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Typically Regulated Pollutants Found In Metal Removal Fluids

Table 1 lists the typically regulated pollutants found in metal removal fluids.

Organics	Inorganics
BOD₅ Biochemical oxygen demand,five-day	Al Aluminum	CN Cyanide
COD Chemical oxygen demand	Fe Iron	As Arsenic
TOC Total organic carbon	Ag Silver	Se Selenium
O&G Oil and grease (Freon extractables)	Ni Nickel	Hg Mercury
TPH Total petroleum hydrocarbons	Pb Lead	NO₃ Nitrate
TSS Total suspended solids	Zn Zinc	SO₄ Sulfate
TTO Total toxic organics	Cu Copper	TDS Total dissolved solids
_____	Cd Cadmium	_____
Other	NH₄Ammonia
pH	_____
Temperature	_____

Different Pollutant Characteristics For Different Metal Removal Fluid Types

As a result of the wide variations of wastes that can be presented to a wastewater treatment system, six different metal removal fluid types were tested across various technologies. This was done to give an indication of relative performance. The results discussed in this section are not intended to be reflective of all possible combinations of fluids, fluid types and mixtures. Each method should be evaluated on actual spent metal removal solutions.

Table 2 lists some of the characteristics of six different metal removal fluids.

Fluid	Identification
A B C D E F	Basic emulsified oil Basic emulsified oil, hard water stable Premium emulsified oil, hard water stable, with organic chlorine Semi-synthetic fluid, hard water stable Semi-synthetic fluid, hard water stable, with organic chlorine Pure synthetic fluid, hard water stable, with amines and fatty acids

MRF Influent Pollutant Characteristics

                   BOD₅      COD          O&G            pH

Fluid A        5,000     500,000       35,000            8.7

Fluid B        6,500     680,000        34,000           9.0

Fluid C        8,500     750,000        29,000           8.9

Fluid D        3,500        45,000          3,500           9.3

Fluid E         3,900         50,000         3,600          9.2

Fluid F            500        30,000             900         9.2

All readings are in milligrams per liter (mg/L) except pH, which is in standard units. Al fluids are mixed at a ratio of 5% volume/volume ratio. Biocides were not present in the base products.

It should be noted that there are different test procedures for certain pollutants. Before starting on a testing program, make sure your local testing laboratory is following the proper testing protocols for the region that is regulating your discharge

A caution regarding the BOD₅ test:

The BOD₅ was designed to measure basic organic compounds in sewage and industrial wastes by aerobic biochemical action. However, due to the high degree of variation of complex organic materials present in metal removal fluids, relying solely on the BOD₅ test to determine organic loading can be misleading. This test is quite sensitive to site conditions, and can produce a wide variation of results on the same sample from laboratory to laboratory. Since the BOD₅ day test is a biological process, the results can be even more misleading if a strong biocide is present in the fluid being tested, thus resulting in artificially low results.

Oil and grease can produce a very high BOD₅ but, in general, oils and grease can be readily removed by several of the discussed methods. On the other hand, fluids high in amines or glycol ethers can produce high BOD₅results but conventional wastewater treatment processes do not easily remove these materials.

A caution on the oil and grease test:

The approved EPA test method for oil and grease is an extraction process using n-hexane, or in the recent past trichlortrifluoroethane (Freon _TM) as the extracting solvent. Most medium and heavy weight oil and grease compounds extract well with this method, thus yielding accurate results. Fuels and petroleum hydrocarbons lighter than #2 fuel oil do not extract well by this method, thus yielding artificially low results. However, some fatty acids, while not truly oil and grease, extract as oil and grease by this method, thus yielding false positive results. Fatty acids can be present in soluble oils, semi-synthetics, synthetics and straight oil metal removal fluids. Even though a sample can be completely clear (water white), the n-hexane oil and grease extractables with fatty acids present can still be well over 100 mg/L.

A secondary test, following the n-hexane extraction, referred to as the silica gel method, can further distinguish between n- hexane extractables and total petroleum hydrocarbons (TPH). This can help eliminate the false positive error with fatty acids. However, if your local agency requires oil and grease by n-hexane extraction, they may not accept results after silica gel extraction.

Metal Removal Fluids Effluent Pollutant Characteristics After Ultrafiltration Separation

	BOD₅	COD	O & G	pH
Fluid A	200	600	55	8.7
Fluid B	230	700	70	9.0
Fluid C	290	1200	120	8.8
Fluid D	250	5500	95	9.3
Fluid E	250	5800	90	9.2
Fluid F	430	25,000	80	9.2

(All readings are in mg/L except pH, which is in standard units.)