Study On The Influence Of Nitrogen Form And No₃^-/NH₄⁺ Ratio In Microcystis Proliferation And Toxin Production

The urban landscape water body is affected by human activities,which is easy to be eutrophication and makes the landscape function difficult to maintain.The proliferation of algae is an important manifestation of eutrophication,among which microcystis aeruginosais a typical eutrophic advantage alga,and its metabolites,microcystin-LR,can cause serious harm to water quality,aquatic products and human health.Excessive nitrogen and phosphorus nutrients are the main causes of eutrophication,especially cyanobacteria.Existing research shows that in addition to nitrogen and phosphorus,nitrogen and phosphorus form also has important effects on growth and algae toxin-producing,therefore,the nutrient composition will lead to the difference of the algae to breed,the different performance of enterotoxigenic.The difference of nutrient composition will lead to breeding of the algae and producing of Microcystin-LR.This study focused on the algae reproduction characteristics in landscape water supplemented by tail water in municipal sewage treatment plant,especially nitrogen form under coexist condition of the influence of nitrate nitrogen,ammonia nitrogen and phosphorus and NO₃^-/NH₄⁺.By designing orthogonal experiments,this study analyzed the effects of nitrate nitrogen and ammonia nitrogen,respectively and NO₃^-/NH₄⁺on the proliferation and MC-LR.The key factors of controlling eutrophication under the condition of tail water replenishment were put forward with the correlation analysis of microcystis aeruginosa growth and MC-LR production.The main conclusions were as follows:?1?Nitrogen form had an effect on the critical concentration of phosphorus limiting algae growth.Under the condition of nitrate nitrogen culture,the limit concentration of phosphorus was 0.1 mg/L,while the concentration was 0.05 mg/L under the condition of ammonia nitrogen culture.Therefore,ammonia nitrogen was needed preferentially controlled in the process of eutrophication.In addition,when TP under appropriate conditions?TP>0.1 mg/L?,in order to control the excessive growth of algae,nitrate nitrogen needed be controlled below 5 mg/L under the condition of nitrate nitrogen culture,and ammonia nitrogen needed be controlled in lower below 1 mg/L under the condition of ammonia nitrogen culture.?2?NO₃^-/NH₄⁺had a significant effect on the growth rate of algal cells in the early stage of algal growth.When TN was sufficient?TN?5 mg/L?,in the experiment NO₃^-/NH₄⁺?3:1,1:1,1:3?,the higher the proportion of ammonia nitrogen was,the faster the growth rate of algae was.The sequence of algae utilizing different nitrogen sources is that first ammonia nitrogen then nitrate nitrogen.Therefore,NO₃^-/NH₄⁺had no significant effect on the amount of the maximal algal cells.Under the same TN condition,the final algal density of different NO₃^-/NH₄⁺was basically close in the experiment.?3?Different nitrogen forms and NO₃^-/NH₄⁺had different effects on microcystin-LR production.When nitrate nitrogen is a single nitrogen source and the concentration of nitrate nitrogen is lower than 10 mg/L,the production of MC-LR will not change significantly with the increase of nitrate nitrogen.When the concentration of nitrate nitrogen was greater than 10 mg/L,MC-LR will increase significantly with the increase of nitrate nitrogen.When ammonia nitrogen is a single nitrogen source,the production of MC-LR will first increase then decrease with the increase of ammonia nitrogen.When the concentration of nitrate nitrogen was 10 mg/L,MC-LR will be the most.When under coexistence conditions of nitrate nitrogen and ammonia nitrogen and TN is sufficient,the larger nitrate nitrogen proportion was,the larger MC-LR was.In the absence of TN,there was no significant difference in the effect of NO₃^-/NH₄⁺on MC-LR.