Bulking Sludge. In many cases MLSS with poor settling characteristics has developed into what is known as a bulking sludge condition, which defines a condition in the activated-sludge clarifier that can cause high effluent suspended solids and poor treatment performance. In a bulking sludge condition, the MLSS floc does not compact or settle well, and floc particles are discharged in the clarifier effluent with good settling sludge, sludge levels may be as low as 10 to 30 cm at the bottom of the clarifier. In extreme bulking sludge conditions, the sludge blanket cannot be contained and large quantities of MLSS are carried into the system effluent, potentially resulting in violation of permit requirements, inadequate disinfection, and clogging of effluent filters Two principal types of sludge bulking problems have been identified. One type, filamentous bulking, is caused by the growth of filamentous organisms or organisms that can grow in a filamentous form under adverse conditions, and is the predominant form of bulking th other type of bulking, viscous bulking, is caused by an excessive amount of extracellular biopolymer, which pre sludge with a slimy, jellylike consistency(Wanner, 1994) As the biopolymers are hydrophilic, water-retentive. and this condition resultant sludge has a low density with low settling velocities and poor ction. Viscous bulking is usually found with nutrient-limite In with high amount of rbCOD Bulking sludge problems due to growt more common In filamentous growt Figure 8-11 bacteria form filaments of single-cell organisms that attach end-to-end. and 以四四 Boc,.tl, oe pride by l on the filaments normally protrude out solved oxgen miaregnisaie w hot Corey o b wld g n iwm f cotone saby mecom bunda of the sludge floc. This structure,in contrast to the preferred dense floc with good settling properties, has an increased surface area to mass ratio, which results in poor settling On Fig. 7-8, a good settling, dense nonfilamentous floc is contrasted to floc containing filamentous growth Many types of filamentous bacteria exist, and means have been developed for the identification and classification of filamentous bacteria found commonly in activated-sludge systems(Eikelboom, 2000) The classification system is based on morphology(size and shape of cells, length and shape of filaments staining responses, and cell inclusions. Common filamentous organisms are summarized in Table 7-3, along with the operating conditions that favor their growth Sludge bulking can be caused by a variety of associated with each of these categories are identified in Table zx nd operational issues. Individual items Tab. 7-3 Filamentous organisms foundin activated sludge andassociated process conditions Filament bype identified Sphaerotilus natans, Halsicomenobacter hydross Low dissolved parv M.parvicella, types 0o4t, 0092, 0675. 185 O2IN ida limicola Complete-mix reactor conditions Beggiatoa, Thiothrix spp. types 021N, 0914 S. natons, Thiothrix pe 021N, possible H. hydrosis, types 0041, 0675 ow pH, nutrient deficiency Tab. 7-4 Factors that affea sludge bulking 7-117-11 Bulking Sludge. In many cases MLSS with poor settling characteristics has developed into what is known as a bulking sludge condition, which defines a condition in the activated-sludge clarifier that can cause high effluent suspended solids and poor treatment performance. In a bulking sludge condition, the MLSS floc does not compact or settle well, and floc particles are discharged in the clarifier effluent. With good settling sludge, sludge levels may be as low as 10 to 30 cm at the bottom of the clarifier. In extreme bulking sludge conditions, the sludge blanket cannot be contained and large quantities of MLSS are carried into the system effluent, potentially resulting in violation of permit requirements, inadequate disinfection, and clogging of effluent filters. Two principal types of sludge bulking problems have been identified. One type, filamentous bulking, is caused by the growth of filamentous organisms or organisms that can grow in a filamentous form under adverse conditions, and is the predominant form of bulking that occurs. The other type of bulking, viscous bulking, is caused by an excessive amount of extracellular biopolymer, which produces a sludge with a slimy, jellylike consistency (Wanner, 1994). As the biopolymers are hydrophilic, the activated sludge is highly water-retentive, and this condition is referred to as hydrous bulking. The resultant sludge has a low density with low settling velocities and poor compaction. Viscous bulking is usually found with nutrient-limited systems or in a very high loading condition with wastewater having a high amount of rbCOD. Bulking sludge problems due to the growth of filamentous bacteria are more common. In filamentous growth, bacteria form filaments of single-cell organisms that attach end-to-end, and the filaments normally protrude out of the sludge floc. This structure, in contrast to the preferred dense floc with good settling properties, has an increased surface area to mass ratio, which results in poor settling. On Fig. 7-8, a good settling, dense nonfilamentous floc is contrasted to floc containing filamentous growth. Many types of filamentous bacteria exist, and means have been developed for the identification and classification of filamentous bacteria found commonly in activated-sludge systems (Eikelboom, 2000). The classification system is based on morphology (size and shape of cells, length and shape of filaments), staining responses, and cell inclusions. Common filamentous organisms are summarized in Table 7-3, along with the operating conditions that favor their growth. Sludge bulking can be caused by a variety of factors, including wastewater characteristics, design limitations, and operational issues. Individual items associated with each of these categories are identified in Table 7-4. Fig. 7-8 Examples of good and poor settling floc particles: (a)nonfilamentous good Settling floc; (b)floc particles bridged by filamentous microbes; (c)floc Particles with limited filamentous microbes and secondary form; (d)filaments extending from floc causing poor settling; (e)Thiothrix filaments with sulfur granules; (f)type 1701 filamentous microbes observed under low dissolved oxygen Tab. 7-3 Filamentous organisms found in activated sludge and associated process conditions Tab. 7-4 Factors that affect sludge bulking