Progress 05/15/04 to 12/31/04
Outputs
Commercial-scale marine aquaculture has the potential to balance the increasing demand for high-quality seafood products with the harvest capacity of our nation's oceans. However, water reuse in recirculating aquaculture systems (RAS) is limited by the accumulation of nitrate (NO3), which can be toxic to many species at high concentrations, especially marine species. Thus, NO3 removal by denitrification presents a pressing need for the continued expansion of intensive recirculating aquaculture. This Phase I SBIR project investigated the potential for using Polyhydroxyalkanotes (PHAs), a biodegradable biopolymer produced from sugar fermentation, as an alternative carbon source for denitrification in recirculating aquaculture systems. Through a series of bioreactor simulations, the denitrification capabilities of PHA were quantified. Additionally, the commercial feasibility of employing PHAs as a simple, low-cost alternative to the relatively complex existing treatment
methods was investigated. Polyhydroxyalkanotes are a family of bioplastic polymers, produced from sugar fermentation. The biodegradation of PHA's in the presence of nutrients releases organic carbon, which makes them an ideal substrate for a self-regulating, passive denitrification reactor. PHAs offer a potential low maintenance and cost effective method to achieve denitrification, since they act as both a carbon source and substrate for denitrifying bacteria. This, in turn, eliminates the need for sophisticated control systems and handling of hazardous chemicals, required by the conventional methods of treatment. Earlier research efforts showed excellent denitrification capability of PHAs. But excessive biofloc formation from the heterotrophic bacteria using the carbon released from the PHAs resulted in biofouling of the columns which limited the process. AST researchers hypothesized that the problems associated with clogging and short circuiting of the PHA filter bed could be
addressed by utilizing the patented PolyGeyser bead filter technology as a denitrification platform. The PolyGeyser bead filter promotes a healthy thin biofilm due to its characteristic frequent, gentle backwashing, which eliminates the clogging problem observed with packed beds. Additionally, the ability to manipulate backwash frequency allows the biofilm abrasion rate to be tuned. A lab-scale PolyGeyser denitrification unit was designed and three units constructed utilized the same design criteria used for the 3-ft3 commercial PolyGeyser Bead Filter. Numerous replicated tests were conducted to quantify the denitrification capacity of the PHAs and the impact of backflushing on performance. For each test, water quality samples of influent and effluent were analyzed for pH, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen, and alkalinity, as well as, dissolved oxygen and temperature. The results of the Phase I research showed a removal rates for nitrate by the lab-scale bioreactor
units surpassed 2.0 kg/m3-day with no clogging or short circuiting of the media bed. Backwash frequency to maintain the biofloc was found to be once every one to two days.
Impacts
Aquaculture Systems Technologies believes that the aquaculture industry is on the verge of a massive expansion in the area of marine aquaculture and that recirculating aquaculture systems will have a major role to play in supporting this expansion. The use of saltwater & the placement of these facilities in sensitive coastal or inland environments will increase the potential for environmental conflict due to nitrate accumulation and will force aquaculturists to seek out denitrification technologies, both for the production system's water and effluent discharge. Additionally, US EPA is imposing stringent nitrate discharge regulations which in the future will force even freshwater recirculating aquaculture systems to implement some type of denitrification strategy. Development of a denitrification PolyGeyser bead filter will significantly increase the economic viability of intensive marine recirculating systems. One of the initial impacts for this denitrification
technology will be in public aquariums and zoos world wide, concerned with meeting ever more stringent discharge regulations for nitrogen rich salt and freshwaters. In addition, many marine recirculating systems with minimal water exchange are becoming limited by nitrate accumulations. Continued intensification and expansion will require the proposed denitrification technology both for treatment of the systems water and the effluent discharge. Finally, there is significant application of this technology for small-scale on-site wastewater treatment systems in areas experiencing ground water nitrate contamination.
Publications
- No publications reported this period
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