Home > CARES > Sandbox > Project Results

CARES Project Results

Recycling greenhouse nutrients with compost tea and digestate

Greenhouse food production in Ontario utilizes a growing area of over 8 million m2, and with this large footprint comes a proportionally large requirement for inputs such as crop nutrients. It is estimated that Ontario greenhouses discharge wastewater (also known as greenhouse nutrient feedwater or leachate) containing 6,400 tonnes of nutrients like nitrogen and phosphorus annually. With funding from the Ministry of Environment and Climate Change (MOECC) and Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), we evaluated the use of recycled greenhouse wastewater as an input for the production of compost tea and digestate. Tea and digestate were analyzed for nutrient content and evaluated as fertilizer and biocontrol treatments for greenhouse grown tomatoes. Tomato shoot dry weight and fruit yield in plants fertilized with tea and digestate were not significantly different than those plants fertilized with the synthetic nutrient control.

Ripe tomatoes grown with digestate as fertilizer
Ripe tomatoes grown with digestate as fertilizer

Nutrient analysis of compost tea produced from recycled wastewater revealed that this liquid treatment could provide 40 % of the phosphorus, 23 % of the potassium, 47 % of the calcium and 21 % of the magnesium requirements of a standard synthetic greenhouse nutrient solution. Tea and digestate were found to inhibit the growth of plant pathogens and to protect tomato plants from infection by Phytophthora capsici and could therefore also be used as a biocontrol treatment in greenhouse production.

Tomato seedlings inoculated with Phytophthora capsici and treated with water (centre) or digestate (right).  Seedling on left is an uninoculated control
Tomato seedlings inoculated with Phytophthora capsici and treated with water (centre) or digestate (right). Seedling on left is an uninoculated control.

Displacing synthetic fertilizer with nutrients recycled from greenhouse wastewater via compost tea and digestate production is feasible and would produce environmental benefits.

Funding provided by MOECC and OMAFRA

Biogas feedstocks

Different types of biogas feedstocks have been evaluated in the CARES anaerobic digester located at the University of Guelph Ridgetown Campus. Biomass yield from wild populations of Phragmites, an invasive plant, was found to be comparable to purpose grown biomass crops. Viability of seeds from Phragmites was greatly reduced after anaerobic digestion, suggesting that risk of spread from use of this plant as a biogas feedstock is low. We also studied the use of corn stover as a feedstock for biogas production, but found that stover is only economically feasible in the smallest on-farm digesters (less than 100 kW) due to favourable pricing under Ontario’s Feed-in Tariff.

Funding provided by OMAFRA and Agriculture and Agri-Food Canada’s CanAdvance program.

Utilization of biofuel co-products

Biodiesel derived crude glycerol is a potentially valuable resource, but has a variable composition and purity. CARES has characterized the composition of this biodiesel co-product and found that the main components are glycerol, water, alcohol, residual oils as well as sodium or potassium depending on the type of strong base used in the transesterification reaction. CARES is currently investigating the bioconversion of glycerol, along with thin stillage from ethanol production, for production of single cell oil. A swine feeding trial with glycerol revealed that pork quality was not compromised when grower pigs were fed up to 15 % crude glycerol on a 90 % dry matter basis.

Funding provided by OMAFRA, Ontario Pork and Agriculture and Agri-Food Canada’s CanAdvance program.

Page reviewed 12/05/2016