Relationship between floc composition and flocculation and settling properties studied at a full scale activated sludge plant.
ABSTRACT The variation in activated sludge floc composition, flocculation and settling properties was studied at a full scale plant over a 2-year period. A comprehensive set of process parameters was analysed and related to the floc properties to increase the understanding of the factors affecting floc formation. The composition of the activated sludge showed a seasonal change with higher concentrations of extractable extracellular polymeric substances (EPS) during the winter months. The protein content of the total sludge and EPS increased significantly during the winter. This coincided with higher effluent suspended solids concentrations and increased shear sensitivity of the sludge flocs. Only poor correlations between EPS contents and stirred sludge volume index (SSVI) could be observed. High iron concentrations in the sludge due to dosage of iron salt to precipitate phosphorus were found to have a negative impact on the settling and compaction properties of the sludge, whereas it had a positive impact on floc stability. Higher organic loading due to by-passed primary settlers leads to improved settling and compaction properties.
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ABSTRACT: The non-Newtonian properties of activated sludge (AS) suspension lead to transfer limitations (oxygen, substrate...) and operation difficulties in Waste Water Treatment Plants (WWTP). The current approach involves assuming the sludge behaves like water on a rheological point of view, and then oversizing pumping and aeration devices, which represent over 60% of the operating cost in WWTP. The objective of this work is to understand the effect of bioflocculation on the rheological properties and the settling ability of AS suspensions, by means of variations in concentration of exo-cellular polysaccharides. Experiments have been conducted in a 20 L laboratory scale bioreactor at a constant retention time of 20 days and with a total suspended solid concentration between 15 and 20 g L(-1). The bioreactor was fed with a synthetic substrate at a constant mass loading rate of 0.3 kg(DCO) kg(-1)(TSS) d(-1). Our results show that increasing the exo-polysaccharide (EPS) concentration from 10 to 80 mg g(-1)(TSS) leads to an increase in shear-thinning properties of AS. An improvement of the settling ability is also obtained, at least when the EPSs increase from 10 to 45 mg g(-1)(TSS). Above 45 mg g(-1)(TSS) of adsorbed polysaccharides, the settling ability seems to decrease again.Environmental Technology 11/2013; 34(21-24):2995-3003. · 1.61 Impact Factor
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ABSTRACT: The membrane bioreactor (MBR) activated sludge process is being applied more and more for wastewater treatment due to its high treatment efficiency and low space requirement. However, the usefulness of the MBR process in low-temperature zones is less studied than that under normal conditions. This study determined the effect of low temperature (∼13 °C) operation on MBR performance and activated sludge characteristics. When the wastewater temperature decreased from 22 °C to 13 °C, the average effluent COD concentration increased from (10 ± 5) to (25 ± 4) mg L(-1) and the nitrogen removal efficiency appeared not to be affected. The abundance and diversity of nitrifying bacteria such as Nitrosospira (ammonia-oxidizing bacteria) and Nitrospira (nitrite-oxidizing bacteria) in the activated sludge were reduced under low temperature exposure. The total biomass concentration decreased from about 10 000 mg COD L(-1) at room temperature to 8200 mg COD L(-1) at 13 °C at the same solid retention time. Furthermore, the sludge became bulking at 13 °C with a significant increase in the sludge volume index. The resultant sludge bulking was accompanied by accelerated membrane fouling resulting in a two-fold increase in the frequency of membrane cleaning. The results suggest that the performance of the MBR activated sludge process deteriorated at low wastewater temperatures even though the effluent water quality was still good enough for its applications in low temperature zones.Environmental science. Processes & impacts. 07/2014;
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ABSTRACT: Since the notable amount of particulate substrate in wastewater, the implications of particulate substrate on treatment efficiency have been a topic of major interest in the field of biological wastewater treatment. The particulate substrate has to be hydrolyzed by the extracellular enzymes, which are mainly embedded in extracellular polymeric substances (EPS) matrix of microbial aggregates, prior to consumption. Therefore, the important relevance between the particulate substrate and the characteristics of EPS can be expected. In this study, two lab-scale sequencing batch reactors were performed in parallel to investigate the effects of particulate and soluble substrate on the physicochemical characteristics of EPS in activated sludge. The results showed that the particulate substrate in the influent could significantly change the properties of activated sludge and the characteristics of EPS. More open and fluffy flocs with poorer settleability and dewaterability were formed with particulate substrate. More protein and humic compounds were introduced into the EPS matrix due to the deep involvement of protein and humic compounds in hydrolysis process of particulate substrate. The increments of protein and humic compounds then caused the slight higher molecular weight, higher hydrophobicity and lower zeta potential of EPS in particulate substrate system. The results in this study permitted for obtaining answers to understand the significant implications of particulate substrate in determining the physicochemical characteristics of EPS in biological wastewater treatment systems.Water Research 04/2014; 58C:1-8. · 4.66 Impact Factor