in hydrochloric acid solutions of various concentrations. The reaction orders of chloride ion and hydrogen ion concentrations were found to be 0.5 and 1.0, respectively. An anodic Tafel slope equal to 120 ± 10 mV · decade⁻¹ was obtained. The dissolution rate of nickel at constant acid concentration was increased with stirring of the solution and increasing temperature. The activation energy, ΔH, for the anodic dissolution process was found to be 12 kcal · mol⁻¹. The presence of oxygen in solutions assisted the passivation process. The effect of addition of aniline and some of its derivatives (o-, m-, and p-anisidine) as inhibitors on the dissolution kinetics of Ni in 1 M HCl was also investigated. These compounds inhibited the anodic dissolution of nickel without affecting the Tafel slope, indicating that the adsorption of such inhibitors could not interfere with the mechanism of metal dissolution.     

Plastic-containing materials as alternative reductants for base metal production

Shredder residue materials are produced after the removal of ferrous and non-ferrous fractions from end-of-life electronic equipment. Despite the high plastic content and metal value in the ash, high percentages of these materials are currently sent to landfills. In this study, the potential of utilising shredder residue material and other plastic-containing materials as reducing agents was studied. Plastic-containing materials were co-injected with coal into a zinc-fuming furnace in Boliden-Rönnskär smelter. The data obtained from the trial, such as the data from the chemical analysis of the slag and the steam production, are discussed. The observations indicate that plastic-containing material can replace up to 1?ton?h^?1 of coal without a significant decrease in the zinc reduction rate.     

Use of irradiation to control foodborne pathogens and extend the refrigerated market life of rabbit meat

This study set out to evaluate the microbiological status of rabbit meat and the possibility of using irradiation to control foodborne pathogenic bacteria and extend the refrigerated storage life of meat. Rabbit meat samples were γ irradiated at doses of 0, 1.5 and 3 kGy. The samples were stored at refrigeration temperature, then the effects of irradiation and storage on their microbiological, chemical and sensory properties were studied. Irradiation at 1.5 kGy significantly reduced the counts of Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis and enterobacteriaceae but was not enough for complete elimination of Salmonella. However, 3 kGy dose reduced the counts of S. aureus, L. monocytogenes, E. faecalis and enterobacteriaceae by more than 3, 3, 1.4 and 4 log units, respectively, while Salmonella was not detected. On the other hand, irradiation at 1.5 and 3 kGy significantly reduced the counts of aerobic mesophilic bacteria, psychrophilic bacteria and molds and yeasts and prolonged the refrigerated shelf-life of samples to 12 and 21 days, respectively, compared to 6 days for non-irradiated controls. Irradiation of samples significantly increased their amounts of thiobarbituric acid reactive substances (TBARS) but had no significant effects on their total volatile nitrogen (TVN) contents, while storage significantly increased the TBARS and TVN for irradiated and non-irradiated samples. γ irradiation showed no significant effects on the sensory properties of raw meat. Moreover, fried burgers prepared from irradiated rabbit meat showed high sensory acceptability similar to those prepared from non-irradiated meat.     

Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite

Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.     

Reduction-Carburization of NiO-WO<Subscript>3</Subscript> Under Isothermal Conditions Using H<Subscript>2</Subscript>-CH<Subscript>4</Subscript> Gas Mixture

Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO₃ oxide precursors using H₂-CH₄ gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.     

A computer-aided teaching package for microprocessor systemseducation

A computer-aided teaching (CAT) package for use in a microprocessor systems course is described. It uses the Z80 CPU as the basis for describing how an eight-bit CPU functions internally and as the master of a microcomputer system. The package, which consists of an assembler and a graphics simulator, aids as a powerful teaching tool that enables the student to learn about the internal architecture of a microprocessor as applied to the Z80 CPU and its instruction set with a step-by-step graphics animation of the instruction execution and timing. The package allows the user to execute a program step by step and to test the operation of the internal registers, buses, and memory contents at every clock edge. It also simulates read/write cycles from/to memory and input-output devices. Finally, it allows the user to write and debug problems at the assembly language or machine code level. The package is menu driven, interactive, flexible, and user-friendly     

A method for treating wastewater containing formaldehyde

Many industrial activities utilise formaldehyde as a key chemical in organic synthesis including: synthesis of special chemicals such as pentaerythritol and ethylene glycol, synthetic resins, paper products, medicinal products and drugs and others, too numerous to mention. Therefore, effluents arising from these applications may contain significant amounts of formaldehyde. In a biodegradation experiments of a wastewater sample containing formaldehyde ranging from 31.5 to 125 mg/l, residual formalin (a solution of formaldehyde gas in water) ranging from 40% to 85%, respectively, was found at the end of the run (16 d) showing the inhibition effect of formalin which increased with the increase in formalin concentration. The biodegradation of formalin decreased significantly at concentrations higher than 300 mg/l. A method to convert formaldehyde to an easily biodegradable substance is herein described. In the commercial manufacture of resins from phenol and formalin the reaction is never completely quantitative. As a result during the dehydration stage phenol and formalin are distilled from the wastewater. Phenol is toxic to several biochemical reactions. However, biological transformation of phenol to a non-toxic entity is possible through specialized microbes. Transformation of phenol is inhibited by the presence of formaldehyde. Biotransformation of phenol in a wastewater containing high concentrations of formaldehyde started shortly after treating the wastewater with calculated amounts of sodium sulphite. Sodium sulphite is believed to react with formaldehyde forming sodium formaldehyde bisulphite, which is not only non-toxic to microorganisms but also a biodegradable substance. From the DO measurements before and after the addition of sodium sulphite, the authors noticed that the dissolved oxygen in a wastewater containing formaldehyde is not affected by the addition of the calculated amount of sodium sulphite, which is just enough to consume the measured amount of formaldehyde in that wastewater.