Anatomy of super‐fast activated sludge process with gravity settling for biodegradation and energy recovery potential ‐ a review

Self Cite

BACKGROUND: This study investigated the anatomy of organic carbon (as chemical oxygen demand, COD) removal from sewage through chemically assisted settling, by means of particle size distribution (PSD) analysis: it showed which size fractions were affected, aside from the particulate COD. The experiments were conducted on the effluent of the existing preliminary treatment plant before deep-sea discharge into the Bosphorus. FeCl 3 , alum and polyaluminum chloride (PAC) were used as coagulants at different doses. The performance of the coagulants on the effluent COD was interpreted with PSD.RESULTS: PAC at 25 mg L −1 , selected as the optimum coagulant, reduced COD below soluble COD level, to around 145 mg L −1 , with an overall efficiency of more than 70%. Although chemical settling was most effective on particulate COD at >450 nm, it also provided a COD removal of 28% in 220-450 nm of the colloidal range and 40% in 13-220 nm of the range, representing soluble hydrolysable COD. The lowest removal rate was observed in the soluble range, consisting of readily biodegradable (only 5%) and a part of the inert COD (<2 nm) identified as 12%twice as high as ordinary domestic wastewaters, with only 1%.CONCLUSION: PSD and COD fractionation analyses were instrumental in depicting the potential of chemically enhanced settling to reduce COD in the soluble range, identifying the distribution of remaining COD fractions in different size intervals. The results also suggested a novel treatment process with additional membrane filtration, namely membrane chemical reactor, (MCR), reflecting a potential for replacing the conventional activated sludge process.

Section: Discussionmentioning

confidence: 99%

“…Lately, a full activated sludge system with nutrient removal has been also envisaged as an arbitrary approach that would ostensibly provide better protection for the Marmara Sea. A recent review offered a detailed modeling appraisal of the A process 46 …”

Section: Discussionmentioning

confidence: 99%

Anatomy of chemically enhanced sewage settling by particle size distribution analysis

Duba

Sözen

Doğruel

et al. 2022

Self Cite

“…11,12 A recent review evaluated the merit of the conventional modified aeration modification and the A process, both operated at extremely low ⊔ X levels of <0.3 d, for performance and energy recovery. 13 The last 10 years have seen an overabundance of energy recovery studies by means of all imaginable HRAS configurations operated within a wide sludge age range of 0.1 to 11 days. [14][15][16][17][18][19][20][21] They were mostly conducted with synthetic wastewater using laboratory-scale systems and all coupled with gravity settling for sludge separation; the reported results were quite erratic and not amenable to a sustainable application.…”

Section: Introductionmentioning

confidence: 99%

“…A high θ X in extended aeration would favor endogenous decay and reduce sludge generation; conversely, a low θ X in high rate activated sludge (HRAS) modifications would increase sludge generation, if the purpose is energy conservation and recovery 11,12 . A recent review evaluated the merit of the conventional modified aeration modification and the A process , both operated at extremely low θ X levels of <0.3 d, for performance and energy recovery 13 …”

Section: Introductionmentioning

confidence: 99%

“…Excess sludge generation and biomass composition in contact stabilization Orhon et al29 estimated the particulate COD in the effluent of a plant, designed in the A process configuration for one of the sewage outfalls in Istanbul, as 170 mgCOD L −1 . Rahman et al17 reported sludge volume index (SVI 30 ) values as high as 580 mL g −1 , basically indicating no settling.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Efficient energy recovery from wastewater with high rate activated sludge process: oversights and misguidances

Orhon

Çokgör

Sözen

2022

Self Cite

Background The major aim of the study was to define a scientific framework to evaluate energy recovery from domestic wastewater, based on model assessment of process stoichiometry and kinetics using relevant experimental data. The evaluation was tailored to reveal and explain all the oversights and misconceptions on the subject. A new approach was adopted to focus specifically on a paper by Liang et al. (2022) to better visualize and indicate scientific ways to remedy the key misguidances. The alternative appraisal utilized the latest available support in terms of the database for chemical oxygen demand (COD) fractionation and process kinetics. Results The evaluation first demonstrated the inherent deficiencies of high rate activated sludge (HRAS) configurations such as the sequencing batch reactor and contact stabilization; then, it presented a new way to define excess sludge components in terms of fractions of the influent COD, indicating the major handicap for energy recovery and biomass loss in the effluent due to gravity settling. Effective energy conservation was computed to remain between 17% and 37% when the sludge age was reduced from 2.0 d down to 0.5 d. Conclusions The study offered conclusive proof that the contact stabilization process with gravity settling was, in fact, inherently unsuitable for energy conservation. Instead, the emerging scientific approach proposed a single‐volume HRAS system with membrane filtration replacing gravity settling. An equally valid suggestion was to replace anaerobic technology for energy recovery with thermochemical technologies, such as high‐rate pyrolysis, with a much higher energy recovery potential. © 2022 Society of Chemical Industry (SCI).

Impact of rainwater intrusion on wastewater characterization and performance of nutrient removal activated sludge process

Orhon,

Hallaç,

Solmaz

et al. 2023

Self Cite

BackgroundThe paper investigated the negative impact of rainwater intrusion and mixing with sewage, on the operation of an existing nutrient removal activated sludge plant. It evaluated the magnitude of observed changes, both in terms of flow increase and modification of major parameters, together with the resulting impact on system performance. The study was carried out on a selected plant. The influent characteristics of the plant have been reviewed for 2021 and 2022, both for the dry and rainy periods. Collected data were evaluated together with the experimental support derived from the selected plant.ResultsStatistical assessment of the collected data revealed significant changes likely to affect the performance of the existing plant: Sewage flow was increased from 580,000 m3/d to 670,000 m3/d. While COD and total N were slightly reduced, a higher level of inorganic solids was observed. Assessment of nitrification‐denitrification processes yielded an aerobic sludge age, θXA of 9 d and a total sludge age, θX of 15 d, with a VD/VT ratio of 0.4. Solids mass balance indicated a biomass level of 6,100 mg/L with 47% of fixed solids, which was increased to 7,300 mg/L with 52% fixed solids with the wet weather flow. These values denoted reactor volume limitation for sustainable/safe operation.ConclusionAside from the impact of substantial treatment cost increase due to the incremental flow of 13.7 million m3/year at wet weather periods, control and decrease of inorganic solids emerged as the key issue to safeguard system operation. The study also indicated clues for diverting runoff mixing as a tangible remedial action.This article is protected by copyright. All rights reserved.