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Geotextile containers for dewatering septage

February 1st, 2010 / By: / Containment, Feature, Geotextiles, IAA

TenCate Geosynthetics wins in 2009 International Achievement Awards

In 2002, Ontario’s provincial legislature and the Ministry of Environment (MOE) produced a policy paper announcing its intent to eliminate the land application of untreated septage (septic tank waste).

While 90% of residents in Ontario used local sanitary sewers to dispose of waste and, therefore, were unaffected by the new policy, there were still more than 1 million residents in rural areas using septic tanks. Haulers across Ontario were left in a bind, scrambling to find methods to treat and dispose of the septage. It was up to the local municipalities and the private haulers to come up with alternate methods to treat and dispose of the septage.

For the small town of Eganville (population 3,455) the solution was found via geotextile dewatering containers. Eganville is situated in the Bonnechere Valley, 87mi (141km) west of Ottawa.

The objective of this project was to design and construct a permanent, cost-effective dewatering and processing facility that would provide a long-term solution for the treatment of septage and biosolids from the wastewater treatment plant.

The process for haulers to empty their truckloads at the dewatering facility is simple and straightforward. Haulers are required to pull their tanker trucks up to the septage station and empty the load from their tankers into the 10,000-gallon (38,000-litre) underground holding tank. After emptying their tanks, haulers drive away.

Haulers no longer have to spend time land-applying septage to fields. A simple bar screen removes solid waste, such as plastics, during emptying to ensure no large objects are pumped into the tank. The septage is mixed with a submersible pump located in the tank.

As the waste is pumped into a geotextile container, it is mixed with a polymer solution to promote flocculation, and then the dewatering occurs.

As the solids settle to the bottom, clear filtrate flows from the container. The filtrate flows by gravity over the concrete pad, where the containers are located, and onto an underground filtrate storage tank. Once full, the filtrate is then sent back to the head works of the treatment plant where it is further treated to meet the stringent MOE discharge criteria.

Once dewatered, the solids are removed and are land applied. Reflecting its commitment to this project, the Bonnechere Valley Township partnered with Renfrew County and the MOE to continue evaluating the dewatering and treatment of septage utilizing geotextile tube dewatering technology.

Beginning in 2008, the township has handled the operation, evaluation, and reporting for this septage management project. Analysis and testing was conducted on three types of materials for comparison: raw septage, septage filtrate, and dewatered septage solids.

The testing focused on the following measures:

  1. Pathogen levels going in, during dewatering, and after completed dewatering
  2. Levels of metals
  3. pH levels
  4. Nutrient levels.

From April to December 2008, about 500m3 (650yd3) of septage was received and processed. At the end of the year, the geotextile container measured approximately 0.6m (2ft) high. This equated to almost 35m3 (46yd3) of dewatered septage in the 10–12% solids range.

  • 98.2% phosphorus captured
  • 82.3% nitrogen captured
  • 99.9% E. coli reduction
  • 100% arsenic reduction
  • 98.8% lead reduction
  • 99.9% mercury reduction

By addressing the challenges facing the septage haulers across the province, the Bonnechere Valley Township is demonstrating environmental responsibility by choosing a treatment option for septage and biosolids that does not produce a waste, but an odorless reusable nutrient.

Sources: TenCate Geosynthetics and the 2009 International Achievement Awards entry information

Editor’s Note: The Industrial Fabrics Association International (IFAI) invites entries for its 2010 International Achievement Awards (IAA) competition. For more information about the IAAs, contact Christine Malmgren, +1 651 225 6926, cmmalmgren@ifai.com, www.ifai.com/home/recognition_iaa.cfm.

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