Relationship between bulking and physicochemical–biological properties of activated sludges

Abstract

SummaryResearch into bulking in laboratory-scale activated-sludge plants are reported upon. A correlation between sludge volume index (SVI) and hiopolymrr content (exocellular polymer, ECP) has been determined for sludge obtained under various operating conditions and with different chemical and physical characteristics. This paper interprets that correlation. A method for ECP determination that is quicker and just as precise as the gravimetric one and which enables this parameter to be used not only to interpret bioflocculation mechanisms but also as a parameter for evaluating optimal plant operation is reported. STATE OF KNOWLEDGEAlthough several types of sludge exist (whose behavior sometimes poses considerable problems for a satisfactory liquid-solid separation in settling tanks),' the term filamentous bulking should be strictly used only for phenomena that result in activated sludge having a significant percent of filamentous microorganisms and. consequentially, poor compaction properties.From an examination of bulking experiments carried out on various types of substrates in laboratory or full-scale plants, it would appear that the principal factors involved in bulking are a) The dissolved oxygen concentration in the mixed liquor. The critical dissolved oxygen value increases proportionally with the average floc diameter. However, values lower than 0.5-1 mgiliter do seem to cause the filamentous microorganisms to d e v e l~p .~-~ b) The flow-dynamic conditions. The sludge obtained in plants with plug-flow systems contain different percents of filamentous microorganisms than the sludge obtained in completely mixed reactors operating under the same conditions.6-8

Physical Characteristics of Activated Sludge Flocs

“…The reported influencing factors include floe size, 4 DO and/or organic loadings, M1 -7381 nitrogen and phosphorus content, 82 -83 elevated metal concentrations, 84 mixed liquor SS, 85 treatments prior to aeration, 86 " 89 deficiency of micronutrient concentrations, 90 -91 mixed liquor turbulence, 4692 different types of carbonaceous sources, 87 -93 " 95 exocellular polymers, 96 substrate feeding patterns, 97101 substrate accumulation capacity of microorganisms or substrates oxidized, 93 -102 aeration basin configurations, 89 -103 pH, septic wastes, temperature, 1 etc. Detailed reviews on these influencing factors are available in the literature.…”

Community structure of micro- and macroflocs in pin-point sludge and the influence of sludge age and potassium addition on microfloc formation

“…The EPS quantity and quality (Table 1) gave additional information about the sedimentation behavior of the sludge. Beccari et al (1980) reported a correlation between EPS quantity and sludge settleability. A very low EPS content causes a reduction in flocculation due to the lack of polymer material.…”

The size of activated sludge flocs in relation to their surface characteristics

“…2,3) or to modify the surfaces in a specific and pre-determined way and then to examine the effect that this has on the sludge itself (eg. 4,5).…”