CRyOfRONT: News and Views from the Far North
Sewage composting in Iqaluit – finding BLACK GOLD By Ken Johnson, NTWWA Director
In the Canadian north, municipal sewage sludge has been virtually ignored because of the predominance of lagoon wastewater treatment systems. The application of mechanical sewage treatment systems in Nunavut, and an increased regulatory scrutiny over the past 15 years have created a demand for sewage sludge handling, treatment, and disposal. The City of Iqaluit, Nunavut has been working toward the implementation of a secondary sewage treatment system since 1998, and with it the need for sludge management. This is an ambitious goal for the community considering the inherent challenges to the design, construction and operation of facilities in the harsh arctic environment. Conventional municipal sewage treatment uses physical, chemical, and biological processes to separate solids and biological contaminants from wastewater. Solids in the sludge are typically processed in a digester system, in which biodegradable materials are “digested” into stable organic matter. Sewage sludge may be further treated through dewatering, heat drying, alkaline (lime) stabilization, composting, or other processes. Regardless of the technology, there are limited options for end use or disposal of sewage sludge, especially in the arctic. Freezing and thawing, as an efficient method of sewage sludge conditioning, has been used for many years in cold climates. An important aspect of this process is that the separation of sludge particles and water is generally irreversible. The final separation is achieved when the “released” water drains away from the solids after thawing, leaving a porous sludge with solids content of 20 to 30%. Following this dewatering and drying process, composting may provide stabilization and destruction of pathogens. The composting process requires bulking materials such as wood chips. The sludge management facility in Iqaluit is located next to the landfill. Raw sludge is piled at the east end of the site, and four composting piles (windrows) have been established on concrete slabs towards the west end of the site. Freezing and thawing is used to dewater the raw sewage sludge. During spring and fall months, the sludge freezes and thaws, which separates Click here to return to Table of Contents
Photos top and bottom: Sludge composting area at Iqaluit solid waste management site
the solid sludge particles from the water. When complete thawing occurs from May to June, some of the separated water drains away. This freezethaw process produces a drier sludge material available for composting. To begin the composting process, dewatered sludge is mixed with wood chips at a ratio of 2:1 wood to sludge, and piled in rows. The compost is turned regularly to provide aerobic conditions inside the pile. Over the summer, composting will occur, and a “maturing” phase can occur over the following winter months. The timeline for freeze-thaw-composting is a two-year cycle: freezing occurs from September to May; thawing from May to June; and composting from June to September. The compost would then “mature” from September to May, with the total process taking 20 months from start to finish. To date, the freeze-thaw dewatering and composting processes are effectively treating Iqaluit’s sewage sludge. Compost samples showed a dramatic reduction in total and fecal coliforms compared to the raw sludge samples. As well, the solids content of compost samples and one partially treated sludge sample was much higher than that of the raw sewage sludge. The City of Iqaluit landfill facility has been able to successfully divert sewage biosolids from the first phase of the wastewater treatment plant. This process is particularly attractive because the finished material is non-hazardous, and will reduce the use of precious granular material at the landfill – granular material may cost close to $40 per cubic metre in Iqaluit so the compost is in some ways BLACK GOLD.
Managing sewage sludge through freeze-thaw-composting is not without its challenges, but the City has successfully implemented its program. Where other centres take for granted the technologies available, the arctic must re-engineer the process to suit the environment. KEN JOHNSON is a consulting engineer and planner, and member of the NTWWA and WCW Boards. He can be reached at ken.johnson@ cryofront.com
Aurora and Hydromatic wastewater pumps
Summer 2009 | Western Canada Water | 15