Development of a De-watering System and Cost Analysis to Transform Fish Waste from Recirculating Aquaculture Systems into Value Added Garden Compost

Final report for FNE21-990

Project Type: Farmer
Funds awarded in 2021: $14,963.00
Projected End Date: 01/31/2022
Grant Recipient: Aroostook Band of Micmacs
Region: Northeast
State: Maine
Project Leader:
Cara ODonnell
Aroostook Band of Micmacs
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Project Information


The purpose of this project was to determine if there was a viable method for dewatering fish waste for a small-scale Recirculating Aquaculture System (RAS). Our aquaculture farm staff built a 20' x 20' x 8" frame structure and prepared the underlying sod surface so that it had a slight slope in one corner to consolidate the liquid into one area as the volume reduced over time. We intended to use a standing canopy frame and aerators while collecting weather data to identify metrics that enhanced or inhibited the evaporation process, however, due to shipping delays we had difficulty accessing all equipment we originally intended to utilize (specifically aerators and a shelter canopy). We were able to construct a structure and cover it with large tarps for the duration of the project. Weather data was collected daily at the farm (maximum air temp, average air temp, precipitation, wind speed, and relative humidity). Farm staff utilized a pump to carefully remove the supernatant, allowing the fish waste to concentrate to a consistency to be sent for lab analysis. Lab results determined the content to be biologically active, near neutral pH, medium salinity, high release potential for nutrients. NPK ratio for fertilizer amendments: 3:9:1. This information has been shared with RAS colleagues during planning meetings for fish hatchery expansion project and has informed our decision to continue with underground septic containment for our expanded facility, rather than lagoon type structure.

Cost benefit analysis shows that the start-up costs are primarily for the wood materials for construction the de-watering frame, as well as the pump to remove waste from the septic, the canopy cover, and associated equipment. Some of this can be minimized by allowing the effluent to settle and pumping off supernatant to expedite the process of de-watering. The costs into this are virtually one-time and very minimal. The majority of the costs come from packaging, marketing, and time spent establishing a sales base. Fish waste is a valuable product to organic and soil-health-conscious farmers.

Our project could have yielded a saleable project, however, not at a scale that is yet economically viable. Due to lack of fish due to covid alterations to our hatchery rearing plans, we ultimately had a fraction of the fish waste of a typical year. This was also important to learn, and helped us understand how much waste we produce, and the benefits that could be achieved by expanding our facility size.

Project Objectives:

This project accomplished the following objectives:

Objective 1: We successfully created a prototype for a dewatering system that addresses the unique composition of RAS waste. We demonstrated how to efficiently build a dewatering bed, and options for a canopy covering. We determined optional materials that can be used, and identified weather conditions that may accelerate or hamper successful evaporation. We provide a model to show how simple, flexible and affordable the process can be. The hatchery has a USDA MET meteorological station on site that collected continuous readings.

Objective 2: We are able to demonstrate a cost -benefit analysis, the cost and potential revenue of creating a value-added liquid fish waste fertilizer product to be sold as a garden supplement. Costs include construction materials, lab nutrient ratio analysis, bottling and marketing.

This project was used to promote our fish hatchery expansion project, as it outlined the environmentally sustainable way to re-use fish-waste for a beneficial purpose. This was included in our discussion of waste disposal in the environmental narrative component of the grant to show minimal to no impact on natural resources due to the hatchery expansion. We will promote this ‘green’ aspect of our hatchery with the marketing and sale for our fish and other small-scale RAS entrepreneurs that we work with.




The vision of the Micmac fish hatchery is to provide a healthy source of protein to tribal members, as well as the local community, who face a myriad of health issues related to abundance of packaged and fast-food options. Our goals are to make brook trout readily available and also affordable, so that it again becomes a staple food source. Both wild Atlantic salmon and brook trout are traditional food sources for Micmac tribal members, however they are no longer abundant in our local waters, due to dams, warming waters, drought and impaired water quality.

However, wild and high-quality farmed fish remains a critical source of omega fatty acids required for brain development of infants, children and are so important for pregnant women, not only here in northern Maine, but globally. Lean protein meals of fish can also reverse the negative impacts of diabetes, high cholesterol and obesity, among many others.

Land based aquaculture is being looked to as an alternative to the pollution caused by large scale marine fisheries which brings disease, nutrient pollution, and other impacts to wild native fisheries. Aquaculture can also ease the pressure of over- fishing of the world’s oceans and last remnants of wild stocks like Atlantic salmon and freshwater brook trout. RAS technology goes one step further and either reduces or eliminates discharge of wastewater effluent, which can pollute groundwater or ambient river water, causing eutrophication. The RAS technology at the Micmac Farms facility generates low volumes of organic wastes compared to traditional aquaculture systems, which is collected in the form of solid and liquids in our septic system.

Aquaculture (both marine and land based) is a growing industry within the state of Maine. Development of a successful and efficient method for dewatering of RAS fish waste will bring RAS technology closer to becoming a viable option for those interested in small scale aquaculture as a profitable endeavor. Small scale aquaculture brings numerous benefits to rural communities. Local fish is fresh, reduces the environmental emissions of long-distance transportation, and brings local economic growth and jobs. RAS fish can be fed top quality food, creating a healthier end product. The problem with small scale aquaculture such as RAS systems is that they do not reap the benefits that come from mass production and economy of scale. Small scale aquaculture typically places emphasis on producing a superior product by feeding top quality food, and other factors, thus the profit margin is slim. Though there is a market demand for the brook trout, even with our facility processes optimized, and producing at max capacity, we are still at the cusp of maintaining a profit. In order to provide fresh trout to customers at a price point they can afford we hope to utilize this study to develop a dewatering process of our waste effluent to provide economic benefit. The additional revenue gained by selling fish waste as a value-added product can make the endeavor more appealing to those who are interested in pursuing the RAS option.  We gained insight into how to streamline the dewatering process, determine the scalability of the process, and determine optimal concentrations of Total Solids and nutrient content for a concentrated liquid fish waste product. The end result will also provide a cost analysis to demonstrate the potential net increase in farm income.

Description of farm operation:

The Micmac Fish Hatchery has been in operation since 2015. We produce Eastern Brook Trout (Salvelinus fontinalis) for our tribal and local communities using RAS (recirculating aquaculture system) technology, which is an environmentally sustainable alternative for providing fish as a commodity. Our current facility has the ability to raise up to 12,000 lbs. of brook trout per year in the form of both food fish and pond stockers. The latter is as a conservation strategy, to enhance wild populations that surfer from warming waters and over-fishing. Together these products are the core of our hatchery efforts. We currently provide food fish to the tribal and local community food banks and sell wholesale to fish markets in the southern part of Maine, as well as Good Shephard Food Bank (GSFB). GSFB purchases our product for distribution to food pantries in northern Maine. Pond stockers are sold at USDA Soil and Water Conservation District offices through the northern part of Maine at annual pond stocker sales. This is an efficient venue for our sales. In addition, we sell to larger venues such as Fishing clubs and an international power company in the state that stocks the local fishery near their power plant. Gross sales are approximately $60K.


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  • Mark Hutchinson


Materials and methods:

The goal of this project is to demonstrate that other small scale RAS users can utilize their waste to both create an economic benefit to their production system and eliminate solid and liquid waste from their waste stream. Objectives and the associated methods to accomplish this are listed below. 

Objective 1: create a prototype for a dewatering system that addresses the unique composition of RAS waste. 

Materials Used:

  • We used 2”x10” boards to create a frame that was 10” high. The final structure was approximately 20’ square. We lined this with a heavy-duty pond liner, as opposed to a tarp that would easily rip and leak. We were unable to use aerators, however as an alternate method of enhancing evaporation we allowed the emulsion settle and used a pump to pump the supernatant off the top. We located a piece of land nearby the septic that had a gentle grade to it, so that the product would accumulate at one corner, to make gather the material easier. We used a pump to transfer the fish waste from the septic to the protype using a 4” hose. We found that a pump was extremely efficient at expediting evaporation of the surface water.
  • Preparation for weather anomalies: It was critically important to have the structure covered from precipitation events. Ideally, we would have like to have used a semi-permanent run-in type canopy cover, however because of supply chain delays the canopy did not arrive until the project was nearly complete. We improvised using a tarp supported on each end and in the center. This is not an ideal option as the intense rainfall accumulates at the low point on top of the canopy and with substantial accumulation can potentially displace water from the evaporation structure. We experienced displacement, however only of surficial water and not of the fish waste emulsion settled at the bottom.

We experienced two intense rainfalls;

    • Total of over 1.25” on September 7, 2021
    • Total of over 1.5” on September 8 and 9, 2021
    • An NRCS MET meteorological weather station is located on site that collects continuous meteorological data: The link to the data can be found here
  •  We collected meteorological data daily including maximum and average daily air temperatures. Precipitation, relative humidity and wind speed. The daily evaporation rate was difficult to measure as it was a very slow process, and a permanent in-place depth marked on the liner may have functioned in this way.


Objective 2:  Provide a cost benefit analysis.

The initial lab costs are expensive, though essential to understanding the nutrient profile and suitability of the product for marketing purposes. The material cost are also high at the outset. Volume of fish waste produced in 2021 were not indicative of a typical year, due to reduced fish waste volume.  A full cycle of to grow fish to pond stocking and food fish size takes 16 - 23 months respectively. Due to the pandemic, we sold all fish for pond stocking in March of 2020, as we were unsure of potential restaurant sales for 2020. This led to less waste than a typical year. Because of this, it did not make sense to test the percent solids of the filtrate material and associated nutrient concentration at various stages in the evaporation process.

The feasibility study estimate indicates an estimated revenue of $10,000 per year based on a typical year of fish production and sales. The study accounts for production capabilities based on tank size, fish grown to 1 lb. size, packaging, and expenses such as administrative costs, salaries, as well as sales and marketing expenses. We estimate that revenue generated will be a benefit to our overall business venture at Micmac Farms. For more information on future marketing potential please see the Market Assessment for Production of Fish Waste Fertilizer.

Research results and discussion:

Objective 1: create a prototype for a dewatering system that addresses the unique composition of RAS waste. 

The final wooden structure measured 20'x20'x10"tall, it was lined with a rubber pond liner purchased online from a pool supplier. We created a slight slope under the structure so that materials could consolidate as evaporation progressed. A squeegee was useful during the process. To account for weather events, we covered the structure. We originally intended to cover the structure with a run-in shelter type structure with a frame, roof and four sides. Supply chain issues delayed the arrival of this unit until August. We decided to begin the evaporation process before the shelter arrived to ensure enough time to complete the evaporation process. Because the structure was located outdoors, we covered it with one large tarp tented over the evaporation pool to reduce rainfall into the structure. The tent was not as functional as our original intended covering at preventing rainfall into the pool. Two rainfalls with significant duration and intensity caused the tarp to collect rainfall and sink into the evaporation pool, this was the most significant drawback, and caused displacement of water. Fish waste solids had settled to the bottom by this time. Observations showed that the water displaced was clear supernatant, and that the solids on the bottom had not been displaced. We observed that the material was not homogenous, but that the solids separated distinctly.

To remove the water from the septic we pumped the effluent using a tractor with three-point hitch 3" diameter trash pump. We first measured the depth of water in the septic tank, and multiplied that by the dimensions of the tank to determine the original volume of effluent. Using a 3" diameter hose to convey the effluent to the evaporation pool. This was a quick process and took approximately one hour total to set up and complete the process. It took approximately ten minutes to move approximately 1,000 gallons from the tank to the pool.

To expedite evaporation, we used a small transfer pump to remove clear surface supernatant from the evaporation pool. This step took a couple of hours. A sample of the remaining slurry was collected and sent to a laboratory that specialized in nutrient analysis.


Objective 2: Provide a cost benefit analysis.

Costs incurred to build the dewatering structure:

(8) 2" x 8" x 10"boards, supplies - $240. run-in frame covering - $2,690.00

3-point hitch, 3' trash pump - $3,700.00 heavy duty rubber liner - $530.00 threaded hose line, adapters - $245.00

500-gallon heavy duty poly agriculture tank - $800

For our RAS facility we determined that approximately 30% of food fed to fish becomes fish waste.

Contractual costs with a specialized lab for conducting nutrient audits totaled $4,900 per sample to provide the following analysis:

Contractual costs with a specialized lab for conducting nutrient audits totaled $4,900 per sample to provide the following analysis:

  • ORGANIC PRODUCT STANDARD QUALITY Analysis. Includes Testing Ranges of TDS (total dissolved solids) and any trials to compare or adjust for high solids recovery. Evaluate alkalinity and pH, Conductivity (EC) to document nutrient potential, Total Organic Solids, Total Nitrogen and break out the N into species of ammonia and NO3; determine C:N. Process includes interaction with client on preparation of test samples and solids content
  • VOLATILITY STUDY - After selecting a suitable candidate liquid, test for Volatile Ammonia before, during after 5-day aging at room temp. Repeat trial with pH/alkalinity Test at pH start and altered pH. Determine storage stability.
  • Chemistry Trial; titration or buffer pH- to include adding: Natural Acetic Acid, or similar to std stable pH and storable. Prepare recommended product Label (How nutrients would be reported to customers).
  • Market Assessment report for solid and liquid compost products


Research conclusions:

The final project evolved slightly from the original intended design due to challenges from covid supply chain issues and directly from having substantially less fish in our facility than in any other year due to selling out all fish at the onset of the covid pandemic. Despite these constraints we continued with the project to determine if our prototype evaporation structure would become a feasible method for dewatering fish waste. Despite our reduced scale of fish waste and less than optimal equipment, we determined that this method was viable. One critical fact that we learned, that altered our design and expedited the process, was that fish waste does not form a homogenous mixture, instead it separates out and settles to the bottom. With this knowledge, we determined that we did not need to wait for evaporation, but instead could assist by using a pump to carefully remove the clear liquid supernatant on top. This significantly reduced the time to process the waste. At this time, evaporation still seems to be most useful way to fine tune the consistency of the final product. Because of the relatively insignificant costs to process fish waste, and the highly beneficial, eco-friendly product produced, we will continue to pursue the feasibility of using fish waste as a commercial garden product. This venture would be most profitable as we move forward with our fish hatchery expansion project, which will increase our current amount of fish waste by four-fold.

Participation Summary
1 Farmers participating in research

Education & Outreach Activities and Participation Summary

1 On-farm demonstrations

Participation Summary:

1 Farmers participated
Education/outreach description:

This dewatering system was able to identify the that de-watering is a possible for our hatchery, which was previously unknown. This knowledge was shared with tribal planners to support them to determine if pursing this option is feasible and lucrative, given the cost balance.

Learning Outcomes

1 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:


This dewatering system was able to identify the that de-watering is a possible for our hatchery, which was perviously unknown. This knowledge allows for the tribal planners to determine if pursing this option is feasible and lucrative, given the cost balance. This can be combined with the knowledge of fish waste produced by our RAS in a given year, to determine if de-watering will provide an avenue for income for the hatchery. For hatcheries that do not have an avenue for disposing of fish waste in a productive way, this method can provide extra income in lieu of an expense of waste disposal. 

Project Outcomes

1 Farmers changed or adopted a practice
1 Grant applied for that built upon this project
1 Grant received that built upon this project
$28,800.00 Dollar amount of grant received that built upon this project
1 New working collaboration
Project outcomes:

This project created a new market for our fish hatchery business by introducing a new product to our line. This project confirmed that fish waste is a feasible endeavor to add to our efforts, and aligns with the tribe’s vision of environmental sustainability, by utilizing waste that would otherwise be disposed of. This product enhances organic gardening practices and promotes soil health, and the concept of regenerative agriculture. This could be beneficial both economically but also to the carbon crisis, as among other benefits, regenerative agriculture aims to reverse climate change by rebuilding soil organic matter and restoring degraded soil biodiversity – resulting in both carbon drawdown and improving the water cycle.

This concept of this project could be carried forward to all scales of aquaculture.

This project dovetailed well with the market assessment for this potential product that was funded by an Intertribal Agriculture Grant.

Assessment of Project Approach and Areas of Further Study:

We used the information from this study to affirm the benefit and vialbity of fish waste as a beneficial product, rather than a waste stream issue. We recently used this information to apply for a $4 million dollar EDA Economic Development grant to expand the fish hatchery from our current size of 12,000 lbs produced annually to a total of 48,000 pounds produced annually. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.