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

Abstract

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 of granulation observed in the Test train was between 32 and 56% of the mass greater than ≥250 μm in particle size whereas 16% of the mixed liquor in the Control was ≥250 μm over the entire study period. The improved settling behaviour of the Test configuration may translate into an increase of secondary treatment capacity during winter by 32%.

Biological process architecture in continuous‐flow activated sludge by gravimetry: Controlling densified biomass form and function in a hybrid granule–floc process at Dijon WRRF, France

“…Specifically, in our proposal, densified biomass is a hybrid floc–granule sludge showing a dSVI of approximately between 30 and 80 ml/g, with a mass proportion of approximately 20% to 50% of dense biomass aggregate particles greater than 200 μm. These range also fall in accordance with Avila et al (2021), which exposed a similar relationship of granule proportions to dSVI with hybrid granule floc sludge obtained from similar external gravimetric selection method, but with a granule definition of size >250 μm.…”

“…Specifically, in our proposal, densified biomass is a hybrid floc-granule sludge showing a dSVI of approximately between 30 and 80 ml/g, with a mass proportion of approximately 20% to 50% of dense biomass aggregate particles greater than 200 μm. These range also fall in accordance with Avila et al (2021), which exposed a similar relationship of granule proportions to dSVI with hybrid granule floc F I G U R E 9 Seasonal form and function biological architecture evolution describing the vicious annual bulking circle of CAS sludge (in blue), revolving in large span range of dSVI seasonal variations, while densified biomass (in green) breaks the loop and stabilizes in a new steady state circle under the cyclone-induced morphology shift sludge obtained from similar external gravimetric selection method, but with a granule definition of size >250 μm.…”

“…The first facility to implement the technology using hydrocyclones in continuous‐flow configuration was Strass in Austria in 2012 in an oxidation ditch process, with over 25 installations in the past 9 years in various other formats of continuous‐flow configurations, including continuous‐flow anaerobic‐anoxic‐oxic (A 2 O) configuration (Avila et al, 2021), anaerobic‐oxic (AO) simultaneous nitrification/denitrification (SND) configuration (Regmi et al, 2019), modified Ludzack‐Ettinger (MLE) configuration (An et al, 2021; Partin, 2019) integrated fixed‐film activated sludge (IFAS) four‐stage Bardenpho configuration (Ford et al, 2016; Partin, 2019), and membrane bioreactors (Noguchi et al, 2018; Zhuzbay et al, 2021). Despite this large diversity of installations, a detailed morphological transition of hydrocyclone based densification is missing, and opportunities for its control are needed.…”

Effect of the famine phase length on the properties of aerobic granular sludge treating greywater

“…The EPS content is a factor which define the strength and stability of the granular biomass (Rusanowska et al 2019;Avila et al 2021). EPS tightly bound with cells (TB-EPS) form an inner matrix which provides structural stability to granules.…”

“…The installation of decentralized greywater treatment systems to reclaim water for non-potable uses and nutrients, requires a set of low footprint and efficient technologies (Bajpai et al 2019). Greywater can be efficiently treated by sequencing batch reactors (SBR) with aerobic granular sludge (AGS), which is a biofilm that presents remarkable properties, such as high density (κg) and settling velocity (v s ), low sludge volume index and a structure which withstands toxics and organic shocks with high substrate (r s ) and oxygen (OUR) uptake rates (Sengar et al 2018;Sharaf et al 2019;Avila et al 2021). These characteristics allow an efficient solid-liquid separation, as well as the application of high volumetric exchange ratios (V er ) and short aeration and settling stages; key parameters to reduce the hydraulic retention time (HRT).…”