Sustainability principles and tightening regulatory restrictions throughout North America are rapidly changing the way aquaculture operations handle their effluent. TSS, BOD, TAN, phosphorus, and fish escapement are all common targets for meeting stringent effluent limits. There is also growing concern over the discharge of pathogenic organisms from aquaculture operations back into the environment.
In aquaculture facilities the primary pollutants of concern are particulate waste composed of fish excrement and uneaten feed. Settling ponds have traditionally been the standard for removal of particulate waste from aquaculture effluent water. Although settling ponds provide acceptable reduction of TSS, long retention of the solids can result in decomposition which may further degrade water quality. Other disadvantages include high footprint requirements and challenges related to management and removal of collected sludge.
While settling ponds may remain an integral component to some effluent treatment systems, more advanced treatment alternatives are now available that offer improved effluent quality in a more space efficient and cost effective manner. Swirl separators and radial flow settlers are smaller, more efficient gravity settling vessels that are specifically designed to minimize turbulence and maximize capture of aquaculture waste particles. Microscreen drum filters are automated, self-cleaning screen filters that are ideal for the quick and continuous removal of suspended solids or for pre-filtration upstream of disinfection processes. Media filters may also be used for certain low-intensity culture system such as laboratories and aquariums.
Other components of complete effluent treatment systems may include chemical injection for phosphorus binding or pH adjustment, and UV irradiation or ozonation for control of pathogens.
Solid waste handling can be a major cost consideration for an aquaculture facility due to the high volumes of waste produced. Use of sludge thickening or dewatering technologies can significantly reduce the volume of sludge produced, allowing for more cost effective storage, handling, or disposal. Technologies available for sludge thickening include gravity settling, gravity belt thickeners, drying beds, and geo-membrane bags. Polymers addition may also be added to optimize the performance of sludge thickening processes.
Prevention of fish escapement in aquaculture facility effluent is an issue of growing importance for both sustainability and for regulatory compliance. Although traditional static screen systems are available, PR Aqua’s self-cleaning fish exclusion screens provides complete exclusion of fish and eggs from aquaculture facility discharge water with greatly reduced operating head and maintenance labour.
Flow-through aquaculture systems generate high flow rates of relatively dilute waste water. Effluent treatment processes for such facilities must be low-intensity and must have a low operating cost to handle the large flows economically. When more extensive treatment is required to meet discharge requirements, the incorporation of recirculation or partial re-use technologies into the culture systems design may significantly reduce effluent volumes and the associated cost of effluent treatment.
Packaged Solutions
PR Aqua packages equipment and design to solve effluent treatment problems for aquaculture facilities and other waste water applications. We provide solutions for the following:
PR Aqua’s design experts can also provide comprehensive waste management planning services and custom treatment solutions to meet with your sustainability objectives. Please contact us to see what PR Aqua can do for you.
