The end product is a dry, organic fertilizer (85-87% dry matter), ready for commercial use that can easily be shipped or stored. It can also be used as an efficient combustible with a calorific value in the range of 6,000-9,000 Btu/lb.

The FEOS process insures that the product retains all the nutrients, carbon and biological properties while odors and pathogens are destroyed. But, if the goal is to simply produce an efficient combustible, the FEOS bio-drying system can be adapted to work with an existing centrifuge process.

Transforming sludge into a dry, stable, organic fertilizer using FEOS instead of fossil energy is not only good for the environment, it can also provide a sizeable return on investment, says Chabot.

“This return might even increase if the facility would also process sludge or biosolids from other sources, like local municipal waste, with over 20% DM,” he says.

A recent study made by École polytechnique of Montreal, using Envirogain's FEOS, sized to treat 14,440 lb. of biomass extracted from 13,000 gal. (US, liquid)/day of fresh pig manure at an approximate cost of $400,000, states that the rate of return for the process was 14%, but it could reach 25% if the price of fertilizer increases as expected.

The same logic applies if the FEOS system is used to produce dry fuel. “The payback for producing methane with a biodigester is a minimum of 10 years,” explains Chabot. “You can cut that by half when producing dry fuel with hog manure using FEOS. And, the same plants now burning chicken or cow manure, can now burn hog manure just as efficiently.” Envirogain plans on making a foray into the United States this fall.

On-site drying reduces greenhouse gas (GHG) emissions since there is little or no transportation involved for the treatment of the sludge, and most of the energy source required to dry the fertilizer can be redirected from the Biofertile treatment station. There are no methane (CH₄) emissions since the sludge is treated shortly after it is recovered, and there is no need for storage tanks.

Nitrogen oxide (N₂O) and CH₄ emissions, which are usually released when disposing sludge, become minimal. Since the dry organic fertilizer is reintroduced to soils within the same region, the need to haul nutrients from greater distances is avoided.

Further reductions of GHG's can be achieved if each FEOS plant also processes waste from local industrial, agri-food and municipal wastewater treatment stations, which have a minimum organic load concentration of 41.8 lb./gal. SS (suspended solids).

The GHG assessment of the Biofertile process, done by Natural Resources Canada, shows that GHG emissions are reduced by 1,779 tons of carbon dioxide equivalent (CO_2eq)/year for a treatment capacity of 21,662 gal. of hog manure/day. The corresponding reduced emission with the basic 13,000 gal./day Biofertile station was then evaluated at 1,085 tons CO_2eq/ year.

The FEOS for this corresponding Biofertile unit was also evaluated to reduce the GHG emissions at 1,192 tons of CO_2eq /year, for a total of over 2,205 tons of CO_2eq/year when Biofertile plus FEOS are installed.

Table 1. Fertilizer Values of the Dry Organic Fertilizer Produced (Biofertile Organic Base, or BOB).

Parameters	Content, %
Nitrogen (N)	3.5
Phosphate (P2O5)	8.0
Potash (K2O)	2.0
Calcium (Ca)	5.0
Magnesium (Mg)	1.5
Sulfur (S)	1.0
Iron (Fe)	0.5
Copper (Cu)	0.11
Zinc (Zn)	0.16
Boron (B)	0.006
Organic matter	72
Humidity	13
Total of fertilizing elements: 22%

Table 2. Estimated Levels of Metals and Coliforms

Parameter	Content, %
Aluminum	0.12
Arsenic	0.0001
Cadmium	0.00004
Chromium	0.0035
Cobalt	0.0006
Manganese	0.066
Mercury	0.000007
Molybdenum	0.0008
Nickel	0.0036
Lead	0.0004
Selenium	0.0004
Fecal coliforms	<10 cfu/g*
*cfu = coliform-forming units

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