Focus on Harsh Environments: Maintenance of dirty, corrosive plant requires a sense of humour
By Judy & David van Rhijn
Sewage treatment is a dirty and dangerous business, but one that you get used to, according to Jim Sehle. Contaminants, gases, and the severe nature of the process "keep things interesting," he says.C...
Sewage treatment is a dirty and dangerous business, but one that you get used to, according to Jim Sehle. Contaminants, gases, and the severe nature of the process “keep things interesting,” he says.
Currently maintenance manager and acting assistant manager at the Brantford Waste Water Treatment Plant in Brantford, Ont., Sehle recently completed a placement as assistant manager at a Cambridge, Ont., plant and is still very involved with day-to-day operations there. Both plants managed by the Ontario Clean Water Agency of Toronto. OCWA is a provincial Crown corporation that provides water and wastewater services to Ontario municipalities. It currently operates 429 facilities in the province, making it the largest operator of water and wastewater facilities in Canada.
Sehle considers the Cambridge Waste Water Treatment Plant to be as advanced as any there is, due to fairly recent upgrades. It became due for major expansion in 1995 and new technology was available then. “Cambridge is one of the most sophisticated plants we operate. It is a large facility for having a fan filter. It utilizes ultra-violet disinfectant so no chemicals are released in the outflow water, and it has an expanded aeration capacity. It is completely run by computer systems. All plants are going that way but Cambridge is right at the top.”
The Cambridge plant has a total operating staff of three. All employees are operator-mechanics, although only one specializes in maintenance. Steve Reid, the maintenance mechanic, handles preventive maintenance in the facility and can call on employees from other plants when required.
The plants operate on a hub concept, giving them a job pool of five maintenance staff with mechanical backgrounds. They are all encouraged to take regular training to increase their knowledge of electrical systems and instrumentation for troubleshooting.
The upgrade opened many opportunities for the staff. “There is more equipment,” Sehle says, “so a lot of guys are more knowledgeable now.” The new equipment did not decrease the workload, but there are other benefits. “It gave us more control — more historical information. If something happens during the night, we are able to trend back two days and see what happened. That sort of control is beautiful; on the other hand, we have to maintain that control.”
Increased control is welcome in the light of increasingly stringent government regulations. “Since the Walkerton disaster, there has been more documentation for everything,” Sehle says by way of explanation. (Contaminated drinking water led to seven deaths and the illness of hundreds of people in Walkerton, Ont., in 2001, resulting in beefed-up water treatment regulations in the province.)
“A historical database proves repairs have been done.” Sehle’s motto is, “Cover thine arse.”
Waste water treatment plants operate around the clock, which can pose problems when repairs are required. Larger facilities can usually cope as they are all built a little oversized. Smaller facilities can make use of a portable plant that is available to them.
The Cambridge plant has the capacity to treat 56,000 cu m of raw sewage a day, and would do more if it weren’t for a bottleneck at the filter. Sehle estimates that the rest of the plant could manage 90,000 cu m a day without this limitation.
Not surprisingly, the filter equipment has been the focus of recent maintenance. “We’ve been getting an outside contaminant fouling the system,” Sehle explains. “If it gets plugged, it will cause a rupture of the porous plates.” The source of the problem is still being tracked and the filter is being taken down monthly. This is more labour-intensive than usual maintenance regimes.
The facility’s computerized maintenance management system (CMMS) generates monthly and weekly orders. Weekly checks are done by operations staff. “That’s visual,” says Sehle. “Monthly checks are done by the maintenance staff. They get down and look at fluid levels, fasteners and belt conditions.”
The regime then expands to manufacturers’ recommendations of quarterly, semi-annual and annual checks. “That’s the full gamut, such as analysis of lubrication levels.” Sehle favours a common sense response to complying with recommendations. “For example, Cambridge has an effluent screw pump because it is situated on a flood plain. I don’t believe it has been used since it was installed. The staff just does the analysis of its 220 litres of lubricant. They don’t need to change it.”
Despite the upgrades, some equipment at Cambridge still dates back to the 1950s and requires careful watching. “It’s a pretty corrosive atmosphere. The raw sewage itself is very corrosive,” says Sehle. In particular, the scraping mechanism that brings the waste to the centre of the cones rots apart and often needs replacement or repair.
Another area that keeps the staff busy is the reconditioning of pumps. They are the most common piece of equipment in the plant and about 80 per cent of maintenance work focuses on them.
Sehle likes to keep most mechanical repairs in-house, sourcing the parts himself, doing some fabricating and all the assembly. “We only outsource large projects and specialty work such as instrumentation. In addition, the Occupational Health & Safety Act requires that flow meter calibrations and gas meters be checked by outsiders.” For this, a stationary gas monitoring system is used.
The plant stocks most hard-to-get parts on site, but finds that regular parts such as bearings, mechanical seals and shafts can be purchased locally from a distributor, or can be manufactured within a week. “There a very good support services in the area,” confirms Sehle.
Now and then, the plants need outside help to meet an unusual challenge. In a recent incident, a 900 mm force-main split. “That’s very unusual,” says Sehle. “It is 15 inches underground, in a very busy area full of pipes and electrical conduits. We had to get a contractor with a vacuum truck and another contractor to weld the pipe back together.”
Not surprisingly, there are serious safety concerns. Sehle describes the plant as “a biological area.” This is of particular concern if staff have open wounds. They must have their tetanus shots up-to-date and take safety training. Gases are also a big worry. “It takes its toll, especially in a confined space entry. We normally don’t enter. We pump fresh air in. It’s always a concern.”
However, the Cambridge plant does harness the enemy for its own uses. The gas produced in the digester system is recovered to be used as part of the heating process.
A constant annoyance is when someone discharges something abnormal into the sewers and it ends up in the system. “It throws the process for a loop,” says Sehle. He cites pieces of clothing and some plastics as the main causes, but sometimes there are more unusual contaminants. “Once we had a beef liver. It held things up because we thought it was human for a while.” A sense of humour is a helpful quality to possess in the world of waste treatment.
Judy van Rhijn is a freelance writer. David van Rhijn is a systems integrator and proprietor of SD Control Systems. They are based in Kitchener, Ont.