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Biofilter is one of key components of recirculating aquaculture system (RAS) that affect initial investment, executing cast and success or unsuccess of system. Hence in this research, performance of barley straw, wood chip, sponge (as cheap and available media) and PVC pure pipe (to compare) based biofilters was surveyed in Common carp recirculating aquaculture system. To conduct this research 12 pilot recirculating aquaculture systems designed and 50 common carp individuals (mean weight: 4/8 g) were stocked in each system. After activation period (about 1 month), waste removal efficiency of biofilters and growth performance of Common carp were surveyed. Results indicated that sponge based biofilters had the best performance. Barley straw and wood chip based biofilters showed acceptable waste removal efficiency, while PVC pure pipe biofilters had poor performance. The highest feeding and growth performance of fish were observed in systems involved barley straw based biofilter. In conclusion barley straw, wood chip and sponge because of having low cast, being available, having relatively high specific surface area and showing acceptable waste removal efficiency, can be used in RAS and semi reuse systems.

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  The current approaches applied for removing nitrate from drinking water, commonly uses many chemical additives that may have undesirable or unknown effects on human health and in some cases caused many by products more dangerous than nitrate in drinking water. In present there are few appropriate and economic processes in this field and because of water scarcity in many areas development a suitable technology for treatment of nitrate contaminated drinking water for application in actual scales is crucial. In this research we develop an economic process with high selectivity for nitrate removal and minimum disturbance in other drinking water quality parameters that utilizes only hydrogen and carbon dioxide, produced in a methanol based electrochemical gas generator by applying a very low DC voltage (5-10 volt). We evaluate the ability of hydrogenotrophic denitrification for removal of nitrate in a bioreactor packed by light expanded clay aggregates known as LEACA. The results showed by proper coupling of electrochemical gas generator and denitrification bioreactor only by injection of tow clean and harmless gases, hydrogen and carbon dioxide and without any other chemicals addition for common concentrations of nitrate in natural waters by hydraulic retention time of 2-5 hr, removal efficiencies greater than 95% can be achieved. Also in comparison with other conventional methods such as ion exchange, reverse osmosis, electrodialysis, and biological heterotrophic with organic carbon source this system has several advantages such as: high selectivity for nitrate ion, low biomass yields, low electrical energy consumptions, without any problems resulted from organic carbon source addition (for example: taste and odor problem, carcinogenic THM production in disinfection process and rapid clogging of biofilter), easy operation, and compatibility with health issues in drinking water treatment.