As cities grow, so does their sewage.
And with more sewage comes more sewage problems especially in booming communities like Calgary, which are increasingly challenged to find solutions for what to do with it all.
Most cities separate the sludge, referred to as biosolids, which is everything we flush down the toilet, from waste water.
The water is treated and returned to the system, while biosolids are held for years in lagoons. Since 1983 Calgary, like many cities, has spread its biosolids as fertilizer on nearby farmland.
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“We’ve got hundreds and hundreds and hundreds of lagoon systems in the province,” said Craig Reich, a municipal approvals technologist for the Alberta government.
“Each one of them, on the average of 10 and 15 years, have to take the sludge out of their cells and put it to agricultural land.”
Reich said the use of human biosolids on farmland is regulated to ensure the soil and food grown on it is safe. The soil must maintain a neutral pH, must not be too rich in phosphorus and nitrogen, and cannot be overly sandy or clay-based.
“If it’s clay, it could be really difficult to work the biosolids in and break down,” he said. “If you put this kind of material on sandy soil and it rains or whatever, it will drive whatever nutrients through the sand and into the local ground water.”
The biosolids are also monitored, Reich said, “to make sure that there’s no kind of weird and wonderful things in there that are generally in biosolids,” such as heavy metals or pathogens.
Also, the land cannot be used for crops like root vegetables because heavy metals and toxins in the soil accumulate in the edible parts of the plant.
Calgary uses Terra-Gator trucks to inject the biosolids about 10 centi-metres under the topsoil to aid rapid microbial breakdown and prevent digging animals from spreading pathogens from the soil.
The city’s biosolids spreading program, called Calgro, spreads about 20 million kilograms of biosolids every year on farmland within a 50 kilometre radius of Calgary, about 70 percent of the total sewage produced.
In February 2013, Calgary revealed its sewage lagoons were 20 percent over-capacity and problems are mounting.
The province limits the amount and frequency at which sludge can be applied to farmland, and the municipal population increases by about 35,000 people every year. This means the city is now desperately searching for new solutions.
“If we dig deeper lagoons or build more lagoons, all we would really be doing is building space for more accumulation and creating a larger stockpile.
“What the city would prefer to do is develop a more resilient and sustainable biosolids management plan,” said Calgro program specialist Natasha Harckham.
Calgary has come up with three ideas. The first is to use a centrifuge to reduce the water content of sludge from 95 percent to about 75 percent, making it easier to handle and store.
Second, administration wants human biosolids to be added to a food and yard waste composting program set to begin in 2017.
“There are other municipalities here in Alberta that do that. Primarily Edmonton, also Medicine Hat and Okotoks and Fort McMurray all do that,” Harckham said of adding biosolids to city compost.
She said pasteurized human waste can be mixed with other compost materials and sold for garden use as Class A compost without restrictions.
The city’s largest test project to alleviate the abundant sewage problem involves applying it in much greater quantities than provincial regulations normally allow to turn marginal agricultural land into fertile soil.
Its two primary demonstration projects began this spring. One involved planting 400 acres with willow saplings. The other consisted of 1,000 acres of canola and wheat on substandard land.
Vancouver-based biosolids and waste management company Sylvis is contracted to operate the five-year projects. Team leader John Lavery said Sylvis uses traditional agricultural parameters to measure the crops’ success under heavy biosolid application.
“We’ll be looking at protein content and seed oil content… how much fresh and dry weight in a sq. metre of area…. Does the application of the biosolids lead to too heavy a seed crop, which results in lodging and can we manage that?
“With respect to the willows, we’ll be looking at crude biomass, so essentially how much wood has grown,” Lavery said.
Sylvis is trying willow because it is a fast-growing, woody plant that manages in a range of difficult growing conditions and can quickly produce material ideal for use as mulch, a compost feedstock or even biofuel. It can also be repeatedly cut back to its base and regrow from the root without adverse effects to the plant’s health.
The project plans to harvest the willow every three years.
Lavery and Harckham said they are excited by the crops’ early success. Harckham said the willow saplings are already five feet tall.
If the projects are successful, Harckham and Lavery said it would demonstrate to the province that human waste can be safely used to grow a large supply of crop and improve soil quality on land that was virtually useless before.
“The willows stay in place for about 30 years,” Lavery said. “The trees take up nutrients and then release them back into the ground through their leaf litter because they drop their leaves every year. So we have 30 years of accumulated organic biomass and the materials required to really nourish and sustain really sandy marginal soils.
“The bright idea behind the willows is we hope that over that period of time we take a Class 4 or 5 agricultural land and turn it into a 1 or 2 by virtue of being able to change the soil … and at the same time we’re able to take biomass off of it every three years,” he said.
