Determination of Oil and Grease in Water

INTRODUCTION 

The term grease is used to describe semisolid lubricants. Although the word grease is also used to describe rendered fat of animals, in the context of lubrication, grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil. Any filterable solvent-soluble substances (e.g., elemental sulfur, complex aromatic compounds, hydrocarbon derivatives of chlorine, sulfur, and nitrogen, and certain organic dyes) that are extracted and recovered are defined as oil and grease. No known solvent will dissolve selectively only oil and grease. Heavier residuals of petroleum may contain a significant portion of materials that are not solvent- extractable.

The characteristic feature of greases is that they possess a high initial viscosity, which upon the application of shear, drops to give the effect of an oil-lubricated bearing of approximately the same viscosity as the base oil used in the grease. This change in viscosity is called thixotropy. Grease is sometimes used to describe lubricating materials that are simply soft solids or high viscosity liquids, but these materials do not exhibit the shear-thinning (thixotropic) properties characteristic of the classical grease. For example, petroleum jellies such as Vaseline are not generally classified as greases.

Oil and grease has the natural tendency to float on the water surface under quiescent conditions, as the density of oil and grease is usually less than one. Not all the oil and grease is in liquid or solid form. Appreciable amounts remain in a finely divided emulsified form.

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Oil and grease is an important parameter for water quality and safety. Regulatory bodies worldwide set limits in order to control the amount oil and grease entering the water reservoirs or the sea through industrial discharges and also limit the amount present in drinking water.

Greases are used where a mechanism can only be lubricated infrequently and where a lubricating oil would not stay in position. They also act as sealants to prevent ingress of water and incompressible materials. Grease-lubricated bearings have greater frictional characteristics due to their high viscosity.

OBJECTIVE(S)

• To learn how to measure the oil level in water.
• To learn the partition gravimetric method.
• To calculate the oil and grease content in water sample (SST Lake).

METHODOLOGY

MATERIALS

• Petroleum ether
• Sulfuric acid (1:2, prepared by adding 50 ml concentrated sulfuric acid slowly to 100 ml distilled water)
• Ethyl alcohol (C2H5OH)
• Separating funnel (500 ml)
• Filter paper
• Filter funnel
• Conical flask
• Hot water bath

Analytical balance

The sample is allowed to stand until two layers, which are petroleum ether at the upper and water at the bottom.

The water at the bottom is discarded from the funnel and the petroleum ether on the top is drained through the filter paper inside the filter funnel into the pre-weighed conical flask.

Some fresh petroleum ether is poured through the filter paper to ensure no oil and grease stuck in the paper.

The conical flask is placed in the hot bath and allows the petroleum ether to evaporate. The conical flask is allowed to cool and weigh.

10mL of sulfuric acid, 50mL of Petroleum ether and 3mL Ethyl alcohol are added to 230 mL sample in separating funnel. The funnel is well shaken.

METHOD

PRINCIPAL ANALYSIS

Chemicals which contained mainly aliphatic and aromatic hydrocarbon also referred to the term “oil and grease” which derived from varied sources that is from the crude petroleum and also from the industrial derivatives. Because of low biodegradability the major contaminant of concern are oil and grease originate from petroleum (fossil fuel) and also their derivatives which can be found widely used in industries.

Based on the Environmental Quality (Sewage and Industrial Effluents) Regulation 1979 there are standard had been made that is Standard A is for the discharge upstream of drinking water take-off and Standard B is for the inland water.

Sample is extracted into petroleum ether in the presence of sulphuric acid. The acid acts to release fatty acids, which are present as insoluble calcium and magnesium precipitates, for further analysis; for an example:

Ca (C17H33COO)2 + 2H+ –> 2C17H35COOH + Ca2+

RESULT

Table 2.0 Determination of oil in water

Items: Conical flask

Weight (g): 113.955

Items: Conical flask + oil

Weight (g): 113.993

Items: Oil

Weight (g): 0.038

Formula: Oil and grease (mg/L-1) = 1000 x (Wa – Wb)

Wa = weight conical flask + residue after evaporation

Wb = weight of pre weighted conical flask

V = volume of sample

= 1000 x (113.993 – 113.955 )

250 ml

= 0.152 mg/L-1

DISCUSSION

Oil and grease are the important parameters that are used in water quality measurement. The presence of oil and grease always can be seen in a water sample. What varies in the presence of the oil and grease in a water sample is the amount. The amount of oil and grease can be high or low depending on the water sample and the nature of the water. To determine the amount of oil and grease that present in the water sample we use the partition gravimetric method. This method involves the extraction of dissolved or emulsified oil and grease from water by using an extracting solvent. Oil and grease in the water sample are referred to the all the filterable solvent soluble substances such as elemental sulfur, complex aromatic compounds, hydrocarbon derivatives of chlorine, sulfur and nitrogen and certain inorganic dyes that are extracted and recovered. Heavier residuals of petroleum may contain a significant portion of materials that are not solvent extractable.

In this water quality analysis, we had determined the amount of oil and grease in SST lake water. First the water sample was collected from the lake. When the sample was collected, the lid of the bottle was closed below the water surface. This is to avoid the content of the oxygen to be high. First, 10ml of sulfuric acid, 50ml petroleum ether and 3ml ethyl alcohol added to 250ml sample in separating funnel. The mixture was shaken well to ensure that all the mixture mix well and the oil and grease will be able to separate from the water. When the mixtures mix well, it allowed standing till 2 layers are formed. The upper layer is petroleum while the second layer is the water. The water layer discarded from the funnel and the remaining petroleum filtered through the filter paper. This to ensure that the oil and the grease to remain at the filter paper. The final weight was determined in order to find out the weight of the oil and grease content in the water.

According to the calculation, the final weight of the oil and grease content in the water is 0.152 mg/L-1. This shows that the content of the oil and grease in lake water is low. This is because the lake is not exposed to any factors that contribute to the content of oil and grease content in the water. The sources of oil and grease in water can be caused by some factors such as petroleum refining, used oil refining and crude oil production facilities.

There is a theory which describes the gravity oil-water separation. The primary function of an oil-water separator, such as the API Separator is to separate free oil from wastewaters. Such gravity separators will not separate oil droplets smaller than the size of free oil nor will it break down emulsions. The three main forces acting on a discrete oil droplet are buoyancy, drag and gravity. The buoyancy of oil droplet is proportional to its volume and the drag is proportional to the area of the droplet.

Water pollution caused by the discharge of harmful chemical substances in the water bodies is termed as chemical pollution. The discharge of industrial wastes into rivers and lakes is the major source of water pollution. Other than that, domestic waste, agricultural waste, leakage of oil and grease in water body are another example of pollution sources.

Industrial plants use water as a coolant. They draw water from the nearby water bodies like a river or a lake. The used-up water is returned to the water bodies. The temperature of discharged water is higher than the temperature in the water bodies. The difference in temperature can be harmful to aquatic lives as they are not adapted to this temperature change. The pollution thus caused is called thermal pollution. The thermal pollution also causes decrease in the level of dissolved oxygen present in the water which affects the aquatic lives on the earth.

CONCLUSION

As a conclusion of this experiment we can conclude that we had achieved all the objectives of this experiment. From this experiment we had learnt on how to conduct partition gravimetric method. apart from that we had also calculated the amount of oil and grease in the SST Lake water that is 0.152 mg/L-1. Based on the standard given the amount of oil and grease in SST Lake water is still in a preferred level.