Methods of using carbon nanotubes as filter media to remove aqueous heavy metals

Although carbon nanotubes (CNTs) are well known to have a strong affinity to various heavy metals in aqueous solution, little research has been dedicated to exploit their use in fixed-bed water treatment systems (e.g., trickling filters). In this work, batch sorption and fixed-bed experiments were conducted to examine the ability of functionalized multi-walled CNTs as filter media to remove two heavy metal ions (Pb2+ and Cu2+) from infiltrating water. Batch sorption experiments confirmed the strong sorption affinity of the CNTs for Pb2+ and Cu2+ in both single and dual metal solution systems. In addition, sonication-promoted dispersion of the CNT particles enhanced their heavy metal sorption capacity by 23.9–32.2%. For column experiments, laboratory-scale fixed-bed columns were packed with CNTs and natural quartz sand by three different packing: layered, mixed, and deposited. While all the three packing methods enhanced the fixed-bed filtering efficiency of Pb2+ and Cu2+ from single and dual metal systems, the CNT-deposited packing method was superior. Although the amount of the CNTs added into the fixed-bed columns was only 0.006% (w/w) of the sand, they significantly improved the fixed-bed’s filtering efficiency of Pb2+ and Cu2+ by 55–75% and 31–57%, respectively. Findings from this study demonstrate that functionalized multi-walled CNTs, together with natural sand, can be used to effectively and safely remove heavy metals from water

Biomass gasification for syngas and biochar co-production: Energy application and economic evaluation

Syngas and biochar are two main products from biomass gasification. To facilitate the optimization of the energy efficiency and economic viability of gasification systems, a comprehensive fixed-bed gasification model has been developed to predict the product rate and quality of both biochar and syngas. A coupled transient representative particle and fix-bed model was developed to describe the entire fixed-bed in the flow direction of primary air. A three-region approach has been incorporated into the model, which divided the reactor into three regions in terms of different fluid velocity profiles, i.e. natural convection region, mixed convection region, and forced convection region, respectively. The model could provide accurate predictions against experimental data with a deviation generally smaller than 10%. The model is applicable for efficient analysis of fixed-bed biomass gasification under variable operating conditions, such as equivalence ratio, moisture content of feedstock, and air inlet location. The optimal equivalence ratio was found to be 0.25 for maximizing the economic benefits of the gasification process

Decoking of fixed-bed catalytic reactors

A mathematical model for the description of the non-steady state process of decoking of a fixed bed catalytic reactor is presented. The relevant dimensionless groups are identified and their influence on the process discussed. Appropriate relationships are given for the estimation of the maximum temperature in the bed. Methods of monitoring the process and of controlling it in the case of unknown or variable coke contents are explained

Fixed bed gasification of wood char: characterisation of a new continuous downdraft reactor

A staged gasification process coupled with a gas engine is one of the most promising technologies for small and medium sized electricity production. The purpose of this work was to design and build new experimental equipment to characterise the wood char gasification stage in fixed bed/staged reactors. The Continuous Fixed Bed reactor (CFiB) at CIRAD replicates the gasification zone separately from the rest of the process. Instrumentation is a key point of the equipment. Sampling and measuring probes are positioned all along the char bed, every 10 cm, enabling online analysis of temperature, pressure and gas composition, along with condensate tracking. Accurate heat and mass balances were carried out to validate reactor performance and the methodology. Lastly, to illustrate the high potential of this research, equipment profiles for temperatures and gas concentrations along the bed are presented and discussed. (Résumé d'auteur

Distribusi Substrat Di Dalam Fixed Bed Reactor (Fbr)

Fixed Bed Reactor was the biological wastewater treatment reactor thatwas one of the Cakung Slaughterhouse (RPH Cakung) wastewatertreatment. Biological wastewater treatment process in principle wasprocess use of the microorganism to degrade the wastewater pollutant,where the wastewater will be changed into gas and the particle bio-solidthat enabled to be sediment. The capability of the microorganismdegrading this pollutant was influenced by various factor, some amongthem were the distribution of the substrate (microorganism group) inthe reactor. The distribution of this substrate could be known bymeasuring the value of pH and organic content as Chemical OxygenDemand (COD) or Total Solid (TTS). Considering the importance of theparameter then must be keep so that both of them, did not exceedlimits that were allowed in the FBR operation. This paper was discussedby the condition for the distribution of the substrate in various hydraulicretention time (HRT). Analysis was held for the operation with the up-flow system. Results of the research could be known that the value ofthe pH and TS in various HRT relatively constant, that is between 6.93– 7.15 (for the pH) and 0.32% - 0.56% (for TS). This value is still inlimits that were allowed. This showed that the FBR reactor had thegood performance was inspected from the condition for the distributionof the substrate inside

Removal of sulfamethoxazole and sulfapyridine by carbon nanotubes in fixed-bed columns

Sulfamethoxazole (SMX) and sulfapyridine (SPY), two representative sulfonamide antibiotics, have gained increasing attention because of the ecological risks these substances pose to plants, animals, and humans. This work systematically investigated the removal of SMX and SPY by carbon nanotubes (CNTs) in fixed-bed columns under a broad range of conditions including: CNT incorporation method, solution pH, bed depth, adsorbent dosage, adsorbate initial concentration, and flow rate. Fixed-bed experiments showed that pH is a key factor that affects the adsorption capacity of antibiotics to CNTs. The Bed Depth Service Time model describes well the relationship between service time and bed depth and can be used to design appropriate column parameters. During fixed-bed regeneration, small amounts of SMX (3%) and SPY (9%) were irreversibly bonded to the CNT/sand porous media, thus reducing the column capacity for subsequent reuse from 67.9 to 50.4 mg g−1 for SMX and from 91.9 to 72.9 mg g−1 for SPY. The reduced column capacity resulted from the decrease in available adsorption sites and resulting repulsion (i.e., blocking) of incoming antibiotics from those previously adsorbed. Findings from this study demonstrate that fixed-bed columns packed with CNTs can be efficiently used and regenerated to remove antibiotics from water

Dynamics of a three-phase upflow fixed bed catalytic reactor

A dynamic model of an upflow fixed-bed catalytic reactor is developed to examine numerically transient axial temperature and concentration profiles obtained for the consecutive hydrogenation of 1,5,9-cyclododecateriene on a Pd/Al2O3 catalyst. This non-isothermal heterogeneous model includes the resistances to heat and mass transfer at the gas–liquid and liquid–solid interfaces, as well as the heat exchange through the jacket of the reactor. The predictions of the model are compared to experimental data for various gas and liquid flow rates to describe dynamic events, such as the start-up of the reactor and the effects of sudden changes in the operating conditions on the reactor behaviour and its thermal stability. The predicted transient profiles are in good agreement with the experimental measurements. Still, the dynamic model is not able to correctly predict hot spots and runways experimentally observed at very high hydrogen flow rates

Study of the efflux velocity induced by two propellers

Present analysis is related with seabed erosion caused during docking and undocking maneuvering. Twin propellers without rudder were studied using a physical model with a fixed clearance distance and three different rotating velocities. Experimental results were compared to theoretical expressions of the efflux velocity, axial velocity and finally maximum bed velocity. Efflux velocity equations overestimate the experimental results, whereas axial velocity computed using the Dutch method fits reasonably well the experimental data. However, when maximum bed velocity expressions are compared to experimental results, German method behaves better with an over estimation if a quadratic superposition of the single jets is used.Postprint (published version