Nitrogen Removel Via Anammox Process Based On Partial-denitrification And Microbial Characteristics

The excesss nitrogen in water body is one of the main cause of eutrophication.The nitrification and denitrification process,which is currently widespred adoption aroud the world,could achieve a effective nitrogen removal from wastewater,but it usually consumes large amounts of electirc energy and chemicals.Th e ANaerobic AMMonia OXidation?ANAMMOX?,which firstly discovered in 1990 s,could convert ammonia and nitrite into nitrogen directly under anaerobic condition,it possesses the advantages of low consumption,high efficiency and environmental friendliness,which is deemed as the most economical and efficient nitrogen removal process.However,the nitrite,one of the most important substrate for anammox,is hard to acquire stably,and the anammox process could not remov e the nitrogen from nitrate wastewater.In response to these questions,based on the previous achievement of partial-denitrification?PD: NO3-?NO₂^-?,futher studies were conducted to investigate the granulation of PD sludge in both sequencing batch reactor?SBR?and upflow sludge bed?USB?reactor in order to achieve a high efficient nitrite production.The novel anammox combined with PD process was then developed for nitrogen removal from nitrate wastewater derived from the effluent of high-strength anammox,the secondary effluent of wastewater treatment plants?WWTPs?,and industrial wastewater with high-strength nitrate,so it could promote the widely application of anammox process.The main research results were as follows:?1?The PD granule sludge with good biochemical properties was developed,and the characteristics during granulation process as well as microbial community structure were explored.The results found that the Ca CO3 precipitation was acted as the “crystal nucleus” in the initial operation of PD SBR,which played an important role in promoting granular sludge rapid formation.Mature granular sludge was obtained with a dense structure,it had a good deposition performance?SVI is around 32.0 m L/g MLSS?,and SEM obsearation showed that the granule surface is densely packed with a large number of short bacillus.High throughput sequencing analysis indicated that the PD functional bacteria of Thauera was always dominated in the reactor during the granulation?61.1%⁶3.8%?.Besides,it was observed that the norank_p<sub>Gracilibacteria and Flavobacterium had underwent a great increase,and its proportion had a good consistency with partial size change,which was speculated to be related with PD sludge granulation.An ideal nitrite production was obtained during the granulation of PD sludge,which the nitrite production ratio?NTR?was as high as 88.3%.?2?The continuous-flow PD system with nitrite production was established,and the control technology for stable operation was proposed.The PD was performed in a continuous flow USB reactor and it indicated that a stable and efficient nitrite production could be obtained in both moderate and low temperature,with the mean nitrite production rate?NPR?of 6.63 Kg N/m3/d and 3.35 Kg N/m3/d achieved at 28? and 15.7?,respectively.However,it should avoid the too high influent loading rate,in case of the occurrence of sludge bulking.The gas automatic circulation?GAC?control technology was proposed,it was demonstrated that the application of GAC to the USB reactor could enhance the mass transfer,and thus improve the nitrite production.Besides,it showed that the GAC played an important role in maintaining the stability of USB reactor by preventing the sludge floatation.However,an excess GAC should be avoided in cased of sludge washed out.High throughput sequencing analysis indicated that the Thauera for nitrite production was slight decreased during the operation?from 67.2% in the initial declined to 50.2% on day159?,correspondingly a increase of Zoogloea?0¹6.0%?and Rhodocyclaceae_unclassified?0⁹.0%?were observed.?3?The Anammox+PD process was setted up for further nitrogen removal from high-strength wastewater,and the synergy mechanism between anammox bacteria and denitrifiers were revealed.With respect to the high nitrate in effluent of anammox treating high-strength wastewater,a PD reactor was installed for converting nitrate to nitrite,then refluxing to anammox reactor for removing.Under the influent NH4+-N of 400 mg N/L and NO₂^--N of 420 mg/L,a mean effluent NO3--N of 22.8 mg/L was obtained at the reflux ratio of 300%,which was much lower than the theoretical value of around 110 mg/L with anammox solely.The domestic wastewater was also treated simultaneously in the combined process by introducing to PD reactor,and the demand of external carbon source was reduced from COD/NO3--N of 3.0 to 2.0.Meanwhile,the effluent nitrate was further decreased to 13.8 mg N/L,with the total nitrogen removal efficiency as high as 97.8%.High throughput sequencing analysis indicated that the Candidatus_Brocadia?7.52%¹.32%?was the major bacteria for nitrogen removal and a large number of denitrifiers of Thauera?6.43%¹8.37%?was existed in anammox reactor,these two kinds of microorganisms could be coexistent harmoniously at low organic matter,and collaborated for nitrogen removal,thus improved the total notrgen efficiency.?4?The technology of PD+Anammox process was proposed for tertiary nitrogen removal from low C/N domestic wastewater,and the operation efficiency,feasibility as well as potential risk were evaluated.To solve the problem of nitrate,which dominated in the secondary effluent of WWTPs,an innovative PD-Anammox process was proposed for tertiary nitrogen removal from low C/N domestic wastewater.Results indicated an excellent nitrogen removal performance was obtained by adjusting the nitrate and domestic wastewater feeding volumes,the effluent total nitrogen was maintained at around 5.0 mg N/L with the nitrate varied from 20 to 40 mg N/L.The combined process had a huge economic advantages in oxygen consumption,external carbon demand and excess sludge production when compared with traditional nitrification/denitrification process,which would not require oxygen,reduce 80% carbon demand and 64% sludge production,and it is environmentally favourable in reducing CO2 and N2 O production.In addition,the combined processs is easy to upgrade for existing plants as well as has a low risk in engineering application?5?The PD+Anammox process was developed for high-strength nitrate wastewater treatment,the optimize strategy was proposed,and the advantages were analyzed.The results showed that the high-strength nitrate?1000 mg N/L?in industrial wastewater was effectively removed via the novel PD-Anammox process,and the domestic wastewater could be simultaneously treated.A desired effluent nitrogen concentration could be achieved by gradual optimizing the feeding volume ratio of nitrate and domestic wastewater as well as the external carbon dosage,a mean effluent TN of 11.0 mg/L was obtained at the volume ratio of 7.0 between domestic wastewater and high-strength nitrate,and a COD/N ratio of 1.7.The PD-Anammox is an economically and technically attractive solution to the treatment of high-strength nitrate wastewater,it not only lowered the requirement of carbon demand,reduced sludge production,and treated municipal wastewater simultaneously,but also avoided the problems that occur in traditional denitrification?i.e.long lag times for acclimating biomass,high effluent of soluble microbial products,and low-efficiency caused by nitrite accumulation?,which is a promising process for treating high-strength nitrate wastewater.