Rresearch On Nitrogen Removal From Secondary Effluent In Constructed Wetland Using Biochar Coupled Acetic Acid

The secondary effluent is characterized by low C/N ratio,and nitrate nitrogen is the main pollutant.The constructed wetland is used for the deep denitrification of the secondary effluent,and the carbon source is an important factor limiting the nitrogen removal.Acetic acid is a common liquid carbon source,which also exists in plant root exudates,but it is easy to lose and has poor stability.Biochar can release a certain amount of dissolved organic matter and has a good adsorption effect.The application of biochar in constructed wetlands has the ability to improve the removal of nitrogen in wetlands.However,the relationship between biochar and carbon sources in wetlands has not been systematically explained.In this experiment,the characterization of biochar,the adsorption test of biochar on acetic acid,to study the adsorption and regeneration performance of biochar on acetic acid;In simulation of plant root secretion and acetate as additional carbon source,acetic acid and biochar was applied to the vertical,the undercurrent of artificial wetland to deal with nitrate nitrogen mainly secondary low carbon and nitrogen ratio,by setting different groups:add,biochar,acetic acid and acetate biochar group without plant cultivation and planting of calamus constructed wetland system,monitoring the water indicators,determination of the physical and chemical properties,plants and the microbes were characterized,biochar and acetic acid coupling effect on denitrification effect,plants,microorganisms,explain the biochar applied to artificial wetland,is likely to continue to provide carbon source,concentration of carbon source to strengthen the mechanism of the nitrogen.The main research results are as follows:（1）The surface of wheat straw biochar showed irregular loose lamellar structure with uneven flaky debris attached.C and O are the main surface elements,accounting for 49.12%and 35.30%of the total weight,respectively.The main crystal components of biochar are Si O₂ aluminosilicate KCl and graphite.The organic components include aromatic compounds and a small amount of alkaldic ketones and acids,while the inorganic components are mainly Si O₂.Biochar has a excellent adsorption capacity for acetic acid in aqueous solution.Q_max=124.07mg·g^-1 was calculated by the Langmuir model.The quasi second order kinetics could better fit the adsorption process.In addition,biochar has good regeneration ability.After repeated regeneration with deionized water,it can still maintain a constant regeneration rate and has a buffer effect on the adsorption of acetic acid.（2）In the constructed wetland without plant planting where the influent water is simulated wastewater,the best NH₄⁺-N removal efficiency is achieved when the HRT is 3d.The removal rates of NH₄⁺-N in CK1,AA,BC and AA-BC groups are77.82±1.51%,79.40±0.58%,99.03±0.96%and 96.68±1.68%,respectively.The addition of acetic acid had no significant effect on the removal of ammonia nitrogen,and the addition of biochar increased the removal rate of ammonia nitrogen by17.08～21.18%.When HRT was 6 days,AA-BC group had the highest nitrate nitrogen removal rate of 97.10±0.07%and total nitrogen removal rate of 94.61±0.69%.The addition of biochar makes COD concentration decrease first and then increase with hydraulic retention time,and biochar has a certain buffer effect on COD.（3）In the Acorus acorus constructed wetland with simulated wastewater as influent,when HRT was 3d,the removal rate of ammonia nitrogen in PR-AA-BC and PR-BC groups reached the best,which were 97.50±1.72%and 99.15±0.21%,respectively.The addition of biochar significantly increased the removal rate of ammonia nitrogen,but the addition of acetic acid had little effect on the removal rate of ammonia nitrogen.The maximum NO₃^--N removal rates in PR-BC group and PR-AA-BC group were 97.06±0.02%and 97.01±0.03%,and the COD concentration in PR-AA-BC group always maintained a high level,greater than 35.00mg/L.In the Acorus calamus constructed wetland,when HRT was 3d,the TN removal rate of ABC group is 93.66±0.03%,which is 13.60±0.02%higher than that of ACK,and has a good nitrogen removal effect.At this time,the effluent concentration of COD is the lowest,which is 26.01±3.42 mg/L,and the overall purification effect is the best.The addition of biochar had a significant effect on the chlorophyll fluorescence value Fv/Fm Y（Ⅱ）of calamus calamus,but the addition of acetic acid had no significant effect.The addition of biochar made calamus have a stronger photosynthetic rate.（4）Apha diversity index showed that biochar coupled with acetic acid significantly increased microbial abundance and microbial diversity.The addition of acetic acid or biochar could significantly increase the proportion of nitrogen-containing bacteria such as Bacteroidetes and Microflora verrucoides,and significantly increased the ratio ofβ-proteobacteria toδ-proteobacteria with degradation and nitrification of organic matter,and increase the proportion of denitrifying bacteria from Pseudomonas Vogesella Hydrogenophaga Sulfurisoma,Streptophyta,Opitutus.In conclusion,biochar has a good adsorption effect on acetic acid and plays a role in regulating carbon sources in wetlands.The application of biochar coupled acetic acid in constructed wetlands can effectively promote the removal of nitrate nitrogen,improve the abundance and diversity of microbial community and promote plant photosynthesis.The experiment explained the mechanism of action between biochar and acetic acid,and effectively solved the problem of denitrification of secondary effluent.There are 39 figures,18 tables and 163 references in this paper.