Tag Archives: Methods of Wastewater Treatment

Activation of Catalysts for Carbon Nanomaterial Production

The most important stage of preparing heterogeneous catalysts for carbon nanomaterial (CNM) is their activation, which is understood as a complex of physical influence on the catalytic material, which allows to significantly increase the efficiency of nanostructure synthesis.

This can be achieved by researching mechanical (dispersion) and physical (electromagnetic and ultrasonic) activation methods.

One of the most important factors defining catalyst efficiency is its granulometric composition. It is known that reduction of the particle size (less than 3 nanometers) causes capsulation inside nanotubes, while increasing it above 25 nanometers leads to uneven size distribution and defects in nanotubes. This is due to the fact the using large catalyst particles (25 to 100 nanometers) prevents carbon scattering from the surfaces where hydrocarbon decay occurs to the surfaces where carbon is deposited; as a consequence, no CNM growth occurs on such particles. Therefore, it is important to define reasonable catalyst particle size, as well as dispersion and classification methods.

Note that dispersion of catalyst microparticles causes both the reduction of size and the changes in the microstructure, e.g. destruction and reduction of pore depth, increasing the boundary of nano-seeds, where graphitized carbon is deposited.

Catalyst was activated in a drum mill and an electromagnetic vortex layer device (AVS). The distinguishing characteristic of the vortex layer in electromagnetic units is the multitude of high frequency and strength shocks, as well as friction, which not only break solid particles, but significantly activate their surfaces due to the deformation of their crystalline lattice. Enormous energy is concentrated in a volume of this process, which direct influence on the material. The influence is so high that it changes the structure as deeply as the atom’s valency shells. The process causes deep changes in the structure of the material.

Mean energy conducted to a volume of the vortex layer reaches 103 kW/m3. This is several orders of magnitude higher than in vibration mills, for instance. Besides, the energy is localized in certain areas, e.g. in the locations where the ferromagnetic particles collide, where mean power reaches even higher.

The electromagnetic vortex layer unit consisted of a process section and a control section, connected by oil tubes and a power cable. The process section consisted of a support, an enclosure, an induction coil for the rotating electromagnetic field, and a detachable operating chamber.

The catalyst activation process was performed with 1…1.5 mm by 10…15 mm PVC encapsulated ferromagnetic particles.

The chamber was loaded with 0.120 kg of the catalyst and 0.060 kg of ferromagnetic particles; retention time varied from 5 to 60 seconds. The granulometric composition of the Ni/MgO catalyst after the dispersion was done by fractionating sieve analysis. The catalyst after activation was separated into fractions and used for CNM synthesis under a unified method of testing various catalyst samples.

The results of the experiment show that the optimal duration time for the finest grinding constitutes 10 seconds, with initial catalyst particle size of 500 micron.

The observed increase of catalyst particle size after 10 or more seconds of dispersion is apparently due to the fact that with time the particles accumulate sufficient energy for spontaneous aggregation.

The analysis of the influence of the catalyst size composition on the mean output of CNM leads to the conclusion: the output increases in inverse proportion to catalyst particle size. This is due to the increased active surface of the catalyst. The experiments demonstrated that the actual method of catalyst dispersion has no significant influence on nanomaterial output.

Traditional and Alternative Methods of Household Wastewater Treatment

Methods of Wastewater Treatment. Among the traditional wastewater purification technologies, one of the most common is aerotank treatment.

Those are, as a rule, rectangular reactors with many chambers, which contain high concentrations of aerobic microbes in suspended floccules (biological sludge) and are equipped with a system of continuous aeration and recirculation of sludge. Aerotanks with prolonged aeration promote the development of bacteria which can effectively remove organics, as well as oxidize ammonia nitrogen to nitrates.

For complete removal of nitrogen from wastewater after nitrification, anaerobic denitrification is required by installing additional vessels or creating special chambers in existing ones.

Phosphorus can be removed by chemical sedimentation or microbial assimilation.

Single reactor systems are also widely used in the world: sequencing batch reactors and membrane bioreactors, as well as oxidation ditches.

The other type of devices are systems with immobile biomass (biofilm). These include trickling filters and rotating biological contactors.

Methods of Wastewater Treatment. Trickling filters are usually cylindrical vessels filled with natural or artificial materials with high mean surface area, on which aerobic and anaerobic bacterial proliferate, and which is in contact with wastewater. Rotating biological contactors consists of several disks up to 3 meters in diameter, installed vertically on a horizontal shaft and submerged (35-40%) into wastewater.

The biological purification of wastewater can also be performed in conditions close to natural. One of the simple methods that can be used for secondary treatment of wastewater is the biological pond. Stabilization ponds are usually artificial rectangular ponds (without higher plant life), connected in a three level cascade: anaerobic pond (2 – 5 meters deep), optional anaerobic pond (1-2.5 meters deep), and an aerobic pondа (0.5-1.5 meters deep). These systems are constructed in at least two parallel lines. Minimum temperature for operation is 8°С.

Stabilization ponds can also be equipped with aeration devices (mechanical aerators usually), which improve the efficiency of purification and makes it possible to use the ponds in lower temperatures.

Another technology of the same nature is the ponds with horizontal subsurface flow of wastewater. They consist of a reservoir covered by watertight material, a layer of filtration material (gravel, sand etc), higher plant life and waste water that moves mostly horizontally below the filter layer.