Biosolids/Organic Residuals Strategy Evaluation (031-DP-9)

Discussion Paper Summary

It's important to consider the management of biosolids and organic residuals with wastewater treatment and overall wastewater management. Potential exists to co-manage solid waste organics (food wastes) with wastewater biosolids, as these materials share a fundamental characteristic--they are both comprised primarily of the element carbon. Over the past months the CRD has developed and evaluated a variety of biosolids management strategies that consider various levels of solid waste management integration with wastewater management. Discussion Paper 031-DP-9 details these findings.

How were biosolids/organic residuals evaluated?

Biosolids and organic residuals strategies were looked at in light of energy recovery (e.g. to produce biomethane), as a beneficial reuse product (e.g. compost, coal substitute) or using some combination of these approaches. Integration of the wastewater and solid waste programs was considered and the consulting team does not recommend full integration of biosolids and solid waste. Four broad strategies were developed and evaluated, including:

  • Strategy 1 - Maximum beneficial reuse
  • Strategy 2 - Maximum integration and maximum energy recovery
  • Strategy 3 - Separate digestion and balanced energy recovery / beneficial reuse
  • Strategy 4 - No digestion and balanced energy recovery / beneficial reuse

Within these broad strategies a number of sub-strategies were developed to allow further investigation of specific elements within the strategies. In the end, a total of eight sub-strategies reflecting the four broad strategies were developed and evaluated.

What was learned?

Evaluation of the strategies included:

  • Carbon footprint analysis (CFA)
  • Life-cycle analysis (LCA)
  • Capital costs, operations and maintenance costs
  • Revenue generated from saleable products
  • Greenhouse gas emission costs/credits

The CFA and LCA findings were considering using the CRD's triple bottom line methodology, which takes into consideration the environmental, social, economic impacts of wastewater treatment.

Which biosolids management strategy is most promising?

Strategy 1d provides the CRD with an excellent opportunity to beneficially reuse material and recover energy in a sustainable way and with low risk.

Strategy 1d would see 50% of biosolids co-digested with organics and used as a coal substitute for a cement kiln; resources from this portion would include biogas, biomethane and heat. The other 50% of biosolids would be dewatered and applied to willow coppice farms as fertilizer; willow woodchips would be harvested for a green biofuel source.

The consultant team chose to use Strategy 1d when looking at Distributed Wastewater Management Options. Use of Strategy 1d does not imply a final decision, but rather gives the CRD a method of comparing distributed treatment options using a level platform.

Moving Forward with Distributed Wastewater Management Options

The three distributed management options offer scenarios for three, five or eleven treatment plants. Site locations for each plant are not a part of this stage of the planning process.

Option One
  • Three treatment plants; heat energy recovery using effluent from all three plants; wet weather flow at Clover Point and organic energy and phosphorus recovery at two plants.
Option Two
  • Five treatment plants; heat energy recovery using effluent from all five plants; modification of sewerage area boundaries; wet weather flow at Clover Point and Macaulay/McLoughlin Point and organic energy and phosphorus recovery at one plant.
Option Three
  • Eleven treatment plants; aggressive water recycling at individual buildings; heat energy recovery using effluent from all eleven plants; wet weather flow at Clover Point and Macaulay/McLoughlin Point and organic Energy and phosphorus recovery at two plants.