WATER CONSERVATION STRATEGIES FOR URBAN SALTWATER AQUACULTURE FACILITIES WITH A CASE STUDY REVIEW OF A (145) METRIC TON (MT) BRANZINO Dicentrarchus labrax FACILITY IN WATERBURY CONNECTICUT, USA
Many saltwater fish species are demanding a premium price in local markets throughout North America. Couple this with increased consumer knowledge and the demand for locally grown traceable products, and saltwater urban aquaculture starts to trend toward a feasible reality. But how realistic is it to consider building and operating a saltwater system that relies completely on municipally supplied water, waste disposal, electricity and liquid oxygen?
Creating seawater from a municipal water source is expensive. It drives the process toward water conservation and reuse. The impact on the Recirculation Aquaculture System (RAS) process design is dramatic. This paper describes the design considerations and strategies that can be applied to conserve water and reduce operating costs in urban saltwater aquaculture systems. The strategies will cover aspects from the saltwater mixing systems, salt water storage and delivery, RAS design with denitrification and waste water recovery and purging systems. The intent is to provide understanding and insight into the costs and complexities of designing and operating an urban saltwater aquaculture facility.
Within the RAS design, special consideration needs to be paid to solids filtration. Current RAS technology can only dewater solids to a certain extent on system. When Nitrate-N is removed as the primary contaminant requiring water exchange, the dilute solids effluent flow is next in line as the primary water consumer within the RAS. Additional processes like foam fractionation, ozonation and radial flow settling can help to concentrate this effluent stream and reduce your water consumption. Modification to drum filter operation can also play an important role in increase the solids concentration of the effluent. However, even with these secondary and tertiary processes in place, additional off system dewatering technology is often justified from an economic perspective.
Additional consideration needs to be paid to the purge systems and the water exchange required for that process. Additional filtration can often be applied to offset the water flushing requirements on purge tanks. Serial reuse of water leaving the purge system by the growout system should also be considered when designing these facilities.
The results of these applied strategies will be reviewed with preliminary operating data from Great American Aquaculture, LLC., a 145 metric ton (MT) Branzino (Dicentrarchus labrax) production facility currently in production in Waterbury Connecticut, USA.