Technorati Profile

Application of taguchi method in the optimization of wastewater treatment using spiral-wound reverse osmosis element

A pilot study for wastewater treatment in Exir pharmaceutical Co. (Borojerd, Iran) was conducted using a RO system with the capacity of 14.38 m3/d. A Filmtec TW30HP-4641 RO element (polyamide, thin-film composite) was used in this study. The pilot plant consists of two spiral-wound RO elements. The RO train was configured in series. Trial runs were conducted at different operating conditions including pressures, temperature and concentration.
The pilot results showed that flux of water containing nitrate, nitrite, phosphate and sulfite was about 58 l/m2 h. Taguchi method was employed for flux optimization. Analysis of the experiments indicated that the temperature of feed solution and transmembrane pressure have the most contribution in water flux. The flux was improved to 69 l/m2 h by setting the control factors according to the Taguchi method. The technique showed that concentration of feed solution has the highest contribution in rejection of a solution containing nitrate, nitrite, sulfite and phosphate. After setting the control factor according to the Taguchi method rejection was enhanced to 99.9% for this case study.

Read Full Text at
http://www.geocities.com/castro_che2000/water15.pdf

A comparative study of platinised titanium and niobe/synthetic diamond as anodes in the electrochemical treatment of textile wastewater

An electrochemical method for wastewater treatment in the textile industry based on an electrolysis process is discussed in this paper. In a laboratory scale electrochemical cell made of Plexiglas, carbon fleece is used as a cathode while two materials such as niobe/synthetic diamond (Nb/D) and platinised titanium (Pt/Ti) are tested as anodes. Synthetic samples, containing specific amounts of four reactive azodyes and electrolytes diluted in tap water, are treated using Pt/Ti. Parameters affecting the procedure such as the nature and the quantity of the electrolyte, the pH and the applied potential are researched and discussed. Temperature, current and pH are measured on line. Samples are taken at appropriate intervals during the process and UV–vis spectra are received. Real wastewater samples are treated with no further addition of electrolytes. Biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total organic carbon (TOC), energy consumption and efficiency of the anodes, as well as the chloride (Cl−) and hypochlorite (ClO−) concentrations, are measured using both Pt/Ti and Nb/D as anodes, comparing their efficiencies. Color removal up to 90% is achieved resulting in practically colorless final wastewater, while BOD5, COD and TOC are decreased up to 49.6%, 93.3% and 52.4%, respectively, using Nb/D.

Read Full Text at

http://www.geocities.com/castro_che2000/water14.pdf

Chemical oxidation with hydrogen peroxide for domestic wastewater treatment

The recycling of domestic wastewater is an effective means of coping with the water shortage in Tunisia. After hydrogen peroxide oxidation, the refractory organic substances in wastewater were decomposed. COD, offensive odor and foaminess in the effluents were reduced with increasing dose. Hydrogen peroxide oxidizes both organic and inorganic pollutants which contribute to BOD and COD. The Oxidation of sulfides into sulfates by H2O2 may be applied directly to aqueous wastes containing these odorants. Inactivation efficiencies of bacteria in the secondary effluents by H2O2 oxidation was investigated. The number of total coliforms exponentially decreased with increasing dose and fell to low levels at the dose of 2.5 ml/L.

Read full text at

http://www.geocities.com/castro_che2000/water12.pdf

Biological activated carbon treatment of industrial wastewater in stirred tank reactors

The industrial effluent under investigation was the simulated aqueous discharge from a carpet printing plant in Northern Ireland, comprising of a ternary solution of acid dyes. This effluent was investigated using the biological activated carbon (BAC) process for colour removal in an aerobic stirred tank reactor configuration. The following systems were experimentally investigated: bacteria immobilised on granular activated carbon (GAC); bacteria immobilised on sand particles; GAC (with no biological activity) and free bacterial cells. The bacterium used in this study was Pseudomonas putida (NCIMB 9776) and the activated carbon was Filtrasorb 400. Ternary dye concentrations were determined by spectrophotometry. Results indicated that BAC system outperformed the combination conventional GAC and biological water treatment processes. For biodegradable anthraquinone dyes, this enhanced colour removal was due to higher dye utilisation rates caused by the increase in substrate concentration at the granule surface found in BAC systems. For non-biodegradable azo dyes, increased biosorption was found in BAC systems compared to conventional immobilised systems.

read full text here...
http://www.geocities.com/castro_che2000/water12.pdf

Process analysis for treatment of industrial plating wastewater: simulation and control approach

One of the better options to remove chromium VI (Cr(VI)) from wastewaters is the electrochemical continuous reactor. This process can be used to clean rinse waters from the plating industry. A mathematical model of the reactor is developed by classical application of mass balances for Cr(VI) and Fe, both corroborated in a bench scale electrochemical reactor. The reactor model is employed as the real process where the proposed controller is implemented. For the controller synthesis a reduced order uncertainty estimator is employed to infer the reaction rate, which is assumed unknown and an input/output linearising controller is designed, using the input flow to the reactor as control input and the Cr(VI) concentration in the wastewater as controlled variable. This procedure yields a nonlinear PI controller; where new tuning rules are given. Stability analysis of the closed loop behaviour of the reactor under the proposed methodology is done via mathematical analysis of the equations that describe the dynamic behaviour of the estimation and regulation errors. The performance of the controlled reactor is illustrated with numerical simulations.

read full text here...
http://www.geocities.com/castro_che2000/water11.pdf

Decolourization and removal of phenolic compounds from olive mill wastewater by electrocoagulation

The effective performance of electrocoagulation (EC) technique in the treatment of olive mill wastewater (OMW) has been investigated using sacrificial aluminium electrodes. The optimum working pH was found to be in the range 4–6, allowing OMW to be treated directly without pH adjustment. In addition, it is found that an increase in the current enhanced the speed of the treatment significantly. However, simultaneous increase of electrode and energy consumption was observed. The optimum current density allowing the quickest treatment with a low cost was found to be 75 mA cm−2. Therefore, a current density of 75 mA cm−2 was selected as an optimum that allows fast and low cost treatment.
Application of electrocoagulation procedure permitted high removal efficiencies of pollutants with both fresh and stored olive mill wastewater. The process produces a removal capacity of 76% of COD, 91% of polyphenols and 95% of dark colour, just after 25 min. The electrode consumption was found to be 2.11 kg m−3 of treated OMW. The results show that electrocoagulation could be considered as an effective alternative solution for the treatment of OMW or may be combined with a classical biological process to achieve a high quality effluent water.

read full text here...
http://www.geocities.com/castro_che2000/water10.pdf

Study of different membrane spargers used in waste water treatment: characterisation and performance

In urban waste water treatment, a novel gas sparger based on flexible rubber membrane has been used for the last 10 years. The objective of this present work is to compare two flexible membranes (the new membrane and the old membrane provided by ONDEO-DEGREMONT group) used in waste water treatment. For this purpose, the different membrane properties (hole diameter, pressure drop, critical pressure, deflection at the centerline and elasticity) have been characterized. The bubble generation at the membranes with a single orifice and with four orifices have been studied and their performances have been compared in terms of interfacial area and power consumption. From the experimental and theoretical approach, the new membrane is less elastic (or more rigid) than the old membrane. The bubble diameters generated from the new membrane remain constant with the gas velocity through the orifice, whereas they increase logarithmically for the old membrane. The inverse behaviours are observed in terms of the bubble formation frequency. Moreover, the bubbles generated from the new membrane have significantly larger sizes and lower formation frequencies than those obtained with the old one. From these results, it can be noted that the new membrane has a behaviour comparable to a rigid orifice. No coalescence phenomenon at the bubble formation is observed from the new and the old membranes with four orifices. The interfacial area and the power consumption are evaluated and show slight differences between the interfacial area provided by the old and the new membranes for one value of power consumption.


read full text here....
http://www.geocities.com/castro_che2000/water9.pdf

Removal of methyl orange dye and Na2SO4 salt from synthetic waste water using reverse osmosis

The efficiency of reverse osmosis (RO) membranes used for treatment of colored water effluents can be affected by the presence of both salt and dyes. Concentration polarization of each of the dye and the salt and the possibility of a dynamic membrane formed by the concentrated dye can affect the performance of the RO membrane. The objective of the current work was to study the effect of varying the Na2SO4 salt and methyl orange (MO) dye concentrations on the performance of a spiral wound polyamide membrane. The work also involved the development of a theoretical model based on the solution diffusion (SD) mass transport theory that takes into consideration a pressure dependent dynamic membrane resistance as well as both salt and dye concentration polarizations. Control tests were performed using distilled water, dye/water and salt/water feeds to determine the parameters for the model. The experimental results showed that increasing the dye concentration from 500 to 1000 ppm resulted in a decrease in the salt rejection at all of the operating pressures and for both feed salt concentrations of 5000 and 10,000 ppm. Increasing the salt concentration from 5000 to 10,000 ppm resulted in a slight decrease in the percent dye removal. The model’s results agreed well with these general trends.

Read full text at
http://www.geocities.com/castro_che2000/water8.pdf

Multifunctional system for treatment of wastewaters from adhesive-producing industries: separation of solids and oxidation of dissolved pollutants usi

To eliminate non-biodegradable organic compounds from wastewater application of semiconductor photocatalysis has been done. Experiments have been performed on immobilizing the photocatalyst titanium dioxide in an organic PAN microfiltration membrane and illuminated by UV-A light in order to improve oxidation performance and avoid particle separation. The organic pollutants are oxidized by in situ-produced hydroxyl radicals or directly by the catalyst. The membrane causes a convective flow of the pollutant towards the catalyst. The separation properties of the membrane can be used in a multifunctional way to extract remaining solid particles. A module containing membranes and a UV light source was developed. 4-Chlorophenol was completely mineralized at a high reaction rate. A two-step process has been developed for the clarification of highly polluted waste waters from adhesive-producing plants. First, the suspended solids which reach up to 10% of the mass stream are precipitated, flocculated and separated by means of a decanting centrifuge and flotation. Then the photocatalytic process was applied on the dissolved organic contents.

read full text at

http://www.geocities.com/castro_che2000/water7.pdf

A two-scale PBM for modeling turbulent flocculation in water treatment processes

A population balance model (PBM) that incorporates two scales of turbulent motion in the breakup frequency function has been presented. The breakup frequency function is designed such that particles smaller than the impeller-region Kolmogoroff microscale will erode according to a critical velocity related to the local energy dissipation rate. Particles larger than the impeller-region Kolmogoroff microscale will fracture according to a critical velocity related to the impeller tip speed. The two-scale model was found to better predict the experimental steady-state particle size distribution in 5, 28, and 560 l tank sizes and with a Rushton turbine and A310 fluid foil impellers. The two-scale PBM was also used to investigate the most appropriate scale-up law for drinking water flocculation processes. In addition, the impact of higher tank average energy dissipation rate, primary particle concentration, and coagulant concentration on the volume mean particle size with increasing tank size and different impeller types was also presented.

read full text at

http://www.geocities.com/castro_che2000/water6.pdf

Modelling and design of thin-film slurry photocatalytic reactors for water purification

Photocatalytic oxidation processes are highly effective clean technologies for the degradation and mineralization of a wide variety of priority pollutants in water and wastewater. However, the application of heterogeneous photocatalysis for wastewater treatment on an industrial scale has been impeded by a lack of mathematical models that can be readily applied to reactor design and scale-up. As a results current photocatalytic reactors in research and development have been designed by empirical or semi-empirical methods only.
In this paper, a simple and generic mathematical model for steady-state, continuous flow, thin-film, slurry (TFS) photocatalytic reactors for water purification using solar and UV lamps is presented. The model developed is applicable to TFS flat plate and annular photoreactors of (a) falling film design or (b) double-skin design, operating with three ideal flow conditions: (1) falling film laminar flow, (2) plug flow and (3) slit flow. The model is expressed in dimensionless form and scale-up of TFS photocatalytic reactors can be carried out by dimensional analysis. In addition, the model parameters can be estimated easily from real systems and model solutions can be obtained with little computational effort.
Comparison of a number of ideal flow systems shows that both falling film laminar flow and plug flow operation modes give higher performance than the slit flow system. Slit flow operation mode results in lower conversions due to the non-correspondence of fluid-residence time and the transversal radiation field. The effect of optical thickness, on reactor performance and the evolution of radial profiles of a model pollutant with photoreactor length are presented for each of the operation modes. The falling film laminar flow system was found to be more efficient than the plug flow system when the reactor conversion is above 80%. For lower reactor conversion the plug flow system was found to be marginally more efficient than the falling film laminar flow system. A methodology for the optimal geometrical design of a highly efficient configuration of TFS photocatalytic reactors is also presented. The mathematical models presented may be used as a tool for the design, scale-up and optimization of these types of photocatalytic reactors.

read full text at

http://www.geocities.com/castro_che2000/water5.pdf

High strength wastewater treatment in a jet loop membrane bioreactor: kinetics and performance evaluation

Treatment of wastewater containing high organic matter was investigated by means of a jet loop bioreactor combined with a membrane process. Volume of jet loop bioreactor and area of membrane filtration unit were 23 l and 155 cm2 respectively. It was found that jet loop reactor had high mass transfer coefficient (KLa) varying from 58.8 to 486 h-1 depending on the water flow rate (i.e. power input) and air flow rate. Oxygen transfer efficiency and oxygenation capacity of the reactor varied from 12 to 22.5% and from 0.2 to 1.8 , respectively. The efficiency of jet loop membrane bioreactor was found to be approximately 97% for a volumetric organic load of 2– over a period of 10 weeks. The reactor was not disturbed from the organic loads up to , but the treatment efficiency decreased to about 60% at higher organic loads. This decrease was due to insufficient oxygen transfer rate. The relationship between the effluent substrate concentration and the specific oxygen uptake rate (SOUR) values was determined. Applied food/microorganism (F/M) ratio was varied between 2.5 and . Critical sludge age of the system () was evaluated to be 7.2 h. Sludge with unsatisfactory settling characteristics formed at high F/M values under turbulent conditions. Therefore, membrane process was used for solid–liquid separation and effluent solid concentration was approximately zero. Specific cake resistances (α) changed with F/M ratio. It was found that permeate fluxes were significantly effected with F/M ratio much more than mixed liquor suspended solids (MLSS). Average flux was for pore sized cellulose acetate membrane. It was concluded that the jet loop membrane bioreactor has distinctive advantages such as the ability to treat high strength wastewater, low area requirements and easy operation.

read full text at

http://www.geocities.com/castro_che2000/water4.pdf

Model for predicting the performance of membrane bioadsorber reactor process in water treatment applications

This research focuses on the development of a mathematical model for performance prediction/simulation of the membrane bioadsorber reactor (MBR) process. The MBR process integrates biodegradation, adsorption and membrane filtration, for water or wastewater treatment and water reclamation. The model sub-processes include the following phenomenological aspects: (a) biological reaction in bulk liquid solution, (b) film transfer from bulk liquid phase to the biofilm, (c) diffusion with biological reaction inside biofilm, (d) adsorption equilibrium at the biofilm–adsorbent interface, and (e) diffusion within the adsorbent (powder activated carbon) particles. The model exhibited good simulative capability for three model organic compounds, namely, phenol, para-nitrophenol, and toluene, chosen based on their varying adsorption and biodegradation characteristics. A phenomenological approach was employed to examine the relative contributions of adsorption and biodegradation to contaminant removal, and to obtain insights into adsorbent bioregeneration. Therefore, simulation studies were conducted under three different scenarios: (a) adsorption and biodegradation in biofilm and liquid phase suspension are operative, conforming to the assumptions of the generalized model; (b) biodegradation is operative in biofilm as well as liquid phase suspension, but adsorption is absent; and (c) adsorption alone is operative without biodegradation. Sensitivity studies were preformed to investigate the dependence of process dynamics on model parameters pertaining to adsorption equilibrium and kinetics, liquid film transport, biofilm diffusion, biochemical reaction kinetics, influent concentration, and reactor flow conditions.

Read full text at

http://www.geocities.com/castro_che2000/water3.pdf

Modeling and scale-up simulation of U-tube ozone oxidation reactor for treating drinking water

In the present study, we developed a novel simulation model of the U-tube reactor for treating drinking water, which is composed of a coaxial inner tube serving as an efficient concurrent down-flow ozone dissolver and an outer column carrying out reactions between ozone and organic substances including odorous materials (2-methylisoborneol: 2-MIB) dissolved in the raw water. We assume that the U-tube is composed of a plug flow section (inner tube) followed by a tanks-in-series section (outer bubble column) and take into account the effect of the hydrostatic pressurization on the flow and absorption equilibrium for the gaseous components including ozone and other inactive species in developing the mass balance models. An algorithm is constructed of the differential multiple mass balance equations for the inner tube sections and multiple difference mass balance equations in the series tanks in the outer column section to enable the scale-up from a pilot plant to a full-scale plant. The gas holdup and gas–liquid mass transfer coefficient were measured in a model reactor and correlated for the use of the simulation calculation. Available literature data and correlations on the rates of reactions between ozone and organic substances including odorous material 2-MIB, gas–liquid equilibrium for active and inactive gases and axial fluid mixing properties are also incorporated in the simulation calculation. The simulation results well explained the available data of the ozone absorption efficiency and the removal efficiency of the odorous material in a pilot U-tube reactor. The simulation procedure was also successfully extended to verify the performance of a full-scale U-tube reactor. It is shown that the ozone absorption is practically a single function of the gas/liquid ratio while the removal efficiency of the odorous material is a single function of the ozone dose for a specified U-tube configuration.

Read full text at

http://www.geocities.com/castro_che2000/water2.pdf

Dewatering behaviour of water treatment sludges associated with contaminated site remediation in Antarctica

Sludge reduction and dewatering is an important aspect of water and waste water treatment. This is especially true in the case of Australia's Antarctic contaminated site remediation program, where the reduction in volume of wastes to be returned to Australia can lead to significant transport and handling cost savings. The dewatering characterisation of water treatment sludges from an Antarctic contaminated site was conducted using a theory of suspension dewatering developed by Buscall, Landman and White. This theory uses fundamental material properties of compressibility and permeability to determine the diffusivity of a suspension. Diffusivity is a useful property that can be used to directly compare the dewaterability of various sludges. In this investigation, several water treatment sludges were collected and characterised in the field to determine the impact of temperature and additives on compressibility, permeability and diffusivity. The Antarctic sludges were found to be less compressible and less permeable than materials such as mineral suspensions and alum water treatment sludges. Compressibility was found to decrease with the addition of powdered coagulation aids such as bentonite and chitosan.

Read full text at

http://www.geocities.com/castro_che2000/1.pdf