Factors influencing the density of aerobic granular sludge (original) (raw)
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Water, 2016
The aerobic granular sludge process is a promising technology for the removal of nutrients and organic contaminants from wastewater. However, a large amount of the sludge is often washed out during the start-up of granular reactors, which results in reduced process performance and a protracted start-up phase. In this study, the possibility of a rapid start-up of the nitrification process through a stepwise decrease of the settling time was investigated, and the bacterial population dynamics in two lab-scale sequencing batch reactors were studied. The results demonstrated that the stepwise decrease of the settling time enabled fast granulation and rapid start-up of the process. Small cores of granules were already observed after 10 days of operation, and the biomass was dominated by granules after 28 days. The removal of organic matter and ammonium was >95% after one day and 14 days, respectively. The bacterial community composition changed rapidly during the first 21 days, resulting in strongly reduced richness and evenness. The diversity increased at a later stage, and the bacterial community continued changing, albeit at a slower pace. The rate of the stepwise decrease in settling time strongly affected the abundance of nitrifying organisms, but not the general composition of the bacterial community. The results of this study support the idea that a stepwise decrease of the settling time is a successful strategy for the rapid start-up of aerobic granular sludge reactors.
Critical Reviews in Biotechnology, 2011
Aerobic granular sludge can be classified as a type of self-immobilized microbial consortium, consisting mainly of aerobic and facultative bacteria and is distinct from anaerobic granular methanogenic sludge. Aerobic granular technology has been proposed as a promising technology for wastewater treatment, but is not yet established as a large-scale application. Aerobic granules have been cultured mainly in sequenced batch reactors (SBR) under hydraulic selection pressure. The factors influencing aerobic granulation, granulation mechanisms, microbial communities and the potential applications for the treatment of various wastewaters have been studied comprehensively on the laboratory-scale. Aerobic granular sludge has shown a potential for nitrogen removal, but is less competitive for the high strength organic wastewater treatments. This technology has been developed from the laboratory-scale to pilot scale applications, but with limited and unpublished full-scale applications for municipal wastewater treatment. The future needs and limitations for aerobic granular technology are discussed.
Settling behaviour of aerobic granular sludge
Water Science and Technology, 2007
Aerobic granular sludge (AGS) technology has been extensively studied recently to improve sludge settling and behaviour in activated sludge systems. The main advantage is that aerobic granular sludge (AGS) can settle very fast in a reactor or clarifier because AGS is compact and has strong structure. It also has good settleability and a high capacity for biomass retention. Several experimental works have been conducted in this study to observe the settling behaviours of AGS. The study thus has two aims: (1) to compare the settling profile of AGS with other sludge flocs and (2) to observe the influence of mechanical mixing and design of the reactor to the settleability of AGS. The first experimental outcome shows that AGS settles after less than 5 min in a depth of 0.4 m compared to other sludge flocs (from sequencing batch reactor, conventional activated sludge and extended aeration) which takes more than 30 min. This study also shows that the turbulence from the mixing mechanism an...
Determining the distribution of granule diameter from biological sludge
MethodsX, 2018
Anaerobic granule sizes from various types of anaerobic biological wastewater treatments were investigated in order to understand the influence of this characteristic on the performance of the treatment system. To date, there is no standardised methodology in the current literature, which provides details of a process to obtain data, such as a suitable sample volume, a description of the precision and limitations of the techniques used. Therefore, the aim of this protocol is to standardise the granulometry assay that can measure granule sizes accurately and quickly. In addition, the proposed methodology comprises about 1500-3000 granules in a single sample, a representative number compared to the currently applied methodologies.
Enzyme and Microbial Technology, 2006
To evaluate the effect of sludge removal methods on the stability of aerobic granules, three different removal methods of sludge were investigated in sequencing batch reactors (SBR). Results demonstrated that (i) in R1, removing fresh granules effectively maintained granules with sizes of 1-2 mm and SVI of 31-45 ml g −1 for more than 432 cycles (one cycle length was 3 h); (ii) in R3, removing aged granules led to disintegration of granules; (iii) in R2, removing completely mixed sludge resulted in granules with good settleability. However, the morphology of granules in R2 was similar to that of granules in R3 with sizes of about 4-5 mm. It was also found that removing fresh granules built up more ash solids in granules than removing aged granules did and removing aged granules significantly led to lysed granules with void shells. Results suggest that removing fresh granules is an effective approach of selective force for aerobic granulation, and the mature phase plays an important role on the stability of granules by rearranging granule structure (e.g. the buildup of ash solids).
Settleability assessment protocol for anaerobic granular sludge and its application
Water SA, 2004
A simple method for settleability assessment of anaerobic granular sludge was proposed and its applicability as an operating parameter was evaluated in a lab-scale UASB reactor treating brewery wastewater. Based on the settleability protocol, the OLR was increased up to 28 kg COD·m -3 ·d -1 (67 kg COD·m -3 of granular bed volume·d -1 ) which corresponds to an HRT of 1 h. The results revealed that the protocol was sufficiently sensitive to define the settleability of the sludge samples and to accurately determine their allowable upflow velocities, resultant organic loading rates, and recycling ratios according to the settleability of the granular bed. Also, a series of graphical procedures with settling tests which are very easy to apply for settleability monitoring was improvised, capable of direct use as an operational and monitoring parameter of the granular bed with laboratory and full-scale reactors, without need for additional sludge bed control such as dosing of chemicals. In addition, this method was also found to be applicable to improve and monitor system performance according to high or low-strength wastewater characteristics. Image analysis of the granular biomass supported the suitability of this graphical method.
Environmental Science Water Research & Technology, 2022
Aerobic granular sludge (AGS) plants have gained growing interest and application due to their low energy demand, small footprint, and low operational costs. However, the fulfilment of strict discharge limits for nitrogen and phosphorus, vast seasonal temperature variations, and large peaks in influent flows may pose challenges to the implementation of AGS. Moreover, the knowledge about microbial community assembly and process performance under varying environmental conditions in full-scale reactors is still limited. In this study, the first implementation of the AGS process in the Nordic countries was assessed. In two full-scale AGS reactors with different seeding sludges, the start-up was associated with rapid changes in microbial community composition in both, but only successful granulation in one. As a consequence, the nongranulated reactor was eventually reseeded with biomass from the better granulated reactor. This resulted in a convergence of the microbial communities in the two reactors with the maintenance of stable sludge concentrations (6-8 g L −1) with large granules (50-80% with diameter >2 mm) and fast settling of biomass (SVI 30 /SVI 10 of 0.9-1). Immigration from the influent wastewater was a minor factor affecting the microbial community once the granules had formed, while the seasonal variations in environmental factors were identified as important. Key guilds of AOB (Nitrosomonas), NOB (mainly Ca. Nitrotoga), PAOs (mainly Tetrasphaera), and GAOs (mainly Ca. Competibacter) varied considerably in abundance throughout the study period. After 15 months, stable organic matter, nitrogen, and phosphorus removal were attained with low effluent concentrations. During the start-up, the BOD 7 /N ratio, influent flow, and temperature were important factors influencing the performance of the AGS.
Effect of the food-to-microorganism (F/M) ratio on the formation and size of aerobic sludge granules
Process Biochemistry, 2011
Laboratory experiments were carried out to investigate the effect of the sludge loading, or the food-to-microorganism (F/M) ratio, on the rate of aerobic granulation and the size of the granules in biological wastewater treatment. Four column batch reactors were used with a similar sludge suspended solids (SS) concentration of around 2000 mg/L. The reactors were fed with a glucose-based wastewater at different chemical oxygen demand (COD) concentrations, resulting in F/M ratios from 0.3 to 1.1 g COD/g SS-d. A higher F/M ratio appeared to promote faster formation of larger granules and a lower F/M ratio led to slower 2 formation of smaller granules. Upon complete granulation, the granules became rather stable in size, and the mean diameter of the granules in different reactors increased from 1.2 to 4.5 mm linearly with the F/M ratio applied. Molecular analysis of the sludge did not show the domination of any particular bacterial species during the granulation process. In is apparent that applying different F/M ratios in different granulation stages, e.g., a higher F/M in the early stage and a reduced F/M in the later stage, can be an effective start-up strategy to facilitate rapid granule formation and sustain small and healthy granules in bioreactors.