Composting Wastewater Sludge, cont' blends these components into a homo geneous mix prior to discharging onto the elevating conveyor. The elevating conveyor moves the mix horizontally and vertically in a "C"configuration by sandwiching the material between two continuous vulcanized rubber belts. The
elevating conveyor discharges the com post into a series ofscrew conveyors that allow the material to be deposited into the top of any of the three reactors. Five days per week, the finished
compost material is withdrawn off the bottom of the two initial reactors and
transferred to the cure reactor. Compost is also withdrawn daily off the bottom of the cure reactor and conveyed to trucks for transport off-site. As the ma terial moves in a plug flow fashion from the top of the bioreactors to the bottom of the cure reactor, bacteria and fungi consume the organics in the mix as they grow and replicate. Heat is produced by the growth of the micro-organisms, quickly raising the temperature of the compost mix in the reactors. The tem perature ranges between 40 and 60 de grees Celsius for the 28 days of mate rial residence time within the facility. Temperatures of 55 degrees or greater
HzAU
are attained for a minimum of three con
truck loads. The truck trailers are self-
secutive days, which safeguards against harmful bacteria and viruses that may be found in the sewage sludge. The oxygen required to support the growth of the micro-organisms is sup plied by aeration blowers that are part of the compost building ventilation sys tem. The positive displacement aera
unloading and deposit the amendment into a live-bottom receiving bin. From
tion blowers draw air from within the
building and deliver it to a distribution grid in the bottom of the reactors. From there, the air travels through the com post mass, delivering oxygen to the mi crobes and drawing off the heat and moisture created. Centrifugal exhaust blowers draw off the aeration air, now
warm and moist, from the top of the compost reactors and maintain a slightly negative pressure within the reactors to ensure no escape of odours,. These offgases are passed through an air-to-air heat exchanger, where the heat is recov ered and used in the building during winter months. The off-gases are sub sequently diffused into the WWTP ac tivated sludge aeration tanks, where any odourous compounds are neutralized. Amendment is typically delivered to the compost facility in 90 cubic metre
Environmental Monitoring Equipment
Area Velocity Flow Meters are [ntrinsicaliy Safe Class 1. Division i. Groups C & D American Sigma's new 911 and 940 Model Area Velocity Flow Meters are certified for operation in Class i, Division i, Groups 0 & D hazardous locations. Manhole safety is always of primary concern to monitoring crews. Two new Sigma meters help alleviate those safety concerns at an affordable price. Monitoring crews always check manholes for explosive gases, but seldom have equipment rated for such environments.
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92
Can-Am Instruments Ltd.
Ontario Office
Atlantic Province Office
2495 Haines Road
Phone: 905-277-0331
Phone: 902-477-8344
Mississauga, ON, L4Y 1Y7
Fax: 905-277-2588
Fax: 902-477-8345
For more Information, circle reply card No. 266
the receiving bin, the amendment is ei ther conveyed to a hammermill for size reduction or the hammermill is bypassed and the amendment is pneumatically conveyed directly to the amendment storage silo. Damaged wooden pallets which have been ground up are typically used as an amendment source; however,
larger wood chips, which can be recov ered in the screening system, may also be used.
A screening system, consisting of a flexible perforated mat, has been incor porated to allow the final product to be screened prior to discharge from the fa cility. The mat allows smaller compost particles to fall through the perforations during agitation of the mat, while the larger particles continue to travel off the end of the mat. The "overs" from the
screen are typically larger wood chips, which may be used again in the proc ess. These are metered out of the recy cled chip storage bin and blended in the mixer with the sludge, amendment and compost recycle. The material that passes through the mat of the screen is conveyed to trucks for transport off-site. City of Guelph Works Department data provided by CH2M Gore and Storrie Limited. Conclusion
The two plant profiles provided il lustrate that composting is an effective method of producing useful biosolids from sewage sludge, treated alone, or in a matrix of other organic residuals. The two approaches to design, technology, and implementation indicate room for creativity and cost-effectiveness. If each existing and anticipated fa cility is operated with end-product qual ity as its focus, and if systems are in place to preclude potential impacts to the local community, then composting can help to achieve local waste diversion goals while providing a source of valu able organic soil amendment products. Composting,along with alkaline stabili zation and heat drying/pelletization can produce marketable products which will offset the cost of production. In order for marketing to occur and expand, we will need to develop a regulatory frame work which supports the merchant ability of these useful products, and builds public confidence which will lead to their acceptance in the marketplace. For more Information, circle reply card No. 265
Environmental Science & Engineering, January 1998