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.
Utilization patterns of volatile fatty acids in the denitrification reaction
Abstract This research investigated the utilization pattern of volatile fatty acids (VFAs) in the denitrification process. To be thorough, both synthetically produced and naturally generated VFAs were considered with the synthetic compounds being acetate, propionate and a mixture of these acids. The natural VFAs (acetate, propionate, butyrate and valerate) were produced from a laboratory-scale, completely mixed anaerobic digester. The wastewater used was a 1:1 mixture of municipal sludge and a potato-processing wastewater diluted to 5000 mg L−1 of total solids (TS). Steady-state, acidogenic conditions produced net VFAs of approximately 780 mg L−1. In addition, 36 denitrification experiments were conducted in 0.6 L batch reactors (18 using natural VFAs (the N-series) and 18 using synthetic VFAs (the S-series)). Nitrates completely disappeared and the average specific denitrification rate (kN) for the N-series (0.0111 g NO3−-N g VSS−1 d−1) was close to the mixture of the S-series (0.0134 g NO3−-N g VSS−1 d−1). Within the S-series, the kN value for acetate was more than double that of propionate reflecting a preference for acetate. The average specific carbon consumption rate (kC) for the N-series (0.0252 g VFA-C g VSS−1 d−1) was similar to the kC for the S-series (0.0248 g VFA-C g VSS−1 d−1). A hierarchy (acetate followed by butyrate followed by propionate) was evident when the kC rate was calculated on the basis of individual acids within the natural mixture. This hierarchy was also supported by the carbon consumption profiles.
Influence of filler addition, storage medium and evaluation time on biaxial flexure strength and modulus of adhesive systems
Abstract Objective. This study evaluated the effects of filler addition, storage medium and time on biaxial flexural strength and flexural modulus of six adhesive systems. Materials and methods. The adhesives were either unfilled resins: Single Bond, Prime&Bond 2.1 and One-Step; or filled resins: Single Bond Plus, Prime&Bond NT and One-Step Plus. Resin discs of each product (0.5 mm thick × 6.0 mm diameter) were prepared using silicon molds (n = 10). The discs were stored dry, in water, mineral oil or ethanol for 1 week or 3 months before biaxial flexural testing. Data were statistically analyzed by 3-way ANOVA and Tukey's post-hoc test (α = 0.05). The specimens were tested in a universal testing machine at 1.27 mm/min until failure occurred. Results. In general, the storage in ethanol led to significantly lower flexural strength and flexural modulus values than the other storage conditions for all adhesives in both storage periods. Filler addition increased flexural strength and flexural modulus for Prime&Bond NT, when it was stored dry or in water for 1 week. For Single Bond Plus, the filler addition resulted in higher flexural modulus, when it was stored for 1 week in oil and in ethanol. No significant differences in flexural modulus were observed between One-Step and One-Step Plus in any storage medium. Conclusions. Results suggested that filler addition does not necessarily have to increase the flexural strength and flexural modulus. Ethanol and oil storages tended to yield opposite effects.