Study On Selection Of External Carbon Sources For Better Denitrification In Constructed Wetlands

Lacking of carbon source in treatmening of high nitrogen low carbon sewage by constructed wetlands, the paper aims to compare several organic solid carbon sources to strengthen the effect of denitrification by laboratory simulation of organic solid carbon source decomposition and denitrification process, screening out the optimal carbon source and pretreatment, adding in a small pilot plant constructed wetlands, to examine aquatic plants and types, the carbon source by assaying denitrification effect of system and analying the number of different periods of artificial wetlands microbial distributionand activity of matrix analysis of the to discuss carbon source decomposition and nitrate removal mechanism, in order to strengthen the artificial wetland nitrogen removal and provide theoretical support.1. Selecting artificial wetland common cattail dead leaves, reed straw, reeds dead leaves, vetiver, and then force flower dead leaves as external carbon source, different pretreatment methods (alkali treatment and simple treatment), laboratory simulation of anti-nitrification process, analysis of the law of biomass component degradation as well as carbon, nitrogen, phosphorus release to select the optimal carbon source and pretreatment. The results showed that again force flower stalks by the alkali treatment, the early days (0～2d) organic matter emission can be increased to311.7mg/L from63.01mg/L, the latter can be kept at5～25mg/L, and N, P release remains at a low level. Simple treatment group, the nitrate removal rate the then force flower stalks (96.92%)> reed stalks of cattails dead leaves (90.60%)> reed dead leaves (84.16%)> vetiver (81.08%)> reed straw (80.60%); alkali treatment group, the nitrate removal rate and then force flower stalks (99.00%)> the cattail reed stalks of dead leaves (95.92%)> reed dead leaves (93.72%)> vetiver(91.04%)> reed straw(86.24%). Selected alkali treatment and Thalia dealbata as external carbon source.2. Building8sets subsurface flow constructed wetland small pilot plant to study aquatic plants and their types, plus the impact of the carbon source, such as denitrification effect of system. The results showed that the nitrate removal rate, no carbon source system, the system of planted vegetation higher plant system, there is a certain difference between the different types of plants, Thalia dealbata System> Arundo donax var.versicolor system> Phramites australis var.iegatus systems. The carbon source system, the removal rate is generally higher reaction early and mid-denitrification rate stable at a high level, between92%to100%, the small differences between the plant species; reaction final available carbon source reduction, plant species differences began to show nitrate removal rate still is Thalia dealbata System> Arundo donax var.versicolor system> Phramites australis var.iegatus systems. System without plants or planting of plant species under the same circumstances, the carbon source, the presence or absence of Denitrification greater impact on the carbon source case, denitrification rate is always at a high level, there is no carbon source system denitrification rate2to2.5times.3. Analying of the different periods of artificial wetlands distribution of number of micro-organisms and matrix activity of the situation. The results show that:artificial wetlands ammonification bacteria, nitrifying bacteria and denitrifying bacteria in their denitrification efficiency is closely related to experimental mid-stage denitrification efficiency, the number of denitrifying bacteria in each system are the largest, at this stage carbon source decomposition reaction is more active, of ammonification bacteria and nitrifying bacteria carbon source decomposition aerobic competition, the amount is less than the experimental late stage10. The beginning of the experiment, the β-glucosidase enzyme cellulose decomposing carbon source decomposition enzyme activity is higher, as the reaction proceeds, the above two kinds of enzyme activity decreased. Are closely related with the denitrification of nitrate reductase, and its activity in a higher stage of the denitrification stage5is high, its activity is also decreased with the decrease of the removal effect.