| With broad use of nitric acid and related nitrate compounds in industrial occasions,high-nitrate industrial wastewater is widely generated from metal processing industries,production of explosives,nuclear fuel and fertilizer,and circulating cooling water treatment by reverse osmosis accompanying with high salinity.The treatment technologies of nitrate and total nitrogen at present are not that mature,among which the traditional active sludge process still exists many limitations when treating such nitrate-concentrated wastewater.Biogranulation is a promising bio-technology due to its advantage of greater biomass kept in reactor,excellent sludge settleability,higher removal loading capacity and device miniaturization.However,unstable quality problem of denitrifying granular sludge at high-load has not been effectively solved.In addition,few researches were made over denitrifying granular sludge treating nitrate-concentrated saline wastewater.Based on the granulation of denitrifiers and long-term stable operation in the denitrifying reactor,this study sought optimizing strategies to enhance the stability of granular sludge,investigated the operation performance of the reactor at high loads and analyzed the feasibility of denitrifying granular sludge treating nitrate-concentrated saline wastewater.1.With the aerobic flocculent sluge as seed in a USB reactor,the influent nitrate loading and ascending hydraulic velocity were gradually raised.The granulation of denitrifiers was achieved in 56 days covering 30-day interval stage and 26-day continuous operation.In the initial stage of granulation,excessive nitrate loading rate and ascending velocity can easily become disadvantages to sludge stablity.When the NLR was 3.5 kgNO3--N/m3/d,sludge floating occured.While at the ascending velocity of 5m/h,most of denitrifying granular sludge disaggregated.By dosing particle active carbon and taking periodic air-water strategy as degasification of N2,mechanical strength and stability of denitrifying granular sludge were effectively enhanced and mature granular sludge was cultured.2.Mature denitrifying granular sludge is pale yellow with smooth surface and compact structure,characterized by 1.02.5 mm in diameter,94.6140.5 m/h in settling velocity,1.11±0.015 g/cm3 in wet density,27.6830.91 in MLVSS and 0.33±0.02 in VSS/SS.3.Denitrifying granular sludge showed steady denitrifying performance with effluent TN lower than 15mg/L in the long-term operation under 1.52kgNO3--N/m3/d.Denitrifying reactor has strong resistant impact load capability facing the rapid increase of nitrate concentration and inflow rate.Denitrifying performance at high-load by increasing nitrate is better than that of increasing influent flow within certain range,with nitrate removal rate as high as 94.9%at the influent nitrate loading rate of 16.5 kgNO3--N/m3/d.4.Denitrifying granular sludge has its feasibility and applicability to treat nitrate-concentrated saline wastewater in a certain range of salinity and nitrate loding rate.No significant changes in denitrifying performance was observed and the average TN removal efficiency was 98.7%by stepwise increment of the salinity from 2%to 8%.The reactor adapted rapidly to the influent nitrate loading rate as high as 10.3 kgNO3--N/m3/d and the TN removal efficiency reached over 95.8%when the salinity was 4%.The carbon source usage amount of denitrification decreased under saline water,leading to notably lower sludge yield.The salt made the granule became smaller so that maintains stable granular structure and better settling performance under high nitrate loading rate. |
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