Reduction of COD and Color by Polymeric Coagulant (Chitosan)

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2. Material and Method

2.1. Material

The waste water is arranged from soap and detergent industry whose parameter is given in Table 1.

Table 1. Parameters of Wastewater

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Tables index

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2.2. Method

A 0.40dm³ of Food industry was taken in a 1.0 dm³ glass beaker, later on pH of the effluent was adjusted by adding aqueous NaOH (1 M) or H₂SO₄ (1 M) solution and mixed with glass rod for dispersion. The effluent and mixed for 5 min rapidly at 150 rpm, thereafter, slowly mixed for 30 min at 80 rpm. The effluent sample was then kept quiescent for 3 h. The supernatant liquor was taken and analysed for its COD value. These steps were repeated at different dosages of the coagulant. The settling and filtration characteristics of the slurry were also studied. Various parameters like COD, color, chlorine and protein were estimated as per standard parameter properties of various pollutants. The jar test apparatus is shown in Figure 2.

Figure 2. Jar test Apparatus

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3. Result and Discussion

3.1. Effect of pH

pH is play important role for ionic reaction , the pH of the sample will decided the how much coagulant are effective. To determine the effectiveness of chitosan on wastewater sample, pH from 2 to 10 at 20 mm coagulant was used, which is shown Figure 3. It was observed that at pH 2, 3, 4, 5, 6 (acidic nature) the COD 30%, 33%, 35%, 37%, 40% and color 33.5%, 38.9%, 44%, 46.5%, 49% reduction respectively. The maximum percentage of COD 55% and color 62% reduction shows at pH 7. At pH 8, 9 and 10 the 48%, 39%, 31% of COD and 57%, 48%, 35% of color reduction was observed. It is due to at higher pH, chemical functional groups associated with organic are ionized and results in increasing of negative charge. Whereas, at lower pH there is no ionization of any functional groups and organic removal is achieved mainly due to adsorption. Analysis of the species of aluminum in water indicates that polycationic polymers predominate below pH 6 and hydroxide precipitate dominates in the pH range 6 to 9 ^[11]. The mechanism of pollution removal, therefore, is different under the different pH condition.

Figure 3. Effect of pH on COD and color reduction at pHi = 8.8, massloading = 20 mm

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3.2. Effect of Mass Loading

The removal of pollution fractions was dependent upon treatment conditions such as applied coagulant dose, pH, etc. and that treatment conditions can be optimized based on the character of the organic matter present in the raw water ^[12]. To determine the effect of mass loading of chitosan at optimum pH 7 on wastewater sample is shown in Figure 4. The mass loading were varies from 20 mm to 60 mm. The maximum COD 83% and color 90% was found at 50 mm of chitosan. At initial when mass loading was 20 mm, 30 mm, 40 mm the COD 55%, 63%, 75% and color 62%, 71%, 78% was observed. Further increases in mass loading the COD 73% and color 76% were decreased. Over dosing of coagulant reduced the performance of treatment is due to restabilisation of colloids in effluent. In addition, coagulant overdosing will inevitably result in excessive sludge formation and increased chemicals and residuals management costs. In under dosing the amount of coagulant is not sufficient to neutralise the colloidal and optimum dosing mechanism of coagulation is relevant ^[13].

Figure 4. Effect of mass loading on COD and color at optimum pH=7

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3.3. Effect of Mixing

Rapid mixing after coagulation is an important design parameter. The coagulant must be uniformly mixed with the raw water. In case mixing is poor local under- and overdosing occurs, resulting in poor performance of the process. The parameter expressing mixing intensity is called the velocity gradient. To determine the effect of mixing 50, 80, 120, 150 and 200 rpm on wastewater sample was carried out at pH 7 and mass loading 50 mm is shown in Figure 5. It was observed that at initial 50 rpm, 80 rpm, 120 rpm the COD 58%, 65%, 72% and color reduction 63%, 70%, 81% respectively. The maximum COD and color reduction 83% and 90% was found at 150 rpm at the beginning 5 miniutes. Further increase in mixing speed 200 rpm decrease the COD 74% and color 79% reduction performance. Mixing intensity and time has significant effect on the mechanisms (e.g. sweep coagulation, sedimentation) involved in the following process of coagulation ^[14]. Between the hydrolysis of the coagulant in water and the development of large flocs, short-lived water soluble hydroxide complexes, metal hydroxide sols are formed, which also carry a positive charge ^[15]. The bond between the suspended solids to be removed and the polymeric sols and water soluble hydroxide complexes must be established within this short period. Rapid mixing of the coagulant will ensure rapid hydrolysis of the coagulant, contact between the sols and the suspended solids and will retard the development of large flocs which are inactive in destabilizing the dispersion and removing of pollutant.

Figure 5. Effect of mixing on COD and color at optimum pH=7 and mass loading =50mm

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3.4. Scanning Electron Microscope

The scanning electron microscope of wastewater before and after treatments was investigated which is shown Figure 6. It was found that before treatment without chitosan the sludge are look compact and rigid. After treatment with chitosan the sludge generated looks jelly type, it is due to structure of polymeric coagulant which are trapped the pollutant and bind up in like rope. Therefore the polymeric type’s coagulants have more effective than the other coagulant.

Figure 6. Scanning Electron Microscope picture (a) before treatment (b) after treatment with chitosan at pH =7 mass loading =50mm, mixing 150 rpm

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