**2.4. Chemical analysis**

The efficiency of the new EC reactor for the entire treatment was analyzed based on color removal performances, TSS and COD. For every iteration, the electrical potential was kept constant at 30 V. The COD was determined using a Closed Reflux-Titrimetric technique. The determination of TDS and TSS was performed using gravimetric technique. The phenol content was determined using HPLC. ODS Hypersil C18 column (4.6 mm×150 mm×5 μm) at 25 was employed for separation of aromatic and phenolic compounds with the aid of water/ acetonitrile (40/60, v/v) being the mobile phase. The flow rate of the mobile phase and the injection volumes was 1 mL/min and 5 μL. 254 nm detection wavelength was used. The samples were subjected to filtration by using a 0.25 μm membrane filter. The amount of grease and oil (G&O) was determined using solvent extraction technique. The amount of dissolved oxygen (DO) and BOD was determined using DO meter. The turbidity, conductivity and pH were also determined in the present study. The color was analyzed through absorbance using a UV–Vis spectrophotometer with a wavelength corresponding to the peak absorbance value for the textile effluence (533 nm). The sample filtration was carried out with the aid of Whatman 934 AH filter. The rotating anode speed was monitored using a microprocessor digital meter. The ion was analyzed using ionic chromatography ICS-2000. The whole analytical works were performed based on the prescribed procedures in the standard techniques [11]. The determination of color removal, TSS and COD was done using formulas stated by [12–15] among others.

#### **2.5. Sludge compaction analysis**

The sludge of the textile wastewater was allowed to sit for 1 h to boost the alliance of the sediments. The two concentrations of cationic polymer (LPM 3135 polymer, 10 and 40 mg/L) were examined to enhance the settling process. The volume of the space engaged by the solid (mL) was measured at fixed time intervals. The weight of the wet residue (the solid portion) was determined, after which the samples were dried for approximately 24 h at 100°C to obtain the whole residual solids. The specific resistance to filtration (SRF) and the cake-dry solid was estimated to properly depict the dewater capability of the sludge using Buchner funnel filtration with pressure (0.015 mPas). The SRF formula (in m/kg) is defined as [16].

$$\text{RF\text{(SRF)} = (2\text{KbPA2})/\mu\text{a}\_w} \tag{1}$$

where P is the pressure during sludge filtration (mPas), A is the filtered area, μ is the viscosity of the filtrate (N.s/m<sup>2</sup> ), aw is the weight of the solid per unit volume of filtrate (kg/m<sup>3</sup> ) and Kb is the slope of the *V* vs. t/*V* plot. Whatman glass fiber filter (Grade 934-AH) was used. Measuring and estimating dryness of the general cake were performed by the following equation:

$$\text{Sludge} \cdot \text{dryness} \left( \% \right) = 100 \times \left[ (\text{m}\_3 - \text{m}\_1) / (\text{m}\_2 - \text{m}\_1) \right] \tag{2}$$

where m<sup>1</sup> and m2 are the mass of the cup (with the membrane) after and before the filtration process and m3 is the mass of the same cup after the drying for 24 h at 100°C.

A sludge volume index (SVI) was implemented to decide the settling properties of the sludge suspensions. The SVI (mL/g) is the volume (in mm) used by 1 g of a suspension subject to 30 min of settling [11]. The SVI is defined as.

$$\text{SVI} = \text{VD}\_{y}/\text{TSS} \tag{3}$$

where TSS is the concentration of suspended solids (g/L) and VD30 is the volume of settled sludge after 30 min (mL/L).

#### **2.6. Economic analysis**

(1:25 of the original size) as the working electrode, a platinum wire as a counter electrode and

The efficiency of the new EC reactor for the entire treatment was analyzed based on color removal performances, TSS and COD. For every iteration, the electrical potential was kept constant at 30 V. The COD was determined using a Closed Reflux-Titrimetric technique. The determination of TDS and TSS was performed using gravimetric technique. The phenol content was determined using HPLC. ODS Hypersil C18 column (4.6 mm×150 mm×5 μm) at 25 was employed for separation of aromatic and phenolic compounds with the aid of water/ acetonitrile (40/60, v/v) being the mobile phase. The flow rate of the mobile phase and the injection volumes was 1 mL/min and 5 μL. 254 nm detection wavelength was used. The samples were subjected to filtration by using a 0.25 μm membrane filter. The amount of grease and oil (G&O) was determined using solvent extraction technique. The amount of dissolved oxygen (DO) and BOD was determined using DO meter. The turbidity, conductivity and pH were also determined in the present study. The color was analyzed through absorbance using a UV–Vis spectrophotometer with a wavelength corresponding to the peak absorbance value for the textile effluence (533 nm). The sample filtration was carried out with the aid of Whatman 934 AH filter. The rotating anode speed was monitored using a microprocessor digital meter. The ion was analyzed using ionic chromatography ICS-2000. The whole analytical works were performed based on the prescribed procedures in the standard techniques [11]. The determination of color removal, TSS and COD was done using formulas stated by

The sludge of the textile wastewater was allowed to sit for 1 h to boost the alliance of the sediments. The two concentrations of cationic polymer (LPM 3135 polymer, 10 and 40 mg/L) were examined to enhance the settling process. The volume of the space engaged by the solid (mL) was measured at fixed time intervals. The weight of the wet residue (the solid portion) was determined, after which the samples were dried for approximately 24 h at 100°C to obtain the whole residual solids. The specific resistance to filtration (SRF) and the cake-dry solid was estimated to properly depict the dewater capability of the sludge using Buchner funnel filtra-

RF(SRF) = (2KbPA2)/μaw (1)

where P is the pressure during sludge filtration (mPas), A is the filtered area, μ is the viscosity

the slope of the *V* vs. t/*V* plot. Whatman glass fiber filter (Grade 934-AH) was used. Measuring and estimating dryness of the general cake were performed by the following equation:

Sludge dryness (%) = 100 × [(m3 − m1)/(m2 − m1)] (2)

), aw is the weight of the solid per unit volume of filtrate (kg/m<sup>3</sup>

) and Kb is

tion with pressure (0.015 mPas). The SRF formula (in m/kg) is defined as [16].

Ag/AgCl (3 M KCl) electrode as a reference electrode.

**2.4. Chemical analysis**

116 Wastewater and Water Quality

[12–15] among others.

of the filtrate (N.s/m<sup>2</sup>

**2.5. Sludge compaction analysis**

The total operating costs for treatment of wastewater process include electricity, equipment, chemical usage, labor, maintenance and sludge disposal. For EC process, the major costs of operation include the cost of electricity and electrode material. In this study, the cost of chemical supplements and sludge disposal was added as well. The total cost of operation (TCO) was computed using [3].

$$\text{TCO} = a\,\text{C}\_{\text{energy}} + b\,\text{C}\_{\text{electrode}} + d\,\text{C}\_{\text{sludge}} + e\,\text{C}\_{\text{chemical}}\tag{4}$$

$$\mathbf{C}\_{\text{enogy}} = \mathbf{U} \mathbf{I} \mathbf{R} \mathbf{T} / V \tag{5}$$

$$\mathbf{C}\_{\text{electrode}} = \mathbf{M}\_{\text{w}} \text{ IRT/ZFV} \tag{6}$$

where Cenergy = denotes intake of energy per cubic meter of wastewater (kWh/m<sup>3</sup> ); Celectrode = intake of electrode for treatment of 1 m<sup>3</sup> of wastewater (kg/m<sup>3</sup> ); Csludge = quantity of sludge per m3 of wastewater (kg/m<sup>3</sup> ); Cchemical = amount of chemicals (kg/m<sup>3</sup> ).; *a* = total cost of electricity (about 0.075US\$/kWh); *b* = cost of iron or aluminum (2.5US\$/kg); *d* = sludge disposal cost excluding the drying and including transportation (0.06US\$/kg); *e* = cost of chemicals that can be added: LPM 3135 polymer (3.0US\$/kg), NaOH (0.5US\$/kg), Na<sup>2</sup> SO<sup>4</sup> (0.25US\$/ kg) and NaCl (0.06US\$/kg); U = voltage; I = intensity of the current; RT = EC electrolysis time; *V* = textile wastewater working volume; M<sup>w</sup> = molar mass of the iron (55.84 g/mol) or aluminum (26.98 g/mol); Z = quantity of electrons moved (3); F = Faraday constant (96,500 C/mol).

The operating expense was computed according to the Iraqi market prices for the year 2017. For EC rotating anode, the total consumption of electrical energy was estimated as follows:

$$\mathbf{C}\_{\text{energy}}\text{ (kWh/m}^3\text{)} = \left(\mathbf{C}\_{\text{energy}}\right)\_{\text{S}} + \left(\mathbf{C}\_{\text{energy}}\right)\_{\text{M}}\tag{7}$$

where (Cenergy)M signifies the rate at which the DC motor anode rotation consumed electrical energy and (Cenergy)S signifies the amount of electrical energy consumed by the reacting system (electricity received by the cathode and the anode because of DC power supply). The values of (Cenergy) <sup>M</sup> and (Cenergy) S were determined from Eq. (5).
