Extracellular polymers in partly ozonated return activated sludge: impact on flocculation and dewaterability

Abstract

The purpose of this study was to evaluate the influence of partial ozonation of return activated sludge on settling properties and dewaterability of sludge. Sequencing batch reactors with two sets of aerobic and alternating anoxic/aerobic conditions were used. In each set, one reactor served as a control and the other was subject to the ozone treatment (doses in the range of 0.016-0.080 mg O3/mg TSS of initial excess sludge). The level of total suspended solids (TSS) in each reactor was controlled at 1,800 mg/l. To evaluate settleability and dewaterability, settling kinetic studies, sludge volume index (SVI) and capillary suction time test (CST) were used. For extraction and quantifying sludge biopolymers, thermal-ethanolic extraction was employed. The ratio of bound-to-total extracellular polymer substances (EPS) was higher for the strictly aerobic reactor than for the alternating anoxic/aerobic one, indicating the stronger structure of the aerobic flocs. After ozone treatment, the fraction of bound EPS was released and solubilized, increasing soluble EPS. Increased apparent food-to-microorganism (F/M) ratio favoured production of EPS in ozonated reactors, enhancing flocculation, which had potential to improve settling. Dewaterability, measured by CST test, was better in alternating anoxic/aerobic reactors than in aerobic ones, indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation.

High Mineral Content of Biomass: Implications for Advanced Wastewater Treatment Through Hydrogen-Driven Denitrification

“…According to results stated by other researchers (Dytczak et al, 2006) for short SRT and nitrification and denitrification combining systems (operational pH ~7.6) most of the flocs is smaller then 1000µm 2 .In present research, microscopic observation showed that, when pH control was not implemented only 11 % and 23 % of flocs (pH <7-8> and pH>8 respectively), were smaller then 1000 µm 2 . Majority of flocs was bigger then 4000 µm 2 with maximum observed floc size equal to over 134000 µm 2 .The big size of flocs resulted in also relatively high values of determined flocs perimeter.…”

“…Majority of flocs was bigger then 4000 µm 2 with maximum observed floc size equal to over 134000 µm 2 .The big size of flocs resulted in also relatively high values of determined flocs perimeter. For only around 20% of flocs its value was smaller than 200 µm mentioned by Dytczak (2006) as most frequent flocs perimeter. The big floc size correlated with previously presented data regarding mineral precipitation, EPS content and composition (Tables 4, 5 and 6) appear to confirm the role of biopolymer -cation floc models (Bruss et al, 1992, Higgins andNovak 1997) in bioflocculation process.…”

Sludge Reduction Technologies in Wastewater Treatment Plants

“…EPS content -C omparing activated sludge beforea nd immediately after ozonation, an increase of soluble EPS was observed at ozone dosages from 0.022 to 0.070 gO 3 /gTSS of initial sludge (Dytczak et al, 2006). Ozone destroys part of the flocs, thus af raction of the bound polymeric material is released and solubilized, increasing soluble EPS.…”

“…With regard to prolonged,everyday ozonation, both the total and bound EPS levels were higher in the ozonated reactorsincomparison to the initial (control) reactor and stronger flocs were created.O zonation integrated in ab iological treatment with long SRT system favours not only EPS production, buta lso the degree of binding into the floc structure (Dytczak et al, 2006).…”

Improving dewaterability of waste activated sludge through advanced oxidization process

“…Some results reported that the sludge dewaterability was actually deteriorated due to the effect of ozonation. The possible reason for the deterioration of sludge dewaterability was suggested to be the formation of smaller particles due to the destruction of sludge floc, which then blocked the filter during the measurement (Dytczak et al, 2006;Liu et al, 2001;Weemaes et al, 2000). It was also reported that the aerobic digestion process following ozonation further improved the sludge dewaterability by degrading the fine particles produced by ozonation process (Hwang et al, 2006).…”