Reduction Of Suspended Solids From Wastewater Biology Essay


In the wastewater, floc size and density significantly influence the performance of solid/liquid separation processes. Large and dense flocs may be preferable since they have high sedimentation velocities and are more easily dewatered. In this paper, a combined electrocoagulation (EC) technology and magnetic treatment was designed to enhance reduction of suspended solids from wastewater. The experiments carried out in this work were setup into continuous flow methods. The effects of important process variables such as current density and operating time on the suspended solids, chemical oxygen demand (COD), and turbidity removal efficiencies were explored. The artificial wastewater was made from powder milk with concentration 700 mg/L and acidic condition was employed. In this experiments, the monopolar iron (Fe) plate anodes and cathodes were employed as electrodes. DC current was verified between 0.8 and 1.4 A, and flowrate from 0.4 to 3.1 mL/s. Two permanent magnets with different strengths were used in this experiment, namely SmCo of 0.16T and AlNiCo of 0.08T. The results show that using combined magnet and EC process obtain result better than without magnet.

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Keywords: magnetic field, electrocoagulation, suspended solid removal, wastewater treatment.

1. Introduction

Among different physical and chemical methods of water and wastewater treatments; magnetic methods attract a special attention due to their ecological purity, safety, simplicity and less operating costs. Alteration of physical and chemical properties of water-dispersed systems in the mode of magnetic treatment imply a certain influence of magnetic field on the structure of water and aqueous solutions. Previous researches made by several scientific societies has discovered that magnetic field can improve technological characteristics of the water, i.e. better salt solubility, kinetic changes in salt crystallization and accelerated colloidal coagulation. Magnetic field is known to create the asymmetry of hydrated shells due to its effect on water molecules situated around the charged particles (colloid). Exposure to magnetic field would lead to higher electro-kinetic movement among the colloid. This definitely will help in attributing to a higher probability of attracting particles to cloak with one another. The theory of magnetic field impact on technological processes for water treatment falls into two main categories; crystallization at magnetic water preparation and impurity coagulation in water systems (Fadil Othman,, 2001).

The scientific explanation of magnetic water treatment has been the subject of investigation by British, Russian and American researchers. These studies involved the formation of scale and the methods for its prevention (Florenstano et. al., 1996). Magnetic treatment of water was first patented by Vermeiren in Belgium in 1945, and he is recognised as the discoverer of the fact that magnetic fields affect water. Magnetic treatment of water is an attractively simple approach by which the water to be treated flows through a magnetic field, and consequently changes some of its physicochemical properties.

Florenstano, et. al. (1996) concluded that there is only the mineral content i.e., TDS (Total Dissolved Solids) that builds up after water is contacted with magnetic fields. Faseur and Vanbrabant (1987) developed a continuous electromagnetic sedimentation tank in wastewater treatment to enhance settling velocity of the suspended particles. Another researcher, VanVelsen (1990), has also developed a very efficient magnet for wastewater treatment. Johan Sohaili, et. al. (2004) explained magnetic technology is potential to be a promising treatment process that can enhance the separation of suspended particles from the sewage.

Meanwhile, a host of very promising techniques based on electrochemical technology are being developed and existing ones improved that do not require chemical additions (Mollah et. al., 2001). These include electrocoagulation (EC), electroflotation (EF), electrodeposition (ED), electrooxidation (EO), and others (G. Chen, 2004). Even though one of these, electrocoagulation, has reached profitable commercialization, it has received very little scientific attention (Mollah et. al., 2001).

Treatment of wastewater by EC has been practiced for most of the 20th century with limited success (Daneshvar, 2004). Using electricity to treat water was first proposed in UK in 1889, and the application of electrolysis in mineral beneficiation was patented by Elmore in 1904 (G. Chen, 2004). The principle of EC was used to treat bilge water from ships was first patented in 1906 by A. E. Dietrich (Pathak, 2003).

EC has been used for the traetment of wastewater by various authors, and several differences were found in comparison to the chemical coagulation process. A literature survey indicates that EC is an efficient treatment process for different wastes, e.g. soluble oils, liquid from the food, textile industries, or cellulose and effluents from the paper industry (Carmona et al., 2006; Kumar et al., 2004; Calvo et al., 2003; Larue et al., 2003; Holt., et al. 2002). EC is an effective process for the destabilisation of finely dispersed particles by removing hydrocarbons, greases, suspended solids and heavy metals from different types of wastewater (Carmona et al., 2006; Kumar et al., 2004). According to Can (2006), EC has been proposed in recent years as an effective method to treat various wastewaters such as: landfill leachate, restaurant wastewater, salina wastewater, tar sand and oil shale wastewater, urban wastewater, laundry wastewater, nitrate and arsenic bearing wastewater, and chemical mechanical polishing wastewater.

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Alumunium or iron are usually used as electrodes and their cations are generated by dissolution of sacrificial anodes upon the application of a direct current (Carmona et al., 2006). Kobya et al. (2003) has been investigated EC technologies to treatment of textile wastewaters using iron and aluminum electrode materials. The results show that iron is superior to aluminum as sacrificial electrode material, from COD removal efficiency and energy consumption points.

In the preliminary research, the authors have investigated the effect of a combined magnetic field and EC with iron (Fe) bar electrodes in the batch experiment. The results shown that the SS and turbidity removal are as high as 91.4 % and 85.5 % with the combined process, while for EC process is as high as 88 % and 72.1 % (Ni’am et al., 2005).

In another research, Fadil et al., (2005) have investigated that the SS and turbidity removal are as high as 92.3 % and 81.25 % with the combined process, while for EC process is as high as 89.3 % and 75.16 %. These results obtained from batch experiment by a combined magnetic field and EC with iron (Fe) plate electrodes.

2. Experimental Details

This study to investigate the effect of magnet and EC process. The objective of the present study is to examine the feasibility of EC and magnetic field in treating wastewater, to determine the optimal operational conditions and to establish which iron hydroxide, formed during electrolysis be combined magnet. This research is mainly focused on the capability of magnetic field and EC technology to removal and increase the sedimentation of suspended solid through static processing methods.

Wastewater Characteristics

An artificial wastewater prepared from milk powder with concentration 700 mg/L (Table 1). The wastewater treated by using HCl 1 M and NaCl as a buffer, pH adjustment and electrolyte. Concentration of HCl in this fluid is 5 mL/L (0.5 %) and NaCl is 125 g/L. The current was adjusted to a desired value between 0.8 A and 1.4 A before the coagulation process was started.

Table 1. Characteristics of wastewater



Chemical oxygen demand COD (mg/L)


Total suspended solids TSS (mg/L)


Turbidity (NTU)


Initial pH


pH after adjusted by HCl


Experimental Procedures

The experiments carried out in this work were setup into single flow method. EC and the synthetic wastewater were performed in the reactor glass cell (volume 2000 mL). Fifteen monopolar iron plate electrodes were set-up as a baffle at distance of 14 mm and placed in the reactor (Figure 1).

The wastewater flows from reservoir (volume 6000 mL) through out the system is provided by means of a pump controlled and can be adjusted from zero to maximum 100 mL/s. In this research, the wastewater was circulated with a constant flowrate, verified between 0.4 and 3.1 mL/s. The laboratory experimental equipment was shown in Figure 2.

Two permanent magnets with different strengths were used in this experiment, namely SmCo of 0.16T and AlNiCo of 0.08T. All magnets are cubic-shape rare earth permanent magnet size (50 mm x 50 mm x 20 mm) and placed under reactor.

Figure 1. Detail of EC reactor

Figure 2. Experimental setup: (1) reservoir with mixing, (2) circulation pump, (3) flowrate meter, reactor, and (4) effluent & sample collecting

During each 5 minutes of treatment time, samples were collected and then filtered before being analyzed. The effect of relevant wastewater characteristic such as turbidity, COD, and SS removal efficiencies have been explored.

Analytical Method

The turbidity removal was measured from wastewater samples by HACH DR/4000 (HACH Method 10047). COD measurments were determined according to the Standard Methods for Examination of Water and Wastewater (APHA, 1992). The COD samples were analysed using UV-Vis HACH DR/4000 spectrophotometer (HACH Method 8000).

To measure total suspended solid (TSS), the wastewater samples were filtered through a standard GF/F glass fibre filter. The residu retained on the filter was dried in an oven at 1030C to 1050C until the weight of the filter no changes. The increase in weight of the filter represents the total suspended solids (APHA Method 2540 D).

The calculation of turbidity, COD and suspended solid removal efficiencies after electrocoagulation treatment were performed using this formula (Daneshvar, et al., 2006) :


Where C0 and C are concentrations of wastewater before and after electrocoagulation in NTU or mg/L, respectively.

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According to Matteson et al., (1995), the rate of change of wastewater concentration, such as turbidity, COD and suspended solid removal can be expressed as a first order kinetic model, as follows:


Where C, Co, and k2 are wastewater concentrations after EC, initial, and kinetic constant, respectively.

Hence, the loss of particles due to coagulation after treatment process (Johan, 2003), as follows:


Where k is kinetic constant ; a and b are constant values.

3. Results and Discussion

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4. Conclusions

The removal efficiencies of COD, turbidity and SS from wastewater were experimentally done by combination of magnet and electrocoagulation technique. The processes were measured in the single flow apparatus. Fifteen monopolar iron (Fe) plate electrodes were used in this work and were set-up as a baffle at distance of 14 mm in the reactor (volume 2000 mL). The cubic-shape rare earth permanent magnet were placed under reactor.

The results show that the COD removal efficiency is as high as 74.21% for EC process and 77.54% for combination with magnet. Turbidity removal in the process of wastewater was obtained 97.15% for EC process and 98.17% for combination with magnet. While SS removal efficiency is as high as 74.21% for EC process and 77.54% for combination with magnet.

The results suggest that using a combined magnet plus EC process obtain result better than without magnet. In general, the results explain that the magnetic field and EC technology can enhances removal of COD and turbidity from wastewater and improve its quality.