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Advances in Treatment of Vegetable Oil Refining Wastes

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Environmental and Natural Resources Engineering

Part of the book series: Handbook of Environmental Engineering ((HEE,volume 19))

Abstract

Vegetable oils are mainly extracted from soybean, sesame, sunflower, corn, canola, and cotton seeds. Their yields, compositions, and physical and chemical properties determine their usefulness in various applications aside from edible uses. Crude oils obtained by pressing of such vegetable seeds are not usually considered to be edible before the removal of various nonglyceride compounds through an operation known as refining. The vegetable oil refinery uses various types of physical and chemical processes to offer a premium quality of oil. The refining processes remove undesirable materials, such as phospholipids, monoacylglycerols, diacylglycerols, free fatty acids, color and pigments, oxidized materials, etc., but may also remove valuable minor components, such as antioxidants and vitamins (carotenes and tocopherols). The major steps involved in chemical refining include degumming, deacidification, deodorization, and neutralization processes. During these processes, a high amount of water is used, and highly polluted effluents are formed. The treatment of vegetable oil refinery wastewaters has been a major problem of environmental concern in developing countries for the last decades due to their complex nature consisting of water and soluble and insoluble substances that contain fats and oil, carbohydrates, phenolic compounds, and suspended solids. Therefore, a suitable wastewater treatment prior to their discharge into the receiving bodies is required. Numerous treatment technologies have been applied to treat oily wastewaters. Coagulation/flocculation, electrocoagulation, reverse osmosis, flocculation/membrane filtration, air flotation, microfiltration, and enzymatic catalysis are the most common ones. However, due to the complex nature and low biodegradability of the oily wastewater, some of these technologies may not be efficient in treating such wastewaters, while others may be of high cost and generally require a pretreatment. As a result, in this chapter, the processes involved in the vegetable oil refining, the environmental impacts of those processes, the characterization of the waste produced during the processes, waste reduction at source, recovery from waste, and treatment technologies are discussed.

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Abbreviations

BOD:

Biochemical oxygen demand

COD:

Chemical oxygen demand

DAF:

Dissolved air flotation

DGF:

Dissolved gas flotation

FFA:

Free fatty acids

IAF:

Induced air flotation

MBR:

Membrane bioreactors

NOx:

Oxides of nitrogen

TSS:

Total suspended solids

UF:

Ultrafiltration

VOC:

Volatile organic compounds

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Author information

Authors and Affiliations

  1. Department of Civil and Environmental Engineering, University of Maryland, College Park, MD, USA

    Devrim Kaya

  2. Department of Civil and Environmental Engineering, Cleveland State University, Cleveland, OH, USA

    Yung-Tse Hung

Authors
  1. Devrim Kaya
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  2. Yung-Tse Hung
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Editor information

Editors and Affiliations

  1. Rensselaer Polytechnic Institute Troy, Lenox Institute of Water Technology, Newtonville, NY, USA

    Lawrence K. Wang

  2. Lenox Institute of Water Technology, Krofta Engineering Corporation Lenix, MA, Newtonville, NY, USA

    Mu-Hao Sung Wang

  3. Department of Civil and Environmental Engineering, Cleveland State University, Cleveland, OH, USA

    Yung-Tse Hung

  4. Lenox Institute of Water Technology, Krofta Engineering Corporation Lenix, MA, Newtonville, NY, USA

    Nazih K. Shammas

Glossary [81,82,83]

Aerobic

An environmental condition in which free and dissolved oxygen is available in an aqueous environment (for instance, nitrification is an aerobic process).

Anaerobic

(a) An environmental condition in which free, dissolved, and combined oxygen is unavailable in an aqueous environment (i.e., dissolved oxygen = 0 mg/L). (b) A condition in which atmospheric or dissolved molecular oxygen is NOT present in the aquatic (water) environment.

Coagulation

(a) The clumping together of very fine particles into large particles (floc) caused by the use of chemicals (coagulants). (b) A process of destabilizing charges of suspended and colloidal particles in water by adding chemicals (coagulants). In coagulation process, positively charged chemicals are added to neutralize or destabilize these negative charges and allow the neutralized particles to accumulate and be removed by clarification (flotation or sedimentation) and/or filtration.

Dissolved air flotation (DAF)

(a) A method of solids separation, whereby a side stream is saturated with air at high pressure and then injected into the flotation tank to mix with the incoming water stream. As the air bubbles rise to the surface, they attach to floc particles and create a sludge layer at the surface of the tank, which is then removed for disposal. (b) One of the dissolved gas flotation (DGF) processes when air is used for generation of gas bubbles. A typical example is Krofta Engineering Corporation’s Supracell clarifier; see dissolved gas flotation (DGF).

Dissolved gas flotation (DGF)

It is a process involving pressurization of gas at 25–95 psig for dissolving gas into water and subsequent release of pressure (to 1 atm) under laminar flow hydraulic conditions for generating extremely fine gas bubbles (20–80 microns) which become attached to the impurities to be removed and rise to the water surface together. The impurities or pollutants to be removed that are on the water surface are called float or scum which are scooped off by sludge collection means. The clarified water is discharged from the flotation clarifier’s bottom. The gas flow rate is about 1% of influent liquid flow rate. The attachment of gas bubbles to the impurities can be a result of physical entrapment, electrochemical attraction, surface adsorption, and/or gas stripping. The specific gravity of the bubble-impurity agglomerate is less than one, resulting in buoyancy or non-selective flotation (i.e., Save-All).

Electroflotation

It is process involving the generation of hydrogen and oxygen bubbles in a dilute electrolytic aqueous solution by passing a direct current between two electrodes: (a) anode and (b) cathode. Anode reaction generates oxygen bubbles and hydrogen ions, while cathode reaction generates hydrogen bubbles and hydroxide ions. Either aluminum or steel sacrificial electrodes can be employed for generating the gas bubbles as well as coagulants at the same time. Non-sacrificial electrodes are employed for generating the gas bubbles only and can be made of titanium (as the carrier material) and lead dioxide (as the coating material). Electrical power is supplied to the electrodes at a low voltage potential of 5–20 VDC by means of a transformer rectifier. Small bubbles in the range of 20–50 m microns are produced under laminar hydraulic flow conditions feasible for flotation separation of fragile flocs from water in a small system. The floats on the water surface are the impurities/pollutants removed from water. The clarified water is discharged from the flotation clarifier’s bottom. There can be unexpected advantages and disadvantages when electroflotation is employed. For instance, chlorine bubbles may be generated as a water disinfectant if the water contains significant amount of chloride ions. Certain unexpected gas bubbles may be generated and may be undesirable.

Filtration

It is usually a granular medial filtration process which involves the passage of wastewater or water through a bed of filter media with resulting deposition of suspended solids. Eventually the pressure drop across the bed becomes excessive or the ability of the bed to remove suspended solids is impaired. Cleaning is then necessary to restore operating head and effluent quality. The time in service between cleanings is termed the filter run time or run length. The head loss at which filtration is interrupted for cleaning is called the terminal head loss, and this head loss is maximized by the judicious choice of media sizes. Dual media filtration involves the use of both sand and anthracite as filter media, with anthracite being placed on top of the sand. Gravity filters operate by either using the available head from the previous treatment unit or by pumping to a flow split box after which the wastewater flows by gravity to the filter cells. Pressure filters utilize pumping to increase the available head. A filter unit generally consists of a containing vessel; the filter media; structures to support the media; distribution and collection devices for filter influent, effluent, and backwash water flows; supplemental cleaning devices; and necessary controls for flows, water levels, and backwash sequencing. Backwash sequences can include air scour or surface wash steps. Backwash water can be stored separately or in chambers that are integral parts of the filter unit. Backwash water can be pumped through the unit or can be supplied through gravity head tanks.

Induced air flotation (IAF)

It is one of the induced gas flotation processes in which the gas is air.

Refinery

A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.

Refining waste

A refining waste or refinery waste is the waste or wastewater from a refinery.

Vacuum flotation

In vacuum flotation, the influent process water to be treated is usually almost saturated with air at atmospheric pressure. There is an air-tight enclosure on the top of the flotation chamber in which partial vacuum is maintained. The fine air bubbles (20–80 microns) are generated under laminar hydraulic flow conditions by applying a vacuum (negative pressure) to the flotation chamber. The theory is that the lower the pressure, the lower the air solubility in water. The soluble air originally in water is partially released out of solution as extremely fine bubbles due to a reduction in air solubility caused by negative vacuum pressure. The bubbles and the attached solid particles rise to the water surface to form a scum blanket, which can be removed by a continuous scooping or skimming mechanism. Grit and other heavy solids that settle to the bottom are raked to a central sludge sump for removal. Auxiliary equipment includes an aeration tank for saturating the water or wastewater with air, vacuum pumps, and sludge pumps.

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Kaya, D., Hung, YT. (2021). Advances in Treatment of Vegetable Oil Refining Wastes. In: Wang, L.K., Wang, MH.S., Hung, YT., Shammas, N.K. (eds) Environmental and Natural Resources Engineering. Handbook of Environmental Engineering, vol 19. Springer, Cham. https://doi.org/10.1007/978-3-030-54626-7_8

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