Application of electrochemical treatment for domestic wastewater A. - - PowerPoint PPT Presentation

Application of electrochemical treatment for domestic wastewater

• A. E. Yilmaz, T.M. Massara, O.T. Komesli, E. Katsou

6th International Conference on Sustainable Solid Waste Management, Naxos Island, Greece, 13–16 June 2018 Naxos 15th June 2018

Contents

• Introduction
• Objective
• Materials & Methods
• Results
• Discussion

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Introduction

• Limited water resources & inadequately treated

wastewater = immense global environmental issues

• Mitigate water pollution & promote water reuse =

absolutely essential

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Highly variable:

• over time
• in terms of

quantity

Causes:

• industrialization
• recent technological

advances

Target Pollutants

Optimization of water treatment = very important research topic!

Introduction

• Optimization of key process parameters: important for maximizing

process effectiveness

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• Electrocoagulation:
• in‐situ generation of coagulants by electrical dissolution of

electrodes

• effective pollutant removal (e.g. toxic metals, oil mill wastewater,

metalloids, COD, etc.) especially with aluminum/steel electrodes

Objective

Examine the effectiveness of electrocoagulation for COD removal from domestic wastewater

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 different initial pH values

Materials & Methods

• Domestic wastewater from the city of

Erzurum (Turkey) (COD=250 mg L‐1, BOD5=175 mg L‐1, SS=80‐100 mg L‐1, conductivity=1,000‐1,050 μS cm‐1, temperature=15±3 °C)

• Lab‐scale, jacketed, rectangular reactor

(V=1 L)

• 7 stainless‐steel electrodes (cathode) & 7

aluminum electrodes (anode)

• distance between the electrodes=5 mm;

total surface area=2,400 cm2

• Constant current density=10 A
• Reaction time=30 min

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Experimental setup: 1: circulator, 2: multimeter, 3: pH control cell, 4: peristaltic pump, 5: reactor, 6: anode electrode (aluminum), 7: cathode electrode (stainless‐ steel), 8: control panel, 9: power supply.

Materials & Methods

• Equation 1: calculation of the

treatment efficiency

• Equation 2: calculation of the

system’s energy consumption

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100 (%) x C C C

e

          

• Eq. (1)

C0: initial pollutant concentration (mg L‐1); Ce: the remaining concentration of the pollutant in the wastewater at time t (mg L‐1)

• ∗ ∗
• Eq. (2)

W: energy consumption (kW‐h m‐3), I: applied current (A), V: potential difference in the system (V), t: reaction time (min), ϑ: total wastewater volume (m3)

Results

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Initial pH effect pH>8: tetrahydroxyaluminate ion (Al(OH)4

‐)

predominance; flocs 6.5<pH<8: Formation of aluminium hydroxides with high adsorption capacity (e.g. Al(OH)2+, Al(OH)2

+, Al2(OH)2 4+,

Al(OH)3, Al13(OH)32

7+)

Aluminum hydroxide (Al(OH)3)= amphoteric coagulant; pH‐dependent formation

Results

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Initial pH effect

• Solid Al(OH)3dominant
• Higher adsorption

capacity; enhanced pollutant precipitation Different initial pH values (i.e. 5, 6, 7 & 7.8) tested; (current density=10 A; electrocoagulation duration=30 min)

20 40 60 80 10 20 30 COD removal (%) Reaction time (min) pH 5 pH 6 pH 7 Original pH

Highest COD removal (≈87%) at the

• riginal wastewater pH value (i.e. 7.8)

Lowest COD removal (≈55%) for an initial wastewater pH=5

Results

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System Energy Consumption

 pH ↓ → electrical conductivity ↑ → potential difference applied to the system ↓  Eq. 2: potential difference ↓ → energy consumption ↓ if current=constant Different initial pH values (i.e. 5, 6, 7 & 7.8) tested; (current density=10 A; electrocoagulation duration=30 min) Highest energy consumption (i.e. 95%) at the wastewater original pH (i.e. 7.8) Lowest energy consumption (i.e. 66.5%) at the lowest pH (i.e. 5)

20 40 60 80 100 10 20 30 Energy consumption ( kW-h m-3) Reaction time (min) pH 5 pH 6 pH 7 Original pH

Discussion

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Initial pH effect:

• ptimal COD

removal at pH=7.8

• Al(OH)3 dominant aluminium hydroxide;

high adsorption capacity; pollutant precipitation

Electrocoagulation with initial pH=7.8: (i) potential to achieve high COD removal (≈73%) even at very short reaction times (e.g. after only 5 min of operation) (ii) higher COD removal with increased process duration (5→30 min)

• Higher anodic dissolution→ higher

release of coagulants

• Longer contact time between

coagulants & pollutants

Electrocoagulation efficient in domestic wastewater treatment after optimizing key process parameters

• Future work

focus: other parameters (e.g. current density, etc.)

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