EDITOR'S NOTE: Wastewater treatment is a front-burner issue for some central Colchester residents. In part two of a three-part-series, Ramesh K. Ummat, the director of public works for the Municipality of Colchester County, raises some interesting questions.
By Ramesh K. Ummat
Special to the Truro Daily News
OLD BARNS - The quality of raw wastewater is of utmost importance and is fundamental to the quality of treated wastewater that will finally flow out of treatment facilities such as the one in Old Barns.
It not only influences the quality of treated wastewater, but also the treatment processes required to ‘manufacture' raw wastewater into treated wastewater.
Unfortunately it is also one of the most difficult to control.
Legislation can be enacted to specify what can and what cannot be dumped into a sewer system, but all such by-laws and policies are prone to deliberate or accidental violation. Consider, for example, how many people drive their vehicles after consuming alcohol although there is a strict law prohibiting the activity.
Then again, compliance of the law can be improved by education and enforcement but cannot be totally eliminated.
Active community participation is therefore the key to improved quality of raw sewage received at any treatment facility.
‘What gets measured, gets managed' or so the saying goes. In order to manage effective treatment of wastewater, therefore, it is necessary to know the type and amount of pollutants contained in the incoming wastewater.
Although there are general guidelines available, the pollutants and their concentration in wastewater vary greatly not only with the community served by the sewer system, but also on a day-to-day, hour-to-hour basis.
Some of the most common pollutants or constituents associated with wastewaters are suspended solids (SS), total dissolved solids, pH (a measure of acidity or alkalinity of wastewater), nitrogen, phosphorus, sulfur, calcium, copper, iron, mercury, potassium, sodium, zinc and a number of other organic chemicals such as traces of veterinary and human medicines, prescription and non-prescription drugs as well as other industrial and household chemical products.
Some of these constituents are relatively easy to measure. Say, for example, if you dissolved 10 grams of common salt (sodium chloride) in a litre of clean drinking water and gave that water to someone to find out how much salt there was in the water, it would be relatively simple to carry out some tests to tell you the quantity of salt and its constituents in the water.
The calculations would become a little more complicated though, if you were to dissolve a mixture of, say, sodium chloride, potassium sulfate, calcium phosphate, sodium nitrate and then ask someone about their quantities. It would be quite difficult to pinpoint the exact quantities of each of these substances, although it would be possible to calculate the total amounts of sodium, potassium, calcium, chlorides and other constituents.
Things get more complex with more pollutants added to the mix. The silver lining is that there are ways to determine the quantities of these constituents despite the complex mix of chemicals.
Things start getting murkier, however, when dealing with organic pollution. Although it is possible to determine the quantity of carbon or oxygen or other elements that constitute organic pollutants, the challenge is determining their ‘pollution causing potential.'
That is where the familiar acronym BOD (biochemical oxygen demand) steps in. Some readers may have heard that BOD is associated with polluted waters and that more of it means more pollution. Unfortunately, it is only partially true. BOD is at best an indirect measure of the bio-degradable organic matter present in the wastewater. Quite evidently therefore, it gives an estimate of only the bio-degradable organic matter and non-bio-degradable organic matter does not figure in. For example, if there was sawdust, wood chips or cotton fibre in the wastewater, even though they are organic materials, they would not contribute significantly to the BOD evaluation.
The reason BOD is an indirect measure is because it is actually a measure of the amount of oxygen that the bacteria and other microorganisms use when they consume or degrade organic material.
The theory is that when bacteria and other microorganisms come in contact with bio-degradable matter dissolved in water, grow and multiply, and in turn, consume oxygen. The more oxygen they consume means more organic pollution was present in the water to begin with. The internationally accepted time gap between measuring the initial amount of oxygen and the final amount of oxygen in the water after bacterial activity is five days at a steady temperature of 20 degrees Celsius. The oxygen consumed within those five days is the BOD of the polluted water.
But wait a minute here! Is a liquid with very high BOD, automatically ‘highly polluted?' That question merits a little more discussion. Think back, for example, when someone told you to drink a glass of water with a spoonful of sugar in it if you were feeling a little bit down. Or perhaps in the past your mother had advised you to take a glass of water with a spoonful of glucose to get instant energy. Or in a hospital, doctors hook up a patient who cannot be fed orally, to a dextrose drip.
All these are pointers to the energy giving nature of easily digestible sugar or its components. But did you know that a spoonful of glucose mixed in a glass of water has a BOD of nearly 38,400 milligrams per litre of water? And that is not all.
Next time you have a glass of whole milk, remember that the liquid that you are drinking has a BOD of nearly 100,000 milligrams per litre (a little lower if you prefer skimmed milk with a BOD of only 67,000 milligrams per litre).
Even blood, that is considered the life-giving fluid in the body has a BOD of one million milligrams per litre of blood. So much for the bad name that BOD has earned.
Have I caused enough confusion?
Well, here is another point to ponder. How is it that when we ask our children to drink milk every day, we consider it a source of nourishment and as soon as we dump that glass down the kitchen sink, it becomes that dreaded ‘P' word - pollution, and that too is nearly 100,000 milligrams per litre?
Or, when we drink a glass of sugared water, it is an energy giving drink, but the same glass down the drain is a source of high organic pollution. I close this discussion with a question. Is pollution in wastewater a misplaced resource?