Methodology in purifying contaminated wastewater by using nanotechnology
-Formulas that will be used for Membrane nanotechnology experiment.
-What is the result for all of the three types of waste water (agricultural, industrial, storm water)by using Membrane nanotechnology and compare the results of the three types of wastewater ( Type of the data:Quantitative data).
-Why we choose any one from the three types of waste water (agricultural, industrial, storm water) for Membrane nanotechnology.
-Advantage and disadvantage of the Membrane nanotechnology
Methodology in purifying contaminated wastewater by using nanotechnology.
As water undergoes purification, the only resistance caused (Rm) is the membrane material. The resultant flux refers to the clean water-flux. The formation of cake on the membrane (Rc; particles) is as a result of particle accumulation through water filtration with some degree of water suspension (Chang, Le Clech, Jefferson & Judd, 2002). Pore plugging (Rpb; scaling) is a term used to describe a scenario when particles block the pores (Khalili-Garakani, Mehrnia, Mostoufi, & Sarrafzadeh, 2011). As a result of adsorption in or on the membrane, a resistance referred to as biofouling (Ra) is realized. Therefore total resistance can be expressed as below;
Rtotal= Rpb+ Ra+ Rc+ Rm
Where Rpb is the pore plugging, Ra is the adsorption biofouling, Rc is the cake layer, and Rm is the membrane resistance.
The theory that governs the transportation of fluids through membrane has an expression below;
NA = ρAv – DAB∇ρA
Where NA is the mass flux of A component through the membrane which is mass per time per area, ρA is the mass density of A component, v is the average mass velocity of the fluid via the membrane. DAB is the effective diffusion coefficient of A component in the membrane and finally, ∇ρA is the mass density gradient.
In other words, the trans-membrane flux for each element could expressly translate as;
Flux = Force × concentration × mobility (Laganà, Barbieri, & Drioli, 2000).
In focusing on the pressure drove membrane nanotechnology, four techniques are employable namely, in the order of decreasing permeability: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) (Carns, 2005).
The following are the requirements for the membrane system; the first one is the pretreatment which entails secondary treatment followed by chemical coagulation, sedimentation as well as filtration. An addition of chemicals to prevent soluble salts or organic materials from fouling the membrane gets undertaken at pretreatment. The second requirement is pumping which aims at raising the pressure to a level of 1 to 15 psi and maintain sufficient velocity across the membrane. The third element is a cartridge filter of about 5 microns and larger in size. This filter offers protection against any upset in the pretreatment step. The membranes are also needed since they lie at the heart of the treatment system. The last requirement is the post-treatment which may include a de-gasifier for the removal of hydrogen sulfide and carbon dioxide, and an addition of lime to prevent the corrosion of the piping system (Humplik, Lee, O’hern, Fellman, Baig, Hassan & Wang, 2011).
Spiral- wound element, as a configuration of the membrane technology, usually range from 5 to 20 cm in diameter and 25 to 125 cm in length. It consists of a two flat membrane sheet kept apart by a thin, mesh-like spacer and sealed on the tree sides. The fourth side fixed on a perforated plastic center tube to collect product water. The membranes are therefore rolled up around the tube in a spiral form. The feedwater gets pumped through the layers, and the product water goes through the membranes following the spiral configuration up to the central perforated tube. Water that fails to penetrate the membrane exits the element in the form of a concentrate. This type of configuration is useful for MF, UF and RO (Xu, Peng, Tang, Fu & Nie, 2010).
The result for the three types of wastewater is presented in the table below
Table 1: Comparison of the waste water types
Waste water type Storm water Agriculture Industrial
Retained compounds Very small suspended particles, most bacteria and some colloids, Organics > 1000 MW, pyrogens, viruses, bacteria, colloids
Organics > 300 MW, THM precursors, some dissolved solids,
Divalent > monovalent.
Operating pressure, psi 1 to 15 1 to 15 1 to 15
Storm waters were chosen over the other waste waters since it exhibits a higher recovery rate as a percentage of the products recovered from the feed-water. From the table 1 above, it is evident that the retained compounds for storm water at the same operating pressure results in low suspended particles, some colloids, and bacteria in comparison to the rest.
Some of the advantages of membrane nanotechnology include; the reduction of many treatment chemicals, elimination of residual disposal and handling, removal of bacteria, viruses, and Cryptosporidium (Qu, Alvarez, P, & Li, 2013). The decrease of labor requirement due to ease of automation, small space requirement of about 90 to 95% less the conventional plants, and finally is the removal of natural organic matter are the additional advantages.
On the other hand, the following are the disadvantages of the membrane nanotechnology; recovery rate may be less that 100%, it requires disposal of concentrate, it works best on low solid surface water or ground water. It also lacks a low-cost and reliable method of monitoring low-pressure membrane process integrity (Pendergast, M & Hoek, 2011). The gradual decline in flux rate over time and use of more electricity for high power systems are additional disadvantages.
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Xu, Y., Peng, X., Tang, C. Y., Fu, Q. S., & Nie, S. (2010). Effect of draw solution concentration and operating conditions on forward osmosis and pressure retarded osmosis performance in a spiral wound module. Journal of Membrane Science, 348(1), 298-309.
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