厌氧膨胀颗粒污泥床反应器水力优化数值模拟研究

厌氧膨胀颗粒污泥床（EGSB）反应器内部流场及浓度场分布影响反应器运行效率,污染物不均匀分布会导致反应器内微生物无法与污染物充分接触,使处理效率下降。对EGSB反应器内部流场及浓度场进行模拟,研究污染物浓度分布对处理效率的影响,可实现对反应器结构的优化。在流体力学模型的组分浓度输运方程源项中嵌入厌氧消化数学模型,构造CFD-厌氧消化耦合模型进行模拟。结果表明,EGSB反应器内部污染物浓度分布呈现中轴处高近壁处低的不均匀分布,在一定高度处甚至出现死区,不利于微生物的生长,严重降低了反应器处理效率。通过在反应器内增设挡流板,使中轴处污染物随水流向壁面分流,可以有效提高近壁面附近污染物浓度,减小死区体积,提高反应器处理效率。     

Modeling the influence of temperature on degree of concentration polarization in reverse osmosis systems.

A model describing the influence of temperature on degree of concentration polarization is proposed. The model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) transport characteristics of membrane are invariant with coordinate; (3) specific water permeability of the membrane is based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence of membrane rejection is assumed to be linear. Proposed models permit quantitative correlations of longitudinal mass flow and degree of concentration polarization at different operating temperatures. It enables analysis of the influence of temperature, mass flow, bulk concentration, axial velocity, channel geometry, physical properties and membrane rejection on longitudinal distribution of concentration polarization degree. The submitted model does not contain digital integration and can be segmented into optimization algorithms.     

Performance evaluation and effect of biogas circulation rate of a bubble column for biological desulfurization

Biological desulfurization using a bubble column reactor was investigated in a continuous biogas treatment. Rapid biogas circulation between the digester and the bubble column for biological desulfurization was used to stimulate the gas-liquid mass transfer of H(2)S. A positive correlation between the biogas circulation rate and H(2)S removal rate was observed. Moreover, the increase in the circulation rate stimulated the O(2) mass transfer, eventually translating into an increase in sulfate production from the oxidation of H(2)S. Throughout the continuous experiment, the reactor retained sufficient levels of sulfide-oxidizing bacteria. A comparison of the results of the continuous biogas treatment and batch tests suggests that the gas-liquid mass transfer rate of H(2)S was the rate-limiting step in the biological desulfurization in the reactor, indicating that the mass transfer efficiency of H(2)S needs to be improved to enhance the desulfurization performance.     

Application of PTFE membrane for ammonia removal in a membrane contactor

The feasibility of a membrane contactor system for ammonia removal was studied. The mass transfer coefficient was used to quantitatively compare the effect of various operation conditions on ammonia removal efficiency. Effective removal of ammonia was possible with a Polytetrafluoroethylene (PTFE) membrane contactor system at all tested conditions. Among the various operation parameters, contact time and solution pH showed significant effect on the ammonia removal mechanism. The overall ammonia removal rate was not affected by influent suspended solution concentration unlike other pressure driven membrane filtration processes. Also the osmotic distillation phenomena which deteriorate the mass transfer efficiency can be minimized by preheating of influent wastewater. A membrane contactor system can be a possible alternative to treat high strength nitrogen wastewater by optimizing operation conditions such as stripping solution flow rate, influent wastewater temperature, and influent pH.     

A comparison of BNR activated sludge systems with membrane and settling tank solid-liquid separation.

Installing membranes for solid-liquid separation into biological nutrient removal (BNR) activated sludge (AS) systems makes a profound difference not only to the design of the membrane bio-reactor (MBR) BNR system itself, but also to the design approach for the whole wastewater treatment plant (WWTP). In multi-zone BNR systems with membranes in the aerobic reactor and fixed volumes for the anaerobic, anoxic and aerobic zones (i.e. fixed volume fractions), the mass fractions can be controlled (within a range) with the inter-reactor recycle ratios. This zone mass fraction flexibility is a significant advantage of MBR BNR systems over BNR systems with secondary settling tanks (SSTs), because it allows changing the mass fractions to optimise biological N and P removal in conformity with influent wastewater characteristics and the effluent N and P concentrations required. For PWWF/ADWF ratios (fq) in the upper range (fq approximately 2.0), aerobic mass fractions in the lower range (f(maer) < 0.60) and high (usually raw) wastewater strengths, the indicated mode of operation of MBR BNR systems is as extended aeration WWTPs (no primary settling and long sludge age). However, the volume reduction compared with equivalent BNR systems with SSTs will not be large (40-60%), but the cost of the membranes can be offset against sludge thickening and stabilisation costs. Moving from a flow unbalanced raw wastewater system to a flow balanced (fq = 1) low (usually settled) wastewater strength system can double the ADWF capacity of the biological reactor, but the design approach of the WWTP changes away from extended aeration to include primary sludge stabilisation. The cost of primary sludge treatment then has to be offset against the savings of the increased WWTP capacity.     

Radial distribution modeling of liquid-phase phenol concentration in a liquid-solid fluidized bed photoreactor

A fluidized bed photoreactor with titanium dioxide-immobilized spherical activated carbon particles was examined. The light intensity profile was modeled using the Lambert-Beer rule for the modeling of the radial distribution of liquid-phase phenol concentration in the fluidized bed photoreactor, when considering the reactor composed of numerous differential annular drums and no mass transfer between drums. The model could be well matched with the experimental data which indicated the liquid flow rate of 13.8 L/min was the optimum in the balance of flow rate-related light penetration and photocatalyst concentration. By integration of liquid-phase phenol concentration along the radius, photocatalytic oxidation performance of the photoreactor was evaluated in comparison with the experimental data and model prediction. The results showed that the errors were less than 30% for most of the predictions. It is suggested that mass transfer and flow rate difference along the radial direction should be considered to obtain more precise prediction.     

Design and performance of BNR activated sludge systems with flat sheet membranes for solid-liquid separation.

The use of immersed membranes for solid-liquid separation in biological nutrient removal activated sludge (BNRAS) systems was investigated at lab scale. Two laboratory-scale BNR activated sludge systems were run in parallel, one a MBR system and the other a conventional system with secondary settling tanks. Both systems were in 3 reactor anaerobic, anoxic, aerobic UCT configurations. The systems were set up to have, as far as possible, identical design parameters such as reactor mass fractions, recycles and sludge age. Differences were the influent flow and total reactor volumes, and the higher reactor concentrations in the MBR system. The performances of the two systems were extensively monitored and compared to identify and quantify the influence of the membranes on system response.The MBR UCT system exhibited COD, FSA, TKN, TP and TSS removals that were consistently equivalent or superior to the conventional system. Better P removal in the MBR was attributed to lower observed P uptake in the anoxic zone. High nitrate loads to the anoxic reactor appeared to be the determining factor in stimulating P uptake.The MBR UCT system had a greater sludge production than the conventional system. This was partly attributable to the retention of all solids in the MBR reactor. For steady state design this increase is accommodated by increasing the influent unbiodegradable particulate COD fraction. Additionally an attempt was made to determine the Alpha values in the oxygen transfer rate.This paper briefly summarises and compares the results from both systems, and the conclusions that can be drawn from these results.     

Reactor scale-up in AOPs: from laboratory to commercial scale.

A procedure to scale-up photoreactors employed in AOPs using laboratory information has been developed. Operating with a model compound the proposed procedure was applied to the decomposition of formic acid in water solution using hydrogen peroxide and UV radiation. With laboratory experiments the parameters of the kinetic equation were obtained in a small batch reactor operated within a recycling apparatus. The whole system was modeled employing radiation and mass balances. These balances were used together with a non-linear parameter estimator to derive the model kinetic constants. Then, these results were used in the modeling of the large-scale reactor to predict exit conversions in an isothermal, continuous, tubular flow reactor that is 2 m long and has a volume of 12 I. Once more, radiation and mass balances were used to predict formic acid output concentrations. Experimental data in the large-scale apparatus are in good agreement with theoretical predictions.     

Analysing sludge balance in activated sludge systems with a novel mass transport model

In activated sludge systems the mechanically treated wastewater is biologically cleaned by biomass (activated sludge). The basic requirement of an efficient biological wastewater treatment is to have as a high biomass concentration in the biological reactor (BR) as possible. The activated sludge balance in activated sludge systems is controlled by the settling, thickening, scraper mechanism in the secondary settling tank (SST) and sludge returning. These processes aim at keeping maximum sludge mass in the BR and minimum sludge mass in the SST even in peak flow events (storm water flow). It can be, however, only reached by a high SST performance. The main physical processes and boundary conditions such as inhomogeneous turbulent flow, geometrical features of the SST, wastewater treatment plant (WWTP) load, return sludge flow, sludge volume index etc. all influence settling thickening and sludge returning. In the paper a novel mass transport model of an activated sludge system is presented which involves a 2-dimensional SST model coupled with a mixed reactor model of the biological reactor. It makes possible to investigate different sludge returning strategies and their influence on the sludge balance of the investigated activated sludge system, furthermore, the processes determining the flow and concentration patterns in the SST. The paper gives an overview on the first promising model results of a prevailing peak flow event investigation at the WWTP of Graz.     

双室(层)曝气生物滤池充氧性能及流态特征

研究了双室 (层 )曝气生物滤池 (DBAF)的充氧性能和流态特征 ,结果表明氧传质系数与曝气强度成正比 ,加滤料前后氧传质系数的差别与曝气强度的大小有关 ,曝气强度较低时 ,两者相差4 0 % ,随着曝气强度的增加 ,两者逐渐接近。DBAF可用n值为 8～ 10阶式CSTR描述 ,流态接近推流式反应器。降低水力负荷和增大滤料高度时 ,DBAF的流态更趋近于推流式     

Study of rotating biological contactor performance in wastewater treatment using multi-culture biofilm model.

The rotating biological contactor (RBC) process offers the specific advantages of a biofilm system in treatment of wastewater for removal of soluble organic substances and stabilisation of nitrogen compounds. Being a unique adaptation of the moving-medium biofilm system, it facilitates easy and effective oxygen transfer. However, process optimisation and adaptability under different conditions remain challenging tasks for the efficient use of this technology. Although modelling helps to study system performance under various external conditions, satisfactory mathematical representation is lacking due to the dynamic nature of the RBC system. In this work, it has been attempted to frame a mathematical model for a three-stage RBC process in simple and realistic ways. The model is based on the well-known principles of one-dimensional mass transfer and transport of substances. The biochemical conversion process is adopted from the Activated Sludge Model No. 3 which represents a mixed-culture biomass environment. Owing to the dynamic nature of oxygen transfer, which is the typical limiting substrate in municipal wastewaters, the boundary layer is assumed to be completely mixed and concentrations averaged over the entire volume. A part of the boundary layer is assumed to be exposed to air and the rest submerged in bulk liquid at all times. The model results are compared with laboratory-scale experimental data available at 25 'C. Sensitivity analysis is performed with the model to study the significance of variation of different system parameters or the surrounding environment. In essence, the model helps to explore the flexibilities within a RBC system and optimise the process design accordingly.     

我国跨流域调水管理问题探讨

 在我国跨流域调水存在“体制不顺、机制不全、原则不明”问题的基础上,较全面分析了我国跨流域调水的各方面问题,并绘制了我国跨流域调水的问题树。借鉴国外跨流域调水管理经验以及水资源综合管理理念,对我国跨流域调水管理进行了探讨,重点在跨流域调水的管理机制与体制、规划期管理、取水管理、用水管理等方面提出了许多建议。     

Operation of a SHARON nitritation reactor: practical implications from a theoretical study.

This contribution deals with the behaviour of a SHARON reactor for nitrogen removal from wastewater streams with high ammonium concentrations. A system analysis is performed on a two-step nitrification model, describing the behaviour of such a reactor. Steady states are identified through direct calculation using a canonical state space model representation. Practical operation of a SHARON reactor aims at reaching ammonium conversion to nitrite only (nitritation), while suppressing further conversion to nitrate. It is shown how this desired behaviour can be obtained by setting the dilution rate dependent on the influent ammonium concentration. The impact of microbial growth characteristics on the suitable operating region is examined, as well as the effect of reactor temperature and pH. Advice is given for robust reactor design and operation.     

Can we assess the model complexity for a bioprocess: theory and example of the anaerobic digestion process.

In this paper we propose a methodology to determine the structure of the pseudo-stoichiometric coefficient matrix K in a mass balance based model, i.e. the maximal number of biomasses that must be taken into account to reproduce an available data set. It consists in estimating the number of reactions that must be taken into account to represent the main mass transfer within the bioreactor. This provides the dimension of K. The method is applied to data from an anaerobic digestion process and shows that even a model including a single biomass is sufficient. Then we apply the same method to the "synthetic data" issued from the complex ADM1 model, showing that the main model features can be obtained with two biomasses.     

COUPLING DISTINCT AND CONTINUOUS MEDIUM MODEL FOR FLOW ANALYSIS IN A FRACTURED ROCK MASS AND ITS APPLICATION

Fractures in a rock mass can be divided into dominant fracture system and network fracture system. An approach for the analysis of three dimensional ground water flow in a fractured rock mass is presented, in which flow in the dominant fracture system is described by a distinct medium model while flow in the network fracture system plus rock matrices (if considered) is described by a continuous medium model, and the two models are coupled by hydraulic head and flux. The coupling model facilitates to calculate one-by-one the fluid flow in the dominant fractures which are functioned as the major water transmission conduits, and it avoids unnecessary calculating fluid flow in individual network fractures which are numerous in number. In this way, the method can be applied to a large-sized calculation domain. In addition, a method of using network geometry data to calculate its equivalent porous permeability is presented in the paper, and the model implementation of water source and sink such as the pumping     

Treatment of source-separated urine by a combination of bipolar electrodialysis and a gas transfer membrane.

Urine contains nutrients which can be applied usefully as a fertiliser in agriculture, but the relatively high pH can lead to ammonia evaporation. Electrodialysis with bipolar membranes was combined with an additional mass transfer unit in order to render a product containing ammonium and phosphate at a low pH. In one case, the additional mass transfer unit consisted of bubble columns placed in acid and basic concentrate streams, connected with a circulating gas phase. In the other case, the unit consisted of a gas-filled (hydrophobic) membrane placed in between the circulating acid and basic concentrate streams. The results showed that ammonia was transferred through the gas phase, but also carbonate, which is present in stored urine originating from the hydrolysis of urea. Although the pH in the product stream decreases initially, it rises above pH 7 at longer operation times. This pH increase can be attributed to a combination of proton compensating effects. The use of ammonia-selective membranes for the transfer into the acid concentrate could provide a solution to generate an ammonium phosphate product at low pH and high recoveries.