Botanical Filters In Recirculating Aquacultural Systems Based On Fish-Grass Symbiosis Ecological Principles

Supported by modern science and technology there is hope that aquaculture may become the second largest food industry after agriculture. However, traditional aquacultural production technology requires far too large a demand on resources. Compared with those traditional technologies, recirculating aquacultural technology has obvious advantages on resource demands, environmental protection and production ability, which have been leading to more and more attractions and applications worldwide to achieve sustainable productions.Water management is the key to a successful recirculating aquacultural system and will directly decide the production ability of the whole system. Because of increasingly stringent legislations and higher culture density, water treatment systems in developed countries are becoming increasingly complicated, with resulting high production costs which restricts the application of recirculating Aquacultural systems in developing countries. Making use of nitrogen and phosphorus in high density aquacultural wastewaters is not only a low-cost and sustainable treatment technology, but can also be a source of additional income. Some terrestrial grasses, such as Lolium multiflorum Lam., Lolium perenne L., Festuca arundinacea Schreb., and so on, have a wide adaptability to climates and grow rapidly with a great root to leaf ratio. At the same time, these grasses have high economic values due to their rich nutrients and are liked by many domestic animals and fishes. These grasses have been studied and applied in the field of environmental treatment widely, but information is still very limited on utilizing NFT (nutrient film technology) -cultured terrestrial grasses as a botanical filter to treat wastewaters from recirculating aquacultural systems and realize zero-discharge aquaculture.In this project, "botanical filters in recirculating aquacultural systems based on fish-grass symbiosis ecological principles", a prototype recirculating aquacultural system with a typical and simple water treatment system was developed and the nitrification efficiency of the biofilter which was inoculated with certain commercial bacterial amendments was checked. As a simple utilization of botanical filters, several fish-grass symbiosis ecosystems with different fish:grass ratios in weight were used to investigate basic principles in such ecosystems. Then, botanical filters were used to treat five types of manually-composed nitrogen-rich wastewaters and that from the prototype system. Finally, a botanical filter was combined into the prototype system to realize zero-discharge production. Details were listed as followed:(1) System analysis and development of a prototype systemA prototype recirculating aquacuitural system was set up based on the analysis of a typical and simple water treatment system. The system mainly consisted of a solids removal basin (including a plate settler and a mechanical filter), a nitrification basin (i.e. biofilter) and two fish tanks. The total volume of the system was 5.090 m3 and the expected water volume was 4.236 m3, 2.651 m3 of which, supplied by two fish tanks, was used to stock fish. Waters was periodically recirculated by a timer controlled pump.(2) Inoculation and nitrification efficiency test of the biofilterWhen used to inoculate new biofilters for recirculating aquaculture production systems, we have found certain high quality commercial bacterial amendments are easier to use than getting media from an established biofilter. A known commercial bacterial amendment was used to inoculate for a new biofilter of a pilot recirculating aquaculture system. At the beginning, 20 ml amendment in all (= 75 billion CFU bacteria) was injected into the biofilter basin in four applications during a period of three days. On the first day and the third day of the experiment, 200g of feed containing 32% protein were dissolved into fish tanks. The peak of total ammonia nitrogen (TAN) concentration was found on the seventh day and that of nitrite nitrogen (NO2--N) was found four...