Research

In 2009, University of Washington researchers conducted research to field test results of a 2008 greenhouse study. They studied how biosolids and reclaimed water affect the growth of edible and ornamental plants.

Research and demonstration program

The goal of the program is to use the best available science and applied research within the parameters of our budget to demonstrate the safe and appropriate use of reclaimed water and biosolids compost. Our results are used to:

• Answer questions from customers, users, regulators, and management.  
• Collaborate with treatment plant operators on process issues.
• Develop Best Management Practices for use of reclaimed water.

What did we look at?

• Plant health: Are the plants getting the nutrients they need?
• Plant growth: How fast and big are the plants growing?
• Presence of trace metals or pathogens: Is it safe to eat the food crops?
• Soil pH and nutrient levels: Is this good for the earth?
• Salinity: Will salt build-up in the soil?

What did we find?

• Plant health: The plot with the biosolids amended soil and reclaimed water irrigation grew the biggest and had a plentiful yield.
• Plant growth: Plants irrigated with reclaimed water showed better growth than plants irrigated with tap water.
• The plants are safe to eat: Soil and plant  trace metal concentrations were at similar levels in all plots; trace metals are found in non-amended soil. Pathogens weren't a concern for any of the plots. It is normal for all soils to contain some metals and bacteria.
• Soil pH and nutrient levels: Soil pH was within normal levels. There is a slight nutrient value in reclaimed water and greater nutrient value in biosolids compost amended soil.
• Salinity: There was no salt increase in soils from using reclaimed water.

The plants

Food crops studied:

Lettuce	Strawberry	Carrot

Ornamental flowers studied:

Delphinium	Sunflower	Amaranth

Additional food crops were also planted and were on the menu at a community luncheon held in September 2009.