The Establishment Of Marine Nitrifying Bacteria In The Enrichment System And The Analysis Of Denitrification Performance

With the improving demand of marine protein, marine aquatic scale and densityhave been constantly expanded. This activity has contributed to the excessiveincrease of the wastewater concentration and discharge amount. The wastewaterreleased large amount of nutrients into aquatic ecosystems and leaded toeutrophication of coastal waters. In order to solve this problem, scholars began tostudy the recirculating aquaculture systems. Denitrification of wastewater is the keyto the success of factory recirculating aquaculture and it is also the key to thecurrently research all over the world. There were so many ways for wastewatertreatment, but this experiment was intended to achieve the purpose of nitrogenremoval by biological methods. Therefore, this project focused on the recirculatingwastewater denitrification research from the following four aspects：the heterotrophicenrichment of nitrifying bacteria, the establishment of the biological nitrogenremoval reactor, the building and the denitrification by stable biological filter.The marine nitrifying bacteria were treated by autotrophic enrichment first andheterotrophic enrichment later. After60days of autotrophic enrichment, the numberof ammonia oxidizing bacteria increased by25times and the number of nitriteoxidizing bacteria increased by seven times.the ammonia removal rate reached to4mg/L·d, nitrite concentration remained stable and eventually stabilized atapproximately15mg/L,The Total nitrogen loss was34.10%. The results show that thereaction system enriched denitrifying bacteria. At the end of heterotrophicenrichment, the number of heterotrophic bacterial was higher than the ammoniaoxidizing bacteria and nitrite oxidizing bacteria, the ammonia removal rate wasreduced and the COD degradation rate was increased. Nitrite concentration increasedup to20mg/L, Nitrate concentration has been stabilized. It was proved that COD caninhibit the metabolism of nitrifying bacteria and the inhibition effect to nitriteoxidizing bacteria was even more serious.The Biological nitrogen removal unit was a submerged biofilm reactor whichwas made of transparent plexiglass.The column diameter (D) was10.5cm and high(H) was120cm, the total volume was about10L. Oyster shell as carrier packing,particle size of the oyster shell from top to bottom was2cm,1.5cm and1cm, the highratio was1:2:1and the total fill high (h) was about75cm. Its filling volume wasapproximately6.5L and porosity was about35%. The circulating seawater we usedfrom the end of the autotrophic enrichment and the heterotrophic enrichment to formbiofilm. The temperature was controlled between26-28℃, the HRT was200mL/min,The dissolved oxygen concentration was5mg/L at least. Added ammoniaconcentration was4mg/L·d. We used the bait extract to ensure C/N ratio was5:1. The results showed that the reactor that from the end of autotrophic enriched to formbiofilm was better than that from the heterotrophic and natural seawater. Its biofilmgrowth cycle was about40days. When the biofilm was stabilized, the ammonianitrogen removal rate was100%and the nitrite concentration was less than0.1mg/L.Finally, this experiment using orthogonal experiment method to study theinfluence of temperature, ammonia concentration and flow rate on the biofilm reactor.The results showed that biofilm was most sensitive to the change of temperature,followed by ammonia concentration and HRT. The optimal reaction parameters was20℃, the optimal ammonia concentration was3mg/L and HRT was200mL/min.Explored the denitrification performance of the reactor at the optimum reactionconditions, when ammonia concentration is4mg/L·d, Ammonia removal reached to129.26mg/L·d, nitrate removed864mg/L·d and the nitrite concentration in0.1mg/Lor less. The wastewater can be good to the breeding pool to be reused after biologicalnitrogen removal.