外文文獻翻譯---循環(huán)水網(wǎng)箱養(yǎng)殖系統(tǒng)

1、外文文獻翻譯 外文文獻翻譯Recirculating Aquaculture TankProduction SystemsAn Overview of Critical ConsiderationsThomas M. Losordo, Michael P. Masserand James RakocyTraditional aquaculture production in ponds requires large quantities

2、 of water. Approximately 1 million gallons of water per acre are required to fill a pond and an equivalent volume is required to compensate for evaporation and seepage during the year. Assuming an annual pond yield of 5

3、,000 pounds of fish per acre, approximately 100 gallons of water are required per pound of fish production. In many areas of the United States, traditional aquaculture in ponds is not possible because of limited water su

4、pplies or an absence of suitable land for pond construction. Recirculating aquaculture production systems may offer an alternative to pond aquaculture technology. Through water treatment and reuse, recirculating systems

5、use a fraction of the water required by ponds to produce similar yields. Because recirculating systems usually use tanks for aquaculture production, substantially less land is required. Aquatic crop production in tanks

6、and raceways where the environment is controlled through water treatment and recirculation has been studied for decades. Although these technologies have been costly, claims of impressive yields with year-round producti

7、on in locations close to major markets and with extremely little water usage have attracted the interest of prospective aquaculturists. In recent years, a variety of production facilities that use recirculating technolog

8、y have been built. Results have been mixed. While there have been some notable large-scale business failures in this sector, numerous small- to medium-scale efforts continue production.Prospective aquaculturists and inve

9、stors need to be aware of the basic technical and economic risks involved in this type of aquaculture production technology. This fact sheet and others in this series are designed to provide basic information on recirc

10、ulating aquaculture technology.Critical production considerationsAll aquaculture production systems must provide a suitable environment to promote the growth of the aquatic crop. Critical environmental parameters includ

11、e the concentrations of dissolved oxygen, un-ionized ammonia-nitrogen, nitrite-nitrogen, and carbon dioxide in the water of the culture system. Nitrate concentration, pH, and alkalinity levels within the system are als

12、o important. To produce fish in a costeffective manner, aquaculture production systems must maintain good water quality during periods of rapid fish growth. To ensure such growth, fish are fed high- protein pelleted die

13、ts at rates ranging from 1.5 to 15 percent of their body weight per day depending upon their size and species (15 percent for juveniles, 1.5 percent for ammonia production rate, and the desired concentration of ammonia-n

14、itrogen within the tank determine the recirculating flow rate from the tank to the treatment unit. Using the example outlined above, if a treatment system removes 50 percent of the ammonia-nitrogen in the water on a si

15、ngle pass, then the flow rate from the tank would need to be twice the flow required if fresh water were used to flush the tank (93 gpm/0.5 = 186 gpm). A key to successful recirculating production systems is the use of

16、cost-effective water treatment system components. All recirculating production systems remove waste solids, oxidize ammonia and nitrite-nitrogen, remove carbon dioxide, and aerate or oxygenate the water before returning

17、 it to the fish tank (see Fig. 1). More intensive systems or systems culturing sensitive species may require additional treatment processes such as fine solids removal, dissolved organics removal, or some form of disinf

18、ection.Waste solids constraintsPelleted feeds used in aquaculture production consist of protein, carbohydrates, fat, minerals and water. The portion not assimilated by the fish is excreted as a highly organic waste (feca

19、l solids). When broken down by bacteria within the system, fecal solids and uneaten feed will consume dissolved oxygen and generate ammonia-nitrogen. For this reason, waste solids should be removed from the system as qu

20、ickly as possible. Waste solids can be classified into four categories: settleable, suspended, floatable and dissolved solids. In recirculating systems, the first two are of primary concern. Dissolved organic solids can

21、become a problem in systems with very little water exchange.Settleable solids control:Settleable solids are generally the easiest of the four categories to deal with and should be removed from the tank and filtration co

22、mponents as rapidly as possible. Settleable solids are those that will generally settle out of the water within 1 hour under still conditions. Settleable solids can be removed as they accumulate on the tank bottom throu

23、gh proper placement of drains, or they can be kept in suspension with continuous agitation and removed with a sedimentation tank (clarifier), mechanical filter (granular or screen), or swirl separator. The sedimentation

24、 and swirl separator processes can be enhanced by adding steep incline tubes (tube settlers) in the sedimentation tank to reduce flow turbulence and promote uniform flow distribution.Suspended solids control: From an aq

25、uacultural engineering point of view, the difference between suspended solids and settleable solids is a practical one. Suspended solids will not settle to the bottom of the fish culture tank and cannot be removed easi

26、ly in conventional settling basins. Suspended solids are not always dealt with adequately in a recirculating production system. If not removed, suspended solids can significantly limit the amount of fish that can be gro