Electrocoagulation of pulp and paper industry effluent with SS-304 electrode has been carried out under varying process variable such as pH, current density, time and dose of electrolyte to find out the optimum conditions. Maximum reduction efficiency of Chemical Oxygen Demand (COD) 82% and color more than 99% from pulp and paper industry wastewater at the following conditions pH = 7, current density = 24.80 mA/cm 2 time = 40 min and dose of electrolytes = 1.0 g/L. Moreover, effects of electrolytes dosage on electricity consumption were observed and found to be that NaCl is better in comparison of Na 2SO 4 in respect of lower down the electricity consumption. But application of NaCl causes the formation of hazardous compounds as secondary pollutants within treated water. Therefore, Na 2SO 4 could be a potent replacement of NaCl to enhance the conductivity of paper industry effluent treated by EC process. The treated water has been compared with standard of Central Pollution control board (CPCB) and World Health organization, and found to be suitable for the reuse in irrigation.
The manufacturer of paper fundamentally relies upon the natural resources such as water, forest, agro-product, and fossil fuels (energy) for the production of paper [
Nowadays electrocoagulation (EC) method has intensively attracted the researchers from around the world due to its unique feature in comparison to the chemical and biological treatment facility. EC process exhibits environmental compatibility, proper setup, shorter reaction time, meager chemical requirement along with negligible generation of sludge [
At anode:
F e ( s ) → F e ( a q ) 2 + − 2 e − (1)
F e ( a q ) 2 + + 2 ( O H ) ( a q ) → F e ( O H ) 2 ( s ) (2)
At cathode:
2 H 2 O ( I ) + 2 e − → H 2 ( g ) + 2 O H ( a q ) − (3)
Overall reaction:
F e ( s ) + 2 H 2 O ( I ) → F e ( O H ) 2 ( s ) + H 2 ( g ) (4)
These Fe(OH)n metal ions behave as coagulant or destabilize the pollutants present in wastewater by charge neutralization and having a great potential to separate them by electro-flotation. In recent years, the EC process has usually been used for the separation of pollutants present in different types of water and wastewater [
The wastewater has been collected after primary treatment from nearby paper industry followed by immediate storage at temperature below than 4˚C. The analysis of the samples for several parameters such as pH, BOD3, COD TOC, color and TDS were performed as per standard method [
Treatment efficiency ( TE% ) = C 0 − C t / C 0 × 100 (5)
where,
TE = Treatment efficiency (%), C0 = Initial concentration of pollutants, Ct = concentration of pollutants after time (t).
Total Energy consumption ( kWh / m 3 ) = V I t Treated volume ( l ) (6)
where, V = Volume potential of electricity (V), I = Current (ampere), t = time of treatment (h) and l is the treated volume in liter [
S. No. | Parameters | Values |
---|---|---|
1 | pH | 7.65 |
2 | BOD (mg/L) | 176 |
3 | COD (mg/L) | 534 |
4 | BOD/COD | 0.32 |
5 | TOC (mg/L) | 209 |
6 | Color (Pt. Co. Units) | 1154 |
7 | TDS (mg/L) | 1858 |
8 | Conductivity (mS) | 3.32 |
The batch scale laboratory diagram of experimental assembly is depicted in
The electrode configuration and EC experiment details are depicted in
S. No. | Electrode characteristics | |
---|---|---|
1 | Material (anode and cathode) | SS-304 |
2 | Shape | Rectangular |
3 | Size (mm) | 40 × 70 |
4 | Number | 4 |
5 | Plate arrangement | Parallel |
6 | Connection mode | Monopolar |
7 | Effective area of electrode (mm2) | 504 |
Reactor characteristics | ||
8 | Make | Plastic |
9 | Mode | Batch |
10 | Volume (ml) | 250 |
11 | Used water volume (ml) | 250 |
12 | Electrode gap (mm) | 10 |
13 | Power supply | Direct current |
14 | Voltage range (V) | 1 - 12 |
15 | Current range (A) | 4 - 35 mA/cm2 |
consumption. During the EC treatment, direct current is used so that solar energy could be quite meaningful to dealing with the treatment of water and wastewater at laboratory and industrial scale. Since India is considered to be a tropical country and having vast solar energy potential, it could be more attractive option for the usage of EC process. Moreover, Photovoltaic cells produce the direct current which is directly used in EC process without any change making it an affordable alternative for the treatment of wastewater facilitated by EC process. Earlier reports have also asserted on the successful treatment of different types of industrial effluents by EC [
Pulp and paper industry effluent found to be intensively polluted in nature with heavy organic load in terms of COD and color. This study investigates the optimum conditions for EC on the basis of maximum COD and color removal by varying several variables such as pH (5.0 - 9.0), time (10 - 50 min), current density (4.96 - 34.72 mA/cm2) and electrolytes dose (0.5 - 2.0 g/L).
It has been extensively studied that the pH is one of the crucial parameter to govern the efficiency of EC method [
wastewater for its treatment. A sequence of experiment was conducted by varying the pH from pH 5.0 to pH 9.0, while other parameters like current density 5 mA/cm2, time 10 min and dose of electrolyte 0.5 g/L remained constant. This is clear from
Moreover, the EC method exhibits buffering effect which makes the EC process unique in terms of feasibility for wastewater treatment. Therefore, it is not required to maintain the pH of treated water before releasing it into water system. Additionally the treated water of either acidic or basic pH can cause several negative effects on receiving water bodies and entire ecosystem [
Various study described that current density is a major parameter which leads to the higher treatment efficiency and is also cost effective for the EC process [
Besides, it is also reported that bubbles density increases and their size decrease
by means of rising current density ensuing a larger upwards flux and more rapid removal of pollutants and sludge flotation [
The effect of treatment period was investigated to varying time intervals (10 - 50 min), pH, current density, dose of electrolyte fixed at 7, 24.80 mA/cm2 and 0.5 g/L, respectively to find out the reduction in COD and color in present effluent sample. At the beginning of the run, the solution was transparent which progressively becomes dark and after about 30 min it turns greenish as the reaction progress due to formation of Fe(OH)n(s). After about 10 min a significant reduction in color was observed (
removal of 81% in COD value was observed in 40 min time and after that the small changes occurred in value of COD and finally plot become constant.
Thereafter, no reduction was observed in the COD and color found to be in a nearly steady state. Therefore, 40 min is taken as the optimum time for the degradation of the organic matter in the present effluent sample [
The conductivity of solution plays a key role to boost the process efficiency and reduce the current density. Conductivity maintains the lower potential flowing in circuit during the treatment and reduced electricity energy consumption (EEC) [
The effect of variable concentrations of electrolytes (0.5 - 2.0 g/L) was observed on the removal of chemical oxygen demand and color and the EEC consumption. EC process was performed using current density of 24.80 mA/cm2, time 40 min and pH 7. As shown in
The existence of the sustaining electrolyte also cut down the EEC, as revealed in
and produced water soluble electrolignin, easily oxidizable chlorolignin and chlorophenolics compounds. Earlier researcher suggested that these compounds caused higher toxicity and disturbances in aquatic system [
The kinetics of electro-coagulation was studied in order to assist the rate of reaction during the process of oxidation. Paper industry wastewater contains a mixture of various compounds with differential reactivity. Therefore, it is quite difficult to perform a detailed analysis of individual compounds. To study such a complicated process, the rate of reaction was studied in terms of a combined parameter (i.e. COD).
The experimental data observed with time-dependent COD removal in the presence of Na2SO4 as electrolyte modeled by the assumption of first-order kinetics where the progressive disappearance of COD can be presented as the percentage COD removal is proportional to the pollutant concentration and the numbers of hydroxides [flocks] generated (
− d [ COD ] d t = k [ COD ] [ Fe ( OH ) 3 ] (7)
By the integration of equation (9) yields
log [ COD t ] [ COD 0 ] = − k t (8)
where COD0 refers the initial effluent COD and CODt refers the effluent COD at time t.
The reaction rate constant k, can be estimated from the plot log[CODt/COD0] versus electrolysis time. The experimental data fitted well to first order kinetics, as a straight line with an R2 value of 0.996 been critically examined.
Water shortage is a fundamental problem at present in various parts of world which is badly influencing a huge portion of the world population. With this reality, farming emerges as one of the high water demands, it consuming about 70% of worldwide freshwater. Besides, 28% - 56% of the worldwide irrigated cropland is situated in regions under high (40% to 80%) or very high (>80%) water pressure, in light of the proportion of water withdrawal over accessible water [
According to
Characteristics | Treated water | PL* (CPCB) | PL* (WHO) |
---|---|---|---|
pH | 7.25 | 5.5 - 9.0 | 6 - 9 |
BOD (mg/ L) | 52 | 100 | 200 |
COD (mg/ L) | 91 | NA | 500 |
TDS (mg/ L) | 1059 | NA | 1500 |
Color (Pt-Co. Units) | 6.93 | NA | NA |
Conductivity (mS) | 2.83 | NA | NA |
*PL = Permissible Limit.
The EC method provides inspiring results from the treatment of pulp and paper industry wastewater. The investigation shows that the EC method is a versatile process and has the potent removal efficiency towards the BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), Color, TOC (Total Organic Carbon) and TDS (Total dissolved solid) from pulp and paper industry effluent. The overall reduction in COD, Color, TOC and TDS was 82.00%, 99.4%, 79% and 43% respectively; biodegradability ratio enhanced up to 0.52 at pH = 7.00, current density = 25.20, time = 40 min and a dose of electrolyte 1 g/L with 100 rpm stirring speed. The analysis was repeated in triplicate and result showed the good repeatability in the error range of 2% - 5%. All the physiochemical parameters of EC treated water were found below the permissible limit prescribed by WHO (World Health Organization) and CPCB (Central pollution Control Board); thus, can be used as an alternative to reduce the fresh water input in agriculture fields. The pH of the treated water after EC treatment found to be within permissible limit of environmental standard, it is obtained near neutral pH. It is meaningful feature of EC method and not being needed neutralization process in comparison to conventional treatment.
The research grant for this study provided by the University Grant Commission, New Delhi, Government of India, is gratefully acknowledged.
The authors declare no conflicts of interest regarding the publication of this paper.
Kumar, D. and Sharma, C. (2019) Remediation of Pulp and Paper Industry Effluent Using Electrocoagulation Process. Journal of Water Resource and Protection, 11, 296-310. https://doi.org/10.4236/jwarp.2019.113017