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DECOLOURIZATION OF A PAPERBOARD FACTORY EFFLUENT IN KENYA USING ELCAS METHOD
O. D. Oricho1, L. Etiégni2 , B. O. Orori1, K. Ofosu-Asiedu2, K. Senelwa1, and F. G. Mburu1
Keywords: colour removal; electro-coagulation; waste paper; wood ash; wastewater,
Pollutants can be in solid, liquid or gaseous forms. The liquid pollutants can be industrial effluent or domestic wastes. Industrial effluents have a wider range of characteristics than domestic wastes and are more likely to contain toxic and non-biodegradable compounds (Porteaus3). The extent of the effect of effluent pollution to the environment is measured through bioassays and the determination of its chemical composition, and any deviation from pollution discharge standards indicates a given degree of pollution (Raju4, UNEP5).
Since water is increasingly a scarce resource, planners are forced to consider other alternative sources of water, which might be used economically, and effectively to promote further economic development. Whenever good quality water is scarce, water of marginal quality will have to be considered for use (Henry 6). Recycling of water is considered a better option and undesired water pollutants have to be removed before the water is reused. There are several parameters of water testing for its suitability for papermaking, but colour is one of the most difficult and expensive to remove (Ikeheta & Buchanan 7). Colour removal methods include: adsorption, soil media, coagulation, electrochemical, ultraviolet irradiation, and membrane-based technology such as ultrafiltration (Prasad and Joyce8).
Highlands Paper mill (HPM) in Kenya uses about 3000 tonnes of waste paper per annum and produces less than 6 tonnes of paperboard per day. The mill uses a manually operated process which limits its effectiveness and efficiency (Highlands Paper Mill Annual Report 9). Water forms an important part of the daily's factory operation. It is used in wastepaper pulping, paperboard forming and general cleaning. The factory records estimates its consumption to be slightly more than 15 m3 per day. The water is sourced from municipal tap water. Due to the high cost of the water, the company recycles its effluent for an average period of three weeks. The recycled water is normally passed through a treatment stage where it is screened and left in a tank for suspended solids to settle out before it is pumped back for reuse in the pulping and for felt washing. However, some solids still pass through the screen. Backwater colour is a major problem, which mainly affects the aesthetic value of the final manufactured product forcing the company to dye their products. Besides, wastewater from the factory must also be treated before discharge to conform to the effluent discharge standards and also make mill's production process environmentally friendly. Therefore there was a need to find the most economical and appropriate way of reducing these effluent parameters and also improve the quality of the backwater. In this study, coagulation using alum and electrochemical treatment combined with wood ash leachate (ELCAS) were tested on Highland Paper Mill Effluent in Eldoret, Kenya in order to determine the most cost effective method of colour reduction (Etiégni et al. 10; Orori et al. 11).
2. MATERIALS AND METHODS
The electrochemical with wood ash leachate (ELCAS) experiments were carried out using the set up of electrodes shown below (see Figure 2.1). Three sacrificial iron electrodes were placed parallel to one another and kept 5 mm apart using a non-conducting material. For each run, a sample of 1000 ml wastewater was placed into a beaker with a magnetic stirrer and the electrodes immersed 4/5 deep into the effluent sample to achieve surface area coverage of 75.5 m2/m3 of wastewater. Electrodes were rinsed in a bath of 8% sulphuric acid after every run to avoid fouling.
Wood ash leaching was carried out for 12 hours using distilled water at room temperature. Fifty (50) g, 100g and 150g of ash were leached in one litre of distilled water to dissolve any chemicals in it. Different quantities of wood ash were added in distilled water in order to obtain different concentration of the leachate to be used as supporting electrolyte in the electro-coagulation experiments. After that, different volumes of each leachate (10, 20, 30, 40 and 50 ml) were added to one litre of the wastewater for the treatment. Each run was first carried out at fixed time interval of 3 minutes in order to determine the best concentration of ash required based on the effluent parameters recorded, mainly pH. The final effluent pH was chosen because electro-coagulation with wood ash leachate in other studies tend to yield high pH, making the treated wastewater either unfit for re-use or discharge into a river (Orori et al.11)
Standard jar test method was used to determine the best molar concentration for colour removal with alum. The alum jar test experiment was carried out as follows: the pH of six wastewater samples from HPM was first adjusted to preselected values (pH = 5.0, 5.5, 6.0, 6.5, 7.0, 7.5). An arbitrary equal amount of alum was added to each sample under conditions of rapid mixing. After a short period (3 minutes) during which the coagulation reactions and the initial particle aggregation occurred, the mixing was slowed for about 2 minutes and particle growth through flocculation began. After mixing was stopped, the particles in each wastewater sample settled and the turbidity of the supernatant liquor was measured using a Turbidity meter. The minimum turbidity value was found at pH = 5.5. The experiment was then repeated using a constant pH = 5.5 and different dosages of alum to determine the best molar concentration of alum. Using this best molar alum concentration, HPM effluent colour removal was carried out to determine the amount of alum required to reach different colour levels of treated effluents. The amount of alum needed for a colour of 5oH in the final effluent was determined and its cost compared to the amount wood ash and electric power necessary to achieve the same 5oH colour level in HPM effluent.
Using the wood ash best concentration, the time for complete colour removal was determined by varying the time interval. The time was then used to calculate power required to completely remove colour (see Equation 1).
Power (Watts. hr) = Current (I) × Potential Difference (V)×Time (hr)….…………… (1)
Chemical analysis of the raw and treated paperboard mill effluent was carried out for quality assessment using Atomic Absorption Spectrophotometer (AAS). Data obtained was subjected to analysis of variance, using Statistical Package for Social Scientists (SPSS) version 12.01 and wherever necessary treatment means were separated using Duncan method.
3. RESULTS AND DISCUSSION
In the first treatment where fixed time interval of 3 minutes was used, electro-coagulation without supporting electrolyte had higher values of TS, TDS and COD (see Table 3.3, Table 3.4 and Table 3.5). The reduction of solids was probably due to the fact that wood ash contains significant amount of CaO that acted as a coagulant during the experiment (Etiégni & Campbell15). Wastewater parameters from treatments using different leachates were significantly different (P≤0.05). Fifty (50) ml of leached solution of wood ash gave the best reduction in TS, TDS, and COD of the treated wastewater samples.
During electrochemical coagulation process, there was a significant difference in all the parameters (TS, TDS, COD and pH) using supporting electrolytes made from 50g and 150 g of wood ash dissolved in one liter of distilled water (P≤0.05). However, there was no significance difference between 100g and 150g of wood ash dissolved in one litre of distilled water for all the parameters determined (P≤0 .05). The values of pH for the solutions of 100 g (pH= 9.71) and 150 g (pH=11.02) of ash both of 50 ml leachate were significantly different (P≤0.05). The leachate from 100g of wood ash, which translates to 5kg/m3 gave the most appropriate volume of supporting electrolyte for use in the electro-coagulation if one considered the final effluent discharge standards.
With the best concentration of 5 kg/m3 and time intervals of between 0-6 minutes, the colour levels of the treated HPM effluent is shown below (see Figure 3.1). The mean colour values of each time interval were significantly different and the 6-minute time interval gave the best colour level required (5oH). Chemical coagulation with alum using standard Jar test gave 0.1 M as the best concentration of alum to be used to achieve the lowest turbidity level. With this concentration, different dosages of alum were used to determine the required 5oH colour level (see Figure 3.2). The best alum quantity was found to be 12 ml since it gave the desired colour 5oH.
TS, TDS and TSS of the treated HPM effluent using alum and ELCAS were above the required standards for effluent discharge by the Eldoret Municipality (see Table 3.6). Moreover ELCAS yielded a net increase on the final treated pH. However research work done elsewhere has shown that ELCAS followed by simple aeration or extended settling can substantially reduce the pH and other final effluent parameters (Orori et al.11; Etiégni et al.16). Both alum and ELCAS reduced the colour of the effluent by 99.8%. In addition, ELCAS proved more effective in reducing COD by 67% compared to alum (60%) and the difference was statistically significant. The effective decolourization of the effluent could allow the factory to reuse its treated wastewater for the manufacture of paperboard without the use of dyes and this could result in substantial savings.
Cost estimates were then done on these samples from chemical coagulation using alum and ELCAS. The power consumption calculated by Equation 1 was based on the best time interval (6 minutes), the potential difference and electric current, which were 12V and 1.5A respectively. The average power consumed per treatment of one litre sample was 1.8 Wh. And since the factory usually consumes 15 m3 per day, this translated to 27 KWh. Kenya Power and Lighting Company (KPLC) under "Industrial consumers" rated the daily consumption to be US$3.5 for ELCAS (KPLC 17).
The quantity of solid alum that can be used at this particular concentration (0.1 M) for a treated effluent colour of 5oH was 0.7992g per liter of effluent. Taking the local market purchasing price to be US¢14.00 for 100 g of alum, the daily cost of effluent treatment of HPM (15 m3), was estimated at US$ 17.00. This is over four times the daily operation cost of ELCAS, which will be more cost effective than alum coagulation but achieve the same colour level required. A comparison of a few selected parameters of raw, alum treated and ELCAS treated is shown below (see Table 3.6).
Elemental analysis of ELCAS treated effluent using AAS showed a substantial decrease in minerals concentration except for K and Na (see Table 3.7). This indicates that the treated effluent can be used for pulping and general cleaning within the factory. Additionally, most of the mineral concentrations are within the specified international effluent discharge standards.
4. CONCLUSIONS AND RECOMMENDATIONS
Using ELCAS would not only reduce the total cost of treating its effluent but also save on purchasing dye for their products. Using alum alone requires a large quantity of the coagulant for higher colour reduction. However, this will increase the cost of paper production. It was recommended that, Highlands Paper Mill in Kenya should set up an electro-coagulation colour removal method with wood ash leachate. Further research should be carried out on other colour removal methods and be compared with the above results.
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