an introduction to electrocoagulation

An Introduction to Electrocoagulation Christos Charisiadis

Contents

1. Introduction page 1

2. Process Description page 2

3. Factors affecting the efficiency of electrocoagulation process page 3

3.1 Electrode arrangement page 3

3.2 Type of power supply page 4

3.3 Current density page 4

3.4 Concentration of anions page 5

3.5 Effect of initial pH page 5

3.6 Electrode material page 5

4. Applications of electrocoagulation page 5

4.1 Water containing heavy metals page 6

4.2 Tannery and textile industry wastewater page 6

4.3 Food industry wastewater page 6

4.4 Paper industry wastewater page 6

4.5 Refinery wastewater page 6

4.6 Produced water page 6

5. Advantages and Disadvantages of Electrocoagulation page 7

5.1 Advantages page 7

5.2 Disadvantages page 7

5.3 Advantages of Electrocoagulation in Dissolved Metal Precipitation page 7

5.4 Advantages of Electrocoagulation in De-emulsification of Oil and Grease

page 8

6. Where does EC work well? page 8

7. Where EC doesn’t work? page 8

8. EC as a pretreatment to RO page 9

8.1 Electrocoagulation for the removal of water hardness and silica from Coal seam

gas (CSG) produced water. page 9

8.1.1 Results page 10

8.2 Removal of turbidity and suspended solids by electro-coagulation to improve feed

water quality of reverse osmosis plant. page 10

8.3 Assessment of hardness, microorganism and organic matter removal from

seawater by electrocoagulation as a pretreatment of desalination by reverse osmosis

page 11

9. Emerging usage of electrocoagulation technology for oil removal from wastewater

page 12

9.1 Characteristics of oily wastewater page 13

9.2 Results page 15

10. Electrocoagulation for the treatment of wastewater page 16

10.1 Continuous electrocoagulation process for the post-treatment of anaerobically

treated municipal wastewater page 16

10.2 The electrocoagulation pretreatment of biogas digestion slurry from swine farm

prior to nanofiltration concentration page 16

10.3 Can electrocoagulation process be an appropriate technology for phosphorus

removal from municipal wastewater? page 17

10.4 Removal of Cr ions from aqueous solution using batch electrocoagulation: Cr

removal mechanism and utilization rate of in situ generated metal ions page 18

REFERENCES page 20

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Electrocoagulation Notes – Christos Charisiadis 2017

An introduction to Electrocoagulation 1. Introduction

Electro-coagulation became a proven and effective method for water treatment. It

represents a new alternative for treating water because of its high efficiency in

removing large number of pollutants. Natural and waste water contain dissolved

matters, suspended matters and colloidal particles. Colloidal particles are difficult to

remove since they are stable and this complicates water treatment.

In this process, the electro-dissolution of sacrificial anodes, usually made of aluminum

or iron, to the wastewater leads to the formation of hydrolysis products (hydroxo-

metal species) that are effective in the destabilization of pollutants. The

electrochemical reduction of water in the cathode produces hydrogen bubbles that

can promote a soft turbulence in the system and bond with the pollutants, decreasing

their relative specific weight. In addition, the generated hydrogen can be collected

and used as fuel to produce energy. This treatment has been successfully introduced

in removing suspended solids, dyes, heavy metals, arsenic, hardness, phosphate,

fluoride, pesticides and natural organic matter from wastewater.

For the use of electrocoagulation, there are some advantages such as requiring only

simple equipment, ease of operation, less treatment time, use of less or no chemicals,

and smaller amount of sludge.

2. Process Description

The basic EC unit typically consists of an electrolytic cell with an anode and cathode

metal electrodes connected externally to a DC power source and immersed in the

solution to be treated. Iron and aluminum electrodes are the most extensively used

metals for EC cells since these metals are available, non-toxic and proven to be

reliable. Although EC is considered to be quite similar to Chemical

Coagulation/Flocculation (CC/CF) in terms of the destabilization mechanism, it still

differs from CC/CF in other aspects such as the side reactions occurring simultaneously

at both electrodes. [5]

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During electrocoagulation, the most important chemical reactions involve the

dissolution of metal cations at the anode and formation of hydroxyl ions and hydrogen

gas at the cathode Fig.1 [4],

M → Mn+ + ne-

2H2O(l) + 2e- → 2OH- + H2(g)

The current passes through a metal electrode, oxidizing the metal (M) to its cation

(Mn+). Simultaneously, water is reduced to hydrogen gas and the hydroxyl ion (OH−).

Electrocoagulation thus introduces metal cations in situ, using sacrificial anodes

(typically iron or aluminum) that need to be periodically replaced. The cations (Al3+,

Fe2+, etc.) destabilize colloidal particles by neutralizing charges. They also produce

monomeric and polymeric hydroxide complex species as coagulants.

Mn+(aq) + nOH-

(aq) → M(OH)n(s)

These coagulants form amorphous metal hydroxide precipitates. Their high

adsorption properties impart strong affinity for dispersed particles and dissolved

pollutants. Thus the pollutants can be separated from aqueous phase by coagulation.

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The hydrogen bubbles at cathode promote turbulence in the system and bond with

the pollutants, decreasing their relative specific weight. Consequently, they enhance

the separation process by flotation. [4]

3. Factors affecting the efficiency of electrocoagulation process [5]

3.1 Electrode arrangement

Regardless of the simplicity of the basic EC setup, it is not suitable for practical

wastewater treatment applications, as it requires huge electrode surface area to

overcome the metal dissociation rate; this is overcome by using monopolar or dipolar

electrode setups in series or parallel connections.

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Results showed that monopolar connection gave much higher current efficiency with

lower operating cost compared to bipolar connection. However, bipolar connection

resulted in an almost complete removal of Cr3+ compared to 81.5% with monopolar

connection. The removal of fluoride from drinking water was better when bipolar

electrodes were used but the total operating cost of monopolar electrodes was much

less.

3.2 Type of power supply

DC power supply is typically used for electrocoagulation cells; however, using DC leads

to oxidation/consumption of the anode and a formation of an oxide layer on the

cathode known as cathode passivation. Passivation causes an increase in passive over

potential, which leads to higher power consumption; the passive layer also results in

a decreased flow of current between the two electrodes and decreases the efficiency

of EC.

3.3 Current density

Current density, which is the current per area of electrode, determines the amount of

metal ions released from the electrodes. In general, metal ion dissociation is directly

proportional to the applied current density. However, when too large current is used

there is high chance of wasting electrical energy in heating the water and even a

decrease in current efficiency expressed as the ratio of the current consumed to

produce a certain product to the total current consumption.

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3.4 Concentration of anions

The presence of different anions has different effects on the destabilization properties

of metal ions. Sulfate ions are known to inhibit the corrosion/metal dissolution from

the electrodes and hence they decrease the destabilization of colloids and current

efficiency.

On the other hand, chloride and nitrate ions prevent the inhibition of sulfate ions by

breaking down the passive layer formed. The presence of chloride ions also

significantly reduces the adverse effect of sulfate ions, which lead to precipitation of

salts on the electrodes when the salt concentration is sufficiently high.

3.5 Effect of initial pH

pH is a key parameter when it comes to electrocoagulation as it affects the

conductivity of the solution, zeta potential and electrode dissolution. It is however

difficult to establish a clear relationship between the pH of the solution and the

efficiency of electrocoagulation since pH of the treated water changes during EC

process, therefore it is usually referred to the initial solution pH

3.6 Electrode material

Selecting the proper electrode material is critical since it determines the reactions that

would take place. As mentioned previously Al & Fe electrodes are most widely used

due to their proven reliability and availability, however, studies found that Fe (II) is a

weak coagulant if compared to Fe (III) due to its lower positive charge. A lower positive

charge indicates that the ion's ability to compress the electrical double

layer/destabilize colloids is weaker. In most of the studies, it is generally proven that

Al electrodes enhance the efficiency of removing pollutants better than Fe electrodes.

4. Applications of electrocoagulation [5]

This section presents an overview of the recent application of EC in the treatment of

different types of water and wastewater over the past few years. The review was

divided into six main categories namely:

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4.1 Water containing heavy metals

Heavy metals are discharged from several industries and wastewater containing heavy

metals are challenging to treat as they are non-biodegradable and some metals are

toxic. Heavy metals: include cadmium, chromium, zinc, lead, mercury and arsenic.

4.2 Tannery and textile industry wastewater

Tannery and textile industry effluent is highly contaminated with organics, chromium

and different types of dyes. Chromium on its own is a major concern as it may oxidize

to Cr6+, which is carcinogenic and toxic. The presence of dyes also renders the water

quality very poor by preventing the passage of sun light; it is also known to be highly

stable, toxic and may resist chemical and biological degradation.

4.3 Food industry wastewater

Food industry consumes larger amounts of water for each ton of product compared

to other industries. Various contaminants are found in wastewater from food industry

depending on the sector but the general characteristics of wastewater are being highly

biodegradable and nontoxic with high suspended solids, COD and BOD. In the case of

meat processing industry, color, oil and grease are other concerns.

4.4 Paper industry wastewater

Paper industry consumes large amounts of water and the effluent is usually blackish

in color and highly contaminated with lignin, COD, BOD, organics, suspended solids

and arsenic.

4.5 Refinery wastewater

Includes wastewater generated from petroleum refineries and petrochemical

industries. It usually contains high level of aromatic and aliphatic hydrocarbons,

chemicals, dissolved solids, BOD and COD.

4.6 Produced water

Produced water is the largest by product by volume produced from oil and gas

industry. Although the composition of produced water depends on the nature of

produced hydrocarbon, the geological characteristics of the field, and the method of

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extraction, it is usually very saline and contains various contaminants including

production chemicals, dispersed and dissolved oils, dissolved gases and different

minerals.

5. Advantages and Disadvantages of Electrocoagulation [5]

5.1 Advantages

a) Since no chemicals are needed, there is no chance of secondary pollution due

to high concentration of chemicals such as CC/CF

b) Gas bubbles produced from EC facilitates the removal of pollutants by floating

them on top of the solution so they can be easily collected.

c) EC is easily operated due to its simplicity of its equipment hence, complete

automation of the process is possible.

d) Wastewater treated by EC gives clear, colorless and odorless water.

e) Flocs formed by EC are much larger than CC/CF and more stable, hence they

are easily separated during filtration.

f) EC produces much less sludge volume than CC/CF and the sludge formed is

more stable and non-toxic.

g) Even the smallest colloidal particles are removed by EC since the applied

electric current makes collision faster and facilitates coagulation

5.2 Disadvantages

a) Regular replacement of sacrificial anode used in EC is necessary since the

anode dissolves into the solution.

b) Cathode passivation can occur which decreases the efficiency of the EC

process.

c) In some areas where electricity isn’t abundant, the operating cost of EC can be

expensive.

5.3 Advantages of Electrocoagulation in Dissolved Metal Precipitation [1]

a) EC does not add anions that compete for coagulation with the metal ions

b) The introduction geometry of the coagulant (Fe3+) enhances the chances of

precipitation

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c) The reaction is more efficient that chemical precipitation resulting in less

sludge

d) No anions are left behind to increase osmotic loading on downstream

processes

5.4 Advantages of Electrocoagulation in De-emulsification of Oil and Grease [1]

a) EC offers an alternative to the use of metal salts/polymers/polyelectrolytes for

breaking stable emulsions and suspensions

b) The process destabilizes soluble organic pollutants and emulsified oils from

aqueous media by introducing highly charged polymeric metal hydroxide

species

c) These species neutralize the electrostatic charges on oil emulsions/droplets to

facilitate agglomeration/coagulation and separation from the aqueous phase

6. Where does EC work well? [1]

I. Higher Conductivity Applications (i.e., conductivity greater than 300 μS/cm)

II. Higher Suspended Solid Applications

a. Turbidity greater than 25NTU

b. TSS greater than 20 mg/L

III. Targeted Contaminates

a. Metals

b. Emulsified Oil & Grease

c. Total Suspended Solids

7. Where EC doesn’t work? [1]

I. Low Conductivity Applications (i.e., conductivity less than 300 μS/cm)

II. Low Suspended Solid Applications

a. Turbidity Less than 25 NTU

b. TSS Less than 20 mg/L

III. Non Polar and Monovalent Contaminates

a. Aqueous Salts (Na, K, Cl, F, etc.)

b. Non polar/charged particles

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8. EC as a pretreatment to RO

Since feed water for reverse osmosis units must have specific properties and should

be nearly free from turbidity and suspended matters, it must be subjected to a special

treatment.

Conventional pretreatment of feed water to reverse osmosis plants consists of

physical treatment where water is passed through sand and carbon micro filters to

remove suspended matters and pollutants and prevent precipitation of

microorganisms and its growth on membranes. It also includes chemical treatment

where chemicals such as acids are added to control pH and prevent precipitation of

calcium and magnesium salts, and chlorine for disinfection and chemicals to remove

oxidant matters. The choice and arrangement of flow sheet for desalination plant

depends on the type of feed water and specifications of the water product. This also

depends on the technical and economic choice of the possible units for the required

treatment.

Electrocoagulation (EC) process can be used as an alternative pretreatment in order

to assess its applicability to replace the conventional pretreatments used to mitigate

membrane fouling prior to seawater desalination by reverse osmosis process.

8.1 Electrocoagulation for the removal of water hardness and silica from Coal seam

gas (CSG) produced water. [2]

Coal seam gas (CSG), also known as coal bed methane (CBM) is mostly comprised of

methane (CH4) and has become the subject of considerable commercial interest in

recent years.

The large volume of produced water associated with the production of CSG presents

a challenge to industry. The CSG water mainly contains sodium chloride (ranging from

200 to 10,000 mg/L), sodium bicarbonate and other trace elements.

Conventional pretreatment typically involves a coagulation, flocculation and particle

separation operation. Dissolved air flotation (DAF) and micro-sand ballasted

flocculation are the most commonly used particle separation processes in the CSG

industry.

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EC provides an alternative to conventional chemical dosing, where an inorganic metal

salt such as aluminium chlorohydrate (ACH), polyaluminium chloride (PAC), alum,

ferric chloride or ferric sulphate is added as primary coagulants and settling provides

the path for pollutant removal. Literature suggests that EC is a promising technology

for the removal of silica, suspended particulates, and hardness in water.

8.1.1 Results

EC was able to achieve a 100% removal of calcium, strontium and barium, 98% silica

and 87% magnesium from the CSG water. The parameters used to achieve this

removal were a potential of 37.9 V and 60 sec of contact time, with aluminium

electrodes. Even though stainless steel electrodes did not produce the same removal

rate as aluminium electrodes, they still outperformed all of the chemical coagulants

tested in this experiment

8.2 Removal of turbidity and suspended solids by electro-coagulation to improve feed

water quality of reverse osmosis plant. [3]

Removal of total suspended solids TSS and turbidity from feed water of a reverse

osmosis unit by EC using iron electrodes is investigated. The effect of current density

and residence time were studied in an attempt to achieve a higher removal efficiency.

Water samples from well water with initial suspended solids TSS of 300 mg.L−1 and

turbidity of 150 NTU were prepared.

Experiments were carried out on two identical experimental RO units. The first was

fed with water treated by the conventional treatment while the other was fed with

water treated with addition of EC. All fouling indicators such as flow, pressure drop,

SDI show less fouling by addition of EC to the conventional pretreatment.

Electro coagulation at a current of 1.75A and 6min residence time gives 98% removal

efficiency of turbidity and 99% efficiency of removal of TSS. Addition of a Birm filter is

necessary to remove Fe(OH)3 precipitates formed. These alterations give a feed water

with a silt density index SDI less than 3%/min which is quite suitable for RO plants.

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8.3 Assessment of hardness, microorganism and organic matter removal from

seawater by electrocoagulation as a pretreatment of desalination by reverse osmosis

[6]

The said study underscored the interest of electrocoagulation as an alternative

pretreatment prior to seawater desalination by reverse osmosis through interesting

results on DOC abatement and microorganism removal.

The pretreatment of seawater by electrocoagulation was conducted in a batch cell

with aluminum electrodes in the galvanostatic mode. On the basis of the experimental

results, the following conclusions may be drawn:

• The investigation of the removal of organic matter from seawater showed that

removal efficiency improved with higher current density and lower pH. A high removal

efficiency of seawater organic matter, comparable to that of a hybrid process, was

obtained. Electrocoagulation was able to achieve 57.5% DOC removal efficiency and

81% absorbance removal efficiency for a current density of 5.6 mA.cm−2 in the

optimum operating conditions of this work. It can be concluded that aromatic

compounds were removed more efficiently than the aliphatic compounds from

seawater by electrocoagulation, comparing DOC and UV254 removal efficiencies.

• The removal efficiency of total hardness from seawater by electrocoagulation to

avoid the problem of scaling on the reverse osmosis membrane was found to be weak

(abatement of total hardness around 10%). This also means that scaling on the

cathode was always limited in this work. However, scaling remains a possible

limitation of electrocoagulation which can be easily detected by an increase of cell

potential and power consumption. To prevent scaling, the literature advocates that it

would be better to use stainless steel as the cathode, but practical methods also

involve a limitation of the pH increase by limiting electrolysis time or applying current

reversal (switching anode and cathode electrically) when both electrodes are made of

aluminum.

• When electrocoagulation was used as a disinfection process, a high disinfection

efficiency was obtained with a nearly complete removal of microbial cells. Prior to

seawater desalination, electrocoagulation may be an efficient alternative to

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chlorination, as the latter presents many drawbacks, such as its ineffectiveness to

prevent biofouling and its reactivity with organic compounds that could lead to the

formation of carcinogenic organic byproducts including trihalomethanes, haloacetic

acids and other toxic disinfection by-products. In addition, chlorination of feed

seawater can provoke the fragmentation of humic substances into smaller organic

fragments easily assimilable by microorganisms, thereby causing biofouling.

9. Emerging usage of electrocoagulation technology for oil removal from

wastewater [4]

Oil removal from wastewater is regarded to be a main challenge in treatment

practices. Dispersed oil droplets usually have high surface charges, resulting in the

stability of oil-in-water system. This is especially true when emulsified oil exists.

Emulsion generation and stabilization are usually achieved by mechanical agitation

and addition of emulsifying agents. Although qualitative and quantitative

compositions of oily wastes are different in many effluent sources, significant part of

oil is always present in the emulsified form. Some available technologies such as

gravity separation, cyclone separation, chemical precipitation, sorption, membrane

filtration and chemical oxidation have been used for oil removal.

Although many advantages of these technologies have been reported, some specific

disadvantages associated with these approaches (i.e. low efficiency, long processing

time, secondary pollution and high costs) exist in treatment applications. The

efficiencies of many methods for treatment of oily wastewater remain unsatisfactory.

An alternative to available oil removal technologies is electrocoagulation. In this

process, the electro-dissolution of sacrificial anodes, usually made of aluminum or

iron, to the wastewater leads to the formation of hydrolysis products (hydroxo-metal

species) that are effective in the destabilization of pollutants. The electrochemical

reduction of water in the cathode produces hydrogen bubbles that can promote a soft

turbulence in the system and bond with the pollutants, decreasing their relative

specific weight. In addition, the generated hydrogen can be collected and used as fuel

to produce energy. This treatment has been successfully introduced in removing

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suspended solids, dyes, heavy metals, arsenic, hardness, phosphate, fluoride,

pesticides and natural organic matter from wastewater.

For the use of electrocoagulation, there are some advantages such as requiring only

simple equipment, ease of operation, less treatment time, use of less or no chemicals,

and smaller amount of sludge.

9.1 Characteristics of oily wastewater

The characteristics of oily wastewater depend on the nature of relevant production,

operation, and chemicals used in processing facilities. The compositions of oily

wastewater from different sources can vary by order of magnitude. Constituents

typically associated with oily wastewater include: (i) Dispersed oil. Dispersed oil

consists of small droplets suspended in the aqueous phase. They may also reach the

bottom or rise to the surface of water body. (ii) Dissolved or soluble organic

components, such as organic acids, PAHs, phenols, and volatiles. These hydrocarbons

can often lead to additional toxicity of oily wastewater. (iii) Processing chemicals, such

as biocides, reverse emulsion breakers, and corrosion inhibitors. Some of these

chemicals are lethal at levels as low as 0.1 mg/L. Corrosion inhibitors can make oil-

water separation less efficient due to the formation of more stable emulsions. (iv)

Solids, such as precipitated solids, sand and silt, clays, corrosion products, and other

suspended solids derived from production and operation. The fine-grained solids can

reduce the efficiency of oil-water separators, leading to the exceedance of oil and

grease limit in discharged wastewater. (v) Bacteria. Bacteria can clog equipment and

pipelines. They can also form difficult-to-break emulsions and hydrogen sulfides which

are corrosive. (vi) Dissolved formation minerals, such as heavy metals, naturally

occurring radioactive materials, etc. Besides toxicity, these may cause production

problems. (vii) Salinity. Environmental impacts of salts in oily wastewater exist in all

regions where oil and gas are produced.

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9.2 Results

Each oil removal approach has its own advantages and disadvantages. This is also true

for electrocoagulation. To meet ever-stricter environmental regulations,

electrocoagulation can be used with other treatment techniques as either pre-

treatment or post-treatment process. Choice of the best combination can be

determined based on oily water characteristics, cost-effectiveness, space availability,

and reuse and discharge plans. In such a way, the advantages of various methods can

be maximized to avoid their limitations. The higher percentages of oil-containing

water can be recovered and utilized for reducing operating costs and achieving

environmental sustainability.

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10. Electrocoagulation for the treatment of wastewater

10.1 Continuous electrocoagulation process for the post-treatment of anaerobically

treated municipal wastewater [8]

The potential of continuous electrocoagulation (EC) process with aluminium

electrodes for the post-treatment of upflow anaerobic sludge blanket (UASB) reactor-

treated municipal wastewater was investigated. In order to optimize the performance,

influence of three parameters affecting EC, namely, chemical oxygen demand (COD),

current density (CD) and residence time in the reactor was studied using response

surface methodology (RSM) with Box–Behnken design (BBD) employing real UASB

reactor effluent. The results of the modelling study gave the following optimum

conditions: influent COD concentration 274 mg/L, CD 2mA/cm2 and residence time

5min; and predicted effluent COD, phosphate and turbidity values of 87 mg/L, 0.59

mg/L, and 12.6 NTU, respectively. Confirmatory tests at these optimum conditions

gave 90 mg/L effluent COD, 0.57 mg/L effluent phosphate and 15.2 NTU effluent

turbidity, which were in close agreement with the predicted results. At optimum

conditions, high removals of BOD and suspended solids were also observed, with

effluent BOD and suspended solids concentration of 34 mg/L and 29mg/L,

respectively. High total coliform and faecal coliform removals of 99.81% and 99.86%,

respectively, were also obtained at these conditions. The study thus suggests EC as an

attractive post-treatment option for UASB reactor-treated municipal wastewater. At

present market prices, the operating costs of the process were calculated at ∼0.07

US$ per m3 of effluent treated.

10.2 The electrocoagulation pretreatment of biogas digestion slurry from swine farm

prior to nanofiltration concentration [9]

The relationship between the crucial parameters and the turbidity removal from the

biogas digestion slurry by EC was investigated in this study, and the optimal

combination of the key operating parameters was determined using RSM, achieving

high turbidity removal efficiency at an acceptable electricity cost. The effectiveness of

EC pretreatment for decreasing the flux loss in the NF system as well as the running

cost of EC was also analyzed.

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The main conclusions could be drawn as follows: Except for the electrode gap, current

density, reaction time and A/V all had a significant effect on the turbidity removal from

biogas digestion slurry. Among the operating parameters of current density, reaction

time and A/V, current density had the most significant effect on turbidity removal and

electric energy consumption of EC, and the optimal combination for a high turbidity

removal (65.6%) at low electric energy (0.73Wh.L-1) consumption was determine by

RSM at current density of 35.7 A.m-2, reaction time of 24 min, and A/V of 20.7 m2.m-3.

RSM was a suitable method to optimize the operating conditions and maximize the

turbidity removal rate while keeping the electric energy consumption to minimal.

Furthermore, the EC was capable of alleviating NF membrane fouling by 22.2% in

terms of reducing membrane flux loss for treating biogas digestion slurry. The running

cost of EC pretreatment for biogas digestion slurry was estimated to be 0.29 US$

RMB.m-3 based on the electrical energy use and the loss of aluminum anode. In

summary, it is feasible to use EC as a pretreatment unit for NF concentration system

treating the biogas digestion slurry, given an additional benefit of mitigating

membrane fouling. However, the effect of temperature on the EC process, and the

safety of the sludge generated from the EC system need to be further studied.

10.3 Can electrocoagulation process be an appropriate technology for phosphorus

removal from municipal wastewater? [7]

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This study case evaluated a novel pilot scale electrocoagulation (EC) system for

improving total phosphorus (TP) removal from municipal wastewater. This EC system

was operated in continuous and batch operating mode under differing conditions (e.g.

flow rate, initial concentration, electrolysis time, conductivity, voltage) to evaluate

correlative phosphorus and electrical energy consumption. The results demonstrated

that the EC system could effectively remove phosphorus to meet current stringent

discharge standards of less than 0.2mg/L within 2 to 5min. This target was achieved in

all ranges of initial TP concentrations studied. It was also found that an increase in

conductivity of solution, voltages, or electrolysis time, correlated with improved TP

removal efficiency and reduced specific energy consumption. Based on these results,

some key economic considerations, such as operating costs, cost-effectiveness,

product manufacturing feasibility, facility design and retrofitting, and program

implementation are also discussed. This EC process can conclusively be highly efficient

in a relatively simple, easily managed, and cost-effective for wastewater treatment

system.

10.4 Removal of Cr ions from aqueous solution using batch electrocoagulation: Cr

removal mechanism and utilization rate of in situ generated metal ions [10]

The removal mechanism of batch electrocoagulation (EC) process for removing Cr ions

was investigated. The influence of operation parameters on removal mechanisms was

discussed. The utilization rate of in situ electro-generated Fe ions in the sludge was

introduced to investigate the removal mechanism and optimize the EC process. The

Fe elements’ utilization rate resulting from the specific adsorption is much higher than

that resulting from precipitation and co-precipitation. The initial pH determines which

removal mechanism dominates the Cr removal. At neutral initial pH condition, Cr ions

are mainly removed by flocs’ surface complexation reaction (specific adsorption). The

utilization rate of Fe ions at neutral pH condition reaches its maximum and is higher

than that at other pH conditions. The influence of electrode material on EC

performance was investigated on the basis of utilization rate of Fe ions. For EC with

Fe/Al electrode combination, although direct dissolution of Al ion from Al electrodes

will improve the Cr(VI) removal efficiency, the utilization rate of generated metal ions

is much lower, when compared with EC with Fe/Fe electrode. The utilization rate of in

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situ electro-generated metal ions could be considered as a new index to evaluate EC

performances.

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REFERENCES

1. BANFF; Electrocoagulation: An Innovative Approach for Recycling Produced Water

and as a Pre-Treatment to Reverse Osmosis for Emulsified Oils, Heavy Metals and

Other Constituents in the Oil and Gas Industry

2. ELECTROCOAGULATION AS A PRE - TREATMENT STAGE TO REVERSE OSMOSIS

UNITS (2014)

3. Removal of turbidity and suspended solids by electro-coagulation to improve feed

water quality of reverse osmosis plant (2011)

4. Emerging usage of electrocoagulation technology for oil removal from

wastewater: A review (2017)

5. A comprehensive review of electrocoagulation for water treatment: Potentials

and challenges (2016)

6. Assessment of hardness, microorganism and organic matter removal from

seawater by electrocoagulation as a pretreatment of desalination by reverse

osmosis (2016)

7. Can electrocoagulation process be an appropriate technology for phosphorus

removal from municipal wastewater? (2016)

8. Continuous electrocoagulation process for the post-treatment of anaerobically

treated municipal wastewater (2016)

9. The electrocoagulation pretreatment of biogas digestion slurry from swine farm

prior to nanofiltration concentration (2015)

10. Removal of Cr ions from aqueous solution using batch electrocoagulation: Cr

removal mechanism and utilization rate of in situ generated metal ions (2016)

an introduction to electrocoagulation

Engineering