A novel process maximizing energy conservation potential of biological treatment: Super fast membrane bioreactor

2018

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BACKGROUND This paper aimed to provide a critical appraisal on maximizing sludge generation and energy conservation in high‐rate activated sludge (AS) configurations. The role of gravity settling and the positive attributes of high rate membrane bioreactors were emphasized. The appraisal covered data reported in the literature on 40 different experiments testing high‐rate AS configurations for sludge generation and energy conservation. RESULTS In systems with gravity settling, effluent chemical oxygen demand (COD) was higher than 125 mg L−1 in 60% of the experiments, with similarly high effluent soluble COD values. In high‐rate MBR systems, permeate COD fluctuated around 12–18 mgCOD L−1; in gravity systems, COD loss in the effluent was higher than 200 mg L−1 in 17 runs (65%) and 300 mg L−1 in 12 runs (46%). Corresponding observed yields were only 9–43%. Membrane systems consistently yielded much higher observed yields of 50–60%. CONCLUSION For energy recovery, AS systems require a major transition, reducing the sludge age to 1.0–2.0 d; only high‐rate systems are capable of maximizing energy conservation. This argument does not apply to the contact stabilization process, which is inherently unsuitable for energy recovery. A transition is also needed to replace gravity settling by membrane systems for effective control of particulate and soluble COD components. © 2018 Society of Chemical Industry

Section: Resultsmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Which activated sludge configurations qualify for maximizing energy conservation – Why?

Orhon

Allı

2018

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“…Obviously, this would require extremely high rate system operation at sludge ages below 2.0 d, lowering the sludge age in the contact tank, θ XC ( αθ X ) to the extremely low range of 0.2–0.4 d. Equations and show that in this low θ XC range: (i) a significant fraction of S H and S S will be lost to the effluent since the removal performance of the contact tank will be severely impaired; (ii) the effluent will also contain all the residual COD components S I and S P ; and (iii) the system will run a high risk of not maintaining the stability of gravity settling, which will result in a high particulate COD level (biomass escape) in the effluent. In this operation range, the performance of the CS process cannot be compared favourably with that of the superfast membrane bioreactor (SFMBR), which secures complete capture of biomass, full removal and recovery of soluble biodegradable COD as biomass and minimal utilization of particulate COD under the same operating conditions, as clearly demonstrated in recent studies , …”

Section: Methodsmentioning

confidence: 99%

“…Model interpretation of experimental results showed that SFMBR had the potential to recover 54–77% of the influent COD energy. The recovery rate calculated as 63% when the SFMBR was operated at sludge age of 1.0 d was 1.4 times higher than the high rate activated sludge process . Recently a number of studies also promoted the high rate CS as a process alternative for maximum recovery of energy, although the interpretation of available experimental results to justify their claim was highly debatable,, mainly because excessive substrate and biomass escape in the effluent were not properly accounted for in COD mass balance.…”

Section: Introductionmentioning

confidence: 98%

“…The recovery rate calculated as 63% when the SFMBR was operated at sludge age of 1.0 d was 1.4 times higher than the high rate activated sludge process. 26 Recently a number of studies also promoted the high rate CS as a process alternative for maximum recovery of energy, although the interpretation of available experimental results to justify their claim was highly debatable, 27,28 mainly because excessive substrate and biomass escape in the effluent were not properly accounted for in COD mass balance. This issue is discussed in sufficient detail in Orhon et al 29 Despite the pioneering role in the development of the activated sludge process, the CS modification did not receive the research effort it deserved; it certainly did not benefit from the resources of multi-component modelling concepts to elucidate the major mechanisms involved.…”

Section: Introductionmentioning

confidence: 99%

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A novel modeling approach for evaluating microbial mechanism and design of contact stabilization process

Allı

İnsel

et al. 2017

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BACKGROUND The paper offers a novel interpretation of microbial mechanisms and evaluates the assets of contact stabilization (CS) using multi‐component modelling. A model structure re‐defining microbial processes is adopted, where the function of the contact tank was limited to the utilization of soluble substrate fractions and that of the stabilization tank essentially involved endogenous decay and removal of the adsorbed particulate substrate. RESULTS The model was used to simulate the microbial behaviour and performance of CS in comparison with a conventional activated sludge system (CAS), at an SRT range between 6 and 15 d. The results were confirmed by a stoichiometric description of the process using relevant mass balance relationships, which identified the role of major parameters in system behaviour and performance. A rational process design procedure was proposed based on modelling and process stoichiometry. CONCLUSION The CS process achieved effective carbon removal with a much smaller footprint and/or aeration volume with respect to CAS, due to its ability to work at significantly higher volumetric organic loadings; its flexibility to be operated at much higher SRT compared with CAS with the same HRT, allowed minimizing sludge production and sustaining a microbial composition also supporting nitrification. However, process stoichiometry reflected that the CS process, despite its significant advantages, should not be considered a suitable candidate for maximizing sludge harvest and energy recovery. © 2017 Society of Chemical Industry

Reshaping the activated sludge process: has the time come or passed?

Orhon

2019

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Despite the amazing achievements over the years, the activated sludge (AS) process still maintains inherent drawbacks, namely gravity settling, high sludge ages, low excess sludge generation, etc., which hinder its successful operation and sometimes disrupt system performance. Substantial research on the subject has provided clear scientific evidence that time has come -or even passed -for reshaping the AS process. In the novel AS process, gravity settling will be replaced by membrane filtration, which will convert the system configuration into a membrane activated sludge (MAS) reactor; this configuration will be operated at an extremely low sludge age range of 2 to 4 days, which will maximize sludge generation and it will abandon the traditional anaerobic sludge digestion for optimizing energy recovery. It is suggested that super-fast membrane activated sludge (SFMAS) reactor be the new face of the AS process. SFMAS reactor will be the core unit of the AS process essentially limited to organic carbon (chemical oxygen demand) removal and energy recovery. The core SFMAS unit will also enable to benefit from all the assets of the AS process, such as nutrient removal, biopolymer recovery, etc., by means of hybrid systems in different configurations, i.e. by reactors with various functions that will be attached to the core unit.