The cost of a large-scale hollow fibre MBR

A cost sensitivity analysis was carried out for a full-scale hollow fibre membrane bioreactor to quantify the effect of design choices and operational parameters on cost. Different options were subjected to a long term dynamic influent profile and evaluated using ASM1 for effluent quality, aeration requirements and sludge production. The results were used to calculate a net present value (NPV), incorporating both capital expenditure (capex), based on costs obtained from equipment manufacturers and full-scale plants, and operating expenditure (opex), accounting for energy demand, sludge production and chemical cleaning costs.Results show that the amount of contingency built in to cope with changes in feedwater flow has a large impact on NPV. Deviation from a constant daily flow increases NPV as mean plant utilisation decreases. Conversely, adding a buffer tank reduces NPV, since less membrane surface is required when average plant utilisation increases. Membrane cost and lifetime is decisive in determining NPV: an increased membrane replacement interval from 5 to 10 years reduces NPV by 19%. Operation at higher SRT increases the NPV, since the reduced costs for sludge treatment are offset by correspondingly higher aeration costs at higher MLSS levels, though the analysis is very sensitive to sludge treatment costs. A higher sustainable flux demands greater membrane aeration, but the subsequent opex increase is offset by the reduced membrane area and the corresponding lower capex.     

SBR工艺处理低负荷城市污水经验探讨

以天津市某污水厂SBR工艺的调试运行为例,阐述了SBR工艺的污泥培养过程,并通过试运行期进出水水质的对比分析,得出了在进水有机负荷偏低的情况下,适用于该污水厂的SBR工艺的运行参数,即进水1h、曝气4h、静沉2h、排水1h、运行周期为8h的运行方式。在该运行条件下,出水水质能完全达到设计要求,可为利用生物法处理低负荷污水的工艺设计和运行提供参考和经验。     

The optimum operational condition of membrane bioreactor (MBR): cost estimation of aeration and sludge treatment

A methodology to obtain the most economical operational condition of membrane bioreactor (MBR) is developed. In order to achieve the optimum design parameters of MBR with which operational costs are minimized, aeration and sludge treatment costs were estimated for various operational conditions. Generally sludge treatment cost and aeration cost were inversely proportional to each other, which means sludge treatment cost is minimized when aeration cost is maximized and vice versa. Therefore, there might exist an optimum point between the two extreme cases. However, sludge treatment cost turned out to overwhelm the aeration cost over the reasonable operational conditions. Therefore, sludge minimization was considered to be a key for the economical operation of MBR. In the case of typical municipal wastewater of which COD was 400mgL(-1), steady-state MLSS was expected to increase from 11,000 to 15,000mg/L without sludge removal when HRT was decreasing from 16 to 12h. For the range of operational conditions considered in this study, economically optimum HRT and target MLSS were turned out to be 16h and 11,000mg/L, respectively. Under this condition, aeration for the biodegradation of organic matters would be 13.3m(3) air/min when influent was 1000m(3)/day.     

Using the sewerage system main conduits for biological treatment. Greater Tel-Aviv as a conceptual model

The long-sought idea of using main sewerage conduits as a step-fed plug-flow reactor, where biological sludge is introduced at the head of the main pipelines (hence loop system) and where aeration is provided at various points along the loop, was investigated in this paper in both a bench-scale physical model and using the Greater Tel-Aviv (Dan Region) sewerage with design population of 1.3 million and flow of 300,000 m³ day⁻¹, as a conceptual model.Due to the inherent advantages of a step-fed plug-flow reactor where high substrate concentrations are maintained along most of the length of the reactor, (except for the final section which provides effluent polishing), the viability of the biomass is 3–5.2-fold higher than the one usually encountered in a conventional activated sludge plant, thus substantially increasing its rate and efficiency of organic substrate removal.It has been shown that in the case of Greater Tel-Aviv, replacing the activated sludge conventional treatment plant with the loop system (with only secondary clarifiers to provide the return biological sludge), or alternatively resorting to the loop system instead of doubling an existing overloaded treatment plant, will produce final efluents well below the requirements of 25 mg l⁻¹ BOD₅ and will provide savings of more than 50% in construction costs. An additional advantage of corrosion control along the main conduits thus increasing their longevity is also discussed.     

Including greenhouse gas emissions during benchmarking of wastewater treatment plant control strategies

The main objective of this paper is to demonstrate how greenhouse gas (GHG) emissions can be quantified during the evaluation of control strategies in wastewater treatment plants (WWTP). A modified version of the IWA Benchmark Simulation Model No 2 (BSM2G) is hereby used as a simulation case study. Thus, the traditional effluent quality index (EQI), operational cost index (OCI) and time in violation (TIV) used to evaluate control strategies in WWTP are complemented with a new dimension dealing with GHG emissions. The proposed approach is based on a set of comprehensive models that estimate all potential on-site and off-site sources of GHG emissions. The case study investigates the overall performance of several control strategies and demonstrates that substantial reductions in effluent pollution, operating costs and GHG emissions can be achieved when automatic control is implemented. Furthermore, the study is complemented with a scenario analysis that examines the role of i) the dissolved oxygen (DO) set-point, ii) the sludge retention time (SRT) and iii) the organic carbon/nitrogen ratio (COD/N) as promoters of GHG emissions. The results of this study show the potential mechanisms that promote the formation of CO₂, CH₄ and N₂O when different operational strategies are implemented, the existing synergies and trade-offs amongst the EQI, the OCI and TIV criteria and finally the need to reach a compromise solution to achieve an optimal plant performance.     

Cost-efficient operation of a denitrifying activated sludge process

In this paper, the choice of optimal set-points and cost minimizing control strategies for the denitrification process in an activated sludge process are treated. In order to compare different criterion functions, simulations utilizing the COST/IWA simulation benchmark are considered. By means of operational maps the results are visualized. It is found that it is easy to distinguish set-point areas where the process can be said to be efficiently controlled in an economic sense. The characteristics of these set-point areas depend on the chosen effluent nitrate set-point as well as the distribution of the different operating costs. It is also discussed how efficient control strategies may be accomplished.     

Model-based energy optimisation of a small-scale decentralised membrane bioreactor for urban reuse

The energy consumption of a small-scale membrane bioreactor, treating high strength domestic wastewater for community level wastewater recycling, has been optimised using a dynamic model of the plant. ASM2d was chosen as biological process model to account for the presence of phosphate accumulating organisms. A tracer test was carried out to determine the hydraulic behaviour of the plant. To realistically simulate the aeration demand, a dedicated aeration model was used incorporating the dependency of the oxygen transfer on the mixed liquor concentration and allowing differentiation between coarse and fine bubble aeration, both typically present in MBRs. A steady state and dynamic calibration was performed, and the calibrated model was able to predict effluent nutrient concentrations and MLSS concentrations accurately. A scenario analysis (SCA) was carried out using the calibrated model to simulate the effect of varying SRT, recirculation ratio and DO set point on effluent quality, MLSS concentrations and aeration demand. Linking the model output with empirically derived correlations for energy consumption allowed an accurate prediction of the energy consumption. The SCA results showed that decreasing membrane aeration and SRT were most beneficial towards total energy consumption, while increasing the recirculation flow led to improved TN removal but at the same time also deterioration in TP removal. A validation of the model was performed by effectively applying better operational parameters to the plant. This resulted in a reduction in energy consumption by 23% without compromising effluent quality, as was accurately predicted by the model. This modelling approach thus allows the operating envelope to be reliably identified for meeting criteria based on energy demand and specific water quality determinants.     

Comparison of control strategies for nitrogen removal in an activated sludge process in terms of operating costs: a simulation study

In this paper several control strategies for nitrogen removal are proposed and evaluated in a benchmark simulation model of an activated sludge process. The goal is to determine which control strategy delivers better performance with respect to plant operating costs. In the study, constant manipulated variables and various PI and feedforward control strategies are tested and compared with predictive control, which uses an ideal process model. The control strategies differ in the information used about the process (number of sensors and sensor location) and in the complexity of the control algorithms. To determine the set-points that yield optimal operating costs, an operational map is constructed for each control strategy. Results of the simulation show that with PI and feedforward controllers almost the same optimal operating costs can be achieved as with more advanced MPC algorithms under various plant operating conditions. More advanced control algorithms are advantageous only in cases where the plant is highly loaded and if stringent effluent fines are imposed by legislation.     

The microbiology of an activated sludge waste-water treatment plant chemically treated for phosphorus removal

Microbiological research was conducted on a dual, secondary wastewater treatment system which was part of The Pennsylvania State University wastewater treatment plant. Each aeration basin received identical wastewater which was the effluent from a high rate trickling filter. One of the aeration basins was dosed with aluminum sulfate for the purpose of phosphorus removal. The other aeration basin (control) was operated in the conventional manner without alum addition. Plate counts performed on combined chemical-biological sludge and control activated sludge revealed that a higher number of viable micro-organisms was contained in the chemical-biological sludge, but the magnitude of difference between the two sludges was significant depending on the culture medium employed. Results suggest the aluminum flocs formed in the chemical-biological treatment enmesh dispersed wastewater micro-organisms, some of which are qualitatively unlike those indigenous to natural activated sludge. The combined chemical-biological sludge contained significantly higher numbers of lipolytic, gelatinolytic, and thiosulfate oxidizing micro-organisms and, possibly, fewer nitrite oxidizing micro-organisms than did control activated sludge. Alum did not appear to affect flagellated protozoa in mixed liquor; however, amoeboid and ciliated protozoa were found less frequently in alum dosed than in control mixed liquor. The settled effluent from the combined chemical-biological aeration basin generally contained fewer total coliforms, fecal coliforms, and fecal streptococci than did counterpart control effluents.     

The cost of a package plant membrane bioreactor

The capital and operating costs associated with a small package plant MBR for small-scale domestic duty has been appraised based on a medium-strength municipal wastewater. The three main membrane configurations were considered, these being multi-tube, hollow fibre and flat sheet, with the most appropriate plant design chosen for each configuration. The analysis proceeded via a consideration of the estimated amortised capital costs of the plant individual components and their installation, coupled with operating costs based largely on energy demand and residuals management. Energy demand was calculated from aeration and pumping costs, with aeration based on a combination of empirical relationships for membrane aeration and mass balance, and the modified Activated Sludge Model version 2 used for estimating tank size and sludge generation. Results indicate that it is possible to produce a single household MBR at a capital cost similar to the current market cost for package treatment plants. Desludging and maintenance of these plants is similar but power requirements for an MBR are around 4 times that associated with more conventional package plants. Economies of scale exist from 6-20 p.e. plants but above 20 p.e. there is little cost difference per head, due to the design assumptions made. CAPEX and OPEX are to some extent interchangeable; reductions in CAPEX are associated with an increase in OPEX and vice versa. Whilst costs are high, the market for package MBRs is significantly influenced by the recycling potential of the effluent produced.     

Feasibility of using a chlorination step to reduce excess sludge in activated sludge process

The ultimate disposal of excess sludge generated from activated sludge processes has been one of the most challenging problems for wastewater treatment utilities. Previous work has shown that excess sludge can be minimized successfully by using sludge ozonation to dissolve it into substrates to be oxidized in the aeration tank. However, this approach is a costly option. Therefore, as an alternative solution, we propose to use chlorination to replace ozonation in excess sludge minimization in the light of operational cost. To investigate the feasibility of this low cost approach, this paper mainly focuses on the effect of chlorination on sludge reduction rate, formation of trihalomethanes, sludge settleability, and effluent quality. Two identical activated sludge membrane bioreactors were continuously operated with synthetic wastewater under the same operation conditions for several months. During this period, one pilot unit was used as the reference system without chlorination of excess sludge, while another served as a testing unit, where excess sludge was taken out for conducting chlorination at a dose of 133mg/g MLSS every day and the chlorinated liquor was then returned to the aeration tank. The sludge production rate and the water quality of both the units were analyzed daily. It was observed that the sludge production could readily be reduced by 65% once the chlorination treatment was involved. However, the chlorination treatment also resulted in poor sludge settleability as well as significant increase of soluble chemical oxygen demand in the effluent, which creates potential difficulties in the operation of a conventional treatment plant with gravity clarifiers. However, it has been demonstrated that by integrating the immersed membrane into the activated sludge process these difficulties can be overcome effectively.     

Grey-box modelling of aeration tank settling

A model of the concentrations of suspended solids (SS) in the aeration tanks and in the effluent from these during Aeration tank settling (ATS) operation is established. The model is based on simple SS mass balances, a model of the sludge settling and a simple model of how the SS concentration in the effluent from the aeration tanks depends on the actual concentrations in the tanks and the sludge blanket depth. The model is formulated in continuous time by means of stochastic differential equations with discrete-time observations. The parameters of the model are estimated using a maximum likelihood method from data from an alternating BioDenipho waste water treatment plant (WWTP). The model is an important tool for analyzing ATS operation and for selecting the appropriate control actions during ATS, as the model can be used to predict the SS amounts in the aeration tanks as well as in the effluent from the aeration tanks.     

啤酒污泥用作城市污水厂种泥的试验研究

为考察啤酒厂污水处理站的脱水污泥（简称啤酒污泥）用作城市污水厂接种污泥的可行性，摸索污泥的培养与驯化规律，采用连续操作、全流量同步培养和驯化方法，在处理能力为500m^2／d的UNITANK池中对啤酒污泥进行了培养和驯化。试验结果表明，啤酒污泥完全可以作为城市污水处理厂的接种污泥使用，而且培养时间短，出水水质好。曝气0．5h、厌氧搅拌1h时，活性污泥增长最快。将DO控制在2mg／L左右有利于活性污泥的增长；当DO长时间在7mg／L以上时，污泥浓度下降趋势明显。污泥浓度达到2000mg／L所需的培养驯化时间仅为5d；使出水水质达到一级B标准所需的培养时间约为6d。这种培养、驯化方法和经验可为其他城市污水处理厂的建设和运行提供参考。     

Influence of operational conditions on the performance of a mesh filter activated sludge process

Recently, a new type of wastewater treatment system became the focus of scientific research, the mesh filter activated sludge system. It is a modification of the membrane bioreactor where a membrane filtration process serves to separate the sludge from the purified effluent. The difference is that a mesh filter is used instead of the membrane. Due to the much larger pore size of the mesh, the effluent is not of the same excellent quality as with membrane bioreactors. Nevertheless, it still resembles the quality of the now most widely used standard treatment system, where settling tanks are used to retain the activated sludge. At the same time, the new system features all the other advantages of membrane bioreactors including elevated sludge concentrations resulting in decreased volumina of basins and complete substitution of the settling tank. Therefore, this process presents a potential future alternative where a small footprint of the plant is required. However, so far only a few preliminary studies on this innovative process type have been done. In this paper, the effects of suspended solids concentration, flux rate as well as aeration rate on the effluent quality are discussed. Furthermore, the characteristic of the sludge floc was identified as a factor of vital importance. Therefore, another influencing parameter, the food to microorganism (F/M) ratio, which is known to have a significant effect on floc characteristics, was studied. The main result demonstrated that the process was very effective under most of the operation conditions. The suspended solids concentration in the effluent was below 12 mg l(-1), the average COD in the effluent was between 24 and 45 mg l(-1) and the BOD(5) was lower than 5 mg l(-1). High flux rates of up to 150 l m(-2)h(-1) were also achieved.     

Minimization of excess sludge production for biological wastewater treatment

Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. This paper reviews current strategies for reducing sludge production based on these mechanisms: lysis-cryptic growth, uncoupling metabolism, maintenance metabolism, and predation on bacteria. The strategies for sludge reduction should be evaluated and chosen for practical application using costs analysis and assessment of environmental impact. High costs still limit technologies of sludge ozonation-cryptic growth and membrane bioreactor from spreading application in full-scale WWTPs. Bioacclimation and harmful to environment are major bottlenecks for chemical uncoupler in practical application. Sludge reduction induced by oligochaetes may present a cost-effective way for WWTPs if unstable worm growth is solved. Employing any strategy for reducing sludge production may have an impact on microbial community in biological wastewater treatment processes. This impact may influence the sludge characteristics and the quality of effluent.     

AmOn一体化污水生物处理装置的开发

AmOn一体化反应器将传统生物处理工艺的反应、沉淀和污泥回流集中于一个反应器中完成,并以自主开发的新型射流扩散式曝气代替了传统的鼓风曝气、表面曝气等形式,反应器的容积负荷大,水力停留时间短,节省了基建投资与运行费用,降低了操作管理强度,增加了系统运行的可靠性。通过自控系统的调节,可根据不同进水水质和出水要求,沿反应进程自动调节曝气量和搅拌程度,根据要求实现脱氮和除磷,具有广阔的应用前景。     

Automatic control of the activated sludge process—II. Efficacy of control strategies

Through the use of computer simulation, the efficacies of the following strategies for control of the activated sludge process were evaluated: single loop feedback control; multiple loop feedback control; single loop feedforward control; feedforward/feedback control; and multiple loop feedforward control. The best improvement in system performance was found with multiple loop feedforward control although the full benefits of the technique could not be achieved due to saturation of the manipulated variables. During the research two types of plants were simulated: Case I in which the concentration of suspended solids in the final effluent decreased as the MLSS concentration entering the settler increased, and Case II in which the effluent suspended solid increased. The best choices for the measured and controlled variables in the multiple loop feedforward control systems depended heavily upon the type of behavior exhibited by the final settler.     

The luxury uptake phenomenon for removal of phosphates from municipal wastewater

Batch experimental studies were conducted to qualitatively assess the Luxury Uptake mechanism and relevant parameters for removal of phosphates from municipal wastewaters by activated sludge. The experiments were conducted with return activated sludge and primary effluent samples from the Bonnybrook Sewage Treatment Plant. Calgary. Alberta. Canada.Aeration rates. aeration time and return sludge/primary effluent ratio were shown to be important parameters affecting biological phosphate removal. High phosphate removals in excess of growth requirements, demonstrated in the laboratory indicate Luxury Uptake by sludge microorganisms. The controversial findings of the Carbon Limitation and Calcium Precipitation Theories were not applicable in this case.     

低DO下曝气方式对分段进水脱氮工艺的影响

采用分段进水生物脱氮工艺处理小区生活污水,考察了在低DO条件下,不同曝气方式对硝化率及污泥沉降性能的影响。结果表明,在曝气量为0．27m^3／h、MLSS平均为2700mg／L左右、好氧区的DO为0．26～2．5mg／L的条件下,当进水氨氮为44～55mg／L时,对氨氮的去除率保持在95％以上,对COD的去除率〉90％;当控制好氧区第1、2格室的DO分别为0．5～0．7和1．0～1．2mg／L时,系统的硝化率维持在90％以上,出水中的氨氮〈2mg／L;在恒定曝气量下,向进水中投加有机碳源,当水质改变较快时,容易引起丝状菌污泥膨胀,但通过恒DO曝气控制,可使污泥的沉降性能得到改善。