Alternative Strategies for Oyster Culture in North Eastern New Brunswick: Application of technology and methods for land-based holding and depuration of oysters

Final Report to the AIMAP Program for 2010-2011

31 March 2011

Table of contents

• Executive Summary
• Introduction
• Cold holding system for suppressing gonad development in oysters
• System for enhanced depuration of pathogenic bacteria from oysters
• The Conceptual Design
• Engineering
• The Designs
• The Equipment
• The Construction
• Predicted timelines for construction completion and initiation of systems in the facility
• Next Steps (post-construction)
• The Coastal Zone Research Institute- proposed program
• Recommendations
• Conclusions

Executive Summary

The AIMAP  project on cold holding and depuration of oysters in land-based intensive culture systems was initiated in 2010. The plan for the 2010-2011 period was to complete construction of the specified building and the culture systems and to begin initial experiments and monitoring programs to test the efficiencies of the systems in suppressing gonad development in oysters (cold holding system) and enhanced depuration rates in oysters (depuration system). Due to a variety of funding issues, weather-related, contractor-related and engineering firm- related delays, the construction phase of the project did not begin intensively until January 2011. Even after this period there were significant delays involving the engineering firms’ commitments and the building contractors’ time estimates to completion of the building infrastructure. The building has now been completed (May 2011) and work progresses quickly on the installation of the culture tanks and recirculation and depuration systems. All major equipment for the cold holding system is on site and ready for installation. The cold holding system is scheduled for completion and will be operational in late June 2011, the depuration system to be finished and operational in July 2011. A monitoring and experimental program to assess the performance and efficiencies of the two land-based systems will be completed in 2011 by the Coastal Zone Research Institute.

Introduction

The AIMAP project to develop techniques for holding oysters in cold intensive recirculation environments and enhanced depuration of oysters in high oxygen environments was undertaken between March 2010 and March 2011. 

This project involved the design and construction of 2 water treatment systems and associated tank holding capacities at the Village Bay Sea Products site in Rexton, New Brunswick. This report describes the progress of the project during the time period stipulated and defines the chronology of previous and predicted construction and infrastructure installation.

The project was premised on 2 biological characteristics which are exhibited by cultured oysters. The objective of the facility construction and operation was to provide controlled environments where the biology of the oysters could be manipulated in land-based systems. The first  biological feature which was the object of manipulation within the land-based systems was: oysters which begin to mature and reach spawning condition near the end of the 4 year grow-out cycle in May-Junel lose soft-tissue weight and develop gonad mass. These conditions render the oyster less desirable for sale. The oysters must be retained at the sites beyond the spawning period in June-July so that gonad mass disappears and growth resumes. The second controllable feature was depuration. In certain seasons, oysters grown in the estuaries collect and accumulate harmful bacteria and algae when filter feeding. Oysters contaminated in this way must be cleaned by depuration before they are safe for human consumption. For some period of time annually, contaminated oysters can not be sold.

We proposed that large, land-based culture systems, where the environment can be controlled and maintained, can serve to partially mitigate the major limiting issues described above. It was the objective to construct and operate a land-based oyster holding facility where controlled system environments would 1) reduce the weight loss and gonad development of mature oysters in a cold holding system and 2) provide an optimal and enhanced (over standard commercial methods) depuration system to remove bacteria and algal contaminants.

It was determined through literature and scientific community review that intensive land-based systems for oyster production could provide much colder or warmer water temperatures than are characteristic of the seasonal values in the estuaries. The environment of the system could be closely controlled so that essential growth-impacting parameters (oxygen, nitrogen, ammonia, nitrite, nitrate, carbon dioxide, ph, alkalinity; and food) could be closely monitored and supplemented and/or reduced to provide optimal holding conditions.

Metabolic rate of oysters was determined to be critically dependant on oxygen levels with the culture environment. Enhanced metabolic rate increases the physiological efficiency of oysters. Very high oxygen levels can be easily maintained within intensive culture systems, so that there are no limitations on metabolic rates of the oysters. With the use of the InVentures gas infusion technology, which is a critical part of the depuration system as designed, extremely high oxygen concentration environments can be produced while simultaneously removing nitrogen from the water. The land-based depuration system designed for the facility was premised on the inclusion of the PuGro apparatus.
 
The intensive recirculation-based system for cold holding of oysters and the enhanced depuration system were designed specifically for the Village Bay project. The systems were designed within the premise that controlled environments will alter and effect oyster metabolic rate (suppression of gonad development and enhancement of waste evacuation rate). We outline briefly herein the rationale for the two culture systems.

Cold holding system for suppressing gonad development in oysters

 The cold holding system is premised on a chilled water recirculating loop. Although the water will be cold (6-8C as compared to summer water temperatures in the bay at 10-22C), there will still be significant metabolic activity from feeding activity by the oysters held in the system. The proposed recirculation system is designed to remove metabolic waste and add oxygen to maintain the animals in optimal condition. The recirculation loop will maintain the water temperature through the use of a chiller barrel loop system. Since some raw water from the bay must be added continuously to introduce food to the oysters in the system, the chiller loop has been specified to have the capacity to maintain the cold temperature based on the extra addition of warm estuarine water. Utilizing a full flow-through chilled system would lose too much energy and not be economical; the recirculation loop is designed to use minimal amounts of energy to continually cool the water. There are five main sub-systems in the design: chilling, oxygenation, settleable solids removal, fine particulate solids removal and biofiltration.
 
The oysters are held in the system in 5 large rectangular concrete tanks. Each holding tank is 12m x 4m x 1m (depth). Maximum capacity of each tank is 200,000 mature, market-size oysters, to give a total system capacity of 1,000,000 oysters. Recirculated water flow through the tanks is laminar from end to end, with a passive end drain system with external standpipes for manual removal of heavy solids. The raw, estuarine, food-containing water is introduced directly to each tank at the influent end to maximize the food availability to the oysters; this strategy also allows for most of the introduced phyto and micro zooplankton to be consumed by the oysters before it returns to the recirculation loop. Since the system will be cold and oyster feeding activity will be reduced, only enough food to maintain the oysters in good condition needs to be added; although this amount will by necessity dependant on the volume of food within the incoming bay water, we suggest that 10gpm per tank be introduced initially. Greater or lesser volumes can be added as required to supply the optimal amount of food (water) and simultaneously maintaining the system at most efficient energy consumption levels. Recirculated water volume through each tank is a maximum of 125gpm with a maximum total system flow (for all 5 tanks) of 625gpm (exclusive of added raw water). However, an average continuous flow volume of approximately 450-500gpm is the operational target.

System for enhanced depuration of pathogenic bacteria from oysters

Oysters grown in open water sites derive nutrition from microplankton filtered from the water. Nutrients for both growth and metabolism are obtained by filtering phytoplankton and micro zooplankton. During feeding activity, the oyster accumulates significant amounts of bacteria and undigestible materials in the digestive tract. If held in water contaminated by large amounts of bacteria and suspended solids, the oysters tend to concentrate these materials, making them unfit for human consumption and marketing. In nature, the oyster will continue to accumulate and retain these materials so long as the water in which they are held is contaminated. If placed in water which is not loaded with bacteria and solids, the oyster will purge itself over time. This phenomenon is the basis for depuration. In the estuarine sites in which oysters are grown for eventual sale, there are significant episodes of seasonal abundance of bacteria and algal/solids production. During these periods the oysters can not be sold. The solids loading in the shellfish is not harmful to humans, but renders the oysters unpalatable; the bacteria loading however, particularly that of colliform bacteria, presents a very significant threat to human health and safety. Colliform abundance in the estuaries where oysters are grown is a seasonal event which generally coincides with yearly high water temperatures and can also be triggered by large rainfall events which wash land-based farm effluent into the estuaries.

Since the bacteria accumulated in the oyster gut can only be depurated with a clean, uncontaminated water source, only land-based systems can be used to purge the oyster during seasons when high levels of bacteria are present in the estuaries. The land-based system can supply water which has been filtered for solids removal, sterilized to remove the harmful bacteria and oxygenated to maintain high rates of oyster metabolism. This high rate results in greater and more rapid depuration.
 
The current closed system depuration methodology is premised on conventional particulate filter/ foam fractionation/ oxygen infusion/ UV or ozone sterilization technology, where particle filters remove bacteria-containing solids, foam fractionation removes bacteria-laden protein floc, oxygen is required for oyster metabolic process and UV and/or ozone kills the bacteria within the recirculated water environment.
 
Since the majority of freshwater run-off events happen during summer-fall in the region, most requirements for depuration occur during this period. Water temperatures are highest during this period and most depuration systems do not add additional heat to the systems to achieve adequate depuration within 48-72 hours (at a maintained water temperature of 14-16C). Since time to adequate depuration depends on temperature (which impacts oyster metabolic rate), we assume that oysters held in much higher temperature regimes will depurate significantly faster than that characteristic of conventional, non-heated systems. We intend to operate an oyster depuration system where water temperatures are maintained at 18-22C. At this temperature range, significantly greater amounts of oxygen will be needed to service the much higher oyster metabolic rate. We will utilize a very high oxygen (250-300% saturation), low nitrogen (total gas pressures of less than 100%) environment created by the application of the InVentures Purgro2 infusion system.
 
Our intention is to construct a closed-loop recirculation system which will have a depuration capacity of a maximum 50,000 oysters. We will follow conventional technology as pertains to particle filtration, foam fractionation and UV sterilization. However, the system will incorporate a significant water heating capacity, and a large-scale oxygen infusion capability. Because of the high water temperature range proposed for the system, there will be higher rates of protein decomposition, so efficient particle filtration (pressurized bead filters will remove particulate down to 20microns) will be critical. Foam fractionation will be used to clear protein floc and dissolved solids from the recirculated water. As stated above, our goal will be to decrease the total time required for depuration with a high oxygen/low nitrogen environment created by the PurGro2 system. The Purgro units can be set to produce a wide range of gas bubble sizes in water, resulting in some in-holding tank foam fractionation of dissolved solid which may assist in the total system fractionation process.

Oversized particulate filters will adequately remove the majority of suspended solids (as well as protein-based solids). Good particulate filtration, in conjunction with optimal oxygen and water temperature, and maximized bacterial kill rates provided by properly sized and installed UV sterilizers, will result in much more rapid depuration rates than have been previously observed. In the heated, closed-treatment configuration, our proposed depuration system can function at any time during the year, so that purged oysters can be marketed during any periods of colliform persistence in the estuaries. The rapidity of the depuration process in the system we propose will greatly increase the total amount of cultured oysters than can be treated and decontaminated.

As indicated above, the design of standard commercial bivalve depuration systems is premised on four essential water treatments: 1) particulate filtration, where solids from the oyster gut are filtered from the recirculated water, 2) sterilization, where water containing bacteria from the gut is treated with ultraviolet light or ozone, 3) oxygenation, where the recirculated water is re-oxygenated after the oxygen had been depleted by oyster metabolism and 4) water heating, where the recirculated water is heated to increase the rate at which the depuration process (dependant on metabolic rate) occurs. The technology to complete these treatment processes is well-known and the equipment required is available, efficient and reliable.

The Conceptual Design

The original proposal to design the culture infrastructure to hold oysters in land-based tanks was developed around a conceptual system which considered the environments needed to impact the oyster metabolic rate and reproductive physiology. The conceptual design included a process flow dynamic for the cold holding and depuration systems and provided the tank areas, flow rates and equipment requirements to service the oyster holding densities proposed. The conceptual design also estimated the potential costs of the systems to engineer, construct and install, and operate as part of the long-term business strategy of Village Bay Sea Products. The conceptual design was completed by the consultant for the project in November 2009. The consultant continued to work on the project during the engineering and construction phases in 2010-2011 (under an IRAP contract: Application of growth, enhancement and depuration technology and methods for land-based oysters; project no. 736339)

Engineering

Although the conceptual design was necessary to initiate the planning of the project, detailed engineered designs and plans were necessary so that construction and installation could be completed. Village Bay retained the professional engineering firm of SilkStevens of St. George, New Brunswick in August of 2010 to provide this service. The firm has significant experience in design of land-based aquaculture systems. The engineers with the company took the conceptual plans for the land-based oyster systems and converted these to as-built engineered drawings and plans for use in the actual construction and installation of equipment. The project managers at Village Bay and the consultant for the project met and conferred with the engineering firm staff continually through the winter-spring of 2010-2011 to finalize the design of the systems to be constructed in the new facility.

Herein we report on the progress of the project in terms of the chronology of past and future construction, provide finalized drawings of the systems to be constructed and list and outline the disposition of equipment required for the system installations.

The Designs

SilkStevens designed the facility building and all internal structures to specified elevations; the company also configured all inside drain fields, above-ground plumbing, electrical services and culture system infrastructure. Village Bay managers and the consultant requested and received quotes for the system equipment, provided advice to the engineering firm on the design requirements and supervised the on-site contractors and construction.

The engineering firm was true to the conceptual design and incorporated the recommended equipment as initially specified in the original AIMAP proposal of 2009. The piping configuration drawing for both the cold holding and depurations systems was completed by the firm in March 2011. A materials list of all piping and fitting components to complete the cold holding system was delivered in March 2011; a similar list concerning the depuration system is now being finalized.

The construction-ready drawings for the cold holding and depuration systems are attached to this report. They include all of the detailed piping and structural characters for the two systems. These are the finalized drawings and there is no plan to modify these unless the on-site construction dictates minor changes. The finalized drawings also detail all equipment locations, to scale, within the site plan.

The Equipment

As was required under the AIMAP protocol, all of the major equipment necessary to operate the oyster cold holding system has been purchased as of 31 March 2011. The equipment and purpose are as follows:

2- PBF50S  600gpm prop-washed pneumatic drop bead filters ( fine particulate removal)
1- OY 140F1 600gpm Oxygen saturator cone (re-oxygenate recirculated water)
2- 3000gal. Polyethylene biofilter vessels (nitrification within vessels)
280ft3- Kaldness media bifilter media (substrate for biofilter bacterial nitrifiers)
2- Barnes 6SE90 900gpm Tungsten Carbide centrifugal pumps (reciculation pumps)
1- Devair 5hp rotary screw air compressor (provide air for fluidizing biofilters and CO2 removal)
1- 20hp titanium chiller assembly (w/condensing unit/barrel) (cooling unit for cold holding)
4- PurGro2 in-line oxygen infusion units (ultra high oxygen for recirc loops)
2- AirSep AS-D Oxygen Generator units (oxygen for system)
2- Sullair Air screw compressors (for oxygen generators)
1- Hydrotech microscreen drum filter (900gpm cap.) (coarse particulate removal)
1- Complete oxygen ceramic plate diffuser system for all tanks

All of this equipment (excepting the microscreen drum filter; to be delivered 30 May 2011) is now on site at the Village Bay plant in Rexton and is ready to be installed. In addition to the major equipment items, there are a number of smaller equipment items which have been purchased for control and monitoring of the systems when in operation. These include 2 testing meters: oxygen (optical probe and digital meter) and Total Gas Pressure (TGP: PT-4 tracker with probe); titration and colorimeter test kits for ammonia, nitrite, nitrate, alkalinity. Digital refractometers for salinity and PH. A complete Sensa-phone alarm system for water level detection and temperature monitoring.

The equipment required for the depuration system has been specified and quoted on. A portion of the major equipment was ordered in late 2010; but due to budget timing issues, the orders were suspended. None of the major equipment for the system has yet to be purchased (as of 15 May 2011), however the holding tanks required for the system were previously purchased by Village Bay and are on site, ready for installation. It is the plan to re-order the equipment for the depuration system in June 2011. The recirculation equipment is to be purchased directly by Village Bay and is not part of the AIMAP program. The major equipment for the depuration system has been identified as follows:

1- PBF25S 300gpm pneumatic-drop bead filter (fine particulate removal)
1- AES Protein Skimmer/ foam fractionator (300gpm, 3min res.time) (dissolved solids removal)
1- Hanovia UV Sterilizer (30,000uWs/cm2) (destroys bacterial loading)
1- Gould 450gpm Stainless steel centrifugal pump (recirculating pump)
2- PurGro2 in-line oxygen infusion units (ultra high oxygen addition)

There are a variety of smaller equipment items that have yet to be ordered that are used in the depuration system. The air compressors and oxygen generators purchased for the cold holding system also provide air and oxygen to the equipment used in the depuration loop. Most of the water quality testing equipment and some of the alarm probes which have already been purchased for the cold holding system can also be used for the depuration process.

The Construction

The project construction began in early Fall 2010; it was plagued by events  beyond the control of project managers and resulted in numerous delays. There were a series of significant delays in receiving the construction drawings from the engineering firm through-out the winter of 2010-2011. The construction could not commence until the drawings were in-hand at Village Bay. Without the drawings, the contractors could not estimate the costs and construction timelines that were required. Another serious delay was caused by the late December 2010 flood which completely submerged the entire building construction site to a depth of 2-3meters. It had been hoped that the building and some of the floor infrastructure would have been completed before January 2011, but the flood destroyed the trenching for the foundation side walls. The facility site was basically underwater for several weeks and by the time the site was drained of water in late January, low winter temperatures made concrete forming a more difficult process. There was a necessity to heat the covered concrete forms which was a significant and unforeseen expense. In spite of this, the building foundation was eventually completed and the erection of the building was begun. The super-structure of the steel building was completed and the roof finished in mid April 2011. The building construction took several weeks longer than estimated by the contractor. The concrete tanks for the cold holding systems were completed in late April 2011. The sump pits, drum filter pits and other in-ground system tanks formed from concrete are being completed now (mid May 2011). Plumbing contractors have been retained to complete all of the piping for the drains and culture systems; most of the drain field plumbing (below ground) has been completed in the building.

The consultant has recently visited the construction site (11 May 2011) and met with the Village Bay project managers; the work completed to date by the plumbing and concrete contractors appears to be as specified by the engineers and is of good quality. 

Predicted timelines for construction completion and initiation of systems in the facility

Currently the construction phase is back on track and the facility is progressing daily. The building superstructure is completed adequately for all inside construction and equipment installation to be completed. The following schedule is suggested for completion of the systems in the facility in spring-summer 2011:

15 – 30 May: completion of all in-ground sumps, tanks and drains
1 June -15 June: completion of all above-ground piping, installation of pumps, filters, oxygen induction equipment for the cold holding system
15 June-30 June: installation of chilling units, oxygen generators, preliminary testing of recirculation flow dynamics of the cold holding system
30 June: Cold holding system complete and ready for testing of operational parameters
1-15 July: installation of equipment and above ground tanks for depuration system
15-31 July: depuration system complete; testing of flow dynamics of system
1 August: depuration system ready for commercial use if required

Next Steps (post-construction)

Unfortunately, by the time the cold holding system is completely installed and operational, some of the season during which the oysters are developing gonad mass may have passed.  If the system is completed before the estimated dates, we will introduce oysters to test the gonad limiting environments. The timing and success of the trials in 2011 will depend on the completion of the construction phase in a timely fashion. Whatever the schedule of completion of the system, it would be useful to stock oysters in the system to measure their growth and condition factor when held for extended periods in the temperature regime targeted for gonad development suppression.
 
July and August 2011 has been targeted as the general timeframe when the operational parameters of the depuration system can be tested and since most depuration requirements occur in the estuaries in late summer, we may be able to do several commercial-scale depuration trials soon after the system is up and running. The time window for trailing the depuration system is very wide and some contaminated oysters are available for testing during most of the year, excepting the coldest winter months.

The success of the land-based systems in impacting and controlling the biological aspects of oyster reproduction and depuration will be the subject of an experimental program undertaken by the Coastal Zone Research Institute in 2011 in collaboration with Village Bay Sea Products.

The Coastal Zone Research Institute- proposed program:

The CZRI has agreed to conduct a monitoring program and experiments to determine the success and efficiency of the cold holding and depuration systems. A synopsis of the work previously proposed (in 2010) is as follows:

Suppression of gonad development: determine optimum temperature and water quality parameters required; determine optimum oyster densities in the system; determine a timeframe for gonad suppression

Enhanced depuration: determine rate of depuration at varying oxygen and temperature levels; determine density impacts on depuration rate and efficacy; determine overall efficiency of depuration in the system

Systems operational performance: determine temperature and salinity stability; loss of phytoplankton in the recirculating system; develop operational and monitoring protocols for both systems

The biologists and technicians of the CZRI will provide technical advice on oyster biology, system operations and best culture practices to the Village Bay staff. The consultant and engineers will rely on the CZRI to provide feed-back on the systems’ performance so that any design changes required can be made. It is hoped that the CZRI will provide a systems operations manual for use by Village Bay staff upon completion of their experimental and monitoring program.

Recommendations

The pace of construction and installation of equipment has been slow due to weather and delays in equipment shipping and contractors’ schedules. It would be useful to have the cold holding system operational by the middle of June 2011 so that some trials on oyster gonad suppression could be completed this year. However, this is unlikely given the current construction progress. Trials to determine the general condition factors of oysters held in the system can be completed during the late summer. The warmer water temperatures of the season will also help define the capabilities of the system in cooling the water down to the target temperatures for gonad development restriction.

The depuration system will be finished during the potential high fecal colliform season in late summer; the performance of this system may be able to be tested in 2011. Since the two systems comprise the only large-scale intensive land-based culture platforms for shellfish in New Brunswick, every opportunity to test their operational performance and efficiencies should be completed. The cold holding and depuration systems will not operate continuously and there will be long periods during the year when the systems will not be used.

Conclusions

The construction of the two culture systems at the Village Bay site is in progress and will be completed in the summer of 2011. The building erected to hold the systems is an excellent design and is a very robust structure. The engineers have produced a functional systems design which will meet the requirements of both the cold holding and depuration processes as defined in the AIMAP project proposal of November 2009.

Once functional, the land-based, cold holding process will allow held oysters to be sold during the summer months when all other oysters taken from estuarine sites have gravid, developed gonads and are unfit for the market. This will be a significant marketing and competitive advantage for Village Bay Sea Products. Similarly, a large commercial-scale, land-based depuration facility will allow sales of oysters in seasons when estuarine-reared oysters are contaminated by bacterial loadings and can not be marketed; another competitive advantage for Village Bay.

Once the construction/installation is completed, there will be an intensive program to monitor the initial performance of the two systems. The staff at Village Bay has been involved in the construction from its beginnings and will operate the facility initially. The Coastal Zone Research Institute staff should begin their dedicated research and monitoring program soon after the systems become operational and are stocked with oysters. The data they collect can be periodically reviewed by the scientific community and AIMAP collaborators/ reviewers to determine the success of the trials.