Bioflocculation management through high-rate contact-stabilization: A promising technology to recover organic carbon from low-strength wastewater

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: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

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

Orhon

Allı

Sözen

2018

“…P XI = QX I (26) or, based on 1 kg COD = 0.9 kg TSS: 36 P XT (TSS) = P XT 0.9 kg TSS kg COD (27) 9 Calculate M XH and M XT (kg cell COD) and M XT (kg cell COD; kg TSS) from -…”

Section: Design Proceduresmentioning

confidence: 99%

“…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%

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

Allı

İnsel

Sözen

et al. 2017

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

Particle size distribution as a major characteristic of domestic wastewater: implications for the modeling and design of membrane bioreactors

Doğruel

Orhon²

2021

This study reviews the evolution of the concept and the methodology of particle size distribution (PSD) analysis for sewage. Evaluation of experimental data indicated that the analytical approach started with an empirical identification of soluble, colloidal and supra‐colloidal organic matter. Then, it evolved into a sequential filtration and ultrafiltration methodology, yielding results useful enough to be an integral complement of respirometric chemical oxygen demand (COD) fractionation based on biodegradation characteristics. Default values could be defined for the distribution of COD fractions in terms of both size and biodegradation characteristics, which practically showed similar profiles, suggesting that PSD of COD could be directly used for model evaluation and design of activated sludge configurations. Size distribution of COD in sewage should be regarded as a prerequisite for activated sludge systems with a membrane module, mainly to assess the fate of COD fractions that would be entrapped and recycled back to the reactor by membrane filtration. © 2020 Society of Chemical Industry