One-step removal of lead from water using an electricity-free and sustainable membrane filtration

Lead (Pb) is a typical contaminant in water with adverse effects on human health. Hong Kong’s incident of drinking water contamination by Pb in 2015 caused severe public concerns regarding drinking water safety. Conventional treatment methods for Pb removal generally require electricity, chemical dosage, and considerable time and space, which significantly restrict their use for rapid water purification under emergency situations. In this study, a polyvinyl alcohol/polyacrylic acid (PVA/PAA) composite nanofibrous membrane was developed for the rapid and effective removal of Pb from water. The PVA/PAA membrane had a high water permeability of 550 L/m2/h/kPa - 710 L/m2/h/kPa, which allowed the filtration to be driven by gravity (e.g. with a water height of 10.0 cm). The membrane showed consistently high removal efficiency of Pb (> 95%) with a volumetric loading up to 3000 L/m2. This high removal efficiency was attributed to the combined effects of complexing and electrostatic attraction between Pb and PAA. An esculent citric acid was used to regenerate the exhausted PVA/PAA membrane. The regenerated membrane maintained its removal efficiency of Pb over a five-cycle filtration. These results imply that the PVA/PAA composite membrane can be repeatedly used in electricity-free filtration devices for rapid elimination of Pb under emergency situations.

Numerical Investigation of the Pressure Drop Characteristics of Isothermal Ice Slurry Flow under Variable Ice Particle Diameter

Ice slurry is an advanced secondary refrigerant that has been attracting considerable attention for the past decade due to the growing concerns regarding energy shortage and environmental protection. To stimulate the potential applications of ice slurry, the corresponding pressure drop of this refrigerant must be comprehensively investigated. The flow of ice slurry is a complex phenomenon that is affected by various parameters, including flow velocity, ice particle size, and ice mass fraction. To predict the pressure drop of ice slurry flow in pipes, a mixture computational fluid dynamic model was adopted to simulate a two-phase flow without considering ice melting. The numerical calculations were performed on a wide range of six ice particle sizes (0.1, 0.3, 0.5, 0.75, 1, and 1.2 mm) and ice mass fraction ranging within 5%–20% in the laminar range of ice slurry flow. The numerical model was validated using experimental data. Results showed that the ice volumetric loading and flow velocity have a direct effect on pressure drop; it increases with the increase in volumetric concentration and flow velocity. The findings also confirmed that for constant ice mass fraction and flow velocity, the pressure drop is directly and inversely related to the particle and pipe diameters, respectively. Moreover, the rise in pressure drop is more significant for large ice particle diameter in comparison to smaller size ice particles at high values of ice concentration and flow velocity.

Effect of sulfate removal in a high sulfate volumetric loading micro-aerobic bio-reactor and study of subsequent bio-sulfur adsorption by iron-modified activated carbon

Removal of sulfide from a micro-aerobic bio-reactor was studied at 10 000 mg L−1 chemical oxygen demand (COD) of inlet water, with the sulfate volumetric loading 0.75, 1.0, 1.5 and 2.0 kg (m−3 d−1), respectively.

CFD Study of Gas Holdup and Frictional Pressure Drop of Vertical Riser Inside IC Reactor

The internal circulation system in Internal Circulation (IC) reactor plays an important role in increasing volumetric loading rate and promoting the mixing between sludge and wastewater. In order to design the internal circulation system, the flow behaviors of gas-liquid inside vertical riser should be studied in detail. In the present study, the Multiple Flow Regimes model is adopted to capture the phase interface for different flow conditions. The flow patterns, internal circulation flow rate, gas holdup, and frictional pressure drop of vertical riser are investigated. The results show that the bubble flow inside a vertical riser is in a stable flow condition. There exists a maximum value for internal circulation flow rate with the increasing superficial gas velocity. The parameters of Martinelli models for gas holdup and frictional pressure drop are improved based on Computational Fluid Dynamics (CFD) results. The deviations between the calculated gas holdup and frictional pressure drop by improved model and experimental value are reduced to 14% and 13.2%, respectively. The improved gas holdup and frictional pressure drop model can be used for the optimal design of internal circulation system.

CFD Simulation on Hydrodynamic Behaviors of Anaerobic Granule Swarms

An internal circulation (IC) anaerobic reactor is widely used in the treatment of municipal and industrial wastewater with high volumetric loading rates. The performance of an IC reactor is closely related with hydrodynamic behaviors of anaerobic granules. Typically, anaerobic granules work in swarms and the settling behavior of a granule is disturbed by other granules. However, the research on anaerobic granule swarms is insufficient. In this work, Computational Fluid Dynamics (CFD) method was employed to study the hydrodynamic behaviors of anaerobic granule swarms with various voidages. The simulated results showed that the average velocity inside granules increased significantly as the voidage of granule swarm decreased and as the Reynolds number increased. The maximum shear stress on the granule’s surface increased with decreasing voidage and increasing Reynolds number. Based on the hydrodynamic behaviors of anaerobic granule swarms, an improved model of drag force coefficient for granule swarms was developed. The predicted expanded height, using the improved model, gives better consistency with experimental results. The improved model can embed in CFD code to improve the precision of the description of the IC reactor model and provide valuable information for designing and operating an IC reactor.

Influence of volumetric loading rate on aerobic sewage treatment for indigenous algal growth

Many rural areas of Latin America and the Caribbean (LAC) region are economically depressed. Rural sewage treatment in most areas of LAC is deficient or non-existent. Consequently, the possibility of generating economic revenue from treated sewage is an attractive option for deprived areas of developing countries. Given its peculiar characteristics, rural sewage may be coupled with biological systems such as algae for nutrient cycling. Acceptable algae growth and nutrient elimination were obtained from rural sewage whose treatment may have fallen short of current disposal standards. In this study, aerobic systems working on an 8-month cycle at three different volumetric loading rates (Bv) were assessed in relation to the lifetime growth of three algae strains native to Ecuador. Results indicate Chlorella sp. M2 as the optimal algal strain, with the highest growth rate at Bv of 1 g COD L−1 d−1 and a removal of organic-N (30%), PO43–-P (87%) and NH4+-N (95%). Concomitantly, the kinetic constants of the sewage resulted in a low biomass yield coefficient, making the proposed system highly suitable for developing countries. Finally, the proposed partial recovery stream method, combining nutrient recovery with economic resource generation, appears to contain great potential.

Biopaq®ICX: The next generation high rate anaerobic reactor proves itself at full scale

The ICX (Internal Circulation eXperience) is the next generation high rate anaerobic reactor. The unique design with a two-stage phase separation device enables excellent biomass retention. The novel biomass retention device allows for high volumetric loading rates to be applied compared to IC (internal circulation) and UASB (Upflow Anaerobic Sludge Bed) reactors. Since the first demonstration test in 2013, more than 70 full scale ICX reactors have been built, ranging in size from 85 to 5,000 m3. This paper presents the results of the first ICX demonstration reactor (85 m3) and from a full scale ICX reference (350 m3). These results confirm that very high volumetric loading rates can be achieved with the ICX, whilst maintaining a stable and high COD removal efficiency. Biomass growth is clearly demonstrated in both the demonstration reactor and in the full scale reference, proving that efficient biomass retention is achieved in the ICX.

Effect of Helical Winding Angle on External Pressure based Buckling of Partially Filled Thin Composite Cylindrical Shells

Effect of helical winding angle on buckling load of thin composite tubes is investigated in this work. Experiments are conducted on both empty and partially filled S2 glass tubes to estimate contribution of strength to the tubes by the filler material. Chosen filler material mechanically simulates behavior of typical solid propellant used in aerospace application. FE analysis with non-linear effect correlates well with the experimental data. Three series of experiments are conducted to quantify effect of helical winding angle and increase in volumetric loading fraction(VLF). Results confirm appreciable improvement in strength of filled tubes for higher VLF. For the chosen pattern of winding, lower winding angle provides more strength to the tubes against external pressure buckling.