Study On Controlled-release Carbon-source For In-situ Biological Nitrogen-removal In Groundwater

Controlled-release carbon-source materials of GP、GSP、GSP-N、GSP-B、GSP-BN, GSP-A, GSP-AN, GSP-AB and GSP-ABN were prepared by usingpolyvinyl alcohol（P） as vector and corn starch（S） as carbon source， anddepending on whether modifying with boric acid（B）, attapulgite（A） or sodiumsulfate（N）.Carbon release of GSP and availability of GP in denitrification process wereinvestigated respectively. The both effect of different nutrient substrate anddifferent material particle-size on denitrification in the static denitrificationexperiment with GSP as carbon-source were investigated too. As indicated instatic experiment, the more freezing-thawing cycles showed higher materialstability and more difficult release of carbon-source; the carbon release level ofmaterial in tap water was far greater than it in pure water; polyvinyl alcohol hadcertain anti-biodegradability, so it could not be used as carbon-source but wassuitable as the carbon-source skeleton. The denitrifying efficiency ofcarbon-source in tap water was higher than it in pure water; the smaller materialparticle-size showed faster nitrate degrading rate, but the accumulative level ofnitrite, ammonia and TOC had not decreased.The effect of different modifying methods on nitrogen-removal performanceof carbon-source material was investigated by modification of GSP. The staticexperimental results showed that, the significant effective modified methods wereA+B+N, N, A+N and B+N, the most effective of which was A+B+N.The nitrate removal effect of sand column with GSP-BN as activity materialof the PRB was investigated. The nitrate-nitrogen removal rate was respectivelyabove99.6%,92.3%and84.8%when nitrate-nitrogen of inflow was20mg/L、30mg/L and40mg/L in effective operating period（48d）. nitrite-nitrogen andammonia-nitrogen of outflow was respectively below1mg/L and2.3mg/L.Nitrate-nitrogen removal velocity of PRB was respectively71.63gNO₃^--N/（m³·d）、91.08gNO₃^--N/（m³·d） and92.56g NO₃^--N/（m³·d）. TNremoval velocity of PRB was respectively70.17gN/（m³·d）、68.18gN/（m³·d） and89.94gN/（m³·d）. TOC concentration of outflow was fairly near inflow, it showedthe organic released by PRB was utilized fully and would almost not cause secondary organic-pollution.The ratio among each component in GSP-ABN was optimized by orthogonaldesign. The result showed that carbon-source had the best overall performancewhen mass ratio of P to S, A to S, and B to S was respectively1.5,0.25and0.25.