**2. Assessment of physicochemical treatment processes on dairy wastewater**

Wastewater characterisation plays an important role when the wastewater treatment system is designed. The COD concentration of dairy wastewater varies considerably [23]. Pollution load of a company wastewater producing yogurt in the sector and pollution load of a company wastewater producing cheese are very different. Since yogurt and ayran production plants have low oil-grease and COD parameters, they generally provide only physical + biological treatment and discharge standards. However, since the oil-grease and KOI parameters are high in the cheese producing plants, the physical + chemical + biological treatment units are generally preferred in the small-scale plants.

In many countries, the wastewater of dairy and dairy products is among the sources that cause significant pollution of natural aquatic environments. Numerous studies have been conducted to date to considerably reduce the adverse effects of these wastewaters [24].

Physicochemical processes are widely used for treatment of industrial wastewaters. Summarised literature of the dairy industry wastewater treated with physico-chemical processes are given in **Table 3**.

#### **2.1. Chemical precipitation and coagulation/flocculation processes**

Some physical-chemical-biological processes are usually interacting such as chemical precipitation, colloids' aggregation by coagulation-flocculation processes. In most processes, both precipitation and coagulation-flocculation happen simultaneously.

Chemical precipitation involves the addition of chemicals to separate the dissolved and suspended solids by sedimentation and used for primary settling facilities. In current practice, phosphorus and heavy metal removal can be realised. Many substances have been used as precipitants over the years such as alum, ferric sulphate, ferrous sulphate, and so on. They are used primarily for the treatment of metallic cations, anions, organic molecules, detergents and oily emulsions [44].

Coagulation/flocculation processes are used basically to separate suspended, colloidal and dissolved contents from wastewater and they applied directly to raw wastewater [45]. The process can be divided into two categories. The first one named coagulation is the process where chemicals (coagulant agents) such as iron or aluminium are used to overcome the factors which promote the stability of the system. The second process named flocculation makes destabilised particles come together and they can be separated easily through gravity settling [46]. A few studies have been studied in the literature for the coagulation of dairy wastewater. The literature studies are summarised at **Table 3**.

#### **2.2. Adsorption process**

**2. Assessment of physicochemical treatment processes on dairy** 

**Dairy effluent**

pH 8.34 7.2–8.8 7.9 ± 1.2 7.2–7.5 6–9 6–9

Oil & grease (mg/L) — — — — 10 30 Total nitrogen (TN) (mg/L) — — — — 10 — Total phosphorus (TP) (mg/L) — — — — 2 — References [17] [18] [19] [20] [21] [22]

**Arab dairy factory**

4840.6 1200–1800 1941 ± 864 1300–1600 50 —

10251.2 1900–2700 3383 ± 1345 2500–3000 250 160

5802.6 500–740 831 ± 392 72,000–80,000 50 —

**Dairy wastewater** **World Bank report**

**Turkish discharge standards**

are generally preferred in the small-scale plants.

**Milk and dairy products factory**

182 Technological Approaches for Novel Applications in Dairy Processing

cesses are given in **Table 3**.

Wastewater characterisation plays an important role when the wastewater treatment system is designed. The COD concentration of dairy wastewater varies considerably [23]. Pollution load of a company wastewater producing yogurt in the sector and pollution load of a company wastewater producing cheese are very different. Since yogurt and ayran production plants have low oil-grease and COD parameters, they generally provide only physical + biological treatment and discharge standards. However, since the oil-grease and KOI parameters are high in the cheese producing plants, the physical + chemical + biological treatment units

**Table 2.** Characteristics of some dairy industry wastewaters and discharge standards of dairy effluents (adapted from [2, 14]).

In many countries, the wastewater of dairy and dairy products is among the sources that cause significant pollution of natural aquatic environments. Numerous studies have been conducted to date to considerably reduce the adverse effects of these wastewaters [24].

Physicochemical processes are widely used for treatment of industrial wastewaters. Summarised literature of the dairy industry wastewater treated with physico-chemical pro-

Some physical-chemical-biological processes are usually interacting such as chemical precipitation, colloids' aggregation by coagulation-flocculation processes. In most processes, both

**2.1. Chemical precipitation and coagulation/flocculation processes**

precipitation and coagulation-flocculation happen simultaneously.

**wastewater**

Biochemical oxygen demand

Chemical oxygen demand

Total suspended solids (TSS)

(BOD) (mg/L)

(COD) (mg/L)

(mg/L)

Adsorption has been found to be attractive for the removal of organic compounds from wastewater [47]. There are many types of adsorbents including activated carbon, synthetic polymeric



and silica-based adsorbents. The most useful one is activated carbon because of cost efficiency and ability to adsorb wide range of organic compounds. Adsorption can be classified as physical and chemical adsorption. Van der Waals forces are used in physical adsorption and activated carbon is the best example of physical adsorption. A chemical reaction occurs between adsorbate and adsorbent, but it does not have a wide application in wastewater

**Table 3.** Summarised literature of the dairy industry wastewater treated with physico-chemical processes.

**Treatment process Characterisation Remove/removal efficiency (%) References**

98.84% COD removal, 97.95% BOD5 removal, 97.75% TSS removal, and >99.9% bacterial indicators at 60 V

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COD: 87% (the optimum current intensity, pH and electrolysis time

75 min, respectively. Mean energy consumption was 112.9 kWh/kg)

and were 3A, 9,

[42]

185

[43]

during 60 min

for 1070 mg/dm<sup>3</sup>

were used in the presence of potassium chloride as

electrolytes

plates were used as sacrificial electrodes

Adsorption onto solid surfaces has various applications and used to remove organics, chemicals, heavy metals, and so on [49]. Fly ash, rice husk ash, and bagasse fly ash and activated

Membrane processes such as microfiltration, ultrafiltration, nanofiltration, dialysis, electrodialysis and reverse osmosis are very promising methods [49]. Membrane filtration can be defined as removal or separation of particulate and colloidal substances from a liquid which

Several works focused on treatment of dairy wastewater by membrane operations. The use of membrane filtration technology offers a wide range of advantages for the consumer. The membrane technology is a novel nonthermal environmental friendly technology within future possibilities that minimises the adverse effect of temperature rise such as change in

Electrolysis is the degradation of organic or inorganic substances by using electrical charge. Oxidation and reduction reactions occur in electrolytic cell which contains an anode and cathode. When you apply electric to cell, negative ions will migrate to anode and positive ions will migrate to cathode and cations will be reduced and anions will be oxidised at both electrodes [48]. Electrocoagulation, electroflotation and anodic oxidation processes are some

phase, denaturation of proteins and change in sensory attributes of the product.

treatment [48].

carbon are some of low-cost adsorbents.

Electrocoagulation Aluminium electrodes

Electrocoagulation Direct current-aluminium

work as selective barrier and are typically 0.0001–1.0 μm.

**2.3. Membrane processes**

**2.4. Electrochemical process**

examples used for dairy treatment.


**Table 3.** Summarised literature of the dairy industry wastewater treated with physico-chemical processes.

and silica-based adsorbents. The most useful one is activated carbon because of cost efficiency and ability to adsorb wide range of organic compounds. Adsorption can be classified as physical and chemical adsorption. Van der Waals forces are used in physical adsorption and activated carbon is the best example of physical adsorption. A chemical reaction occurs between adsorbate and adsorbent, but it does not have a wide application in wastewater treatment [48].

Adsorption onto solid surfaces has various applications and used to remove organics, chemicals, heavy metals, and so on [49]. Fly ash, rice husk ash, and bagasse fly ash and activated carbon are some of low-cost adsorbents.

#### **2.3. Membrane processes**

**Treatment process Characterisation Remove/removal efficiency (%) References**

180 mg/l

500 mg/l

removal efficiency

flux around 10–11 L/h.m<sup>2</sup>

TKN: 96%, conductivity: 97% and

Dairy industry wastewater can be

MBR: COD: 98%, nutrients: 86% (86% nitrogen and 89% phosphorus) NF: COD: 99.9%, TSS: 93.1%

TOC: 99.8%,

lactose: 99.5%

recycled and reused

electrolysis time of 7 min)

COD: 61%

treatment of COD.

density of 100 mA/cm<sup>2</sup>

of 7,4)


IrO2

than 60 min

50 mA/cm<sup>2</sup>

Phosphorus: 89%, nitrogen: 81%,

20 min electrolysis was enough for the

removal was completed at a current

/Ti electrode and complete decolourisation was achieved less

at 10 min

by using

Weak wastewater: Doses: 550,180,

[11]

[31]

[33]

[35]

[36]

[16]

[37]

[38]

[39]

[40]

[41]

COD: 76, 88 and 82%, respectively Strong wastewater: Doses: 500, 500,

COD: 45, 28 and 29%, respectively

TSS: activated carbon had a better

Phospate: 100% in the first 15 min. [32]

as coagulant FeCl3

powdered activated carbon, bagasse, straw dust, saw dust, fly ash and coconut coir as adsorbent

benthonite as adsorbent

osmosis (pre-treated the wastewater with coagulant

Electrocoagulation COD: 98% (at optimum conditions at

Electroflocculation Iron electrodes organic matter: 97.4% (at final pH

Electrochemical process Sn/Sb/Ni-Ti coated anodes COD: 98% at a current density of

and PAC before)

nanofiltration

as used

electrodes

Membrane process Reverse osmosis 95% water recovery with an average

Membrane process Reverse osmosis Conductivity: 98.2%, COD: 97.8% [34]

Coagulation/flocculation FeCl3

Adsorption low cost adsorbents like

184 Technological Approaches for Novel Applications in Dairy Processing

Adsorption lanthaum modified

Membrane process Ultrafiltration + reverse

Membrane process Membrane bioreactor +

Electrocoagulation Soluble aluminium anode

Combined electrode system Iron and aluminium

Electrochemical oxidation IrO2

Membrane processes such as microfiltration, ultrafiltration, nanofiltration, dialysis, electrodialysis and reverse osmosis are very promising methods [49]. Membrane filtration can be defined as removal or separation of particulate and colloidal substances from a liquid which work as selective barrier and are typically 0.0001–1.0 μm.

Several works focused on treatment of dairy wastewater by membrane operations. The use of membrane filtration technology offers a wide range of advantages for the consumer. The membrane technology is a novel nonthermal environmental friendly technology within future possibilities that minimises the adverse effect of temperature rise such as change in phase, denaturation of proteins and change in sensory attributes of the product.

#### **2.4. Electrochemical process**

Electrolysis is the degradation of organic or inorganic substances by using electrical charge. Oxidation and reduction reactions occur in electrolytic cell which contains an anode and cathode. When you apply electric to cell, negative ions will migrate to anode and positive ions will migrate to cathode and cations will be reduced and anions will be oxidised at both electrodes [48]. Electrocoagulation, electroflotation and anodic oxidation processes are some examples used for dairy treatment.

Electrocoagulation is an effective and promising treatment method subject of numerous publications. It has been shown that this method is particularly effective for a wide range of pollutants (heavy metals, organic compounds, microorganisms and various others). For this reason, it is considered as one of the more promising water remediation techniques.

solid material, turbidity, heavy metal, colour removal purposes. The treatment efficiency is affected by such factors such as the parameter to be eliminated, the chemical substance used, the duration of the detention, the intensity of the mixture; the amount of sludge formed can be more or less than the chemical substance. Compared to biological processes, advantages such as ease of operation, removal of the non-degradable part of the organic material, removal of

Physico-Chemical Treatment of Dairy Industry Wastewaters: A Review

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187

the treatment efficiency from changes are caused to be particularly preferred.

Faculty of Engineering, Department of Environmental Engineering, Uludag University,

[1] Tikariha A, Omprakash S. Study of characteristics and treatments of dairy industry waste water. Journal of Applied & Environmental Microbiology. 2014;**2**(1):16-22. DOI:

[2] Kushwaha JP, Srivastana C, Mall ID. An overview of various technologies for the treatment of dairy wastewaters. Critical Reviews in Food Science and Nutrition. 2011;**51**:442-

[3] The World Daıry Sıtuatıon. Bulletin of the International Dairy Federation 485/2016; 2016.

[4] Sivrioğlu Ö, Yonar T. Determination of the acute toxicities of physicochemical pretreatment and advanced oxidation processes applied to dairy effluents on activated sludge.

[5] Singh NB, Singh R, Imam MM. Waste water management in dairy effluents: Pollution abatement and preventive attıtudes. International Journal of Science, Environment and

[6] Sarkar B, Chakrabari PP, Viyajkumar A, Kale V. Wastewater treatment in dairy industries-possibility of reuse. Desalination. 2006;**195**:141-152. DOI: 10.1016/j.desal.2005.11.015

[7] Deshmukh DS.Wastewater generation and its treatment in dairy industries. International Journal of Application of Engineering and Technology. 2017;**2**(3):25-35. ISSN: 2321-8134

[8] Kiliç A. Süt endüstrisi atıksularının arıtımında ardışık kesikli reaktörde (SBR) hareketli

Journal of Dairy Science. 2015;**98**(4):2337-2344. DOI: 10.3168/jds.2014-8278

Taner Yonar\*, Özge Sivrioğlu and Nihan Özengin

452. DOI: 10.1080/10408391003663879

Technology. 2014;**3**(2):672-683. ISSN: 2278-3687 (O)

biofilm uygulaması [thesis]. Selçuk Üniversity; 2006

\*Address all correspondence to: yonar@uludag.edu.tr

**Author details**

Bursa, Turkey

**References**

10.12691/jaem-2-1-4

ISSN 0250-5118

EC is a primary wastewater treatment for inducing the controlled electrogeneration of flocculants/coagulants on site, usually under the application of a constant current. It is a complex process involving several chemical and physical phenomena with the formation of iron or aluminium cations from the dissolution of the corresponding sacrificial anode(s) and the simultaneous production of OH− anions by cathodic reduction of water. The polymeric metal hydroxides formed act as excellent coagulating agents to favour the removal of dissolved, colloidal, or suspended matter, eventually yielding great percentages of removal of colour and turbidity. Coagulation mainly occurs by destabilisation, once the metal cations combine with the negatively charged particles moving towards the anode by electrophoretic motion [49].
