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Over the last 20 years, the Resource Recovery Section of King County's Wastewater Treatment Division has been investigating and assessing wastewater treatment processing technologies for ways to reduce or reuse energy, water and nutrient sources during wastewater processing, benefiting ratepayers and the environment.

Each project description is followed by links to project reports with related information, when available. You can download and view documents (PDF files) using a PDF Reader.

Energy

An investigation of alternative approaches to optimize biogas management and energy utilization facilities at the South Treatment Plant.

 View report (6.8 MB)

A detailed study investigating the feasibility of importing brown (restaurant) grease to WTD's South Treatment Plant and co-digesting with sewage solids to enhance production of renewable biogas.

 View report (5.8 MB)

This report summarizes the results of a two-year project to demonstrate whether a molten carbonate fuel cell power plant could be adapted to use anaerobic digester gas as a fuel source and still achieve a power output target of 1 megawatt.

 Learn more and view final report

This report summarizes an initial investigation on the feasibility of implementing a food waste importation program at South Plant in order to increase methane production.

View report (54 KB)

Biosolids

A variety of studies to evaluate and/or improve the operation of  West Point's solids digestion process are summarized below:

  • Digester Tracer Studies –  to evaluate mixing effectiveness. Initial testing was inconclusive.
  • Temperature profiles – to evaluate mixing effectiveness by looking for temperature gradients within the digester.
  • Solids profiles – to evaluate mixing effectiveness by looking for solids concentration gradients within the digester.
  • Vmax/Acetate uptake rates –  to evaluate health of a digester tank by measuring how it responds to a known artificial feed source.
  • Digester survey – to establish how actual operating conditions of digesters compare to similar systems in other parts of North America.
  • Recirculation gas monitoring – to determine mixing energy input by establishing the flow of digester gas delivered to each mixing draft tube.
  • Evaluation of instrumentation to better monitor digester operation and online gas composition and liquid stream parameters.

The studies ultimately resulted in a multi-phase capital project designed to improve the stability of the digesters. Results of the studies are summarized in this PowerPoint presentation.

View report (244 KB)

This report summarizes a demonstration of the VERTAD™ digestion process to provide Class A pathogen reduction through an aerobic deep shaft design.

View report (17.6 MB)

This study examined temperature-phased anaerobic digestion to improve volatile solids destruction and/or to accommodate reduced hydraulic residence time in existing digesters.

View report (134 KB)

This demonstration project determined that the Centridry™ biosolids drying process was capable of producing biosolids of 50 to 60 percent solids content in a mechanically reliable and operator-friendly manner but also revealed serious issues of odor, and hence product acceptability and siting issues.

View report(41 MB)

This study documents food waste management in WTD's service area and the impact on wastewater treatment process unit loading, and to develop and compare alternatives for managing food waste in a more cost effective way.

View report (5.3 MB) Report appendix (4.4 MB)

Wastewater / Water

The reclaimed water comprehensive planning process explored if, when, where, and by what funding mechanisms King County's existing reclaimed water program should expand over the next 30 years. It examined potential reclaimed water uses and evaluated strategies for serving these uses.

Reclaimed Water Feasibility Study
Reclaimed Water Feasibility Study Report Mar 2008 5.5MB
Reclaimed Water Feasibility Study Appendices Mar 2008 720KB
Purpose and Need Statement
Purpose and Need Statement Jul 2009, updated Jun 2010 1.0MB
Reclaimed Water Policies and Analysis (working drafts)
Benefit-Cost Analysis of Reclaimed Water Strategies Mar 2012 1.2MB
Engineering Analysis and Definition of Reclaimed Water Strategies Mar 2012 3.5MB
Reclaimed Water Strategy Effects on Lakes, Streams and Rivers Mar 2012 770KB
Reclaimed Water Strategy Effects on Puget Sound Mar 2012 705KB
Reclaimed Water Strategy Effects on Wetlands Mar 2012 5.0MB
Reclaimed Water Strategy Effects on the Built Environment Mar 2012 7.4MB
Regulatory Feasibility of Reclaimed Water Strategies Apr 2012 2.5MB
Economic Analysis
Identification of Potential Economic Costs of Production and Use of Reclaimed Water Nov 2009 336KB
Identification of Potential Economic Benefits of Production and Use of Reclaimed Water Nov 2009 550KB
Potential Uses for Reclaimed Water and Development of Strategies to Serve Uses (working draft)
Identification of Potential Nonpotable Consumptive Uses of Reclaimed Water Mar 2010 1.1MB
Preliminary Assessment of Water Resource Conditions (working drafts)
Identification of Streams with Declines in Summer Low Flows Revised Apr 2010 1.1MB
Identification of Wetlands Likely to Have Altered Hydrology that Are Not Bogs or Coniferous Forested Wetlands Revised Apr 2010 560KB
Lowered Groundwater Levels in King County, Washington: A Preliminary Review of Reports Revised Apr 2010 590KB
Preliminary Estimates of Summer Environmental Restoration Flow Targets for Basins in King County with Declines in Summer Low Flows Revised Apr 2010 400KB

The Washington State Department of Ecology has determined that portions of south Puget Sound do not meet Washington State water quality standards for dissolved oxygen. Ecology is concerned that algal growth stimulated by nitrogen loadings to Puget Sound is causing DO depression in near-bottom regions. The Technology Assessment Program conducted this study to evaluate the impact (e.g. costs, footprint, energy, greenhouse gas emissions) of a range of potential future nitrogen removal requirements on the West Point Treatment Plant. The West Point Treatment Plant is a high-purity oxygen (HPO) activated sludge process (non-nitrifying) on a very constrained site with no possibility of expansion.

Report (5 MB)

The Washington State Department of Ecology has determined that portions of south Puget Sound do not meet Washington State water quality standards for dissolved oxygen. Ecology is concerned that algal growth stimulated by nitrogen loadings to Puget Sound is causing DO depression in near-bottom regions. The Technology Assessment Program conducted this study to evaluate the impact (e.g. costs, footprint, energy, greenhouse gas emissions) of a range of potential future nitrogen removal requirements on the South Treatment Plant. The South Treatment Plant is a conventional activated sludge process (non-nitrifying) with significant space available for future expansion

Report (9 MB)
This work was initiated by project staff at King County in 2009 as part of preparations for a potential flood emergency in the Green River Basin (which is tributary to King County’s South Treatment Plant ) due to concerns about instability of abutments to the Howard Hansen Dam. The objective of this study was to evaluate potential strategies to maximize flow capacity through the secondary system at the South Treatment Plat during a flood event without putting the secondary process at risk of failure after the flood event.  This study was limited to evaluation of process effects.

View report (785 KB)

King County pilot-tested multiple membrane bioreactor (MBR) technologies. The technology is now being used at King County’s Carnation and Brightwater Treatment Plants.

View report 1 (917 KB) View report 2 (1.2 MB) View report 3 (248 KB)

View report 4 (651 KB) View poster 5 (2.6 MB) View report 6 (1.7 MB)

This demonstration assessed various emerging wastewater treatment technologies designed to produce Class A effluent. This project was awarded the 2002 National Environmental Achievement Award for Research and Technology by the National Association of Clean Water Agencies.

Learn more.

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