Table 1 displayed the characterization results of the industrial wastewater samples compared with Egyptian Standards (ES); Law 92/201319 for drainage into marine environment and Nile branches, respectively. The results revealed that the pH ranged from 4.84 to 7.51, while TDS, EC and salinity ranged from 0.77 to 40.4 g/L, 1.29 to 78.4 ms/cm and 0.8 to 60.5 g/L, respectively. Moreover, oil and grease were in the range of 139 to 860 mg/L, and TSS ranged from 404 to 2733 mg/L. In addition, TP, TN and COD varied from 0.15-4.24 mg/L, 1.21-4.93 mg/L and 1320.3 to 1526.9 mg/L, respectively.
The results obtained in the present study were nearly matched with that obtained by Shamsan et al.2 who characterized food processing industry wastewater and found that pH value was 6.68, conductivity 3737 µs/cm, oil and grease 52.8 mg/L, BOD 1010 mg/L, COD 2820 mg/L, TSS 1050 mg/L, total nitrogen 154 mg/L ,total phosphorous 18 mg/L. Nidheesh et al.15 analyzed mixed industrial wastewater and reported that the values of pH, TSS, conductivity, BOD and COD were 7.8, 0.26 g/L, 13.31ms/cm, 239 mg/L., and 795 mg/L, respectively. In addition Xu et al.20 examined sugar processing industry wastewater and showed that pH, COD, TSS, conductivity values ranged between 6.8-7.2, 20-22 g/L, 480-520 mg/L, and 28-30 ms/cm, respectively. The characterization results of sugar processing industry wastewater were 3960 mg/L, 17.13 mg/L, 3580 µs/cm, and 1760 mg/L for COD, total phosphorous, conductivity, and TDS, respectively5. Moreover, Ahmed et al.21 investigated petrochemicals industry wastewater and found that pH was 7.4±0.5, TSS 53.4±48.5 mg/L, COD 532.9±528.6 mg/L, BOD 315.8±307.6 mg/L, total nitrogen 43.5±21.1 mg/L, and total Phosphorous was 7.0±4.1 mg/L.
Parameter
|
Unit
|
Food
|
Petrochemical
|
Sugar
|
Composite
|
Law92/2013
|
The Nile River to the Delta
|
Surface water
|
Damietta-Rashid Branch
|
Agriculture use
|
pH
|
-
|
4.84
|
6.96
|
7.51
|
7.11
|
6-9
|
6.5-8.5
|
6-9
|
6.5-8.5
|
TDS
|
g/L
|
0.78
|
40.4
|
2.39
|
19.2
|
1200
|
≤500
|
800
|
≤1000
|
EC
|
ms/cm
|
1.29
|
78.4
|
4.05
|
32.6
|
-
|
-
|
-
|
-
|
Salinity
|
g/L
|
0.8
|
60.5
|
1.8
|
19.3
|
-
|
-
|
-
|
-
|
BOD
|
mg/L
|
720.2
|
453.3
|
1070
|
937
|
30
|
≤6
|
20
|
≤30
|
COD
|
mg/L
|
1320.3
|
684.6
|
1526.9
|
1512
|
40
|
≤10
|
30
|
≤50
|
BOD/COD
|
-
|
0.55
|
0.66
|
0.70
|
0.62
|
-
|
-
|
-
|
≤3
|
O & G
|
mg/L
|
139
|
242
|
2235
|
860
|
5
|
≤0.1
|
5
|
3
|
TP
|
mg/L
|
1.54
|
0.15
|
4.24
|
3.9
|
1
|
≤2
|
1
|
-
|
TSS
|
mg/L
|
404
|
2733
|
1413
|
2110
|
30
|
-
|
30
|
15
|
TKN
|
mg/L
|
1.21
|
2.73
|
4.93
|
2.34
|
5
|
≤3.5
|
5
|
6.5-8.5
|
Table 1. The characterization of the industrial wastewater samples compared with Egyptian Standards (ES); Law 92/2013 for drainage into marine environment and Nile branches19, respectively.
The biodegradability of industrial wastewaters samples
The present study assessed the biodegradability of the composite and individual industrial wastewaters samples collected from industrial zone of New Damietta and Dakahlia City, Egypt within 28 days according to the classification given in Table 222.
Days
|
Biodegradability classification
|
within 5 days
|
easily biologically degradable
|
between 5 and 21 days
|
medium biologically degradable
|
between 21 and 25 days
|
moderately biologically degradable
|
within 28 days
|
maximum inert
|
Table 2. Biodegradability categorization
The biodegradation curves obtained for wastewaters samples under investigation are shown in Fig.2 showing that the plateau of petrochemical industry sample was formed after about 23 days (Fig.2 a) which implied moderately biologically degradable wastewater. While plateau region for food, beet sugar and mixed samples were about 19, 16 and 19 days, respectively (Fig.2 b, c, d) indicating medium biodegradability of the industrial wastewater.
Treatment of composite industrial wastewater sample
As the biodegradability results of the industrial wastewater samples ranged from medium to moderate, therefore the chemical treatment was adopted rather than biological technique and the composite sample was selected for subsequent treatment.
Advanced Oxidation Process (AOP) by Fenton’s Reaction
The Fenton process is a promising eco-friendly treatment technique applied to reduce and eject persistent organic pollutants from wastewater1. The pH is the key factor that greatly influences the efficiency of the process. The hydroxyl radicals were generated by reaction of H2O2 with iron without any iron precipitation. As shown in Fig.3a, the COD removal efficiency was 80.4%, 79%, 72%, 57% and 49.4% for the pH 3, 5, 7, 9, 11 respectively. Increasing pH value than 4 declined the efficiency of Fenton process because of iron oxyhydroxide production and iron deposition as ferric hydroxide (at pH 4) or ferrous hydroxide (at pH 7). At lower pH (2 or less) the instability of hydrogen peroxide was reported23, therefore, pH 3 was selected as an optimum pH for sample treatment in the subsequent work. The obtained results were similar to that recorded (89% COD) by Younes & Al-Sa`ed24 at pH 3, H2O2/Fe+2 (w/w ratio 10:1) and initial COD as15400-18200 mg/L for pretreatment of mixed wastewaters. Cheng et al.25 pretreated petrochemical wastewater at pH 3 and achieved 89.8% COD removal, BOD5/COD increased from 0.052 to 0.62 after 60 min, 120 mg/L Fe2+ and 500 mg/L H2O2.
The iron (Fe2+) concentration plays an effective role in the Fenton process as a catalyst because it influences the performance efficiency, reaction time, and sludge generation. It is clear that the COD removal percentage increased from 60.4 to 81.2% by increasing ferrous ion dose up to 1 mg/L then decreased (Fig.3b). This can be interpreted as the over dosage of Fe2+ not only increases economic costs and iron sludge generation, but also promotes the scavenging effect of OH radical6. Therefore, the optimum concentration of ferrous ion that enhances maximum removal of COD was adopted as 1 mg/L which more less than that applied (60 mg/L Fe+2) by Delil and Gören26 with maximum COD removal of 76% (initial COD 6200 mg/L) at pH 2, and 250 mg/L H2O2 in treatment of sugar industry wastewater; and 120 mg/L Fe+2 by Cheng et al.25 who used Fenton process to pretreat petrochemical wastewater and achieved 89.8% COD removal after 60 min and 500 mg/L H2O2.
The concentration of H2O2 affects the Fenton process as it is responsible for the production of the hydroxyl radical. The effect of hydrogen peroxide concentration (0.05- 0.5 g/L) on COD removal percentages was displayed (Fig.3c). It was observed that increasing H2O2 concentration stimulates pollutant decomposition. However, H2O2 overdose sweeps and converges the generated hydroxyl radicals23. Thus, 0.3 g/L H2O2 was adopted as an optimum dose in the sequent work. The obtained results are consistent with those achieved by Delil and Gören 26and Cheng et al.25 who recorded a maximum COD removal of 76% and 89.8% using 250 and 300 mg/L H2O2 for treatment of sugar and petrochemical wastewater, respectively.
Advanced Oxidation Process (AOP) by Electro-Fenton’s Reaction
The type of electrodes is a significant parameter that affects the electro-Fenton process27. The influence of electrode’s type on the removal efficiency of COD of composite industrial water samples were critically investigated at time intervals (0, 20, 30, 60, 90,120 minutes). The results presented in Fig 4. showed that the COD removal percentage of stainless steel / stainless steel electrodes increased to 63 % by increasing time to 30 minutes then decreased steadily. While, employing iron/ iron and stainless steel/ iron electrodes, the COD removal percentage increased to 46.1% and 74.8%, respectively by increasing time to 30 minutes then sharply decreased and this may be attributed to the ease of iron oxidation and the higher energy required for the treatment process28. Therefore, the optimum electrodes that achieved maximum removal of COD was stainless-steel/ stainless-steel that is used in the subsequent work at 30 min as an optimum time. The obtained results are higher than that reported by Nidheesh, et al.15who treated mixed industrial wastewater (BOD/COD 0.3, initial COD 795 mg/L) using platinum coated titanium electrodes at pH 3, 3 V and 60 min with maximum % removal of 54.57. In addition, Popat et al.14treated mixed industrial wastewater with initial COD value 1152 mg/ L achieving COD removal percent of 60 % at 10 V, 1 cm electrode distance, 25 cm2 surface area, 10mg /L catalyst dosage of and 60 min contact time using Ti/Pt anode and graphite cathode.
pH is a significant factor which affects the performance efficiency of electrochemical reactions during wastewater treatment. It’s clear from Fig.5a that 86.3-87.3 % COD removal percentage was obtained at pH 3-5 as in acidic conditions which favors H2O2 generation due to the reduction of dissolved oxygen to H2O2 by protons, but a very low pH catalyzes the evolution of hydrogen gas, thus decreasing the number of active sites for H2O2 generation and breakdown of H2O23. Therefore, pH 5 is adopted as an optimum pH in the subsequent work. These results are similar to that recorded by Nidheesh et al.15and are not compatible with that reported by Nidheesh et al.28 who found that COD and color removal was 55% and 99.8%, respectively at pH 7.7 and 60 min electrolysis time at initial COD value 1727 mg/ L using graphite plates in treatment of mixed industrial wastewater.
The concentration of H2O2 is a crucial factor in electro-Fenton processes due to the ability to enhance the decomposition of organic pollutants. Fig.5b showed that COD removal percentage increases from 71 to 87% with increasing the concentration of hydrogen peroxide from 0 to 0.3 g/L, and this may be due to the acceleration of hydroxyl radical generation3,27. This behavior is inconsistent with that reported by Delil and Gören26who revealed that COD removal efficiency declined with increasing H2O2 concentration as the free radical hydroperoxyl (●HO2) with the lower oxidation power produced can hindered the effect of hydroxyl radicals.
As clear from Fig.5c the COD removal percentage increased to 88.2% by increasing ferrous ion dose up to 1 mg/L, then decreased due scavenging of OH radicals by higher Fe2+ concentration26. Popat et al.14who achieved COD removal percent of 60 % using catalyst dosage of 10mg /L for treating mixed industrial wastewater. In addition, Nidheesh et al.15showed a significant COD reduction with addition of iron source in treatment of mixed industrial wastewater due to enhancement the production of hydroxyl radical (•OH).
The application of high voltage leads to raising current density which is an important parameter resulted in an increase in hydrogen peroxide production, increase in OH• and accelerate iron ions regeneration, therefore enhances the performance of treatment process27. As presented in Fig.5d, the COD removal percentage increased to 88% by increasing voltage up to 2 volts then slightly decreased. This similar to that obtained by Nidheesh et al.15 who indicated that the applied 3 V is preferable than 5 V in treatment of mixed industrial wastewater (initial COD 795 mg/L, Platinum coated titanium electrodes and 60 min) from energy consumption view point which decreases operating costs and is a favored option for large scale application. In addition, Nidheesh et al.28 showed that the volume of the sludge is increased with rising voltage more than 4 V in the treatment of mixed industrial wastewater by electrochemical oxidation process (initial COD value 1727 mg/ L, pH7.7,60 min using graphite plate) and found that COD and color removal was 55% and 99.8%, respectively.
Estimation the performance efficiency of Fenton and electro-Fenton treatment processes for composite industrial wastewater treatment
The ANOVA analysis results were shown in Table 3 and Fig.6, it is clear that the parameters probability values were 0.000 (lower than 0.05) which indicates statistically significant differences between the initial and pre-treated composite wastewater for the addressed parameters. In addition, the electro-Fenton process was significantly more effective than Fenton process according to the physicochemical analysis of the composite industrial wastewater sample (Table 4). The results illustrated that electro-Fenton process achieved removal efficiency for COD, O&G, BOD, TSS, and TKN, by 84.3%, 69%, 85%, 72% and 71.27 % compared to Fenton which displayed 78.43, 66, 69%, 70.1, and 61 %, respectively. The results matched with that obtained by Kumar et al.29 who used EF to treat composite sample from chemicals and textile industries (77.7% COD removal). In addition, Nidheesh et al.15 treats composite sample from chemical plants, oil, cotton textile, rubber and plastic and recorded ~ 55% removal of COD by EF process.
Parameter
|
Type III Sum of Squares
|
df
|
Mean Square
|
F
|
Sig.
|
BOD
|
1099302
|
2
|
549651
|
53192
|
0.000
|
COD
|
3037416
|
2
|
1518708
|
168745
|
0.000
|
Oil
|
31166066
|
2
|
15583033.07
|
1167171
|
0.000
|
TP
|
6.246
|
2
|
3.123
|
195
|
0.000
|
TSS
|
4477053
|
2
|
2238526.69
|
207698
|
0.000
|
TKN
|
4.883
|
2
|
2.44
|
1878
|
0.000
|
Table 3. ANOVA test results for estimating the efficiency of pollutant removal from composite sample after treatment by AOPs
After AOPs
|
Initial
|
Unit
|
Parameter
|
removal%
|
F
values
|
removal%
|
EF
values
|
3.2
|
5.3
|
7.11
|
-
|
pH
|
4.6
|
18.3
|
3.1
|
18.6
|
19.2
|
g/L
|
TDS
|
28.5
|
-
|
28.7
|
-
|
32.6
|
ms/cm
|
EC
|
6.2
|
18.1
|
4.6
|
18.4
|
19.3
|
g/L
|
Salinity
|
75.6
|
228.2
|
82.2
|
167
|
937
|
mg/L
|
BOD
|
78.43
|
326
|
84.3
|
238
|
1512
|
mg/L
|
COD
|
66
|
2000
|
69
|
1830
|
5860
|
mg/L
|
O&G
|
37
|
2.46
|
51
|
1.92
|
3.9
|
mg/L
|
TP
|
70.1
|
630
|
72
|
598
|
2110
|
mg/L
|
TSS
|
61
|
0.92
|
71.27
|
0.67
|
2.34
|
mg/L
|
TKN
|
Table 4. Estimation the performance efficiency of Fenton and electro-Fenton treatment processes for composite industrial wastewater treatment.
Comparison of maximum COD removal percentages with previous studies
Table 5 displayed a comparative study of the Fenton and electro-Fenton processes with previous studies for the pretreatment of composite samples at optimum operating conditions (pH, voltage, electrode type, Fe2+ and H2O2 concentrations). The current study achieved maximum COD removal percentage 84.3% and 78.43% for electro-Fenton and Fenton process, respectively. It is clear that both processes revealed good performance efficiency for pretreatment of the addressed samples compared to other studies which are unacceptable from economic and environmental view point due to adopting expensive electrodes or combining more than one technique and generation of high amount of sludge that limit their applicability on industrial scale.
Reference
|
Operating Conditions
|
COD Removal %
|
Treatment technique
|
Type of wastewater
|
Current study
|
H2O2 and ferrous ion dose 0.3 g/L, 1 mg/L and stainless-steel electrode, (pH 3-5)
|
84.3%
78.43%
|
EF
F
|
Composite sample (food, Petrochemical, beet sugar)
|
30
|
Initial COD 2676 mg/L, [H2O2]: [Fe2+] = 4.5:1 and pH 4
|
78.41%
|
F
|
Mixed Waste Chemicals
|
29
|
1 h of electrolysis, 1 V, pH 3- and 50-mM hydrogen peroxide
|
77.7%
|
EF
|
Composite sample (chemical, textile industries)
|
28
|
Initial COD 1727 mg/L, graphite electrodes, 1 h electrolysis, pH 7.7, voltage 4 V, and NaCl dose 1g/L.
|
55%
|
EF
|
Composite sample (textile, chemical industries)
|
24
|
H2O2/COD (w/w2:1), H2O2/Fe+2 (w/w10:1), initial COD15400-18200 and pH 3, and settling (2h).
|
33%
|
F
|
Composite sample from agro-food industrial wastewaters
|
15
|
Initial COD 795 mg/L, laterite (catalyst) dosage 10 mg/L, Platinum coated titanium electrodes after 60 min of treatment, voltage 3 V, pH 3
|
54.57%
|
EF
|
Composite sample (chemical plants, oil, cotton textile, rubber, plastic)
|
14
|
initial COD 1152mg/L, voltage10 v, electrode distance 1 cm, pH 3surface area of 25 cm2, catalyst dosage of 10mg /L ,1 hour and persulphate dosage of 200mg /L using Ti/Pt anode and graphite cathode
|
60%
|
EF
|
Composite sample (pharmaceutical, dyes, textile industries)
|
Table 5. Comparative study of maximum COD removal percentages after Fenton and Electro- Fenton processes with previous studies.