Design, simulation, and laboratory test of a single sludge drainage pipe for wastewater treatment sedimentation tank

This study develops a novel design scheme based on engineering fluid mechanics for the single-pipe-type sludge drainage mechanism of sedimentation tanks in the wastewater treatment industry. A laboratory-scale clarifier is fabricated for experimental verification. Sludge drainage ratio and suspended solids (SS) of inflow are selected as two factors for laboratory experiments, and SS values are measured to evaluate the performance of the sludge drainage pipe. Experiment data show that the designed single sludge drainage pipe can successfully achieve the supposed task with a coefficient of variation (CV) of SS less than 8.5%. The variation scope of CV from 1.5% to 8.3% suggests that the sludge drainage performance is relatively steady. Nine sets of 3D computational fluid dynamic (CFD) simulations, which is based on the inhomogeneous Eulerian–Eulerian multiphase model, were conducted for a comprehensive exploration and assessment. Results reveal noticeable deviations of the characteristics of the fluid in the outermost orifice of the sludge drainage pipe from the designed value. Although the fluid velocity through each orifice is matched with the designed values, the mass flowrate differs with a maximum of four times the designed value and a standard deviation of 0.4 of hole among the nine simulations. This study also suggests some considerations in the design process and routine operation of the single-pipe-type sludge drainage system.

Is nitrate a driver for pigments of phytoplankton (a case study from a small shallow European lake)?

The traditional view of biogenic limitation in freshwater ecosystems considers phosphorus as the primary limiting element, but this concept has recently been challenged. There are a number of studies that suggest that photosynthetic indices may depend on the levels of nitrogen (especially, nitrate-nitrogen). To test the hypothesis about the possibility of nitrogen limitation in the lake ecosystem, the present study analysed the water in the littoral zone of a shallow model lake for the relationship between the content of phytoplankton pigments (chlorophyll a and carotenoids) and nitrate. The nitrate-nitrogen was selected because it is the most chemically stable nitrogen species. The study was conducted in a small lake with a pronounced autochthonous regime (as indicated by its small drainage ratio) during a vegetation season with contrasting hydrological conditions. The relationship with the nitrate concentration was not confirmed for chlorophyll a, but the levels of nitrate anion and carotenoids were shown to be related. Chlorophyll a, which is regarded as a metabolically active component of phytoplankton cells, shows a close correlation with air temperature. The corresponding prognostic regression models were created. The data on nominal availability of nitrate-nitrogen for primary production show possible nitrogen limitation on some of the observation dates. If the production potential represented by certain levels of nitrate is not realised by phytoplankton, it can be used by filamentous algae. The results of the study provide first steps toward prediction of one of the indicators of phytoplankton growth, the content of two main types of pigment (chlorophyll a and carotenoids).

The Expansion and Drainage Characteristics of AFFF in Low-Pressure Environment

Tests are conducted in a low-pressure combustion chamber of 3 × 2 × 4.65m3 in volume to investigate the effect of low pressure on the drainage and expansion characteristics of AFFF (Aqueous Film-Forming Foam). A manipulator equipment with the frequency of 4 Hz and the amplitude of 32cm is designed for the foaming of AFFF in the chamber. The parameters of expansion and drainage ratio are obtained under two different ambient pressure of 101kPa and 30kPa. Two fluorocarbon surfactants contained commercial AFFF (AFFF1 is type of 3% and AFFF2 is the type of 6%) that were used in precious studies are both diluted into different quality percentage resolutions, and then achieve foaming in a 130ml measuring cylinder with a cone bottom. The foaming expansion ratio and drainage time are obtained based on the recorded videos. Experimental results show that the expansion ratio of both AFFF1 and AFFF2 resolutions (the expansion ratio <6) is lower under the pressure of 30kPa than that under 101kPa. The drainage time (25% and 50%) of AFFF1 is increasing in the lower pressure environment. On the contrary, 50% drainage time of AFFF2 is shorter under 30kPa than that under 101kPa, but 25% drainage time of AFFF2 is almost the same under two ambient pressures. The variations under low pressure environment are obvious and various from each other, but the further tests should be conducted to reveal and explore the mechanism.

Numerical Analysis on Drainage Parameters in a High Drainage Roadway

The numerical tests of the optimized drainage parameters in a high drainage roadway were conducted with different inlet air velocities, drainage ratios and integrity lengths. The results show that the upper corner's gas concentration decreases gradually with the inlet air velocity and drainage ratio increasing, while there have not obvious change with the Different Integrity Lengthss. Considering from the gas control and gas drainage, the reasonable inlet air velocity is 1-1.25m/s and the right drainage ratio is about 0.3.

Factors influencing the achievement of steady state in mercury contamination among lakes and catchments of south-central Ontario

Mercury (Hg) concentrations in recent (0.5–1 cm) and preindustrial (>30 cm) sediments were examined across lakes in south-central and eastern Ontario, Canada (45.53°N, 82.41°W to 44.15°N, 76.25°W), to determine whether Hg exported from watersheds is at steady state with atmospheric deposition. An examination of headwater lakes revealed that Hg enrichment was not uniform among watersheds but that the enrichment factor (EF = [Hg]present day/[Hg]preindustrial, standardized for organic matter) decreased as a function of drainage ratio (Ad /Ao, watershedarea/lakearea). Furthermore, the model fit was improved after accounting for differences in sulfate concentrations and pH among lakes: EF = (Ad /Ao)–15.96 – 0.07(SO 42– ) – (3.55(pH>8.3)) (R2 = 0.458, p = 0.0001). Hg concentrations in preindustrial sediments of headwater lakes showed a positive linear relationship with drainage ratio (partial t = 4.83, p < 0.0001, n = 66) that was strengthened following an adjustment for mean annual runoff (MAR) ([Hg]preindustrial = 0.011 ± 0.002(Ad /Ao) + 0.0008 ± 0.0003(MAR) (R2 = 0.108, F[1,66] = 8.01, p = 0.006)). Our results suggest that Hg export from watersheds may be currently lagging behind atmospheric Hg deposition, in which case, Hg export would increase into the future, even as Hg deposition from the atmosphere stabilizes.

A paleolimnological investigation of the effects of forest fire on lake water quality in northwestern Ontario over the past ca. 150 years

Fire is an important mechanism of disturbance in boreal ecosystems; however, the effects of fire on lake ecosystems are still not well understood. This study provides a detailed assessment of the impacts of fire on the limnology of a small oligotrophic lake (Lake 42), located approximately 200 km northwest of Thunder Bay, Ont. The study lake is characterized by a small drainage ratio (watershed area : surface area) and a relatively long water residence time. Age establishment and fire scar analyses determined that at least one, and perhaps two, major fires had burned to the lake's shoreline in the past ca. 150 years. Using a paleoecological approach, diatoms were examined in a 210Pb-dated sediment core. Following watershed fires, minimal changes were noted in the diatom species assemblage. These findings may be explained by the low sedimentation rates and small drainage ratio of the study lake, although other studies suggest that the biological response may be minimal compared with physical–chemical responses in some ecosystems. Beginning in the early 1980s, however, distinct changes were noted in the species assemblage and in diatom-inferred total phosphorus. Our findings suggest that the study lake may be more sensitive to precipitation inputs of nutrients than to inputs resulting from watershed disturbances.Key words: paleolimnology, diatoms, forest fire, water quality.