Reporting pollutant releases: example calculations, chapter 1

Examples of How to Estimate Releases for Part 1A and 1B Substances

Purpose:

These examples demonstrate how to estimate releases for Part 1A substances. Estimation methods used includes source testing, mass balance, published emission factor, and engineering calculations.

  1. Calculating the Manufactured, Process or Other Use Threshold
  2. Source Testing
  3. Mass Balance Calculations
  4. Emission Factor
  5. Engineering Calculations

1. Calculating the Manufactured, Process or Other Use Threshold

Example
The following example illustrates the calculation of the 5-kg manufacture, process or other-use reporting threshold applicable to mercury (and its compounds). This facility used several processes in which mercury (and its compounds) were manufactured, processed or otherwise used. There is no 1% concentration exemption for mercury (and its compounds). Mercury (and its compounds), at any concentration, must be considered when calculating the reporting threshold and reporting mercury releases.

The facility met the 20 000-hour employee threshold and the processes used were:

  1. In the first process, mercury was present in a mixture at a 1% concentration.
  2. The facility received a raw material which contained 0.005% mercury, which was processed in stream 2.
  3. In process stream 3, mercury was present at a concentration of 0.01%.
Material Containing Mercury Total Weight of Material Containing Mercury(tonnes) Concentration of Mercury in the Material Net Weight of Mercury(tonnes)
Process stream 1 1 1.0 % 0.01
Process stream 2 (raw material) 50 0.005 % 0.0025
Process stream 3 20 0.01 % 0.002
Total weight 0.0145 tonnes
of mercury 14.5 kg

In this example, the facility would be required to submit a report to the NPRI for mercury (and its compounds) because the quantity manufactured, processed or otherwise used at the facility exceeded the 5-kg total reporting threshold. The facility must report the quantity released on site, disposed of and transferred off site for recycling.

2. Source Testing

This source testing example is based on measured concentrations of the substance in a waste stream and the volume/flow rate of that stream.

Example
A galvanizing facility discharges its wastewater to a nearby body of water. The electroplater is required to monitor this discharge once a month for various parameters, including the release of total zinc. What is the annual release of total zinc to the wastewater by this galvanizer?

Step 1
Gather wastewater flow and concentration data from the monitoring results done in compliance with the municipal by-law for wastewater discharges. Analytical results for total zinc for the year are presented in the table below.

Step 2
Calculate the mass loading for those days on which a zinc analysis was performed. This is done by multiplying the daily flow by the measured zinc concentration.

Concentration of Zinc in Wastewater
Day Wastewater Flow (10 6 L/d) Zinc Concentration (μg/L) Releases(kg/d)
Jan. 8 1.57 918 1.44
Feb. 12 1.49 700 1.04
Mar. 10 1.58 815 1.28
Apr. 15 1.66 683 1.13
May 9 1.38 787 1.09
June 13 1.29 840 1.08
July 11 1.73 865 1.50
Aug. 10 1.60 643 1.03
Sept. 8 1.75 958 1.68
Oct. 12 1.56 681 1.06
Nov. 10 1.80 680 1.22
Dec. 8 1.63 627 1.02
Average 1.21

Step 3
Calculate annual releases.

Based on an average daily release of 1.21 kg over the year and 250 days of discharge during the year, the yearly total zinc discharged to water is:

1.21 kg/d x 250 d/yr = 302.5 kg/yr = 0.303 tonnes/yr

3. Mass Balance Calculations

A mass balance is an accounting of the quantity of a substance going in and out of an entire facility, process or piece of equipment. Releases can then be calculated as the difference between input and output. Accumulation or depletion of the substance in the equipment should be accounted for in the calculation.

Example

An electroplating facility operates a vapour degreaser.

Suppose that 14 tonnes of trichloroethylene are used as a degreasing agent. Spent solvent and sludge that accumulate on the bottom of the degreaser are collected in drums for shipment to an off-site solvent reclaimer. Thirteen drums of solvent were sent to the reclaimer during the past year.

A known volume of a representative sample taken from the drums is weighed, allowed to evaporate, and reweighed. From this, it is determined that the density of the sludge is 1.03 kg/L and that the trichloroethylene concentration in the sludge shipped to the reclaimer is 30%.

Step 1
The entire 14 tonnes of solvent is released from the facility either as an air emission or as a transfer in the sludge. If the quantity of spent solvent shipped to the reclaimer is known, then the quantity transferred can be calculated based on the volume of sludge and the density of the sludge as shown below:

Volume of trichloroethylene to reclaimer

= 13 drums x 210 L/drum = 2 730 L

Mass of trichloroethylene to reclaimer:

= volume of sludge x density of sludge x % trichloroethylene in sludge
= 2 730 L x 1.03 kg/L x 0.30
= 844 kg
= 0.844 tonnes

Step 2
The quantity of trichloroethylene emitted to air can then be calculated by mass balance by subtracting the quantity shipped in sludge to the reclaimer from the quantity purchased:

14 tonnes (purchased) - 0.84 tonnes (to reclaimer) = 13.164 tonnes

Note: In this example, Trichloroethylene is also a VOC covered under Part 4 substances and a report for VOC emissions to air would also be required.

4. Emission Factor

An emission factor is based on average measured emissions from several similar processes. Emission factors usually express releases as a ratio of quantity released to process or equipment throughput. Emission factors have been published by government agencies and industry associations for application to emission sources in their particular jurisdiction or industrial sector. Industrial facilities may also develop their own site-specific emission factors using emission-testing data and source-activity information. This example demonstrates the use of a published emission factor.

Example
Suppose the electroplater previously mentioned has no information about the spent solvent and sludge accumulating on the bottom of the degreaser.

Step 1
In this case, the emission factor is found in a U.S. Environmental Protection Agency publication entitled "Toxic Air Pollutant Emission Factors - A Compilation for Selected Air Toxic Compounds and Sources". For an open-top vapour degreaser without emission control equipment using trichloroethylene (TCE), the emission factor is given as 0.93 tonne/tonne TCE used.

Step 2
Calculate the annual releases to air from the vapour degreaser as follows:

TCE released = TCE used x emission factor (TCE released/tonne used)

14 tonnes x 0.93 tonne/tonne = 13 tonnes

When emission control devices are used, atmospheric releases are estimated by multiplying the "uncontrolled" emission by the quantity (1 - C/100), where C is the control device efficiency.

Note: In this example trichloroethylene is also a VOC covered under Part 4 substances and a report for VOC emissions to air would also be required.

5. Engineering Calculations

This estimation method is based on physical/chemical properties (e.g., vapour pressure) of the substance and mathematical relationships (e.g., ideal gas law).

Example
In this example, rinse water from a copper-plating unit is treated separately from other process wastewater. Sodium hydroxide is added to precipitate the copper (Cu) in the wastewater. The precipitate formed from this reaction is removed as sludge from the facility's central clarification unit. Purchasing and inventory records indicate that 0.9 tonnes of sodium hydroxide were used for precipitating copper last year. The quantity of copper precipitated represents the quantity of copper released from this source as solid waste.

Step 1
For each mole of copper (Cu) present in the rinse water, two moles of sodium hydroxide (NaOH) must be added to precipitate the copper according to the following reaction:

Cu2+ + 2(NaOH) -> Cu(OH)2 + 2Na+

Scientific literature indicates that this reaction would be complete at a pH of 7.7. Sodium hydroxide is added until a pH of 8 is maintained in the reaction mixture to ensure complete precipitation. It is also known that:

Molecular Weight of Cu = 63.5 tonnes/tonne-mole
Molecular Weight of NaOH = 40 tonnes/tonne-mole

Step 2
Calculate the quantity of copper released in the wastewater treatment sludge, as follows:

2 tonne-moles NaOH reacts with 1 tonne-mole Cu

The ratio of NaOH to Cu by mass is calculated as follows:

(40 tonnes NaOH / tonne-mole NaOH) x 2 tonne-moles NaOH: 1 tonne-mole Cu x (63.5 tonnes Cu / tonne-mole Cu)

80 tonnes NaOH: 63.5 tonnes Cu

Using the proportions above the following equation can be derived:

(80 tonnes NaOH / 0.9 tonne NaOH) = (63.5 tonnes Cu / A)

Where
A= the quantity of copper released in the wastewater

A= (0.9 x 63.5 tonnes Cu) / 80

A = 0.71 tonnes Cu

The estimation method is valid only if the NaOH reacts only with the Cu present in the wastewater and the reaction is complete.

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