Municipal MBR Research Articles

Optimal control of backwash scheduling for pumping energy saving: Application to the treatment of urban wastewater

An optimal control strategy for municipal wastewater MBR treatment was applied to investigate its efficiency in minimizing the pumping energy of the system. Based on a simple mathematical model to capture the dynamic evolution of the TransMembrane Pressure (TMP), an optimal switching instant between filtration/backwash was determined to reduce the supplementary pumping energy caused by fouling for a predefined net permeate volume. A MBR pilot treating municipal wastewater was used to generate dynamic data of TMP. The pilot was operated with two different strategies: a classical strategy with known operating conditions (10 min filtration and 45 s backwash) and an optimal strategy where the frequency was determined based on adjustment of model parameters. Results demonstrated that a satisfactory agreement was achieved between experimental data and model prediction. The optimal strategy was then applied experimentally on the MBR pilot. The two strategies were compared in terms of energy consumption and fouling degree. The results showed the feasibility of the optimal solution and its reliability to reduce the pumping energy of the system by 7 % and decrease residual fouling by 14 % compared with a classical strategy.

Energetic refurbishment of an existing large-scale MBR

Abstract Operations of an existing municipal MBR serving 80,000 inhabitants were improved energetically by implementing new automation routines for biology and membrane filtration. Finally, the MBR was refurbished by adding primary clarification and anaerobic sludge digestion to the treatment process, while specific energy consumption was reduced by one third to 0.65 kWh/m3 permeate produced. A combined heat and power engine generates electrical power on site from digester gas. The projected carbon footprint of plant operations will thus be halved by reducing indirect emissions from electricity consumption.

Clogging vs. fouling in immersed membrane bioreactors

Whilst the fouling of MBR membrane surfaces has been very extensively explored by the academic community, there is an increasingly widespread recognition by practitioners of the issue of clogging of membrane channels with sludge solids, sometimes termed “sludging”. The study undertaken has quantified this phenomenon using a bespoke test cell allowing a flat sheet membrane channel to be viewed directly during operation and the accumulated solids determined by digital image processing. Sludging behaviour has then been correlated both with the sludge properties, from sludge samples taken from both an industrial and municipal MBR, and the permeability decline rate data.The work has revealed the expected trends in fouling propensity, as quantified by the exponent n of the Δp/Δt = m.exp(nJ) correlation from classical flux-step tests. With zero membrane aeration the industrial samples exhibited sludging, the filling of the complete thickness of the membrane channel with sludge solids, whereas for municipal sludge the solids formed a cake layer which did not fill the channel. In the absence of sludging the permeability decline followed the expected pattern of increasing at the elevated soluble COD and capillary suction time values of the industrial sludge, compared with municipal sludge at the same solids concentration range (8–12 g.L−1). However, there was no evident correlation between fouling (permeability decline without sludging) and sludging: incipient sludging did not appear to influence permeability, though can be assumed to negatively impact on long-term operation, or relate to the sCOD concentration. Sludging instead appeared to depend on the sludge physical properties, and primarily the viscosity: sludge samples at high viscosities were found to exhibit a different air-scour pattern to that at normal MLSS concentrations.Outcomes suggest that sludging is caused by rheological conditions promoting bubble coalescence and bubble stream constriction, reducing the exposure of the membrane surface to scouring air.

Lessons learned during startup, testing and optimization of membrane bioreactors systems for enhanced nutrient removal

Membrane bioreactors are known for producing high quality effluent from wastewater treatment facilities in order to meet stringent regulatory requirements (Fleischer et al. 2005), accommodate growth (Vadiveloo & Cisterna 2008), provide opportunities for water reuse (Schmidt et al. 2011), and achieve other operational goals for various municipalities, utilities and industries (Cummings & Frenkel 2008). The process of testing, starting up and optimizing an MBR process for enhanced nutrient removal at the end of a construction project is often overlooked. Even a well-designed MBR can fail to meet expectations if the system is not properly configured during the startup phase, making this a critical step in any successful implementation of membrane technology. The startup phase of two municipal MBR plants were compared to demonstrate the importance of various strategies for initial process optimization, with a focus on lessons learned, techniques and performance expectations that can be applied to future projects.

10 years of Industrial & Municipal MBR Systems Lessons from the field

10 years of Industrial & Municipal MBR Systems Lessons from the field

Modelling the Long-Term Evolution of Permeability in a Full-Scale Municipal MBR: A Multivariate Statistical Modelling Approach

Modelling the Long-Term Evolution of Permeability in a Full-Scale Municipal MBR: A Multivariate Statistical Modelling Approach

Energy Reduction and Optimisation in Membrane Bioreactor Systems

One of the major components of MBR operating expenditure is energy consumption. This paper presents our six-year journey of energy reduction and optimization in MBR systems through various pilot and demonstration studies. Through comprehensive and systematic MBR optimisation studies, the specific energy consumption was reduced from 1.3 kWh m−3 to less than 0.8 kWh m−3 by increasing membrane flux and reducing aeration at 300 m3 per day pilot scale plants. Through energy audit, the key energy consumption components including process aeration, membrane scouring rate, SRT, MLSS level, MLSS recirculation, and energy efficient equipment selection were identified, and these were optimised one by one at 23,000 m3 per day municipal scale MBR demonstration plant after the baseline had been set up. The specific energy consumption was further reduced to 0.37 kWh m−3.

Market and design considerations of the 37 larger MBR plants in Europe

By the end of 2007, 10 years after the commissioning of the first full-scale municipal MBR plant in Europe, 37 large MBR plants with a nominal capacity greater than 5,000m3/d were in operation in the region, demonstrating the maturity of the technology. This article presents a review of these large MBR plants, not only in terms of market expectation, but also with regards to specific design considerations such as filtration flux, filtration layout, plant ‘retrofit’ and the inclusion of primary clarification. Due to the low operation costs (energy demand) as compared to side-stream membranes, submerged low-pressure filtration technologies will remain the standard for large MBR applications in the near future. At the time of the study, all the plants within this size segment in Europe were equipped by the two MBR filtration leaders GE/Zenon and Kubota, but other technologies should penetrate this market segment in the coming years.

Efficiency of mechanical pre-treatment on European MBR plants

In order to ensure a stable and reliable operation of municipal MBR plants, an enhanced mechanical pre-treatment of the raw wastewater is essential. Removal of hair, fibrous material and other contraries which can lead to operational problems at the membrane modules is of particular importance. As the number of full scale applications is continuously increasing, now appropriate investigations can be carried out to determine the removal efficiency of different units (screens, sieves) or different combination of units (multi staged system). First results of such investigations on two German MBR plants were already presented [F.-B. Frechen, W. Schier and M. Wett, Water Practice & Technology, Vol. 1, No. 3, IWA Publishing, 2006, doi: 10.2166/WPT.2006057.]. In 2006, DESEE executed further investigations on another three wwtps in The Netherlands, UK and Germany. This paper summarizes the results, thus updates the information available, discusses the present findings and gives an outlook on future developments.

Pre-treatment of municipal MBR applications

Since the mid nineties the MBR technology has been introduced into municipal wastewater treatment in Europe. First wwtps went in operation performing a conventional mechanical treatment without any advanced mechanical pre-treatment unit. After a short operation period braids were hanging between the membranes and hence module sludging was observed. Thus, mechanical pre-treatment was upgraded introducing sieves primarily to reduce hairs and fibrous substances. Today, however, knowledge is still relatively poor concerning effectiveness and treatment efficiency of a large number of aggregates that had been brought to market, varying in gap size, gap geometry and others. This paper describes the fundamentals of sieving, gives an overview of mechanical pre-treatment on municipal MBR plants and finally presents the results of investigations quantifying and comparing the removal efficiency of different types of sieves.

Pre-Treatment of Municipal MBR Applications in Germany- Current Status and Treatment Efficiency

Since mid 1999 MBR technology is introduced into domestic wastewater treatment in Germany. First wwtps went in operation performing a conventional mechanical treatment (covering screens, grit chambers and grease traps) without any advanced mechanical pre-treatment stage. After a short operation period module-clogging and hence module sludging was observed. Thus, mechanical pre-treatment was upgraded introducing sieves, first of all to reduce hairs and fibrous substances. But today knowledge is relatively poor concerning effectiveness and treatment efficiency of the whole bunch of aggregates that had been brought to market and vary e.g. in gap size and gap geometry. This paper gives the basics of sieving, the current status of mechanical pre-treatment on German municipal MBR plants and exemplifies an investigation to determine treatment efficiency of two different sieve aggregates.

MBR-technology in municipal wastewater treatment: challenging the traditional treatment technologies

In The Netherlands a development programme for the application of the MBR technology in municipal wastewater treatment has started. This paper briefly describes this development programme and goes into detail for the first step: a large pilot plant study at the Beverwijk WWTP. Under the supervision of DHV Water four different membrane systems from Kubota, Mitsubishi, X-Flow and Zenon were extensively tested. The objectives set for the study were more than achieved. The available world knowledge regarding municipal MBR was extremely limited and often very specific for a particular country's wastewater and wastewater flow characteristic. The conditions set by the Dutch situation were the first of its kind and lead to new methods of MBR optimisation. After almost two years of intensive research and further development of the technological feasibility of the MBR for The Netherlands, it has been decided to extend it to demonstration scale.