WOOD CHIP BIOREACTORS
What is a Wood Chip Bioreactor?
The Natural Process: Water carries nutrients between the land and water, helping to support life. When concentrations of anything (including basic nutrients like nitrate and phosphorous) get too high, it temporarily throws the ecosystem out of balance. Fortunately, nature has many ways of restoring equilibrium. For instance, nitrate can be reduced via denitrification, the process by which naturally occurring bacteria in the soil under anoxic (without-oxygen) conditions consume excess nitrate, converting it to harmless nitrate gas (which makes up slightly more than three-quarters of the air we breathe!). Phosphorous pollution can be reduced by increasing vegetation cover on landscapes, since its particles “drop out” of water when slowed down. Natural materials like biochar (charcoal made in anoxic conditions) have also been shown to filter out phosphorous and other contaminants.
The Problem: When there is an input of excess nitrate and phosphorous to a stream or water body, such as when fertilizers runoff from agricultural land or septic systems fail, ecosystem imbalance accumulates. This can make drinking water toxic, particularly for pregnant women, infants, and the elderly; not to mention aquatic wildlife! Over time, waterways too rich in these nutrients cause algae overgrowth, which can produce other toxic substances (harmful algal blooms); consume too much oxygen in the water; and cloud the water. This stresses all of the other organisms that live in and rely on the river, bay, or ocean that’s being impacted.
The Solution: By intercepting runoff at the source with natural systems such as a denitrifying bioreactor, we can help restore balance in the environment. This application is purely nature-based and largely self-sustaining. We dig a trench around three feet deep and of a width relative to the volume of flow (on the order of 30-50 feet wide by 80-100 feet long to treat runoff from 100 acres of land). The trench is lined to keep unfiltered water from seeping into the ground. We fill the trench with wood chips to promote the growth of helpful bacteria, which do the work of converting harmful levels of nitrate into harmless nitrogen gas. Ridge to Reefs has pioneered modifications adding biochar to wood chip bioreactors to also filter out phosphorous, greatly improving the water cleaning properties of the process. We add flow control pipes to the bioreactor to help the water flow in, remain for the optimum length of time, and flow out. When rain comes and water flows downhill, it pauses for a time in the bioreactor trench. The natural processes do their work, and out flows safe, clean water.
Bioreactor Videos
Woodchip Bioreactors and Denitrification Walls For the Bay
Benefits of Wood Chip Bioreactors
These practices passively create the conditions that biologically converts nitrate to nitrogen gas.
In agricultural settings, very little tillable land is taken out of production for construction. Most installations are approximately 80 to 120 feet long and 15 to 50 feet wide.
Wood chip bioreactors are low maintenance. Sediment must be cleaned out of the diversion box once or twice a year.
The estimated cost per pound of nitrogen is roughly $7-10/lb. With little to no maintenance costs, they are one of the most cost-effective agricultural best management practices (BMPs) available.
They are one of the only agricultural BMPs that treat nitrates in shallow groundwater, the source of approximately 70% of agricultural nitrate load. Excessive nitrates impact the quality of drinking water.
This practice was developed in Iowa and extensive data exists on their efficiency in the Midwest. Similar results have been found on the Eastern Shore. Natural Resources Conservation Service (NRCS) adopted a standard for bioreactors and they are Environmental Quality Incentives Program (EQIP) eligible.
Wood Chip Bioreactor Structure
A wood chip bioreactor is an edge-of-field practice designed to treat agricultural water from drainage tile lines (underground pipes to help drain fields), drainage ditches, or ponds. The main component of a wood chip bioreactor is a buried trench filled with wood chips. Using an in-line water control structure, water is diverted from the tile line, ditch, or pond to the wood chip trench. The trench provides the proper environment (carbon from wood chips, nitrate-nitrogen from agricultural drainage, and low dissolved oxygen) to promote the denitrification process that converts nitrates to harmless nitrogen gas which makes up 78% of the air we breathe.
Two control structures are important parts of the bioreactor design, and each structure plays a different role. The inflow control structure is responsible for routing water into the bioreactor and for allowing stormwater to bypass the bioreactor during high flow events. The outflow control structure establishes water elevations in the trench and helps to retain water in the bioreactor so the water is held long enough for the bacteria to remove nitrate from the water before it leaves. Water quality data shows that this innovative technology is highly effective at reducing nitrate with a greater than 90% removal rate.
Pioneering Methods to Reduce Phosphorous in Runoff
Biochar in Wood Chip Reactors
Ridge to Reefs implemented the first bioreactor mixed with biochar in a non-research setting in the USA. Phosphorous in runoff is harmful to water quality. The phosphorous isn’t removed by a traditional bioreactor; the physical properties of the biochar charcoal further cleans the water.
This new practice reduces nitrate concentrations by 80% to 90% and reduces phosphorus concentrations by 30%-60%. Read more here.
Denitrifying Bioreactor Resources
Click to View the Presentation
Bioreactor/Biochar Workshop at James River Association
On Nov 10th, 2016 Ridge to Reefs had a free, open to the public workshop at the James River Association. We discussed bioreactors with biochar as a valuable innovation for best management practices reducing nutrient loads to the Chesapeake Bay.
Speakers: Dr. Zach Easton (Virgina Tech)
Charles Hegberg (reGENESIS Consulting Services)
Joseph D. Brown (University of Delaware)
Drew Koslow (Ridge to Reefs)
Click to Read the Report
USDA Natural Resources Conservation Service Report
Conservation practice standard: denitrifying bioreactor
Code 605
Wood Chip Bioreactors are Environmental Quality Incentives Program (EQIP) eligible