The woodchip bioreactor

by George Looby

The Midwest has long been the hotbed of innovative practices that can benefit not only agricultural practices but also other activities that benefit the general population. One of the issues in the Mississippi River Valley has been the excess of nitrates entering the watershed, upsetting the natural balance that existed before fertilization became as intensive as it is today.

Nitrogen runoff into major river tributaries is a problem being addressed in several ways – one of which is treating it in such a way as to render it less toxic. At least one of these methods breaks nitrate down into nitrogen gas which is released into the atmosphere. The most expensive fertilizer used in corn production is used in such quantities that a method must be found to ensure the excess is managed in a way that it doesn’t contaminate the streams and rivers into which it flows.

The EPA has set a goal of reducing the flow of total nitrogen from the upper Mississippi Valley into the Gulf of Mexico by 45 percent. A small step-by-step approach may provide an answer, including a series of small areas that are treated individually at rather minimal expense but achieving the hoped for reduction of nitrate discharge into significant tributaries. Conservationists everywhere are watching to see if this approach is working. By all indications, it does.

The Eastern Connecticut Conservation District watched the progress being made in the Midwest and set out to develop a trial program in Connecticut, where the problem might be on a smaller scale than in other regions of the country but of considerable importance on a regional basis.

The Clean Water Act (CWA) is not new. It had its origins in 1948, being revised in 1972 to expand its scope. Under the terms of the CWA, the Environmental Protection Agency has implemented pollution control programs such as setting wastewater standards for industry. The agency has also developed national water criteria for pollutants in surface water. It is under the mandate of this authority that pollutants from agricultural runoff are managed.

Tile drainage systems have been used for many years to manage fields which, due to their location and soil type, can be difficult to effectively manage during periods of wet weather. When properly placed, drainage tile can make a significant difference in the spring when unmanaged fields are too wet to work. The same holds true in autumn, when many crops are harvested. In areas where high-priced crops are grown the savings can be considerable, when being the first to market is important. The stated benefits of tile drainage systems are that they maintain the water table at the proper level for healthiest plant growth, they keep soil voids free of excess water, which permits air flow and allows important biological processes to take place in the soil and they allow the use of the equipment needed for efficient planting and harvesting of the crop without the hassle of getting stuck.

As is true for many programs, there are both pros and cons, and so it is with managing runoff with tile drainage systems. The impact of the runoff on the farm with tile drainage may be minimal but its effects downstream may be significant. Once the water reaches a point where it empties into a drainage ditch or creek it is beyond the control of the farm from which it originated. In the case of eastern Connecticut operations, it is probably headed for Long Island Sound. Among the contaminants found in runoff are nitrogen, phosphorus and fecal coliform organisms.

What can be done? One answer is the installation of a low tech woodchip bioreactor – a ditch filled with sawdust through which all of the runoff from a tiled field must flow before it is discharged into a water source. During this time the water comes in contact with naturally occurring denitrifying soil bacteria which turns the nitrogen into nitrous oxide gas. Where necessary, phosphorus and E. coli reductions will occur if the effluent is run through an iron-enriched sand filter placed on top of the woodchips.

Woodchip bioreactors were first introduced into Connecticut this past year on Valleyside Farm in Woodstock, CT. Funding for this project was awarded by the Connecticut Department of Energy and Environmental Protection.

The Young family, owners and operators of Valleyside Farm, seem to be always ready to incorporate new technologies into their operation, so the entire region benefits from their forward-looking approach. One feature of this installation is portals built into the system which allow for the periodic sampling of water for analysis at a certified laboratory to monitor the designated nutrients and E. coli.

Based on available information, it is believed the life expectancy of one of these units is up to 20 years. Once depleted, they can be cleaned out and replenished with fresh woodchips.

After more data are accumulated, they will be published for viewing. If results are similar to those already seen elsewhere, it is likely that similar installations will be added to farms elsewhere in the area.

2019-02-19T09:13:39-05:00February 18, 2019|New England Farm Weekly, Western Edition|0 Comments

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