From Waste to Resource
Over the last few decades, when the words "Victoria" and "sewage" have been used together it has usually been in reference to the debate on why one of Canada's last major urban centres continues to di...
Over the last few decades, when the words “Victoria” and “sewage” have been used together it has usually been in reference to the debate on why one of Canada’s last major urban centres continues to discharge untreated wastewater into the marine environment. This debate has been heated and emotional — on both sides of the issue.
Ironically, the delay in moving to wastewater treatment may have been a blessing in disguise. As planning now moves ahead, the region has the opportunity to look at wastewater management from a different point of view — not as a waste to dispose of, but as a resource to use.
In 2006 the Capital Regional District (CRD) embarked on a program to develop a wastewater management strategy for the Victoria area. Associated Engineering, with CH2M Hill and Kerr Wood Leidal, developed a report entitled, “The Path Forward.” The team is now working on developing the CRD’s $1.2 billion wastewater management program.
Environmental factors have driven the change to viewing wastewater as a resource: earth’s resources are limited so there is a need for us to reuse and recover them when possible. There’s also the need for energy efficiency and reducing our carbon footprint.
The opportunities for using wastewater as a recoverable resource fall into four main areas — energy from organic solids, wastewater heat energy, water reuse, and nutrient recovery (see sidebar previous page).
Looking at wastewater management from a resource recovery approach can be coupled with how we look at overall urban water planning. Traditional thinking in urban areas is to configure the wastewater management system as a centralized system, where wastewater is conveyed to a single large treatment plant, then the effluent is disposed of.
While some elements of resource recovery benefit from a larger scale, such as recovering energy from organic sol- ids, other elements such as heat recovery or water reuse can be better achieved on a local basis. Combining the benefits of both a centralized approach with decentralized elements can thus lead to a distributed or hybrid approach to wastewater management. An example of this is to use an existing wastewater trunk system as the system’s “backbone.” The decentralized plants can perform local heat recovery or water reuse, but then can be developed in the sewerage area with the “central” plant at the end of the sewerage system focused on wet weather flow management and energy recovery from the organic solids.
All of these opportunities have been influenced by technology changes in the wastewater industry. One major change has been the development of membrane based separation. In this approach, the traditional secondary clarifier, which separates the solids from the treated liquid portion by gravity, is replaced by a membrane process. Membrane separation allows not only an increase in treatment performance, but also a much smaller plant footprint.
Additionally, there have been significant improvements in technologies aimed at recovering energy from organic solids. And in the long term, there are promising develop ments in microbiological fuel cell technologies that perhaps will lead to the generation of hydrogen fuel from wastewater.
Capital Regional District goes decentralized
After a comprehensive triple bottom line analysis of economic, environmental and social considerations, the Capital Regional District has decided to move towards a more decentralized approach that will see a larger number of wastewater treatment facilities throughout the region. This distributed approach will allow the region to take best advantage of the existing sewerage infrastructure, while setting the direction for more localized wastewater management with potential water reuse and energy recovery opportunities.
The real innovation of this strategy is the flexibility that it will provide the CRD in future decades. The region will no longer need to build larger and larger pipes in the ground to transport the wastewater long distances to a central treatment plant site. Nor will the region continually need to expand the central plant to handle higher wastewater flows due to growth — the decentralized plants will handle the growth in the outlying communities. These plants will use advanced treatment technologies to take advantage of phasing opportunities and “just in time” construction to accommodate future needs.
The direction adopted by the CRD for future wastewater management is a bold change from traditional thinking. It considers wastewater as a resource that can be integrated into urban resource management planning. While not all of the ideas and opportunities for integrated resource management can or will be implemented in the near term, the key is that the region is planning for several decades in the future. The intent is to get the fundamental concept and facility siting decisions correct, so that over time wastewater management truly becomes part of the water and energy resources in the community.
Rick Corbett, M. Sc., P. Eng. is vice president of environmental engineering with Associated Engineering in Burnaby, B. C. and project manager for AE on the CRD’s Wastewater Management Program.
FOUR ENVIRONMENTAL OPPORTUNITIES
ENERGY FROM ORGANIC SOLIDS
The organic solids from wastewater treatment processes have long been recognized as a source of “green” energy, principally through the anaerobic digestion of the solids and the production of a biogas that can be used to generate on-site electrical power. Current trends recognize that this biogas, in fact, has a higher value as a fuel. Technologies are being developed to further refine this biogas to a quality that can be used to fuel vehicles or can be added to a natural gas grid. Biogas generation can be enhanced through the addition of other organic wastes such as food wastes from a source-separated municipal solid waste program.
WASTEWATER HEAT ENERGY
The typical average temperature of wastewater is about 15C. Heat exchange technologies are rapidly advancing to cost effectively allow a portion of this heat to be extracted from the effluent prior to using the effluent for reuse or returning it to the environment. The heat recovered is typically used as a supplemental heat source in a centralized community heating system.
Treated effluent can be used in a beneficial manner in a number of ways: irrigation, industrial use, augmenting the flow in watercourses, and non-potable urban applications such as toilet flushing. There are two potential directions for obtaining effluent water. One is from a local wastewater treatment plant. The second is from an “internal” wastewater treatment plant in a building complex. In the latter, water recycling, often with the integration of rainwater capture, is used to reduce the overall use of potable water in the complex and to reduce the amount of wastewater transported off-site for transmission and treatment.
Wastewater contains phosphorus and nitrogen. While the traditional goal has been to reduce these nutrients in the effluent discharged to sensitive receiving environments, there is ongoing research to develop ways of recovering these nutrients for their resource potential. Phosphorus can be recovered through a crystallization process, producing a high grade phosphate fertilizer. The majority of nitrogen is from ammonia in urine. Work is currently proceeding in Europe on the concept of urine separation at source in specially designed toilets. The “yellow” water could then be processed in a concentrated form, allowing the recovery of nitrogen for use as a fertilizer.