Optimization of operational conditions in a submerged membrane bioreactor

In this study, optimization of operational conditions of a submerged membrane bioreactor treating municipal waste-water was studied. Mixed liquid suspended solid (MLSS), membrane flux (J(v)), aeration (Q), ratio of pumping, time to break time (t(p)/t(b)), and ratio of up flow area to down flow area (A Ad) were chosen as the easily manipulable parameters to study their effects on removal efficiency and membrane fouling. Totally, 16 different runs were designed to compare and select the best combination of the 5 parameters. The results showed that the optimal operational conditions were MLSS = 7g(.)L(-1), J(v) = 10L(.)m(-2.)h(-1), Q = 6 m(3.)h(-1), t(p)/t(b)= 4 min/1 min, and A(r)/A(d) = 1.7 m(2)/m(2). Under such conditions, the SMBR could achieve a double win of high removal efficiency and low membrane fouling.

Optimization of an effective extraction procedure for the analysis of microcystins in soils and lake sediments

Microcystin analysis in sediments and soils is considered very difficult due to low recovery for extraction. This is the primary limiting factor for understanding the fate of toxins in the interface between water and sediment in both the aquatic ecosystem as well as in soils. In the present study, a wide range of extraction solvents were evaluated over a wide range of pH, extraction approaches and equilibration time to optimize an effective extraction procedure for the analysis of microcystins in soils and lake sediments. The number of extractions required and acids in extraction solutions were also studied. In this procedure, EDTA-sodium pyrophosphate solution was selected as an extraction solvent based on the adsorption mechanism study. The optimized procedure proved to be highly efficient and achieved over 90% recovery. Finally, the developed procedure was applied to field soil and sediment sample collected from Chinese lakes during bloom seasons and microcystins were determined in six of ten samples. (c) 2005 Elsevier Ltd. All rights reserved.

Optimization by orthogonal array design and humoral immunity of the bivalent vaccine against Aeromonas hydrophila and Vibrio fluvialis infection in crucian carp (Carassius auratus L.)

Aeromonas hydrophila and Vibrio fluvialis are the causative agents of a serious haemorrhagic septicaemia that affects a wide range of freshwater fish in China. In order to develop a bivalent anti-A. hydrophila and anti-V. fluvialis formalin-killed vaccine to prevent this disease, an orthogonal array design (OAD) method was used to optimize the production conditions, using three factors, each having three levels. The effects of these factors and levels on the relative per cent survival for crucian carp were quantitatively evaluated by analysis of variance. The final optimized formulation was established. The data showed that inactivation temperature had a significant effect on the potency of vaccine, but formalin concentration did not. The bivalent vaccine could elicit a strong humoral response in crucian carp (Carassius auratus L.) against both A. hydrophila and V. fluvialis simultaneously, which peaked at 3 or 5 weeks respectively. Antibody titres remained high until week 12, the end of the experiment, after a single intraperitoneal injection. The verification experiment confirmed that an optimized preparation could provide protection for fish at least against A. hydrophila infection, and did perform better than the non-optimized vaccine judged by the antibody levels and protection rate, suggesting that OAD is of value in the development of improved vaccine formulations.

Optimization of RP-HPLC analysis of low molecular weight organic acids in soil

RP-HPLC analysis for low molecular weight organic acids in soil solution has been optimized. An Atlantis (TM) C-18 column was used for the analyses. An optimal determination for eleven organic acids in soil solution was found at room temperature (25 degrees C) and 220 nm detection wavelength, with a mobile phase of 10 mM KH2PO4 -CH3OH (955, pH 2.7), a flow rate of 0.8 mL/min and 10 mu L sample size. The detection limits ranged 3.2-619 ng/mL, the coefficients of variation ranged 1.3-4.6%, and the recoveries ranged 95.6-106.3% for soil solution with standard addition on the optimal conditions proposed.

The optimization of high performance liquid chromatographic method for analysis of trace microcystins in natural water bodies

The ratio of methanol., water and trifluoroacetic acid ( TFA) was regulated to change the polarity and the pH of the rinse solution and the eluent, so as to improve the high performance liquid chromatography HPLC) detection method for trace microcystines (MCs) in natural water bodies. The results showed that 40 % similar to 45 % methanol-water solution containing 0. 1 % TFA could get good effects on the rinse of impurity, and 70% methanol-water solution containing 0. 1% TFA could elute all the MCs in solid phase extraction ( SPE) cartridge ( C-18), In this way. it is suggested that, in analysis of environmental samples with high concentration of impurity, impurity should be washed with 40% similar to 45% methanol-water solution containing 0. 1% TFA, and MCs should be eluted with 70% similar to 100% methanol-water solution containing 0. 1% TFA.

Optimization of growth and fatty acid composition of a unicellular marine picoplankton, Nannochloropsis sp., with enriched carbon sources

A unicellular marine picoplankton, Nannochloropsis sp., was grown under CO2-enriched photoautotrophic or/and acetate-added mixotrophic conditions. Photoautotrophic conditions with enriched CO2 of 2800 mul CO2 l(-1) and aeration gave the highest biomass yield (634 mg dry wt l(-1)), the highest total lipid content (9% of dry wt), total fatty acids (64 mg g(-1) dry wt), polyunsaturated fatty acids (35% total fatty acids) and eicosapentaenoic acid (EPA, 20:5omega3) (16 mg g(-1) dry wt or 25% of total fatty acids). Mixotrophic cultures gave a greater protein content but less carbohydrates. Adding sodium acetate (2 mM) decreased the amounts of the total fatty acids and EPA. Elevation of CO2 in photoautotrophic culture thus enhances growth and raises the production of EPA in Nannochloropsis sp.

Optimization of control parameters for petroleum waste composting

Composting is being widely employed in the treatment of petroleum waste. The purpose of this study was to find the optimum control parameters for petroleum waste in-vessel composting. Various physical and chemical parameters were monitored to evaluate their influence on the microbial communities present in composting. The CO2 evolution and the number of microorganisms were measured as the activity of composting. The results demonstrated that the optimum temperature, pH and moisture content were 56.5 - 59.5 degreesC, 7.0 - 8.5 and 55 % - 60%, respectively. Under the optimum conditions, the removal efficiency of petroleum hydrocarbon reached 83.29% after 30 days composting.

Design and optimization of photonic crystal coupling layer for bi-color quantum well infrared photodetectors

Finite difference time domain (FDTD) method is used for the simulation and analysis of electromagnetic field in the top coupling layer of GaAs/AlGaAs quantum well infrared photodetector (QWIP). Simulation results demonstrated the coupling efficiencies and distributions of electromagnetic (EM) field in a variety of 2D photonic crystal coupling layer structures. A photonic crystal structure for bi-color-QWIP is demonstrated with high coupling efficiency for two wavelengths.

Optimization of metamorphic InGaAs quantum wells on GaAs grown by molecular beam epitaxy

We investigate the molecular beam epitaxy growth of metamorphic InxGa(1-x)As materials (x up to 0.5) on GaAs substrates systematically. Optimization of structure design and growth parameters is aimed at obtaining smooth surface and high optical quality. The optimized structures have an average surface roughness of 0.9-1.8 nm. It is also proven by PL measurements that the optical properties of high indium content (55%) InGaAs quantum wells are improved apparently by defect reduction technique and by introducing Sb as a surfactant. These provide us new ways for growing device quality metamorphic structures on GaAs substrates with long-wavelength emissions.

Fabrication and optical optimization of spot-size converters with strong cladding layers

A silicon-on-insulator (SOI) optical fiber-to-waveguide spot-size converter (SSC) overlaid with specially treated silica is investigated for integrated optical circuits. Unlike the conventional process of simply depositing the hot silica on silicon waveguides, two successive layers of silicon dioxide were grown on etched SSC structures by PECVD (plasma-enhanced chemical vapor deposition). The two layers have 0.8% index contrast and supply stronger cladding for an incident light beam. Additionally, this process is able to reduce the effective refractive index of the input mode to less than 1.47 (extremely close to that of the fiber), substantially weakening the unwanted back reflection. Exploiting this technology, it was demonstrated that the SSC showed a theoretical low mode mismatch loss of 1.23 dB for a TE-like mode and has an experimental coupling efficiency of 66%.

Overall optimization of high-speed semiconductor laser modules

Based on the high frequency techniques such as frequency response measurement, equivalent circuit modeling and packaging parasitics compensation, a comprehensive optimization method for packaging high-speed semiconductor laser module is presented in this paper. The experiments show that the small-signal magnitude frequency response of the TO packaged laser module is superior to that of laser diode in frequencies, and the in-band flatness and the phase-frequency linearity are also improved significantly.

Optimization of GaInNAs(Sb)/GaAs quantum wells at 1.3-1.55 mu m grown by molecular beam epitaxy

The InGaNAs(Sb)/(GaNAs)/GaAs quantum wells (QWs) emitting at 1.3-1.55 mu m have been grown by molecular beam epitaxy (MBE). The parameters of the radio frequency (RF) such as RF power and flow rate are optimized to reduce the damages from the ions or energetic species. The growth temperature is carefully controlled to prevent the phase segregation and strain relaxation. The effects of Sb on the wavelength and quality are investigated. The GaNAs barrier is used to extend the wavelength and reduce the strain. A 1.5865 mu m InGaNAs(Sb)/GaNAs SQW edge emitting laser lasing at room temperature at continuous wave operation mode is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.

Grating optimization and experiment on high-power distributed feedback lasers

Coupling coefficient is an important parameter for distributed feedback lasers. Modified coupled-wave equations are used to calculate the effect of grating shape on coupling coefficient of the second-order gratings. Corresponding devices demonstrate that the maximum kink-free power per facet reaches 50 mW and the sidemode suppression ratio is 36 dB.

Structure optimization of field-plate AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors (HEMTs) on 6H-SiC with varying field-plate length and gate-drain spacing were fabricated and analyzed. The classical small signal FET model and the well-known ColdFET method were used to extract the small signal parameters of the devices. Though the devices with field plates exhibited lower better f(T) characteristic, they did demonstrate better f(max), MSG and power density performances than the conventional devices without field plate. Besides, no independence of DC characteristic on field-plate length was observed. With the increase of the field-plate length and the gate-drain spacing, the characteristic of f(T) and f(max), degraded due to the large parasitic effects. Loadpull method was used to measure the microwave power performance of the devices. Under the condition of continuous wave at 5.4 GHz, an output power density of 4.69 W/mm was obtained for device with field-plate length of 0.5 mu m and gate-drain length of 2 mu m. (c) 2006 Elsevier Ltd. All rights reserved.

Optimization of mechanically induced long-period fibre grating transmission spectrum

A new double-layer grating template is designed to reduce the out-of-band loss as much as 1.8dB when the loss of LP03 reaches 10.2 dB. Meanwhile, we propose a method to remove the sidelobes in the transmission spectra by the adjustment of the thickness of pressure plates. The plate-thickness-induced shift of resonant wavelength and the attenuation of loss peak intensity when removing sidelobes can be modified by the fibre distance and contact point on the pressure plates.