Bioreactor installation at Seal River

Bioreactor installation at Seal River

A woodchip bioreactor (nitrate filtra­tion system) was installed in a field over­looking the Seal River estuary in the fall and was aimed at providing valuable data about the severity of nitrate pollution in the area. The pilot project is a collabora­tion of Agri-Watershed Partnership, Pis­quid River Enhancement Project Inc (PREP) and Shady Lane Farms.

The Seal River watershed area is under the jurisdiction of PREP. The project was directed and fully funded by the Agri-Watershed Partnership, represented by Gwen Vessey, who personally oversaw and assisted in the installation.

Through the combined efforts of PREP, represented by chairperson Clarence Ryan and with help from Hannah Mur­naghan with Morell River Management Cooperative, the bioreactor was success­fully installed on October 11 on the prop­erty currently run by Gary Tweedy, a sec­ond-generation dairy farmer in Vernon Bridge. He operates the farm with his nephew Matt Hogan.

Agriculture and livestock farming have flourished on PEI for several centuries thanks to the Island’s arable soil and roll­ing landscape.  However, increasingly extensive farming has led to fertile topsoil runoff into streams and eventually the sea. In order to replenish soil nutrients for crop growth, farmers often add either organic or artificial fertilizers, which also get washed into streams over the course of time.

Nitrogen is the most prominent agent and makes up a good portion of conven­tional fertilizers. When nitrogen is being applied to the soil, it can turn into nitrate which can be easily dissolved in water. Because of PEI’s extensive uses of manure and fertilizer for agriculture, the nitrate level in PEI’s groundwater has reached alarming rates.

As early as 2007, six per cent of private wells had exceeded the safety limit of 10 milligrams of nitrate per liter of water and another 10 per cent of wells got close to the limit, in which over 90 per cent of the nitrates came from man-made sources. Nitrate also affects the growth of other vegetation, including various types of algae which can lead to a harmful envi­ronmental effect in the waterways known as eutrophication (overly rich in nutri­ents).

This can sometimes result in hypoxia (a lack of oxygen). The influx of nitrates into a body of water can cause algae to bloom, and such rapid population growth results in mass dying due to algae’s short life span. The huge amount of dead algae can in turn trigger the growth of bacteria and other microbes that decompose organic matter. And with such an amount of dead organic matter, the bacteria and microbes can quickly deplete the dissolved oxygen in the water during the decomposition process. When dissolved oxygen in water reaches a critical low point, hypoxia can happen.

Nitrates can also trigger the bloom of algae species that produce toxins. Algal toxins can build up through the food chain of the aquatic ecosystem, and when larger aquatic organisms and humans consume seafood polluted with these toxins, it can result in serious illness and even death.

This can put the health of the aquatic ecosystem and the prosperity of the fish­ery and shellfish industries in jeopardy. The installation of the bioreactor can help reduce chances of those outcomes.

Another factor that makes the nitrate pollution on PEI worse is the wide-spread implementation of drainage tiles under agricultural fields, which is present at the bioreactor site at Shady Lane Farms. Drain­age tiles purpose is to create an efficient drainage system to drain the water out of the originally wet low-lying portions of the field that were unsuitable for agriculture. After the low-lying portions of the field dried up due to the new drainage system it then became suitable for agricultural usage. However, due to the drainage tiles concentrating all the groundwater outflow into a single pipe, the nitrate in the ground­water gets released in a single spot result­ing in high concentrations. It can cause severe effects on the environment as com­pared to the natural leaching of nitrate from the groundwater system. In the case of the Seal River estuary it has led to the decline or closure of the fishery and shell­fish industries in several localities. At the time that the drainage tiles were imple­mented, farmers and the public were not aware of its negative effects and they have only been noticed and researched in recent years.

The field where the Shady Lane Farms bioreactor was recently installed is on a slope directly next to Seal River, which means any nitrates leaking down the sloped field would directly enter the estu­ary and have an immediate effect on the local marine environment with the closest oyster farm only a few hundred meters away.

The installation of this bioreactor has thus enabled PREP to have an efficient method of monitoring the health of the estuary and investigate any surge in nitrates in the groundwater.

Bioreactor is a broad term that can be defined as a system or device that sup­ports an active biological environment. The wood chip bioreactor at Seal River hosts an anaerobic (no-oxygen) environ­ment, and the microbes thriving in it breathe nitrate instead of oxygen. Its func­tion is to absorb the nitrates in the ground­water going through the drainage tiles, thereby stopping the nitrates from going further downstream into the natural envi­ronment. Through regularly inspecting the bioreactor, scientists are able to calculate the amount of nitrates dissolved in the groundwater by comparing the water sam­ples taken before and after going through the bioreactor, thus a woodchip bioreac­tor can be broken down into three com­partments, the diversion structure, filtra­tion system, and capacity control struc­ture with drainage tiles connecting them together.

The diversion structure leads the groundwater flow into the filtration sys­tem. If the groundwater level is high, the diversion structure also has a bypass drainage tile to divert excess water out of the bioreactor into the environment. The diversion structure has a shaft structure that allows operators to collect samples of the raw groundwater to test its nitrate con­centration. The next compartment is the filtration system, which can be seen as the most crucial part of the bioreactor and can be referred to as the bioreactor itself. Since this is the part where the nitrates in the groundwater get absorbed by microbes, thus serving as a biological reactor that reacts to nitrate. The filtration system is a sealed chamber lined with inlet and outlet drainage tiles at the bot­tom and filled with wood chips, which are the primary food source for the nitrate-breathing microbes. When water flows into the filtration system, it will flow out of the perforated tiles and permeate into the woodchip-filled chamber. It is here that the microbes in the woodchips absorb the nitrates from the water as an energy source. After the groundwater slowly per­meates through the chamber it flows into the outlet tiles that lead to the capacity control structure. The capacity control structure also has a shaft structure to enable operators to take samples of the groundwater that has been through the filtration system. Finally, after the capacity control structure the groundwater then flows out to the environment through the drainage tiles.

The project began with finding the drainage tiles with the use of an excavator and shovels. Then sections of the tiles were replaced with new tiles that have the diversion structure of the bioreactor attached. The next step was to excavate a rectangular hole to house the filtration system of the bioreactor. The bottom and walls of the chamber were then overlaid with plastic sheets to ensure that no groundwater could leak out of the filtra­tion system. Then perforated tiles were added. After that, the capacity control structure was installed in which outlet water samples that have been treated by the filtration system can be taken. The final steps were filling in with wood chips, covering the top of the chamber with plas­tic sheets to ensure the filtration system is sealed, and then backfilling a layer of soil on top to cover the sealed filtration sys­tem. As a means to minimize the soil run­off after construction, the PREP crew spread grass seeds on the site to facilitate the quick recovery of the grassy meadow.

The woodchip bioreactor can be seen as a sign of goodwill from the agricultural industry to the fishery and shellfish indus­tries in the Vernon-Orwell Bay area–as good neighbors, they can set foot in achieving mutual prosperity.

Tackling the environmental hazards of nitrate pollution and eutrophication in its watershed jurisdiction has been a focus of PREP for years. Therefore, this bioreactor in a sense also makes PREP a “good neigh­bor” to the environment and the local communities around the estuary and the greater Vernon-Orwell Bay area.

PREP deeply appreciates the Agri-Water­shed Partnership for leading and funding this project and also Gary Tweedy for agreeing to install the bioreactor on his property. Thanks also go to the crew of the Morell River Management Cooperative for aiding in the installation procedure and to the support from the Hillsborough River Association.

Directors and staff of PREP and the Hill­sborough River Association wish a healthy and prosperous new year to all the agri­cultural, fishery and shellfish producers.


by Mars Brix with Pisquid River Enhancement Project Inc.