Biological nitrification and denitrification of opto-electronic industrial wastewater.
Development and application of biological nutrient removal processes accelerated significantly over the past decade due to more stringent nutrients (nitrogen and phosphorus) discharge limits being imposed on wastewater treatment plants. The opto-electronic industry has developed very fast over the past decade in the world. The wastewater often contains a significant quantity of organic nitrogen compounds and has a ratio of over 95% in organic nitrogen (Org-N) to total nitrogen (T-N). In this study, a 2-stage Anoxic/Aerobic pre-denitrification process was established and the efficiency of wastewater treatment was evaluated. Wastewater from an actual LCD-plant was obtained as the sample for looking into the feasibility of opto-electronic industrial wastewater treatment. Hydraulic retention time (HRT) and mixed liquor recycle rate (MLR) were controlled independently to distinguish between the effects of these two factors. Under suitable HRT and mixed liquor recycle ratio, effluents of NH4-N, NOx-N and COD can fall below 20 mg/l, 30 mg/l and 80 mg/l.
Effects of the activity of heterotrophs on nitrification in a suspended-growth reactor
Ammonia (80 mg l−1 as N), with various concentrations of glucose, was continuously fed to laboratory scale reactors at 25°C to examine the effect of the activity of heterotrophs on nitrification. The assimilation of ammonia by heterotrophs happened in preference to nitrification, and reduced the available ammonia for nitrification. Glucose addition of 160, 500 or 1000 mg l−1 (as COD) decreased ammonia removal and ammonia oxidation to nitrite, and elevated the effluent ammonia concentration. The results clearly indicate that the addition of organic matter, which provokes the growth of heterotrophs, inhibits ammonia oxidation. Determination of the biomass index with batch experiments enabled estimation of kinetic constants for ammonia oxidizers (μm = 0.66 d−1, K = 1.0 mg l−1) and for nitrite oxidizers (μm = 0.58 d−1, K = 0.35 mg l−1) when no glucose was added. The addition of glucose to the reactor resulted in a high K (7.2 mg l−1 when 1000 mg l−1 of COD was added) whereas μm was unchanged in the ammonia oxidation. It is suggested that inhibition takes place by decreasing the affinity between the ammonia oxidizers and ammonia. Experiments using acetate showed that toxic effect by organic matter is unlikely. One hypothesis is that transportation of ammonia from bulk water to the cell of the ammonia oxidizer is hindered by the presence of the crowded cells of the heterotrophs. Nitrite oxidation was not directly affected by organic loading.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.