Study On Effect Of Organic Electron Donor On Nitrate Removal Performance As Well As Mechanism In Single Chamber Bioelectrochemical System

A single chamber bioelectrochemical system (S-BES) was set up and synergistic effect of anode electrogenesis and cathode nitrate reduction by utilizing its internal electron transfer characteristic was achieved. Key factors such as carbon sources and electric field influencing nitrate removal performance in S-BES were investigated and the transform and pathway of organic and nitrate were explored.In order to deeply understand the electrode biofilm formation mechanism, microbial metabolism and signaling molecule secretion were studied in S-BES. Eventually, the engineering feasibility of treating actual nitrification tail water was investigated by designing a small S-BES denitrification reactor. Main conclusions were drawn as following:(1)The nitrate removal performance in S-BES fed with NaHCO3was improved by30%with a volume removal efficiency of0.44±0.08g/(m3.h) comparing to the biological control reactor. Small amount of organic matters were helpful to structure autotrophic and heterotrophic bacteria symbiotic system which could promote nitrate removal and reduce effluent nitrite concentration. The current information collected during the experiment cycle indicated that the anode electrogenesis and cathode nitrate reduction was existed. When the C/N increased from2.0to3.5, the ratio of autotrophic denitrification in S-BES was decreased from72.74%to50.23%.(2)Result of impact of carbon source on S-BES performance indicated that in the S-BES fed with NaHCO3significant nitrite accumulation phenomenon was observed and the SMP/SCOD was high. Adding organic carbon source could decrease the generation of SMP in the S-BES. By analyzing the organic carbon sources metabolism process in the S-BES, it was deduced that simple carbon source was easier to be utilized by heterotrophic bacteria to promote heterotrophic denitrification while the complex carbon source was easier to be used by anode microorganisms to generate electric accompanying with significant nitrite accumulation.(3)Result of electric field influence on S-BES performance indicated when the current increased from5mA to15mA, nitrate removal efficiency of S-BES fed with starch and NaHCO3was improved by20%and37%, respectively. But when continued to increase current to25mA, nitrate removal efficiency continued to rise only in the S-BES fed with NaHCO3. A suitable current was benefit to microorganism to secrete DSF signaling molecule which was helpful for EPS excretion and then resulted in strengthening biofilm formation ability. Once the current exceeded the optimum current, the influence would be adverse and the inhibition effect of high current on heterotrophic bacteria would be stronger than the autotrophic bacteria.(4)When applied IAND-BES coupled system to treat sewage, NH4+-N and TN average removal efficiency was85.5±7.4%and47.8±10.2%, respectively, the coupled system showed a well nitrogen removal performance. But in the latter experiment, nitrate concentration in IAND-BES effluent was on the rise. After detecting the three soluble organic components such as protein, polysaccharide and DNA before and after treating with BES, it was observed that protein and DNA concentration was decreased while polysaccharide increased, but the total organic concentration was no significant change.