activated sludge systems
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Author(s):  
Gayatri Gawande ◽  
◽  
Rucha Dandekar ◽  
Omparv Channa ◽  
Harshali Birari ◽  
...  

Membrane Bioreactors have proved to be a useful alternative to conventional activated sludge systems for wastewater treatment. Merits of membrane bioreactors include more compact design saving a significant amount of space and lower sludge production due to longer sludge retention time. This system unfortunately has a downside with it comes to excessive foaming. Membrane bioreactors often act as foam traps leading to overflowing, wastage of sludge and difficulty in process control. Pre-Treatment of wastewater has proven to significantly reduce foaming caused by surfactants. Generally, physical methods are considered more economical and operationally convenient compared to conventional techniques including chemical treatment and advanced techniques like biological treatment. Polyaluminium chloride as a coagulant is recommended as a chemical treatment due to economic and effectiveness considerations. It has been concluded that the remedies for foaming issue are case specific and should be determined by the causes of foaming. This paper aims at reviewing techniques to analyse the foaming phenomenon, causes of foaming and its remedies to manage or eliminate foam.


2021 ◽  
Author(s):  
Shameem Jauffur ◽  
Zeinab Bakhshi ◽  
Dominic Frigon

AbstractThis work aimed at demonstrating the natural bioaugmentation of biological activated sludge systems with nitrifying biomass from influent wastewater in lab-scale reactors. Three sequencing batch reactors (SBR) were fed with sterile synthetic wastewater. While nitrification was complete at a temperature of 8 °C and a SRT of 20 days, it failed when the temperature was lowered to 5 °C, and the SRT decreased to 7 days. In the test period, the sterile synthetic wastewater fed to the Test Reactor was supplemented by influent solids harvested at a full-scale treatment facility at a total suspended solids concentration of 100 mg/L, which corresponded to approximately 5 mg-COD/L of nitrifying biomass. Upon this addition, nitrification was restores. Subsequent halting the supply of influent solids to the Test Reactor led a rapid failure of nitrification and washout of nitrifiers from the SBR. Reproducibility was demonstrated by switching the feed composition between the Test and Negative control reactors. PCR-based amplicon sequencing analyses targeting the amoA, and nxrB genes of the Nitrospira genus have shown that the influent wastewater governed the structure and composition of the activated sludge nitrifying populations. The most abundant ammonia-oxidizing bacteria (AOB) and Nitrospira-related nitrite-oxidizing bacteria (NOB) in the influent seeds occurred as the most dominant ones in the activated sludge. This pattern was observed even when the influent seeds varied over time. The heterotrophic populations were less affected by the influent seeds with the activated sludge and raw sewage showing distinct microbial populations based on principal coordinate analysis (PCoA). However, the immigrant populations appeared to modulate the structure of the activated sludge heterotrophic communities to some extent. These findings provide concrete evidence of the presence of active nitrifiers in raw wastewater capable of supporting nitrification in an otherwise non-conducive environment. This may have important implications on process design, operation and optimization of wastewater treatment systems.HighlightsLab-scale reactors fed sterile synthetic wastewater at low temperatures and SRTs.Nitrification failed when conditions were adjusted to 5 °C and a SRT of 7 days.Nitrification restored by addition of real wastewater influent solids.Nitrifiers in solids from sewers naturally bioaugment activated sludge systems.Activated sludge models should consider the immigration of nitrifiers with influent.Graphical abstract


2021 ◽  
Vol 9 (4) ◽  
pp. 105427
Author(s):  
Yoan Pechaud ◽  
Sylvain Pageot ◽  
Anne Goubet ◽  
Camilo Duran Quintero ◽  
Sylvie Gillot ◽  
...  

Membranes ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 589
Author(s):  
Derin Orhon ◽  
Ayse Begum Yucel ◽  
Guclu Insel ◽  
Seyda Duba ◽  
Tugba Olmez-Hanci ◽  
...  

A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.


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