Application of image analysis in activated sludge to evaluate correlations between settleability and features of flocs and filamentous species

Abstract

Digital image analysis is a useful tool to estimate some morphological parameters of flocs and filamentous species in activated sludge wastewater treatment processes. In this work we found the correlation between some morphological parameters and sludge volume index (SVI). The sludge was taken from a pilot-scale activated sludge plant, owned by ENEA, located side stream to the Trebbo di Reno (Bologna, Italy) municipal WWTP and fed by domestic wastewater. In order to use image analysis, we developed a correct method to acquire digital microbiological observations and to obtain images altogether representative of the sludge properties. We identified and assessed the parameters needed to estimate the settleability of the sludge and evaluated the morphological filamentous features. It is known that several conditions (i.e. low F/M, nutrient deficiency, low dissolved oxygen) select specific filamentous species and their excessive growth decrease floc-forming/filaments ratio, correspond to the worse settleability properties; we found a relationship between the relative abundance of filamentous species and SVI. We also evaluated the fractal dimension parameter (FD) and determined a threshold value useful to distinguish between the "weak" and "firm" floc and we found a correlation between FD and SVI.

Activated sludge characterization through microscopy: A review on quantitative image analysis and chemometric techniques

“…Fast, simple and effective methodology for deviating conditions in AS [60] Pilot-plant Dark-field Relate the morphology of the sludge flocs with traditional settling indexes [62] Lab-scale SBR Bright-field and TEM Sludge flocs at lower solids retention time (SRT) were more irregular and more variable in size with time than those at higher SRT [65] Full-scale FISH and CLSM Several parameters of flocs were obtained by a 3D reconstructed image [69] Full-scale Bright-field Shape factors were found to be useful as a measure of softness or stiffness of the flocs [74] Lab-scale Bright-field Gram-negative/Gram-positive filamentous bacteria determination [76] SBR Bright-field PHB storage in filaments [93] Lab-scale SBR Epifluorescence and CLSM Antibiotic time-kill activity was quantified [107] Lab-scale EBPR Epifluorescence Novel method for intracellular storage polymers [109] Full-scale FISH and CLSM Demonstration of a quantified method for enumerating bacteria in samples in which cells are not homogeneously distributed [110] Full-scale FISH and CLSM Direct determination of the floc volume, heterogeneity factors and the population structure of AS flocs [141] Lab-scale Bright-field Method for quality assessment of AS [142] Lab-scale SBR Bright-field Biomass deflocculation with antibiotics [144] Shake flasks Epifluorescence Effects on flocs morphology are significantly influenced even at low concentrations of surfactants [145] Full-scale Phase-contrast Flocs and filaments were recognized using shape descriptors [146] Lab-scale Phase-contrast Correlation between SVI and filamentous bacteria and aggregated biomass [147] Lab-scale Phase-contrast Shape descriptors of flocs and filaments correlated with sludge settling ability [148] Lab-scale Phase-contrast Robust procedure with results for a set of parameter values for a wide variety of image types [149] Full-scale and Lab-scale SBR Bright-field The number of microbial aggregates and the influence of dilution was established [152] Pilot-scale Bright-field Flocs fractal dimensions related to SVI [153] Full-scale Bright-field Deflocculation of aggregated biomass with salt addition [154] Lab-scale SBR Bright-field Identification of biomass flocculation and deflocculation [155,156] Lab-scale Bright-field The effect of surfactant on the flocs of activated sludge can be quantitatively described by the morphological parameters…”

Identifying different types of bulking in an activated sludge system through quantitative image analysis

“…Furthermore, the association of image processing and analysis methodologies with microscopy visualization allows an accurate evaluation of the activated sludge status (Li and Ganczarczyk, 1991;Grijspeerdt and Verstraete, 1997). Several authors (da Motta et al, 2002;Cenens et al, 2002;Amaral and Ferreira, 2005;Jenné et al, 2006;Mesquita et al, 2009a,b;Arelli et al, 2009) have already proposed an array of image analysis procedures to characterize and relate operating parameters, such as the SVI, with biomass structure of activated sludge systems, mainly in terms of aggregated and filamentous biomass. However, up to the present, most studies relating SVI and sludge morphological properties have been focused on filamentous bulking conditions solely (da Motta et al, 2002;Amaral and Ferreira, 2005).…”

The effect of alternating influent carbon source composition on activated sludge bioflocculation

“…Monitoring flocs and floc size or in the case of deflocculation, floc break-up into smaller flocs and the subsequent release of microcolonies and primary particles, offers a more direct view on the (dynamics of the) bioflocculation process (Jarvis et al, 2005, Van Dierdonck et al, 2012b. This can be achieved by microscopic image analysis which has already proven its merits, e.g., in the filamentous bulking context (Arelli et al, 2009;da Motta et al, 2001;Jenné et al, 2007). However, monitoring activated sludge flocs and more specific, activated sludge primary particles and microcolonies in the context of bioflocculation has not received much attention yet.…”