The city’s wastewater treatment plant is falling behind the times and needs several key upgrades to be effective, says the city’s manager of Municipal Services.
Chris Gainham said the Grohman Narrows Wastewater Treatment Plant must meet new regulatory targets and discharge an adequately treated effluent to the natural environment.
The city recently applied for $2.8-million grant — with the city contributing an additional $1 million — under the Investing in Canada Infrastructure Program (ICIP) Green Infrastructure – Environmental Quality.
Although the money is not guaranteed, the need for an upgrade to the existing facility is becoming apparent, said Gainham, given that a number of new regulatory changes have come into effect, including the Wastewater Systems Effluent Regulations (federal Fisheries Act).
The BC Municipal Sewage Regulation (MSR) was also repealed and replaced by the BC Municipal Wastewater Regulation. Starting in 2015, these regulations set new effluent quality standards that municipal wastewater treatment plants must meet and the upgrades performed at Grohman Narrows in 2006 are now lacking.
Gainham explained there is now a requirement for wastewater plants to manage loadings and discharge an effluent with an average carbonaceous biochemical oxygen demand (CBOD) and suspended solids (SS) concentration of ≤ 25 mg/L, with maximum concentration of 45.
“The existing headworks is hydraulically overloaded, has no redundancy and is prone to freezing as it is not in an enclosed building,” he said.
Major upgrades have never been completed for process headworks and the electrical system.
The Grohman Narrows Wastewater Treatment Plant — first commissioned in 1972 — provided primary treatment for wastewater that was upgraded to providing secondary treatment 12 years ago.
The upgrade work included conversion of the existing infrastructure to an aerated equalization tank, adding four rotating biological contactors as well as secondary clarifiers.
Gainham said that, at the time, twin banks of ultra-violet (UV) reactors were added, replacing the chlorination system to meet regulatory requirements for a non-toxic effluent.
“Our plant is not consistently meeting these targets, however the upgrades submitted for ICIP funding, coupled with planned future upgrades, will help us achieve these regulatory requirements on a long term and consistent basis,” he said.
The first phase of upgrades planned for the facility include new headworks and electrical upgrades — a requirement for service prior to any future secondary treatment upgrade.
“The upgrades will better manage more frequent and severe wet weather due to storms, rapid snowmelt and rain-on-snow events, and interruptions in power due to extreme weather that is anticipated under a changing climate,” he said in his report to council.
In May the federal and provincial governments committed up to $243 million toward the Investing in Canada Infrastructure Program (ICIP) Green Infrastructure – Environmental Quality with funding available for up to 73.33 per cent of eligible project costs.
Community consultation is planned to inform and solicit feedback on the wastewater treatment upgrades and design strategies.
Going with the flow
Nelson’s wastewater has also been changing, Gainham said in his report, transitioning from a low to medium strength influent wastewater, to a high strength, less treatable wastewater, consistent with ICI sewage including from breweries and food processing facilities.
“This is a trend that is occurring in other communities as well,” he said.
The plant is also operating at or near capacity for both the peak dry weather flows and average wet weather flows — both at 7,300 cubic metre/d — and during wet weather, flows to the plant can almost double.
“Staff continue to deliver infiltration/inflow, sewer lining and point repair programs to reduce wet weather flows in our sewer system and as an operational and ongoing response to these issues,” said Gainham.
A high strength wastewater study is also being undertaken to better understand the sources and trends in influent loadings.
— Source: City of Nelson
A needed assessment on needs
Urban Systems Ltd. was retained in 2017 to provide engineering consulting services and assist in undertaking a comprehensive needs assessment for the treatment plant.
The review produced future design considerations along with a collection of phased upgrades — at the conceptual design level — that would meet the future performance targets expected by the regulations.
In the review a new headworks building is proposed, which will include larger redundant units and more efficient finer screening.
“Efficient and effective headworks are a critical component of the treatment process and this has a trickle-down effect in cost savings and operational improvements throughout a treatment plant,” said Gainham in his report.
“Grit removal helps reduce operations and maintenance costs of downstream equipment.” Grit causes wear on pumps and process equipment, clogs pipes and channels takes up valuable space in the sludge digestion tanks and reduces overall hydraulic and treatment efficiency.
Additional upgrades included solids dewatering improvements in 2010, later followed by digester gas and ventilation works.
Work plan laid out
The planned headworks construction includes the following:
- Construct new headworks building;
- Supply and install new twin 6 mm mechanical screens (replacing a single 15 mm existing screen);
- Install a common wash press;
- Re-align the existing influent force main;
- Modifications and connect to the existing headworks channels.
The existing electrical service was identified as far back as 2005 as approaching capacity and is now required to be upgraded to accommodate future electrical loads, said Gainham in his report.
He noted that the upgrade would replace the existing 480-volt service with a 600-volt system along with the master control centres replacement.
The planned electrical upgrades includes the following:
- Upgraded electrical service – 600 volt to replace existing 480-volt service;
- Upgrade to existing, undersized 200 amp service;
- Replacement of aging master control centres;
- Upgrade to the existing 150 Amp electrical backup generator.
— Source: City of Nelson