EDITOR'S NOTE: Wastewater treatment is a front-burner issue for some residents of Central Colchester. In a special three-part series, beginning today, Ramesh K. Ummat, the director of public works for the Municipality of Colchester County, attempts to demystify the process.
By Ramesh K. Ummat
Special to the Truro Daily News
OLD BARNS - Modern wastewater treatment is both an art and a science.
Environmental consultants, engineers, wastewater treatment plant operators, managers and workers all agree that it is also a challenge. Whereas the treatment processes and technologies are born out of scientific study and mathematical modeling, achieving optimum results is a skill that requires a fine-tuned and focused mind.
A modern wastewater treatment plant is a well-balanced bio-chemical factory that processes raw sewage or wastewater into clean water and generates solids as a by-product.
Like any other industrial production facility, it requires a close control and monitoring of the quality and quantity of raw material received at the factory, needs well-trained staff to manage the ‘manufacturing' process, demands application of precisely controlled machinery and equipment in processing the wastewater, and finally, has to ensure quality of the final ‘product' by continuous testing and maintaining regulatory standards.
A critical component of any industrial manufacturing facility is the quality of raw material received. No amount of equipment, technology and training can transform poor quality raw material into good quality final product.
This is true for wastewater treatment facilities as well. Computer savvy persons would recognize the acronym GIGO (Garbage In - Garbage Out) as applied to computer systems. Poor quality raw data results in poor quality results. Quite obviously, the acronym SISO (Sewage In - Sewage Out) does not, and should not be expected to apply in the case of wastewater treatment plants. Wastewater treatment plants are required and designed to accept sewage or wastewater having potential of causing environmental distress and process it into environmentally friendly, or at least less harmful, products for safe disposal on to land, natural waters and the atmosphere.
Quality of raw wastewater is of utmost importance and is fundamental to the quality of treated wastewater that will finally flow out of the treatment facility. It not only influences the quality of treated wastewater, but also the treatment processes required to convert raw wastewater into treated wastewater.
Pollutants generally present in wastewater are frequently referred to as ‘solids.' Broadly speaking, pollutants present in common wastewaters are grouped as suspended solids or dissolved solids. Further suspended solids could be easily settle-able (sand and grit particles that flow with the sewage) or not so easily settle-able (toilet paper, crushed pieces of food waste, bread crumbs).
Another way to group pollutants is whether they are inorganic (grit, dissolved salts) or organic (wood chips, food waste, organic domestic cleaning products).
The reason why this grouping is important is that the type of treatment process required to treat the wastewater depends upon the kind of pollutants present and that each component of the treatment process addresses a particular group of pollutants.
Grit and large settle-able suspended solids that settle quickly and are most commonly associated with wastewaters are usually removed before actual treatment process begins, in what is generally called wastewater pre-treatment process. Pre-treatment is usually designed to remove only inorganic, suspended settle-able material and not any organic material.
Further treatment of pre-treated wastewater could be as simple as allowing wastewater to sit undisturbed in a tank for a period of time so that organic settle-able particles settle to the bottom of the tank and are removed separately and the clear water is decanted off at the top.
This process is termed ‘primary treatment.' The material that settles to the bottom is the primary settled sludge. Sometimes, coagulating chemicals are added at this stage to encourage flocculation of suspended solids, speed up the settling process and increase the efficiency of primary settling in a process called ‘advanced primary' treatment or ‘chemically assisted primary' treatment.
Wastewater processed through the primary process is then put through the ‘secondary treatment' process, which is also called as the ‘biological' treatment process.
This process addresses dissolved organic (and some inorganic) pollutant group in wastewater. As the name suggests, the process is accomplished with the help of various bacteria and micro-organisms nurtured and maintained in large reactor tanks.
During the treatment, microorganisms, in the presence of oxygen, consume the dissolved material and grow. When the dissolved pollutants have been reduced to regulated levels, the wastewater is passed through a settling tank where microorganisms settle to the bottom and the treated water is decanted off.
Treated wastewater is either chlorinated or passed through UV radiation to achieve disinfection before discharge to natural water bodies. The settled microorganisms from the secondary process are most commonly referred to as bio-solids.
In some instances, depending upon pollutant concentrations, primary treatment is skipped in favor of direct secondary treatment. As an example, in all the wastewater treatment plants operated within Colchester County there is no primary treatment. Instead, the wastewater is treated directly in secondary or biological treatment tanks called sequencing batch reactors.
In 2005, the Canadian Council of Ministers of Environment initiated a process to develop a Canada wide strategy to manage municipal waste water effluents and set up standards for a harmonized approach to manage wastewater from more than 3,500 wastewater treatment facilities resulting in a strategy document endorsed by the Canadian Council of Ministers of Environment (CCME) in 2009. Nova Scotia is a signatory to the strategy document.
To help implement the CCME Strategy, the federal government developed regulations which were published in 2010. The strategy defines, amongst other things, national performance standards for all wastewater treatment facilities across Canada.
In order to achieve the performance standards set in the strategy document, most of the municipal wastewater treatment facilities would be required to ensure wastewater treatment of at-least secondary treatment level. This has huge financial impact on most of the large cities and communities including Halifax Regional Municipality and Cape Breton Regional Municipality where substantial upgrades would be needed to meet the performance standards.
Fortunately for Colchester County though, local municipal councils have been pro-actively investing in wastewater management.
The Central Colchester Wastewater Treatment Facility in Old Barns, which was constructed in 1995 and serves Truro, Bible Hill, Valley, Millbrook, Hilden, Salmon River and other adjoining areas, was designed to provide secondary level treatment to municipal wastewater when many other communities and larger cities had only primary treatment systems to treat their wastewater effluents.
With the current upgrades in place, it will continue to meet or exceed the national performance standards.
All other treatment facilities in Colchester County, Brookfield, Great Village, Tatamagouche and Debert, provide secondary biological treatment to wastewater and meet or exceed the minimum national performance standards.
Thus where many other cities and communities are struggling to raise finances to meet the standards, Colchester invested wisely in the past and is already compliant with those standards.
TAGLINE: Ramesh K. Ummat is the director of public works for the Municipality of Colchester County.