Advanced Nitrogen Bioremoval Process By Combining Denitratation With Anammox

Wastewater containing excessive nitrogen compounds in the form of ammonia, nitrite,nitrate and organic N has the potential toxicity to aquatic life, cause the depletion of dissolved oxygen as well as eutrophication of receiving water bodies, and affect the reuse of wastewater. Nitrogen removal from wastewater is of critical importance in order to protect water resources, especially for regions short of water. Many countries have enforced stringent nitrogen discharge standards in recent years. Recently, the anammox process has attracted much attention as it offers many advantages compared wiht the conventional nitrification-denitrification removal process. Although the anammox process possesses many advantages, the effluent usually contains excess NO₃^--N, limiting the application of anammox process.The aim of this study was to 1) establish a stable denitratation ?nitrate reduced to nitrite? enrichment approach, explore process performance and optimize the operation parameters. 2) establish a novel denitratation combined with anammox process?Anbon?, explore process performance and investigate the microbial community. The major results are as follows:1) Bottlenecks of high-rate denitrification processes were revealed, and the control strategies were studied.The mechanisms of granular sludge flotation and denitrifying self-alkalization were revealed, control strategies for both were studied, and the observed denitrifying performance is better than any other reported values. The results showed that the floatation of granular sludge was ascribed to a low sludge density originating from the retention of gaseous products. The floating granular sludge could recover its settling ability by releasing gas when the sludge was in the state of elastic expansion, but it would become worse by holding gas when it entered the plastic expansion state. We developed a novel denitrifying automatic circulation ?DAC? reactor, which can eliminate the floatation and washout of granule sludge by designing a novel internal structure of the reactor. Moreover,the high shear force resulted in a streamlined granular sludge, which aided settlement. We also revealed the effects of self-alkalization on high-rate biological nitrogen removal and optimized the volumetric capacity of the reactor by the feeding mode of "low concentration & high flux", which significantly improved the nitrogen removal. In the end the nitrogen removal rate of the lab-scale reactor reached 55 kgN·m-3·d^-1,which is higher than any currently reported value.2) Approaches setting up a high-rate denitratation process were investigated,and the process mechanisms of each were studied.Two stable denitratation enrichment approaches, named "alkalinity-trigger" and"nitrate-trigger" were established,respectively. The former resulted in an inhibition of nitrite reductase activity with a nitrite accumulation of 22.3% from the added nitrate.The latter was triggered by transcriptional inhibition of nitrite reductase, leading to a nitrite accumulation of 91.0% from the added nitrate. This method proved to be the most effective denitratation enrichment method. With "alkalinity-trigger", the results showed that nirK-containing Hyphomicrobium nitrativorans strain NL23 was sensitive to high pH ?>9.2?. As a consequence, significant nitrite accumulation occurred due to the 70.5% inhibition of nirK activity by high pH. On the other hand,Halomonas campisalis and Halomonas campaniensis dominated in "nitrate-trigger"denitratation community. Nitrate was found to inhibit the nirS transcription in the Halomonas species, which triggered the nitrite accumulation during nitrate reduction.Moreover, the substitution of acetate for methanol and the lasting starvation of electron donor ?acetate? were two pivotal procedures to enrich the "nitrate-trigger"denitratation culture from a methylotrophic denitrifying culture.3) The operation parameters of high-rate denitratation process were optimized,and the process performance was improved.The effects of key operation conditions ?including substrate, temperature, salinity and pH? on the performance of high-rate denitratation process were optimized. Good denitratating performance was achieved resulting in a nitrite accumulation rate of 17.2 mg·g^-1VSS·h^-1 and a nitrite accumulation efficiency of 93.4%. The results showed that acetate or glucose could serve as electron donor to drive denitratation, with an optimal COD/NO₃^--N of 2.2 and 2.0, respectively; but methanol could not. In addition,acetate-denitratation was demonstrated to have a better performance (nitrate reduction rate of 13.5^-18.5 mg·g^-1VSS·h^-1 and nitrite yield of 96.2%) than the glucose-denitratation (nitrate reduction rate of 4.6-6.5 mg·g^-1VSS·h^-1 and nitrite yield of 71.5%). The weaker performance of glucose-denitratation was ascribed to insufficient electron donor ?i.e. lower NADH/NAD+ ratio?, which resulted from the acceleration of enzymatic reactions for acetate production from glucose ?glycolysis and acetate fermentative pathways? and the decline of enzymatic reactions for acetate utilization ?TCA and glyoxylate cycles?. All the tested environmental factors?temperature, pH, salinity? were found to have a significantly greater impact on the activity of nitrite reductase than that of nitrate reductase in denitratating enrichments.The optimal operation parameters with respect to these conditions were: 32.7?, pH 8.0-9.0, salinity 0% ?w/v?.4) The effects of substrate on the Anbon process were investigated to characterize the performance.The effects of varying substrates ?including ratio and concentration? on the performance of Anbon process were investigated, and the information about denitratation and anammox microflora was obtained. The optimal substrate ratio of NH₄⁺-N:NO₃^--N:COD for the Anbon process was found to be 0.65:1:2.2. The volumetric nitrogen removal rate was as high as 9.0±0.1 kgN·m-3·d^-1 at high influent substrate concentrations of NH₄⁺-N 375 mg·L^-1, NO₃^--N 750 mg·L^-1 and COD 1875 mg·L^-1, which was superior to the values reported for similar processes. Moreover, the total nitrogen concentration in the effluent of this process was able to meet the strict discharge standard (less than 10 mg·L^-1) at the low influent substrate concentration of NH₄⁺-N 26 mg·L^-1, NO₃^--N 40 mg·L^-1 and COD 88 mg·L^-1. Halomonas campisalis and Candidatus Kuenenia stuttgartiensis were found to be the dominant bacteria in the SNR section and Anammox section under the high substrate concentration condition.However, levels of Halomonas campaniensis and Candidatus Brocadia brasiliensis increased significantly at low substrate concentrations.