Temperature and salt effects on settling velocity in granular sludge technology (original) (raw)

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...

Effects of aerated-mixing condition to the settling characteristics of aerobic granular sludge

2008

In aerobic granular sludge (AGS) technology, aerated-mixing is commonly used to introduce shear effects in the system. Sufficient shear stress is needed for the formation of stable and dense AGS. However, over mixing might affect the AGS settling characteristic. Furthermore, in pilot or full scale implementation, as the size of the reactor increases, the effect of mixing mechanism strategy become more significant. Several factors need to be considered particularly in maintaining AGS settling characteristics. This study has been conducted to observe the effect of aerated-mixing condition to the AGS settling characteristics. Special attention was given on two effect parameters to the AGS settling velocity (ν AGS). i.e. different rate of airflow (Q air) and size of bubbles (r). It is found that the turbulent diffusion coefficient (K') depends significantly on the value of Q air and r. Overall results show that over-mixing is not favourable for AGS operation. Under aerated-mixing condition, AGS settling characteristics will be affected by the increase of K' occurring in the system due to the increase of Q air and decrease of r. In order to maintain ν AGS > 10 mh-1 , result shows that, Q air applied to the system should not be greater than 8.0 Lmin-1. For study at different r, the result shows that the ν AGS decreased with the decrease of r but only small changes.

Factors influencing the density of aerobic granular sludge

Applied Microbiology and Biotechnology, 2013

In the present study, the factors influencing density of granular sludge particles were evaluated. Granules consist of microbes, precipitates and of extracellular polymeric substance. The volume fractions of the bacterial layers were experimentally estimated by fluorescent in situ hybridisation staining. The volume fraction occupied by precipitates was determined by computed tomography scanning. PHREEQC was used to estimate potential formation of precipitates to determine a density of the inorganic fraction. Densities of bacteria were investigated by Percoll density centrifugation. The volume fractions were then coupled with the corresponding densities and the total density of a granule was calculated. The sensitivity of the density of the entire granule on the corresponding settling velocity was evaluated by changing the volume fractions of precipitates or bacteria in a settling model. Results from granules originating from a Nereda reactor for simultaneous phosphate COD and nitrogen removal revealed that phosphate-accumulating organisms (PAOs) had a higher density than glycogen-accumulating organisms leading to significantly higher settling velocities for PAO-dominated granules explaining earlier observations of the segregation of the granular sludge bed inside reactors. The model showed that a small increase in the volume fraction of precipitates (1-5 %) strongly increased the granular density and thereby the settling velocity. For nitritation-anammox granular sludge, mainly granular diameter and not density differences are causing a segregation of the biomass in the bed.

Effects of Temperature and F/M ratio On the Settling Characteristics of Activated Sludge

The paper focused on the sludge characteristics taken from secondary sedimentation tank in a laboratory bench scale pilot plant working under extended aeration activated sludge system (EAAS). The results showed that 80 % of activated sludge index (SVI) values appeared to lie within the well –characteristics sludge. SVI was also shown to be highly affected by food microorganism ( F/M) ratio. Tests were conducted under different temperatures ( 20C, 25C, and 30C) to show the effects on settling velocity . Correlation of solid particle concentrations in aeration tanks to maximum flux was also investigated.

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.

Simulations of Granular Sludge Characteristics on the Optimization of Effluent Treatment Plant

2012

Waste water treatment processes are considered to be the largest industry in terms of treated mass of raw materials. However, in terms of meeting the stringent environmental pollution norms, there are still many grey areas that need to be addressed. For example, the understanding of the settling behavior of activated granular sludge in the secondary settler of an Effluent Treatment Plant (ETP). Knowledge of this aspect is essential for the plant designers to determine the efficiency of wastewater treatment in particular. This apart, it reduces the costs related to waste sludge dewatering and disposal and improves the separation of biomass and treated effluent quality requirements before the latter is discharged to the surface water. Any failure in the settling tank, either due to sludge bulking or excessive loss of sludge deteriorates the effluent quality that could lead to uncontrolled low sludge ages and a reduction of efficiency in the aeration tanks. In order to capture the basi...

Temperature effect on settling velocity of activated sludge

Batch settling tests performed at most of the plants and the settling velocity was generally correlated to MLSS concentration. The majority of these MLSS settling test not include any form of temperature compensation. The present work was done to prove that temperature was an important factor on activated sludge settling. Batch settling test was taken at different temperature for the sludge extracted from a Tunisian wastewater treatment plant. The results were shown that a high temperature increases the settling velocity but it can increase the turbidity of supernatant. The evolution of settling velocity function the temperature was not linear. A low temperature also has increased a settling velocity. The Vesilind settling model parameters was also influenced by temperature. Increasing temperature from 21 °C to 40 °C has increased initial settling velocity from 0.143 m/h to 0. 9 m/h and decreased the hindered mass coefficient from 1.107 to 0.556 L/g.

Inducing granulation within a full-scale activated sludge system to improve settling

2021

Most cold-climate biological nutrient removal facilities experience poor settling mixed liquor during winter, resulting in treatment capacity throughput limitations. The Metro Wastewater Reclamation District in Denver, Colorado, operated two full-scale secondary treatment trains to compare the existing biological nutrient removal configuration (Control) to one that was modified to operate with an anaerobic selector and with hydrocyclone selective wasting (Test) to induce granulation. Results from this evaluation showed that the Test achieved significantly better settling behaviour than the Control. The difference in the mean diluted SVI30 between the Test and Control were statistically significant (P < 0.05), with values of 77 ± 17 and 135 ± 25 mL/g observed for the Test and Control respectively. These settling results were accompanied by differences in the particle size distribution, with notably higher settling velocities commensurate with increasing particle size. The degree o...

Full scale performance of the aerobic granular sludge process for sewage treatment

Water Research, 2015

Recently, aerobic granular sludge technology has been scaled-up and implemented for industrial and municipal wastewater treatment under the trade name Nereda ®. With full-scale references for industrial treatment application since 2006 and domestic sewage since 2009 only limited operating data have been presented in scientific literature so far. In this study performance, granulation and design considerations of an aerobic granular sludge plant on domestic wastewater at the WWTP Garmerwolde, the Netherlands were analysed. After a start-up period of approximately 5 months, a robust and stable granule bed (>8 g L À1) was formed and could be maintained thereafter, with a sludge volume index after 5 min settling of 45 mL g À1. The granular sludge consisted for more than 80% of granules larger than 0.2 mm and more than 60% larger than 1 mm. Effluent requirements (7 mg N L À1 and 1 mg P L À1) were easily met during summer and winter. Maximum volumetric conversion rates for nitrogen and phosphorus were respectively 0.17 and 0.24 kg (m 3 d) À1. The energy usage was 13.9 kWh (PE 150 $year) À1 which is 58e63 % lower than the average conventional activated sludge treatment plant in the Netherlands. Finally, this study demonstrated that aerobic granular sludge technology can effectively be implemented for the treatment of domestic wastewater.

PERFORMANCE EVALUATION OF EXTRINSIC FACTORS AFFECTING GRANULATION IN SEWAGE

The up-flow anaerobic sludge blanket reactor (UASBR) has been used to effectively treat the variety of wastewaters. Decades of investigations and explorations in the field of anaerobic wastewater treatment have resulted in the noteworthy indications about the significance function of the sludge granules in biodegradation anaerobic process. It is understood that the performance of reactor depends on the formation of granules. An outline on the theory of up-flow anaerobic sludge blanket UASB reactor process as well as the main parts of the reactor is briefly explained in this paper. The aim of this paper is to investigate and assess the mechanisms of granules initiation and development of granules inside the UASB reactor. The factors reviewed are pH and alkalinity, temperature, nutrients, organic loading rate, cations and heavy metals.