Studies On Biological Removal Of NO_x From Waste Gas And SO₄^2- From Waste Water

In order to remove NOx from boiler flue gas which contains O2and SO42-fromwaste water after absorbing SO2,effectively, the aerobic removal of NOx using abiotrickling filter (BF) and anaerobic removal of SO42-using an upflow anaerobicsludge blanket (UASB) reactor were studied. The enrichment of denitrifying bacteria(nitrifying bacteria and denitrifying bacteria) and sulfate reducing bacteria (SRB)were successfully obtained from the landfill leachate using the highly selectivecoculturing-technique in a BF and an UASB reactor, respectively. The effects oforiginal oxygen concentration, empty bed residence time (EBRT), liquid velocity (VL),initial concentration of NO, substrates (S2-, formaldehyde and sodium acetate) andproductions (nitrate and sulfate) on NO removal were investigated. In addition, theinteractions of NO, sulfide and formaldehyde during removal experiments were alsostudied. The effects of hydraulic retention time (HRT), concentrations of SO42-and S2-,carbon sources (lactic acid, acetic acid, citric acid and ethanol), COD/SO42-ratio andthe light on SO42-removal were investigated. In addition, startup phases and theremoval abilities in the UASB reactor with or without packing were studied.At an EBRT of54s, VLof23.87m3/(m2.h), O2of20%, S2-1000mg/L,formaldehyde500mg/L, NO removal efficiency (RE) reaches approximately100%with inlet NO of1200ppm. NO removal efficiency increases with increasing O2concentration, and is not affected by sulfate even at high levels, but is inhibited bynitrate at high levels (>633.68mg NO3--N/L). Formaldehyde removal is facilitated byS2-but inhibited by NO. NO and formaldehyde almost have no great influence onsulfide removal. The amount of nitrate produced decreases with increasingS2-/formaldehyde ratio. Overall, the study demonstrates that simultaneous removal ofNO, formaldehyde and S2-under aerobic conditions in a BF is feasible.In the UASB reactor,(1) lactic acid is as carbon source, the following results canbe concluded:①the RE of SO42-increases from52.08%to77.78%with HRTincreasing from1h to32h at COD/SO42-of3, SO42-2500mg/L.②the RE increasesfrom11.17%to85.25%with increasing COD/SO42-ratio from o.76to9.46at a HRTof12h. Increasing ratio further to22.8leads to the decrease in RE (70.25%).③thegas is produced much more with light than that without light (Vwith＞4Vwithout),and the concentration of H2S is slightly higher with light.④Under COD/SO42-of3,HRT2h, the RE of SO42-decreases from82.77%to25.21%when concentrations of SO42-increases from1013.08to7612.23mg/L.⑤the SO42-removal is higher at ashorter HRT in an UASB with packing (molecular sieve or activated carbon) than thatwithout packing.(2)acetic acid as carbon source:①the RE increased slightly withHRT increasing from2h to12h.②the RE increases from69.93%to77.1%withincreasing COD/SO42-from o.19to3.8at a HRT of12h, SO42-2500mg/L. Increasingratio further to22.8leads to the decrease in RE (54.79%).③the SO42-removal ishigher at a HRT of12h in the UASB reactor without packing than that with packingat a COD/SO42-of3.8.(3)Comparing with citric acid and ethanol, lactic acid andacetic acid are better as carbon sources. Different carbon sources have differentoptimal COD/SO42-ratios. This UASB reactor can remove SO42-, successfully.