Rate of ammonia oxidation in a synthetic saline wastewater by a nitrifying mixed‐culture

Most of the kinetic studies on nitrification have been performed in diluted salts medium. In this work, the ammonia oxidation rate (AOR) was determined by respirometry at different ammonia (0.01 and 33.5 mg N‐NH₃ L^?1), nitrite (0–450 mg N‐NO₂^? L^?1) and nitrate (0 and 275 mg N‐NO₃^? L^?1) concentrations in a saline medium at 30 °C and pH 7.5. Sodium azide was used to uncouple the ammonia and nitrite oxidation, so as to measure independently the AOR. It was determined that ammonia causes substrate inhibition and that nitrite and nitrate exhibit product inhibition upon the AOR. The effects of ammonia, nitrite and nitrate were represented by the Andrews equation (maximal ammonia oxidation rate, r_AOMAX, = 43.2 [mg N‐NH₃ (g VSS_AO h)^?1]; half saturation constant, K_SAO, = 0.11 mg N‐NH₃ L^?1; inhibition constant K_IAO, = 7.65 mg N‐NH₃ L^?1), by the non‐competitive inhibition model (inhibition constant, K_INI, = 176 mg N‐NO₂^? L^?1) and by the partially competitive inhibition model (inhibition constant, K_INA, = 3.3 mg N‐NO₃^? L^?1; α factor = 0.24), respectively. The r_AOMAX value is smaller, and the K_SAO value larger, than the values reported in diluted salts medium; the K_IAO value is comparable to those reported. Process simulations with the kinetic model in batch nitrifying reactors showed that the inhibitory effects of nitrite and nitrate are significant for initial ammonia concentrations larger than 100 mg N‐NH₄⁺ L^?1. Copyright © 2005 Society of Chemical Industry     

Respirometric estimation of the oxygen affinity constants for biological ammonium and nitrite oxidation

The nitrification process (ie biological ammonium oxidation to nitrate) is a two‐step process with nitrite as an intermediate product. As it is an aerobic process, its kinetics is highly dependent on the dissolved oxygen (DO) concentration in the medium. However, the influence of this limitation on the nitritation (first step) is shown to be less important than in the nitratation (second step). This dependence on DO concentration is generally described using a Monod‐type kinetics with K_O as the oxygen affinity constant. In this work, a procedure for the calculation of both affinity constants is presented. This procedure is based on monitoring the DO drop in the reactor when external aeration is stopped and the biomass is consuming without substrate (ammonium or nitrite) limitations. This methodology includes the contemplation of the oxygen transfer from the atmosphere, the response time of the DO probe and the inhibition of the nitratation step with sodium azide when estimating K_OA (nitritation oxygen affinity constant). The results obtained are K_OA = 0.74 ± 0.02 mg O₂ dm^?3 and K_ON = 1.75 ± 0.01 mg O₂ dm^?3. Moreover the influence of the aforementioned considerations on the estimated K_O values is also discussed. Copyright © 2005 Society of Chemical Industry     

Nitrite accumulation characteristics of high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor

Selective nitrification was carried out to accumulate nitrite from high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor. Nitrification efficiencies and nitrite accumulation characteristics were investigated at various operating conditions such as ammonium load, oxygen supply and free ammonia concentration. The biofilm reactor showed very stable nitrification efficiencies of more than 90% at up to 2 kg NH₄‐N m^?3 d^?1 and the nitrite content was maintained at around 95%. Inhibition by free ammonia on nitrite oxidizers seems to be the major factor for nitrite accumulation. Batch kinetic analyses of ammonium and nitrite oxidation showed that nitrite oxidation activity was selectively inhibited in the presence of free ammonia. However, the activity recovered quickly as the free ammonia concentration decreased below the threshold inhibition concentration. Examination of specific ammonia and nitrite oxidation activities and the most probable number indicated that the number of nitrite‐oxidizing microorganisms in the nitrite‐accumulating system was less than that in the normal nitrification system due to long‐term free ammonia inhibition of the nitrite oxidizers. The reduced population of nitrite oxidizers in the biofilm system was also responsible for the accumulation of nitrite in the biofilm reactor. © 2003 Society of Chemical Industry     

不同运行方式对微生物燃料电池处理氨氮废水的影响

微生物燃料电池(MFC)是一种既能去除污染物又能产电的新型污水处理技术,由于其具有利用生物转化能量的节能优势,MFC废水脱氮处理技术引起了更多的关注。本实验在启动MFC的同步硝化与反硝化(SND)后,首先研究了通路与断路条件对MFC产电脱氮的影响,结果表明:断路时有利于硝化反应的发生,氨氮去除率有最大值95.17%;而通路更有利于COD和总氮的去除,表明氮的去除主要依靠阴极接受电子进行。随后分析了曝气阶段+停曝阶段运行方式对MFC产电和脱氮的影响,结果显示:曝气8.5h(DO为4.0mg/L)后停止曝气,停曝阶段为11.5h,DO逐渐降低到2.0mg/L,输出电压由无曝气运行的31mV提高到120mV左右,氨氮去除率最高达到86.42%、总氮去除负荷由无曝气运行的0.064g/(L·d)升高到0.46g/(L·d)。说明曝气阶段+停曝阶段运行方式既能有效提高MFC脱氮产电性能又可以减少维持高浓度DO的能量输入。     

淀粉废水培养复合型微生物絮凝剂产生菌研究

研究了两株根霉M9和M17复配产生的复合型微生物絮凝剂的絮凝特性,并优化了马铃薯淀粉废水对该复合菌的培养条件.该絮凝剂具有投加量少、絮凝效果和耐热性好的特点.马铃薯淀粉废水对该复合菌的较佳培养条件为:废水COD 1 600 mg/L,添加0.3 g/L尿素、0.04 g/L磷酸二氢钾,无需添加碳源和调节pH,M9接种60 mL/L、M17接种40 mL/L后培养35 h.在此条件下,投加5 mL/L的发酵液即可对高岭土悬液的絮凝率达到92.67%.经过培养微生物后的废水COD为510 mg/L,去除率93.60%,可直接经过好氧处理达标排放,或与净水混合后灌溉马铃薯种植基地,降低了工艺处理的难度.     

基于ETS活性的有机物降解与硝化过程中微生物动力学

通过考察有机物生物降解和氨氮生物硝化过程中活性污泥电子传递体系（ETS）活性的变化规律,研究了ETS活性表征污泥生物活性的可行性,结合米门公式分析了有机物生物降解和硝化反应过程生物活性动力学。试验结果表明,活性污泥的ETS活性可以有效地揭示出有机物生物降解和氨氮生物硝化反应的进程,同时对系统受到的有机物和氨氮冲击负荷及硝化过程中碱度的变化有着灵敏的反映,这说明用ETS活性表征污泥的生物活性是可行的;有机物生物降解过程生物活性米氏常数K_s^T=368.9 mg·L^-1,U_m^T=90.9 mg TF·（g TSS·h）^-1,K_s^I=88.42 mg·L^-1,U_m^I=277.8 mg INTF·（g TSS·h）^-1;氨氮硝化过程生物活性米氏常数K_s^T=16.89 mg·L^-1,U_m^T=34.6 mg TF·（g TSS·h）^-1, K_s^I=6.0 mg·L^-1,U_m^I=196.08 mg INTF·（g TSS·h）^-1;生物活性动力学分析进一步验证了进行有机物生物降解的异养菌生长速率高于进行硝化反应的自养型硝化菌。     

Simultaneous nitrification and denitrification with electricity generation in dual‐cathode microbial fuel cells

BACKGROUND: Nitrogen removal using microbial fuel cells (MFCs) is of great interest owing to the potential benefits of bioenergy production. In this study, simultaneous nitrification and denitrification in dual‐cathode MFCs was investigated. RESULTS: The dual‐cathode MFCs investigated were capable of generating electricity and removing nitrogen, influenced by operating methods, nitrogen loading rates and external resistance. Depending on the ammonium concentration in the anode chamber, 84–97% of the ammonium nitrogen was removed via nitrification in the aerobic cathode. The removals of nitrate and total nitrogen were relatively low (～50%) at the influent ammonium concentration of 80 mg NH₄⁺‐N L^?1, but were significantly improved to more than 90% at a lower ammonium input (40 and 20 mg NH₄⁺‐N L^?1). When the electrode couples were electrically connected for different purposes, with high power output from the anode/aerobic cathode and high current generation from the anode/anoxic cathode, nitrogen removal was also improved. An investigation of aeration suggested that factors other than carbon supply, possibly inefficient reactor configuration, also limited the performance of the developed MFC. CONCLUSION: The experimental results demonstrated that the proposed pathway was feasible with effective nitrogen and organic removal. This study provided valuable information for the further development of a continuously operated dual‐cathode MFC system. Copyright © 2011 Society of Chemical Industry     

Modeling and simulation of the formation and utilization of microbial products in aerobic granular sludge

A mathematical model is established to simulate the formation of extracellular polymeric substances (EPS), soluble microbial products (SMP), and internal storage products (X_STO) in aerobic granular sludge. The sensitivity of these microbial products concentrations toward the key model parameters is analyzed. Independent experiments are conducted to find required parameter values and to test its predictive ability. The model is evaluated by using one‐cycle operating experimental results of a lab‐scale aerobic granule‐based sequencing batch reactor (SBR) and batch experimental results. Results show that the model is able to describe the microbial product dynamics in aerobic granules and provide further insights into a granule‐based SBR. The effect of the initial substrate and biomass concentrations on the formation of microbial products in aerobic granular sludge can therefore be analyzed by model simulation. A higher substrate concentration results in a greater concentration of EPS, SMP, and X_STO. An accumulation of biomass in the bioreactor leads to an increased production rate of EPS, SMP, and X_STO. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Isothermal oxidation kinetics of unstabilized polypropylene in the molten state

This article is devoted to the elaboration of a nonempirical kinetic model for the thermal oxidation of molten unstabilized polypropylene (PP), which occurs typically at 170–250°C, a current temperature range for PP processing. The validity of the kinetic model has been successfully checked with the kinetic curves of mass changes and ketone group buildup of quasihomogeneously oxidized PP films (≈40 μm thick) at 190, 200, and 230°C in atmospheric air. The orders of magnitude of the model parameters, determined with the kinetic model as an inverse method, are physically reasonable. Large differences obtained between some rate constant values determined in this study for PP and published elsewhere for polyethylene are tentatively explained. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

NaClO氧化去除高盐废水中氨氮的影响因素及其动力学研究

采用NaClO氧化降解高盐废水中的氨氮,对其影响因素及动力学进行研究。结果表明:NaClO对氨氮的氧化降解过程符合伪一级反应动力学模型,影响其降解效果的因素有NaClO的投加量、氨氮的初始浓度、盐分、温度等。当NaClO投加量为0.6%时,反应速率常数高达0.015 75 min~(-1)。氨氮初始浓度越大,氧化反应效果越差,且初始质量浓度不超过45 mg/L时,随着初始浓度的增加,其对氧化反应速率常数的影响增大。低浓度盐分对氨氮氧化基本无影响,但超过2.0%时,随着盐分的增加,其对氨氮氧化效果的抑制作用增强,反应速率常数明显降低。提高反应温度,有利于氨氮的氧化降解,当温度从10℃增加至35℃的过程中,反应速率常数从0.001 88 min~(-1)增加至0.010 43 min~(-1)。     

Determination of kinetics in batch cooling crystallization processes—A sequential parameter estimation approach

A comprehensive methodology to carry out a sequential parameter estimation approach has been developed and validated for the determination of the kinetic parameters of the crystallization of a generic organic compound. The strength of the approach lies in the thorough design of isothermal experiments which facilitate the isolation and/or decoupling of the different crystallization phenomena. This methodology has been applied for the parameter estimation of primary and secondary nucleation, growth and agglomeration kinetics. The resulting crystallization model has been able to reproduce the quantiles , and of the volume‐based particle size distribution of an independent seeded validation experiment with an error below 10 μm. The deviation in the prediction has been increased in the case of an independent unseeded experiment, although errors below the uncertainty of the measurement have been always obtained. The methodology here proposed is intended to be an efficient strategy for rapid modeling of batch crystallization processes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3992–4012, 2016     

DMFC多孔Pt-Ru阳极甲醇氧化宏观动力学模型化

本文旨在建立和求解DMFC多孔阳极甲醇氧化宏观动力学理论数模。根据Pt-Ru催化剂上双位机理,得到包含CO和OH覆盖率的甲醇水解本征动力学表达式;通过对该多孔阳极微元体积中的物料和电（荷）量衡算,导出了描述电极中浓度和超电势分布的两个耦联的模型方程。经量纲1化后,获得以量纲1变量和准数表示的普遍化宏观动力学数模。该模型包括催化层厚度l、比表面积a、有效扩散系数D_e和有效液相电导率κ_e等工程参数,特别是包括了与动力学参数相关且作为厚度变量函数的CO和OH覆盖率。进而,文中还给出了DMFC多孔阳极效率因子和极化曲线的计算公式。该数模为一非线性二阶微分方程组边值问题,经解耦,可得到两个同解的微分方程。用Newman的BAND（J）程序对方程进行数值求解,并在每一节点计算中嵌入一个计算CO和OH覆盖率的子程序。将模型预测值与甲醇氧化多孔阳极的极化实验数据进行对比发现：当宏观电流密度较低时二者能很好相符;当宏观电流密度较高、CO₂形成气泡的影响变大时,实验值有规律地偏低于预测值。详细的宏观动力学分析表明：提高催化剂Pt位甲醇电分解活性以减少功率损失、优化多孔电极微观和宏观结构以削弱两相流影响,应是改善该阳极性能的重要课题。本工作也可为直接乙醇燃料电池（DEFC）、直接硼氢化物燃料电池（DBFC）阳极的理论分析提供参考。     

Comparative study of nitrification performances of immobilized cell fluidized bed reactor and contact oxidation biofilm reactor in treating high strength ammonia wastewater

BACKGROUND: The immobilized cell fluidized bed reactor and contact oxidation biofilm reactor are two common choices for high strength ammonia wastewater treatment, however, comparative study of the nitrification performance of the two reactors has not been thoroughly studied. The nitrification performance of the two bioreactors when treating strong synthetic ammonia wastewater was investigated and compared. RESULTS: Results demonstrated that the immobilized cell fluidized bed reactor had a shorter acclimation period, and possessed several advantages over the contact oxidation biofilm reactor, in the form of complete oxidation of 150–360 mg L^?1 ammonia wastewater in a shorter time, higher ammonia removal rates (from 9.6 to 4.32 × 10² mgN L^?1 d^?1) over the temperature range 8 to 32 °C, irrespective of organic load. In contrast, a large reduction in ammonia removal was found in the contact oxidation biofilm reactor with chemical oxygen demand (COD) load. The immobilized cell fluidized bed reactor exhibited stable and high rates of nitrification in the long term. CONCLUSION: These facts demonstrated that the immobilized cell fluidized bed reactor is a suitable selection for high strength ammonia wastewater treatment. Copyright © 2007 Society of Chemical Industry     

液氨卧罐液体实时连续泄漏建模及分析

基于范德瓦耳斯方程和流体力学理论,考虑液氨卧罐泄漏时罐压和液面面积变化,建立了液氨卧罐液体实时连续泄漏模型.利用模型对某制冷企业液氨卧罐进行数学模拟,并将计算结果与PHAST模拟结果进行对比分析.结果 表明,液面高度h下降幅度先减缓后变大,液体泄漏质量流率Qm和泄漏孔处液体泄漏速率v的下降幅度及泄漏液体质量m的增加幅度...     

Storage of biodegradable polymers by an enriched microbial community in a sequencing batch reactor operated at high organic load rate

The production of polyhydroxyalkanoates (PHAs) from organic acids by mixed bacterial cultures using a process based on aerobic enrichment of activated sludge, that selects for mixed microbial cultures able to store PHAs at high rates and yields, is described. Enrichment resulted from the selective pressure established by periodic feeding the carbon source in a sequencing batch reactor (SBR); a mixture of acetic, lactic and propionic acids was fed at high frequency (2 hourly), high dilution rate (1 d⁻¹), and at high organic load rate (12.75 g chemical oxygen demand (COD) L⁻¹ d⁻¹). The performance of the SBR was assessed by microbial biomass and PHA production as well as the composition and polymer content of the biomass. A final batch stage was used to increase the polymer concentration of the excess sludge produced in the SBR and in which the behaviour of the biomass was investigated by determining PHA production rates and yields. The microbial biomass selected in the SBR produced PHAs at high rate [278 mg PHAs (as COD) g biomass (as COD)⁻¹ h⁻¹, with a yield of 0.39 mg PHAs (as COD) mg removed substrates (as COD)⁻¹], reaching a polymer content higher than 50% (on a COD basis). The stored polymer was the copolymer poly(3‐hydroxybutyrate/3‐hydroxyvalerate) [P(HB/HV)], with an HV fraction of 18% mol mol⁻¹. The microbial community selected in the SBR was analysed by DGGE (denaturing gradient gel electrophoresis). The operating conditions of the SBR were shown to select for a restricted microbial population which appeared quite different in terms of composition with respect to the initial microbial cenosis in the activated sludge used as inoculum. On the basis of the sequencing of the major bands in the DGGE profiles, four main genera were identified: a Methylobacteriaceae bacterium, Flavobacterium sp, Candidatus Meganema perideroedes, and Thauera sp. The effects of nitrogen depletion (ie absence of growth) and pH variation were also investigated in the batch stage and compared with the SBR operative mode. Absence of growth did not stimulate higher PHA production, so indicating that the periodic feed regime fully exploited the storage potential of the enriched culture. Polymer production rates remained high between pH 6.5 and 9.5, whereas the HV content in the stored polymer strongly increased as the pH value increased. This study shows that polymer composition in the final batch stage can readily be controlled independently from the feed composition in the SBR. Copyright © 2005 Society of Chemical Industry     

Modeling of non-catalytic partial oxidation of natural gas under conditions found in industrial reformers

Non-catalytic partial oxidation of natural gas/O₂/H₂O mixture at elevated pressures was simulated kinetically using Chemkin package incorporating detailed reaction mechanisms of methane oxidation. The dependence of reaction time was investigated as a function of inlet temperature, system pressure, and O₂/CH₄ ratio. The conversion to products was predicted to complete within a residence time of less than 0.1 ms at pressures greater than 30 atm and temperatures higher than 1450 K. A minimum O₂/CH₄ ratio of 0.64 was found necessary for a complete methane conversion at the conditions typical for the industrial reformer. The effect of O₂/H₂O in the feed gas was examined computationally, and the results suggested that adding H₂O in the feed gas could be a viable tool for adjusting the H₂/CO ratio in the products and for controlling the flame temperature. Formations of higher order hydrocarbons and soot, which may play important roles in the actual fuel-rich conversion environment, are not considered in the present study.