‘Flow variations affect the quality of raw wastewater at the treatment facility in more than one way'
EDITOR'S NOTE: Wastewater treatment is a front-burner issue for some residents of Central Colchester. In the final installment of a three-part series, Ramesh K. Ummat, the director of public works for the Municipality of Colchester County, talks about how flow variations can affect the quality of raw wastewater at the treatment facility.
By Ramesh K. Ummat
Special to the Truro Daily News
OLD BARNS - Being able to measure and put a number to the amount of pollutants in wastewater is only half the story. The other part of the story is how much wastewater is delivered to the wastewater treatment facility.
It is easy to see that each efficiently run industrial facility not only controls the quality of raw material, but also the quantity of raw material delivered at its doorstep. Various methods to control the amount of input and minimize wastage, such as inventory control, just-in-time-stocks are employed to ensure that the raw material is available when needed. But that is where the factory analogy ends.
Wastewater treatment facilities receive sewage through sewer systems connected to homes, factories, commercial establishments and other institutions on a 24/7 basis. The quality and amount of wastewater received at the treatment facility is dependent on how much and what the users dump down the drains of their homes, offices, businesses or factories.
This is a challenge for the engineers, managers and operators - how much water (and what pollutants) should we expect to receive when a new treatment facility is being built? Would that flow be constant or would it vary greatly over a period of time? How would we manage such a variation, if that happens to be very large?
The most common measure of flow used by wastewater operators and managers is ‘average hourly flow per day,' which as the name suggests, is the total daily flow divided by 24 hours of the day. But really, the flow does not remain ‘average' throughout the day. It peaks and ebbs with time with peaks being as high as four times the average flow coinciding with human activity. In its simplest form, peak flows are associated with early mornings when people are getting ready to go to work, and then again in the evening when people are back from work and are busy in the kitchen.
However, imagine a community where most of the residents work in a large near-by factory and the factory works all three shifts of the day. The flow pattern and volume there would be quite complex to model. Add to that natural events such as rain, flooding and natural ground water infiltration, and the variation becomes very complex and significant.
Flow variations affect the quality of raw wastewater at the treatment facility in more than one way.
One way to look at increased flow is that it dilutes the concentration of pollutants in the wastewater, resulting in a reduction in the pollutant load on the treatment facility.
Another way to look at the increased flows is that it overloads the facility, and thus the quality of the product (treated wastewater) suffers because of insufficient time given to complete the treatment process. The reverse happens in very dry months where the inflow is very low causing concentrations to rise and thereby overwhelm the treatment process.
The bottom line is that it is a no-win situation either way if the situation turns extreme.
The wastewater treatment facility is designed for a certain production capacity with a given quality of raw material and a reasonable allowance of variance in quantity and quality. But beyond that, as is expected to happen with any manufacturing facility, the quality of finished product is bound to suffer. Government by-laws and regulations, in general, govern the quality but not the quantity of wastewater received at the treatment facilities.
In Colchester County, the quality parameters are contained in the county's sewer by-law. The sewer by-law does not explicitly address itself to the quantity of wastewater, other than accepting that ‘dilution is not the solution to pollution.'
Sewage treatment facilities are publicly owned, operated and maintained by the municipalities and thus the public has a direct role in ensuring that the facility operates at its optimum level.
So what should we do to ensure quality and quantity of raw material received at the treatment facility?
Simply stated, make sure that what goes down into the sewer system meets the requirements of the applicable sewer by-law.
Here are a few fundamental guidelines that can help you doing your bit in ensuring sewage quality and quantity:
- First and foremost, think before you dump it in the sink. Do you really need to throw out the food into sewers or can you send it on for composting in your green bins? Is there something that you can save and use later, for example half used glass of milk, instead of pouring it in the sink? Paints, organic solvents, etc. are a definite no-no.
- Restaurants and commercial fast food businesses must ensure that they have a working and well-maintained grease trap to prevent entry of fats, oil and grease into the sewer system.
- Industries discharging their process water into the sewer system should install an appropriate treatment system to treat the water before discharging into the sewer to ensure that various pollutants are within the limits imposed by the sewer by-law of Colchester County. Efficiency of such a treatment should be verified by regular monitoring and testing the treated process water.
- Low water consumption fixtures in the shower, toilets and kitchen sinks all reduce the water used and thus reduce the amount of wastewater flowing into the sewers. Some industries have the capability to reuse part of their process water instead of draining all of it into the sewer system. That capability must be explored and used wherever possible. Industrial food industry in the US has started looking at ways to treat their process wastewater into high quality drinking water for reuse. Water is a valuable and costly resource and it makes sense to work actively to reduce its consumption at every level possible.
- Conservation and reuse has its economic benefits too. It has direct financial benefit to individuals as well as industries and commercial establishments, but has indirect financial and other benefits to the entire community by reduction in treatment costs, enhanced quality of treatment and improved environment.
Active community participation is therefore the key to maintaining peak efficiencies at wastewater treatment facilities.