Authors: Gillian Falcon and Dr. Courtney Gardner, Civil and Environmental Engineering
This post highlights the work of researchers funded through the BIOAg Program, a competitive grants program administered by CSANR, created to stimulate research, extension and education investments by WSU scientists and to advance the development, understanding, and use of biologically-intensive, organic and sustainable agriculture in Washington State.
We often encounter worms on the sidewalk after it rains or in our vegetable gardens. Despite how casual these encounters may be, worms are an essential species for ecosystem health. Through this research, I am investigating how worms can benefit agricultural wastewater treatment to improve sustainable and holistic agricultural practices. Agricultural runoff tends to be exceedingly high in nutrients and if left untreated, can lead to disruptions in the nutrient cycle and eutrophication in surrounding water systems. Innovative and effective agricultural wastewater treatment options support a circular economy within agricultural practices.
Worm-based vermifiltration technologies are new and innovative wastewater treatment systems that are low cost, low maintenance, and energy efficient for on-site waste treatment applications. This system takes advantage of the relationship between earthworms and the microbial communities in the soil to reduce the organic load (including nitrogen, potassium, and phosphorus) within the wastewater. The vermifilter that I am specifically looking at currently handles dairy wastewater from a dairy operation of ~3,000 head of cattle located in central Washington.
This system consists of three layers: a top layer of organic material such as woodchips as well as earthworms and microorganisms, a second layer of gravel for drainage support, and a final layer for structural support that includes drainage basins. Liquefied manure is pumped from the dairy stalls towards a holding tank before being sprayed over the top layer and filtered through the system. Larger particles are removed through the woodchips and gravel, and some of the organic load may even stick to these larger particles. The final filtered product, vermicompost tea, can now be used as an organic ingredient fertilizer.
While traditional treatment parameters such as removal of nitrogen and phosphorus are being considered in my study, I am primarily focused on how the activities within the top layer of the vermifilter contribute to the wastewater treatment. I have two primary objectives 1)find out what kind of microorganisms are present within the vermifilter and how they help treat the waste stream, and 2) determine how vermicompost tea amendments produced from the waste treatment process may improve soil fertility compared to traditional nitrogen fertilizers.
For the first objective, I have collected samples from the top layer of the system and the soil plus the wastewater slurry have been separated from the woodchips. These samples were collected at different points within the year so that samples at different temperature ranges can be compared. Worms and microbes are likely to be more active in warmer weather than when the temperature is at or below freezing. The next phase is to determine the specific microbes that are present and what the population looks like in these samples.
For the second objective, I am currently applying vermicompost tea amendments to a model crop (Walla Walla Sweet Onions) as a fertilizer while onions mature. Throughout the growth period, I will collect soil samples regularly from growth chambers to evaluate chemical and biological soil health properties. Once onions are mature, I will also evaluate the ability of vermitea to reduce onion crop loss to microbial pathogens.
Future tasks associated with the work include determining the physical chemical makeup of the vermitea, profiling the nutrient transport over depth within the pots, and characterizing the vermitea’s fertilizer ability as compared to traditional nitrogen fertilizers. Worms are incredible animals that have shown that they are capable of digesting all types of organic material. This system takes advantage of these traits and allows access to sustainable agricultural practices without high maintenance costs and energy requirements that are not feasible for rural areas.
Comments
My understanding is that the N is lost to the atmosphere. It would be of tremendous value to capture some or all of the dairy effluent’s nitrate and ammonia, perhaps in a compost bed of wheat residue, before the microbes have a chance to denitrify it. This would reduce the dairy’s carbon footprint and allow the compost to recycle N that is otherwise lost.