Start-up And Operation Characteristics Of Anammox Reactor And Effect Of Mn (Ⅱ) On Anammox

Anaerobic ammonium oxidation (anammox) is a novel process for nitrogen removal from ammonium-rich wastewater. Compared with conventional biological nitrogen removal processes, anammox presents several advantages in less operational costs and higher nitrogen removal efficiency due to its low dependency of oxygen, none organic carbon consumption, and less sludge production. Therefore, it is supposed to have a broad application prospects. However, the anammox microorganismsare characterized by avery slow growth rate with their doubling time best estimated at10-19d, which results in long start-up time and sensibility to the surrounding environment. The difficult cultivationof anammox granular sludge seriously restricts the engineering application of anammox process. In this paper, the anammox UASB reactor was finally started up and anammox granular sludge was successfully fostered using anaerobic granular sludge as inoculum. Based on the results, the start-up characteristics, operating characteristics of anammox reactorand the effect of Mn (II) on anammox reactor were explored. Main research achievements were as follows:(1) Start-up characteristics of granule-based anammox UASB reactor were revealed. After162daysanammox UASB s of anaerobic granular sludge, the anammox reactor was successfully started up. The overall start-up of the anammox reactor was divided into four phases, namely, cell lysis phase, lag phase, activity elevation phase, and stationary phase. During the start up course, the granular sludge experienced a process of initial disintegration and subsequent reaggregation, turning into blood-red anammox granular sludge. The granular surface is abundant with functional groups. In addition, Zn-Fe precipitation was discovered on the surface of granulesduring the operation, which could impose inhibition tomicrobial activity and penalize the start-up of anammox reactor. Therefore, it is suggested to adequately decrease the concentrations of Fe and Zn in mineral medium to accelarate start-up of anammox reactors. Results of Macro genome sequencing showedthat during the start up course, the dominating bacterial groups in inoculation sludge including Proteobacteria, Bacteroidetes and Firmicutes have reduced sharply, and Planctomycetes containing anammox bacteria has increased by13.6times from1.59%to23.24%.(2) The operational characteristics of anammox reactor under different loading rate were revealed. Under relatively low loading rate, maintaining NH4+-N and NO2--N concentration in the influent at272and300mg/L, respecetively, the volumetric nitrogen loading rate of R1gradually reached6864mg/(L-d) by progressively minimizing the HRT to2h. The average volumetric NH4+-N removal rate was2856mg/(L·d). Granular sludge in R1was mingled with red and black granules with the dominant Planctomycetes which contains anammox bacteria of23.24%. Floating sludge was rare in R1. While under relatively high loading rate, maintaining NH4+-N and NO2--N concentration in the influent at272and300mg/L, minimizing HRT to1h, the volumetric nitrogen loading rate of R2reached15491mg/(L-d), the average volumetric NH4+-N removal rate was7040mg/(L-d). All the granular sludge in R2was in red. The dominant Planctomycetes accounted for42.69%, which was two times of the value of R1sludge. The granular sludge floatation aggravated in R2, which hinders the stable operation of the reactor. Comparative analysis of settled granular sludge (SG) and floating granular sludge (FG) in R2indicated that the average diameter of SG was1.5mm and there was many holes on the granular surface, while the average diameter of FG was2mm with excessive extracellular polymeric substance (EPS) on the granular surface. Due to the limitation of substrate mass transfer, Planctomycetesin FG (36.24%) is lower than that in SG (42.69%), thus, it is proposed that thebreaking floating sludge and returning strategy might be helpful to increase anammox bacteria content in the reactor.(3)The short-term and long-term effects of Mn(II) on anammox was explored by utilizing the fostered anammox granular sludge. Batch tests showed that the half inhibiton value (IC50) of Mn (II) effect on anammox sludge in short term is4.83mg/L. While above3mg/L, Mn (II) possesses acute toxic to anammox bacteria, specific anammox activity (SAA) reduced with the increase of Mn (Ⅱ) concentration. Under15mg/L Mn (Ⅱ), the anammox activity was inhibited severely in0.5h. The nitrogen removal performance was nearly lost. However, by adoptting the strategy of domestication, that increasing the concentration of Mn (Ⅱ) added to anammox reactors step by step, anammox sludge which can bear200mg/L Mn (Ⅱ) was obtained. Under200mg/L Mn (Ⅱ), both the low load reactor(R1) and the high load reactor(R2) performed well, achieving volumetric nitrogen removal rate of6360mg/(L·d) and13990mg/(L·d) respectively.