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Introduction (What is DAF and how it Works)

DAF or Dissolved Air Flotation is a Physio-chemical treatment strategy which utilises the proven efficiency of coagulation-flocculation in combination with injection of very fine air bubbles which attach to and float the flocculated particles to the surface. From here they can be mechanically removed from the clarified water below. This works well for removal of low-density solids.

DAF is a relatively new type of technology – that is compared to some of mankind’s earliest recorded efforts in water purification. This can be dated back to around 2000 B.C. This seemingly endless pursuit started in prehistoric times as recorded in Sanskrit medical lore and Egyptian inscriptions (Baker, 1981).

As we refined, qualified, and quantified our definitions of purified water, new challenges arose. This can be almost entirely attributed to the progression of technology, the industrial revolution and the resultant jump in manufacturing and processing activities which followed. The increasing complexity and difficulty of dealing with effluents, as well as increased pressure on potable water supply has been a driving force which pushed the development of new and unconventional strategies to achieve results. Our objectives have also evolved since the early need to purify our drinking water. “Environmental impact” has become a buzzword due to the systematic degradation of our natural resources as population growth continues. It is therefore of great importance to protect these resources by acting with the best practise hierarchy in mind: The most desirable outcome being avoiding the use of a resource, followed by reducing the amount used. The least desirable outcome is the disposal of waste generated. The second least desirable outcome is treating the waste generated. This is preceded by recovery of waste, recycling and re-use right below reducing use and avoiding use altogether.

Background on Edible Oil Industry in SA

One industry which uses substantial volumes of water and produces equally substantial effluent streams is the edible seed oil industry (Water Research Commission, 2017). According to BFAP, South Africa’s total vegetable oil demand has increased by an average 3% per annum during the past ten years; 41% of this was produced locally in 2017. During the oil production process, waste streams are generated throughout various steps. Much of this includes water used in boilers, heat exchange and cooling towers – these streams are kept separate from the oils and can therefore be reused with ease. There are, however, the processes which make up extraction, washing and refining steps where water is contaminated with oil and by-products leading to this water being wasted. Water usage in general has not been well documented in the South African edible oil industry due to lack of participation. All WRC study respondents from the seed oil industry in SA do however use municipal water and an effort to reduce usage as well as waste can result in significant savings. This will be crucial for the survival of many industries as the water costs in SA are predicted to rise considerably in the coming decades due to climate change, population growth and increased pressure on water supplies.

Recommendations for optimising water efficiency in the EOI

Recommendations for optimising water efficiency in the edible oil industry have been given in the most recent edition of NATSURV 6: Water and Wastewater Management in the Edible Oil Industry (Edition 2) as follows:

 

Applicability of DAF in the EOI

Treating oily effluent is, without a doubt, a challenging undertaking but technological developments and thinking out of the box has made this possible. The use of Dissolved Air Flotation is a particularly effective method of separating solids from an oily wastewater stream.

Refining activities account for most of the wastewater in terms of volume as well as strength. These effluent streams can be broadly classified as being: 1.) Wastewater from distilling, or oil washing and deodorising – This stream will contain large quantities of free fatty acids as well as residual gums, aromatics, pesticides and degumming acids including phosphoric acid. 2.) Acid wastewater from soap splitting which will contain excess sulphuric acid as well as free fatty acids and other organics that may have adhered to the soap. Wastewater from the production of various value-added products like soap, candles, margarine, and mayonnaise will likely all end up in the final wastewater and impact the treatability severely. This is especially true for emulsifying agents used during margarine production which prevent effective gravity settling of solids after flocculation. This is due to one of the elements in the emulsifier having an affinity towards water and the other towards oil – effectively creating a suspension. And this is the point where DAF really begins to shine. A correctly designed chemical dosing pre-treatment program will effectively break these emulsions and allow removal of emulsified and free oil during flotation.

Parameters measured in final effluent from the Edible oil industry are COD, Fats, Oils and Grease (FOG), total suspended solids and pH. Phosphates and sulphates may also be high. If the DAF operates effectively, polishing can be applied in the form of Reverse Osmosis. Effluent can be treated to a degree of purity at which point it can be used as boiler and cooling tower feed water, further reducing freshwater requirements. Complete removal of oil is required prior to carrying out RO treatment to avoid fouling the RO membranes

Watericon has successfully assisted clients in the EOI to treat and re-use almost all of their oily effluent thus reducing their reliance on municipal supply, as well as volumes of waste requiring disposal.

-Background on Edible seed oil industry & water usage

-Benefits (reduced footprint, high rate of clarification, enhanced removal of light materials-organic) specifically to edible oil industry

-Best practises

– Circular economy

Waste as a resource

-Valorization of sludge: second generation biofuels

 

 

REFERENCES

 

  1. BFAP Baseline Agricultural Outlook 2020 – 2029. BFAP.

AgriOrbit. 2020. Market Segmentation Of Edible Vegetable Oils – Agriorbit. [online] Available at: <https://www.agriorbit.com/market-segmentation-of-edible-vegetable-oils/> [Accessed 15 September 2020].

Baker, M., 1981. The Quest For Pure Water. Denver: American Water Works Association.

Crossley, I. and Valade, M., 2006. A review of the technological developments of dissolved air flotation. Journal of Water Supply: Research and Technology-Aqua, 55(7-8), pp.479-491.

Oilngasprocess.com. 2020. Emulsifying Agent | Oil & Gas Process Engineering. [online] Available at: <http://www.oilngasprocess.com/oil-handling-surfacefacilities/emulsifying-agent.html#:~:text=Some%20element%20in%20the%20emulsifier,more%20attracted%20to%20the%20water.&text=It%20decreases%20the%20interfacial%20tension,droplets%2C%20which%20can%20settle%20quickly.> [Accessed 17 September 2020].

Water Research Commission, 2017. Water And Wastewater Management In The Edible Oil Industry (Edition 2). Natsurv 6. [online] Water Research Commission. Available at: <http://www.wrc.org.za> [Accessed 16 September 2020].