In this study nitrogen removal via nitrite >80% was achieved after approximately 80days in a sequencing batch reactor (SBR) treating pre-treated industrial wastewater originating from the potato industry. Thereafter, SBR performance was investigated during the formation of aerobic nitrite granules (ANG). The first granules appeared after 26days leading to full granulation after 64days. ANG showed excellent settling properties, as the Sludge Volume Index (SVI) went down to 16mL/g and a SVI/SVI=1 was obtained. qPCR analysis showed that slow growing organisms, especially polyphosphate accumulating organisms (PAO) were stimulated by an anaerobic feeding strategy. The average nitrogen removal was 95.3% over the entire operational period, and it mainly followed the "nitrite-route". Moreover, with ANG also phosphorus removal efficiencies up to 65.7% could be achieved. However, it has to be mentioned that nitrous oxide was an important denitrification product, which implies some environmental concerns.
In this study, petrochemical wastewater from the port of Antwerp was used for the development of aerobic granular sludge. Two different reactor setups were used, (1) a completely aerated sequencing batch reactor (SBR) with a feast/famine regime and (2) a sequencing batch reactor operated with an anaerobic feast/aerobic famine strategy (SBR). The seed sludge showed poor settling characteristics with a sludge volume index (SVI) of 285mL.gMLSS and a median particle size by volume of 86.0µm±1.9µm. In both reactors, granulation was reached after 30days with a SVI of 71mL.gMLSS and median granule size of 264.7µm in SBR and a SVI of 56mL.gMLSS and median granule size of 307.4µm in SBR. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal was similar in both reactors and above 95%. The anaerobic DOC uptake increased from 0.13% to 43.2% in 60days in SBR.
A laboratory-scale sequencing batch reactor (SBR) was operated for 450 days to assess aerobic granule formation when treating brewery/bottling plant wastewater by consistent application of a feast/famine regime. The experiment was divided into three major periods according to the different operational conditions: (I) no pH control and strong fluctuations in organic loading rate (OLR) (1.18 ± 0.25 kgCOD·(m·day)), (II) pH control and aeration control strategy to reduce OLR fluctuations (1.45 ± 0.65 kgCOD·(m·day)) and (III) no pH control and stable OLR (1.42 ± 0.18 kgCOD·(m·day)). Aerobic granule formation was successful after 80 days and maintained during the subsequent 380 days. The aerobic granular sludge was characterized by SVI and SVI values below 60 mL.g and dominated by granular, dense structures. An oxygen uptake rate based aeration control strategy insured endogenous respiration at the end of the aerobic phase, resulting in stable SBR operation when the influent composition fluctuated. The quantitative polymerase chain reaction results show no significant enrichment of Accumulibacter or Competibacter during the granulation process. The 16S rRNA sequencing results indicate enrichment of other, possibly important species during aerobic granule formation while treating brewery wastewaters.
In this study, a sequencing batch reactor (SBR), treating synthetic wastewater (COD/N = 5), was operated in two stages. During stage I, an aeration control strategy based on oxygen uptake rate (OUR) was applied, to accomplish nitrogen removal via nitrite >80%. In stage II, the development of aerobic granular sludge (AGS) was examined while two aeration control strategies (OUR and pH slope) maintained the nitrite pathway and optimized the simultaneous nitrification-denitrification (SND) performance. Stimulation of slow-growing organisms, (denitrifying) polyphosphate-accumulating organisms (D)PAO and (denitrifying) glycogen-accumulating organisms (D)GAO leads to full granulation (at day 200, SVI = 47.0 mL/g and SVI = 43.1 mL/g). The average biological nutrient removal efficiencies, for nitrogen and phosphorus, were 94.6 and 83.7%, respectively. Furthermore, the benefits of an increased dissolved oxygen concentration (1.0-2.0 mg O/L) were shown as biomass concentrations increased with approximately 2 g/L, and specific ammonium removal rate and phosphorus uptake rate increased with 33 and 44%, respectively. It was shown that the combination of both aeration phase-length control strategies provided an innovative method to achieve SND via nitrite in AGS.
A lab-scale SBR was operated for approximately. 300 days, divided into four periods based on the feeding strategy, to develop stable aerobic granular sludge (AGS) while treating chocolate processing wastewater. Application of a prolonged mixed anaerobic feeding was not sufficient to develop AGS and reach stable reactor performance. Through the application of a partially non-mixed and a partially mixed feeding strategy the reactor performance was increased and stable AGS formation was established characterised by low DSVI10,30 values of 78 ± 27 mL·g−1 and 52 ± 17 mL·g−1, respectively, and a CST/MLSS value of 0.9 sec.(g·L−1)−1. The MBR filtration tests showed a reduction of the fouling rate (FR) and an increase of the sustainable flux (SF0.5) for AGS compared to flocs treating the same industrial wastewater. The SF0.5 (FR > 0.5 mbar·min−1) for the flocs was 10 L.(m2·h)−1 while for AGS the SF0.5 is higher than 45 L(m2·h)−1 since the FR never exceeded 0.1 mbar·min−1. Additionally, the AGS showed reduced irreversible fouling tendencies due to pore blocking. Our results underline the need for an increased substrate gradient during anaerobic feeding for the development and long-term maintenance of AGS under minimum wash-out conditions. Secondly, the AGS-MBR filtration performance shows strong advantages compared to a floccular MBR system due to a high increase of the SF0.5 and reduced reversible and irreversible fouling.
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