Land Application of Spent Filtration Earth From Canola Oil Production to Improve Soil Properties

Term: 3 years, beginning 2024 
Status: Ongoing
Researcher(s): Jeff Schoenau, U of S
SaskCanola Investment: $45,310
Total Project Cost: $163,510
Funding Partners: ADF

Objective

1. Determine effects on soils and crops from application of spent filtration clay that is a by-product of canola crushing. 

2. Reveal rates of spent filtration earth and co-amendments that optimize performance in Saskatchewan soils. 

Project Description

About 2 million metric tonnes of spent bleaching/filtration earths from vegetable oil refining are produced worldwide every year. The canola crush oil processing industry in western Canada creates significant amounts of spent bentonite- based filtration earth from the crushing of 10 million tonnes of canola. New crush facilities being built or expansion of crush capabilities by companies including Viterra, Richardson, Cargill, and others will increase the amount of spent filtration earth produced as a by-product of the crush industry. The spent bleaching/filtration earth material left from vegetable oil refining has traditionally been disposed of in landfills, but this is an undesirable and expensive practice, and many landfills will no longer accept bleaching earth from vegetable oil refining. The high oil content of the material when stockpiled in one place can lead to problems with spontaneous combustion. Recycling through extraction and production of biodiesel from the oil left behind in the clay, making briquettes or clay tiles, among other industrial uses, have been proposed as alternative uses for the material. 

Another potential option that has received little attention is land application of spent filtration earth. This has been suggested as a soil amendment to improve soils lacking in clay content and thereby provide benefits associated with having clay in soils. This includes improved fertility, nutrient and water retention from the added clay. The vegetable oil in the filtration earth can also act as a carbon source to increase microbial respiration and decomposition in soil, which, in turn, influences nitrogen availability, pH and persistence of carbon forms. Vegetable oil added in low concentrations to soil are reported to improve some soil attributes while high concentrations of oils such as cooking oil waste in soil can cause problems with compaction and phytotoxicity. As well, organic materials held in the spent filtration clay in the form of vegetable oil, chlorophylls, and carotenoids in association with the clay may help promote formation of soil humus, enhance microbial activity and the storage of carbon in the soil compared to vegetable oil alone. There is a need to investigate land application of spent filtration clays from canola oil production as a novel means to improve soil conditions and plant growth in marginal soils when added at the appropriate rate, and effectively recycle a material that traditionally is a disposal issue and cost to the canola crush industry. 

Will study 4 different soil types, 4 amendment rates (0, 15, 30, 60 tonnes/Ha), with or without added Nitrogen fertilizer/manure/lime = 160 experimental units in pots.  Lime decreases the acidification effect and prevents spontaneous combustion of the oil-saturated filtration clay.  There will also be 36 treatment plots in the field, where soil properties (water capacity, N2O emissions, microbial respiration, and N and P nutrient availability (PRS Probes)) will be evaluated.