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2020-10-22 12:48:36

Evaluation of the efficiency of the integrated coagulation and flotation process in wastewater treatment of dairy processing industry

Evaluation of the efficiency of the integrated coagulation and flotation process in wastewater treatment of dairy processing industry

Summary
Background and Aims: Dairy wastewater is one of the most important sources of pollutants for aquatic and soil environments. The purpose of this study was to evaluate the extent
.Removal, COD turbidity and pH changes by the process of coagulation and electrical flotation in dairy wastewater treatment


materials and methods

.The present study is an experimental-laboratory study that observes ethical standards and obtains the necessary permits on wastewater
Damavand compatriot dairy processing plant in a cylindrical electrochemical reactor made of steel (cathode electrode), aluminum (electrode anode) with series bipolar connection and the effect of variables, pH reaction time, conduction and current intensity on the efficiency of the combined process of electrical coagulation and flotation it placed


findings

The results showed that the pH of the electric current intensity and reaction time had a significant effect on the performance of the reactor and the values
The optimum was 3, 9 amps and 60 minutes, respectively. Under optimal conditions, the removal efficiency of COD and turbidity are 9.70 and 08.99%, respectively
Was calculated and the pH of the effluent from the reactor increased by 6.1 units. Also the electrical conductivity of the solution has an effect on the removal of contaminants
.The study did not show and the volume index of sludge under optimal conditions was 0.89 ml / g


Conclusion

The results showed that the combined process of coagulation and electric flotation can be used as an environmentally friendly method in treatment
Dairy industry wastewater for initial treatment and its readiness to enter the biological unit due to the increase in BOD5 / COD ratio of (0.41 wastewater
.Raw) to (0.79 effluent)


Keyword

Dairy wastewater, electric coagulation and flotation,, COD turbidity

Introduction


Food industry effluents High oxygen chemical requirements COD
That this is due to their high organic content [.] In this
Among the dairy industry due to the production of large volumes of wastewater (approximately 0.2 to
10 liters of wastewater per liter of processed milk) of special importance
In some cases, such wastewater is not treated
And simply discharged into the receiving waters and because of having
High values ​​of BOD5, COD nitrogen, phosphorus and suspended solids effects
Undesirable will follow in the blue figures of the acceptor. Release
Strong and annoying odors, grease and oil, the possibility of spreading pathogens
And the protein content of this type of wastewater is one of the most important issues
Are. The difficulty of treating wastewater in the dairy industry draws a lot of attention
Attracted in many countries. Therefore, processes
Various are used to treat this type of wastewater
According to the BOD5 / COD ratio of wastewater in the dairy industry
(Approx.) 0.5 It can be concluded that such a sewer is well with
The use of biological methods can be refined
Wastewater treatment plant is mainly based on the removal of BOD and oil load
And fat has been concentrated. Most industrial wastewater treatment plants
Dairy products have oil and fat removal equipment, including
Can be used for degreasing ponds and air flotation systems
The solution pointed out. Efficiency of degreasing ponds in oil separation
And free fat is good. But the points of the refinery where
Equipment is not cleaned regularly, it may build up resources
Unpleasant odors become. This is because decomposition
Biological dairy products, under anaerobic conditions lead to the formation of compounds
Organic stinks. In addition the removal of nitrogen and phosphorus compounds during
Anaerobic purification process is not possible]. [Therefore without considering
And review of the content of wastewater organic matter, selection of the previous anaerobic process
Aerobic treatment is not a good solution to reduce organic matter
Stricter environmental standards in recent years
New processes for efficient and adequate treatment of wastewater types
Industrial demand with relatively easy operation
Accordingly, the process of electrical coagulation () EC: Electro-Coagulation
Due to its adaptability, efficiency and environmental compatibility
It has attracted a lot of attention in industrial wastewater treatment
Is. Simple equipment, easy operation, shorter reaction time, no
Need to inject chemicals and small amounts of sediment or sludge that easily
Also, sedimentation is one of the most important features of this method [.]
Efficiency of electric coagulation process and its success in wastewater treatment
Urban], [Textile], [Poultry], [Landfill Leachate], [
Chemical and mechanical industries], [Groundwater contaminated with metals
Heavy, Restaurant Sewage, Dyeing Industries]
Olive oil processing industry and waste paper recycling
has been proven. Interaction of electrochemical coagulation processes and
Flotation in a reactor, coagulation process and electric flotation
[. Formation]) is ECF: Electro-Coagulation Flotation (
Coagulant by dissolving metal ions from the reacting electrode
Anode, destabilization of pollutants, accumulation of unstable phases and formation
Clots are involved in the mechanism of the electrochemical process
:The process equations with the aluminum electrode are as follows

Reaction at the anode

Reaction at the anode
(1)
Al (s) → Al(aq)3+ + 3e-
Reaction at the cathode
(2)
3H
(2O (l) + 3e-→ H2(g) + 3OH(aq-
General reaction in solution
(3)
Al(aq)3++ 3H2O (l) → Al(OH)3 + 3H+

Despite the considerable amount of scientific research done on
Industrial wastewater treatment by, EC few studies on
Dairy wastewater treatment is done using this method
And most of these studies focus on synthetic dairy wastewater
have been. Therefore in this study the influence of key variables of the EC process of
Such as initial pH, current intensity, reaction time and initial electrolyte concentration
() NaCl on the removal of COD and turbidity using electrodes
.Aluminum and steel have been considered


materials and methods


The present study is an experimental-laboratory study that is observed
Ethical standards and obtaining the necessary permits on real sewage
. Damavand compatriot dairy processing factory was built
The average amount of wastewater production of this factory is 70 cubic meters per day
And now use activated sludge method for wastewater treatment
May be. Sampling every 4 hours during a day
Proportional to the outlet flow from the overflow channel of the initial sedimentation pool to
The combined method was performed with a volume of 60 liters. Sample in a polyethylene container
Collected and transferred to the laboratory under standard conditions and at room temperature
the period . 4 No. 1 Spring 2016 Jalilvand et al. / 3
4oC was maintained. The length of storage time before starting to do
The experiments varied from one day to two weeks. this design
Due to its nature, research was not in conflict with ethical issues.
Experiments in a cylindrical reactor with intermittent flow to height
25 cm and a diameter of 4.13 cm made of non-magnetic steel
Stainless steel is carried out with a sample harvesting valve embedded in the reactor wall
. they got
Also from 3 aluminum electrode plates with dimensions of 22 cm × 8cm × 2mm
As an anode and a total of 2 steel electrode plates along the wall and floor
The reactor was used as a cathode. How to connect the electrodes face
Bipolar series and distance between electrodes were considered 2 cm
(Fig.) 1 For conducting coagulation and electrical flotation experiments, from
A JENWAY 1000 magnetic stirrer with constant speed and one
 . Direct current power supply model RXN-605D was used
All compounds and chemicals used made by Merck Company
Merck () was German. To measure the pH of the model pH meter
, CORNING-120 turbidity from turbidity meter model 2100 N
Conductivity / EC and TDS, and HACH temperature
. HACH TDS Meter was used
In this study the effect of variables, 4 (actual pH of wastewater and,) 9 times
Reaction (30, 10 and 60 minutes,) Electrical conductivity with addition, 0.5, 0.2
1 and 1.5 gNaCl / L were changed to real wastewater samples and
Electrical current intensities of 3, 1, 0.75, 0.5, 0.25 and 5 amps
Process efficiency was evaluated. Before each test,
The electrodes are washed with soft scotch tape and distilled twice with distilled water
. Then they were rinsed with 1N hydrochloric acid solution and distilled water
All experiments in this study were performed at laboratory temperature of 23 ± 1 0C
Were done. To adjust the pH of 4N sulfuric acid and hydroxide
Sodium 4N was used. At each stage of the experiment the amount of 1/4 liter of sample
The wastewater is discharged into the reactor after adjusting the pH and other variables
And taking into account the studied variables, the process with a specific time
Performed on the sample and then by sampling the liquid inside the reactor
After 30 minutes of settling and from the supernatant, tests to determine
The range of optimal parameters was performed. All tests in accordance with
. Standard methods for water and wastewater testing were performed
To evaluate the process efficiency (%) Removal Effciency of the parameter
. COD and turbidity were used according to the following equation
: C0 concentration) mg / L (COD or turbidity () NTU before effluent sample
From doing the process
C: Concentration) mg / L (COD or turbidity () NTU effluent from
Reactor with integrated process of coagulation and electric flotation
Figure 1. Schematic of an electric coagulation and flotation reactor
findings
Results of 3 times analysis of primary effluent pool effluent analysis
Damavand compatriot dairy processing factory is listed in Table 1
. Has been
Table 1 Specifications of effluent from the initial sedimentation pool of the processing plant
Dairy products of Damavand compatriot

Parameter unit amount
6/5 --- pH
1277 NTU animosity
3060 mg/L COD
BOD
5
1260 mg/L
380 mg/L Chlorine
Electrical conductivity 2850 µs/cm
BOD
5/COD Ratio
0/41 ---

As can be seen, the studied wastewater from the content
It has a relatively high organic content, but biological purification capability
Shows average. Results of the effect of changes, pH time
/ 4 Quarterly Journal of Health in the field of efficiency of coagulation and electric flotation in dairy wastewater treatment
Reaction (min,) Sodium chloride concentration () g / L and electric current intensity
(Amps) on COD removal efficiency and turbidity in Figures 1 to 4
. Is brought


Figure 1. Effect of pH changes on COD removal efficiency and turbidity (reaction time
30 minutes, electrical conductivity 2850 µs / cm electric current intensity 3 amps)
Figure 2 - The effect of reaction time (minutes) on COD removal efficiency and turbidity
(PH = 9 electrical conductivity, 2850 µs / cm 3 amps current)
Figure 3. The effect of sodium chloride concentration (,) g / L on COD removal efficiency and
Turbidity (pH = 9, reaction time 60 minutes, electric current intensity 3 amps)
Figure 4 - The effect of electric current intensity (amps) on COD removal efficiency and
Turbidity (pH = 9, reaction time 60 minutes, electrical conductivity) 2850 µs / cm
Results from the influence of initial pH changes of incoming wastewater, time
Reaction (minutes) and electric current intensity (amps) on the pH of the effluent
The output of the reactor is shown in Figures 5 to 7. In the following,
Result of the effect of electric current intensity (amps) on the volume of sludge formation
() Ml / L and sludge volume index () ml / g in the combined process
. Electrocoagulation and flotation are shown in Figure 8


Figure 5 - The effect of changes in the initial pH of the incoming wastewater on the pH of the effluent
Reactor output with integrated process of coagulation and electrical flotation (reaction time
30 minutes, electrical conductivity, 2850 µs / cm electric current intensity 3 amps)
Figure 6 - The effect of reaction time (minutes) on the pH of the effluent from the reactor
With the combined process of electric coagulation and flotation (pH = 9, electrical conductivity
, 2850 /s / cm electric current intensity 3 amps)
the period . 4 No. 1. Spring 2016 Jalilvand et al. / 5
Figure -7 The effect of electric current intensity (amperes) on the pH of the effluent
Conduction from a reactor with an integrated process of coagulation and electrical flotation (pH = 9)
Electric, 2850 µs / cm Reaction time 60 minutes)
Figure - 8 The effect of electric current intensity (amps) on the volume of sludge formed
() Ml / L and sludge volume index () ml / g in the combined coagulation process and
Electric buoyancy (pH = 9, 60 min reaction time, electrical conductivity
) 2850 /s / cm
Discussion


PH effect


pH as an important parameter has a significant effect on process performance
Has ECF]. [1 According to Figure 1, increase the pH from 4 to the actual pH
Sewage () 5.6 leads to a decrease and from the actual pH of the sewage to pH = 9
Led to increased process efficiency. The results of this study are similar to the results
Masoudinejad et al. In 2012 on the removal of paint from
Wastewater of polyacrylic textile industry by electric coagulation process
So that the efficiency of COD removal at pH 7, 4 and 9
Respectively 31, 69 and 46 percent are reported]. [21 This
Photo results The results of Mirji et al. In 2015 were the highest
COD removal efficiency at pH around 7 due to wastewater use
Dairy synthetics (dissolution of powdered milk in water), the distance between the electrodes
(,) Cm1 boric acid, concentration of sodium chloride (,) 5 g / L voltage (8 volts)
And reported reaction time (60 minutes)]. [22
The results of this study also reverse the results of Yavies et al
2011 had the highest COD removal efficiency at true pH
Wastewater 5-7-6 relative to pH = 5 and pH = 6 due to the type of characteristics
Dairy industry wastewater used, type of anode electrode used (iron,)
The use of oxygenated water and sodium sulfate compounds in the coagulation process and
Reported electrical buoyancy]. [23 According to the results
From studies it can be said that changes in process efficiency due to changes
pH depends on the nature of the reaction between aluminum ions and hydroxide
Is. When the pH of the study is between 4-9 ions and
, Various monomeric species such as and and
Polymeric species such as and and
Which eventually become insoluble to non-crystalline
They deform through precipitation / polymerization kinetics]. [24
The clots have a larger surface area for
Absorption of soluble organic compounds and trapping of colloidal particles are useful
21 Studies have shown that at pH = 4 coagulation factors are likely
Effective supplier like and more that leads
. The higher the efficiency of the process compared to the pH of the wastewater has become real
At actual wastewater pH, the removal efficiency of contaminants is lower and
The reason is probably due to the lower density of coagulants
Soluble from be]. [25 Increase efficiency
Removal of contaminants at pH = 9 due to the production of different types of species
It is an effective coagulant that leads to increased process efficiency
The pH of the effluent has been verified]. [21 at a reaction time of 30 min with
Equal pH, 4 real wastewater (5.6 and 9) 76.99, 42.98, respectively
And 37.97% of turbidity during the combined process of coagulation and flotation
Electrical removed. These results are consistent with the results of Shiva Yoghimat and
Partners in 2015 has the highest turbidity removal efficiency
At pH = 7]. [26 So we can say that the ECF process
With aluminum electrode at alkaline pHs for this type
. Sewage is more efficient

Impact of reaction time


According to Faraday's law with increasing electrolysis time, ionic concentration
Production and as a result hydroxide clots increase and to this
The order of coagulation is formed]. [27 According to Figure 2 with increasing time
Reaction from 10 to 60 minutes, COD removal efficiency from 72.45%
It increases to 86.71%. These results are similar to Mirji and
Colleagues in 2015 showed that with increasing reaction time of
/ 6 Quarterly Journal of Health in the field of efficiency of coagulation and electric flotation in dairy wastewater treatment
5 to 30 minutes COD removal efficiency from 30% to 54.88%
Increases]. [22 Also, increasing the reaction time leads to an increase
The efficiency of the turbidity removal process was reduced. These results are consistent with Shiva results
Yoghimat et al. In 2015 showed an increase
Over time, the turbidity removal efficiency increases so that from time to time
15 minutes to 75 minutes on a real wastewater sample with an efficiency of 2.92
Percentage was obtained]. [26


Impact of electrical conductivity


The effect of electrolyte type and concentration on ECF process efficiency is widely understood
has been studied. Use sodium chloride to increase
The electrical conductivity of the environment is often greater than that of other compounds such as chloride
Potassium, sodium nitrate, sodium nitrite, etc. are superior], [28 because
Chloride ions have adverse effects on other anions such as
Reduced by preventing the deposition of calcium ions in wastewater
they give; Due to the deposition of sulfates and carbonates on the electrode surface,
Reduces process efficiency. Actually sediment in the form of a
The insulation layer on the electrode surface inhibits the dissolution of the metal. In a
Constant electric current intensity, the effect of increasing the electrolyte concentration, decreasing
The voltage between the electrodes. Based on a study by Hong et al
2008 Chloride ions can be present in solutions containing Al (OH) 3
.AlCl Medium species of Al (OH) Cl2, Al (OH) 2Cl and 3 Make up

AlCl4 ion formation in the presence of more chloride ions
To some extent, it helps to dissolve the species Al (III)
Aluminum species available for the reduced coagulation process
And thus leads to a reduction in filtration efficiency]. [29,30 Results
Figure 3 shows that with increasing sodium chloride to increase
Electrical conductivity of wastewater, COD removal efficiency under conducting conditions
Real electrical wastewater (2850 µs / cm without added chloride
Sodium) and add 1/5 g / L sodium chloride to the actual wastewater sample
The order decreased from 9.70% to 72.62%
According to a 2011 study on wastewater by Bensadok et al
Dairy synthetics using a combination of aluminum and platinum electrodes /
Titanium yielded similar results, as in the Bensadok study
Et al. In 2011 increased sodium chloride to wastewater samples
Up to a certain concentration (from 0.5 to), 1.5 g / L leads to increased efficiency
Removal of COD and further increase of sodium chloride concentration
Specific (from 1.5 to,) 2 g / L to the wastewater sample leads to a decrease in efficiency
COD removed. The reason for this increase and decrease in efficiency
COD removal is associated with the positive and negative effects of sodium chloride. Effect
Positive sodium chloride concentration, dissolution rate by aluminum electrode
Increases chemical and electrochemical corrosion and has a negative effect
Sodium chloride at higher concentrations by dissolution of Al (III) species
Chloride ions are present]. [30 to confirm the results and review
Further, repeat experiments were performed. In the repetition phase of direction tests
Eliminate most interfering factors in COD experiments such as ions
Chloride, due to the increase in the concentration of sodium chloride () 1/5 g / L in the sample
Actual wastewater and subsequently increase the concentration of chloride ions with the aim
Avoid combining chloride ions with silver and dichromate
Test COD and create an error in the test result, from 3 times the value
. The standard mercury sulfate consumption was used in the COD test
Under these conditions, the COD removal efficiency under electrical conductivity conditions
Real wastewater (without the addition of sodium chloride) and increase the chloride concentration
Sodium () 1/5 g / L to the actual wastewater sample from 9.70 to
Decreased by 45.65%. The cause of reduced efficiency can be affected
Negative sodium chloride searched for higher concentrations than before
It was discussed. Also at this stage by increasing the concentration of sodium chloride
Turbidity removal efficiency decreased from 08.99% to 33.92%
Found. This is in line with the results of a 2010 study by Kooshava et al
Which aims to investigate the removal of organic matter from dairy wastewater by the method
Electrochemical purification was carried out, corresponds to]. [31 So do
The process (on real dairy wastewater) requires the addition of chloride
Sodium does not cause changes in the electrical conductivity of this wastewater
And this point in terms of economics and not producing more volume of chemical sludge
. It is important


Influence of electric current intensity


According to Faraday's law, the production of aluminum ions eliminates COD strongly
The flow and reaction time are dependent. Electric current intensity as
The most important operational parameter determines the dose of electrochemical metal
To water and electrolyte bubble production density]. [32,33 glossy surfaces
Like stainless steel, it produces the best bubbles in terms of size and flux
Plays an important role in flotation of particles of different sizes
Plays; So that as the intensity of the flow increases, the size of the gas bubble
Decreases]. [33 So by decreasing the size and increasing the bubble density
Gas is the best efficiency in the process of electric flotation
34. According to the results of Figure 4, with increasing electric current intensity,
Contaminant removal efficiency increases; In the least amount
Removal of COD and turbidity at an electrical current of 0.25 amps
Respectively 51.57 and 82.96% and the highest rate of COD removal and
the period . 4 No. 1. Spring 2016 Jalilvand et al. / 7
Turbidity at 5 amps electric current 97.97 and 63.99, respectively
Percentage was obtained. This result is consistent with the results of the study of Imam Juma et al
In 2009 corresponds to the goal of examining the elimination of pollutants
By processes of electrical coagulation, electrical coagulation and flotation,
Performed]. [18 According to Figure 8 Increase the intensity of electric current
From 0.25 amps to 5 amps, the sludge volume is 5.62 and 210 ml, respectively
Per liter and sludge volume index of 8.223 and 82.547 mm, respectively
Liters per gram was obtained. But according to a study by Goltick et al
2012 Sludge volume index with good sedimentation in flow intensity
.Electrical 3 amps equivalent to 01.89 ml / g was analyzed]

Effluent pH changes


According to the results of the chart, 5 values ​​of 16.3, 1/96 and 0.86 units to the values
Initial pH during the process of electrical coagulation and flotation with time
The reaction lasted 30 minutes and the current intensity was increased to 3 amps. Increased pH
Output in acidic environment () pH = 4 and real wastewater () 5.6 to
The reason is the gradual production of hydrogen gas around the cathode electrode and formation
Is ion. Increasing the pH of the output in an alkaline environment by a small amount,
Caused by the formation of Al (OH) 3 around the anode electrode which is caused
Release and decrease pH or may be due to formation
Hydroxide deposits of other cations that consume alkalinity
21] Based on the results of Figure 6 with increasing time from 30 to 60
The value of 6.1 units is added to the initial pH of the solution
With increasing time, the production of hydroxyl ions in the cathode increases and
This factor increases the pH of the effluent. In accordance with the results of the chart
7. Increase the electric current intensity from 0.25 to 5 amps, respectively
0.22 and 1/3 units are added to the initial pH of the solution. The results of this
A study with the results of a study conducted by Ruiz in 2012 in
The pH of the effluent during the process of electrical coagulation on industrial wastewater
Dairy with an increase of 2.5-2 units as well as Brahmi et al
Corresponded to 2015]. [36,37


Conclusion


Industrial wastewater treatment plant of Hamatan dairy processing plant
Damavand using aluminum electrodes as anode and electrode
Steel as a cathode in an integrated coagulation and flotation process
Electrical in the electrochemical reactor with intermittent current studied
it placed. Results of investigating the effect of operational parameters on the rate
Process efficiency showed that the pH of the solution, the intensity of the electric current and
Reaction time of parameters affecting COD removal efficiency and turbidity
Is. The range of optimal operating conditions in order to achieve the maximum
Removal efficiency at, pH = 9, electric current intensity 3 amps and time
The reaction lasted 60 minutes under which the COD removal efficiency
And turbidity of 9.70 and 0.99%, respectively, and an increase of 6.1 units in
The pH of the effluent leaving the reactor relative to the pH entering the reactor and
The sludge volume index was 0.89 ml / g. In total according to
The results obtained can be stated that this process can be
As an environmentally friendly method in plant wastewater treatment
Processing of dairy products to reduce the concentration of contaminants and readiness
It is intended for entry into other treatment plants, such as biological plants
The reason for increasing the BOD5 / COD ratio from (0.41 of raw wastewater) to
. effluent should be considered taking into account the economic aspects