Ebru Dulekgurgen

Characterization of exopolysaccharides from floccular and aerobic granular activated sludge as alginate-like-exoPS

AbstractAs a component of activated sludge (AS) extracellular polymeric substances, exopolysaccharides (exoPS) have been associated with contributing physically and chemically to the structural strength and coherence of both conventional (floccular) (CAS) and aerobic granular activated sludge (GAS). The study aims at characterization of exoPS extracted from CAS fed first with synthetic wastewater, then with brewery effluent and from GAS treating the latter. CAS and GAS exoPS were analyzed for their gel-forming capacity, morphology, and moisture content of the formed hydrogels, and chemical properties of the extracted exoPS by Fourier transform infrared (FTIR) spectroscopy. Commercially available sodium alginate was used as the reference polysaccharide for comparison. The extracted exoPS from both CAS and GAS formed hydrogels or gel-like structures in CaCl2 solution, similar to CaCl2 reactions of alginate. Environmental scanning electron microscopy images displayed similarities in the morphologies of hydro...

Experimental evaluation and model assessment of coexistence of PAOs and GAOs

The study evaluated the competition and co-existence of PAOs and GAOs in sequencing batch reactor (SBR) systems sustaining enhanced biological phosphorus removal (EBPR). The SBR operation used acetate as the sole external carbon source and covered a wide range of initial COD/P ratios between 6.5 to 25.9 g COD/g P. A mechanistic model, ASMGG, was adopted for this purpose, which basically incorporated model components and processes associated with GAO metabolism and glycogen metabolism of PAOs. Model calibration was successfully performed with the same set of stoichiometric and kinetic coefficients for all the acetate, phosphate, glycogen and PHA profiles obtained in different experiments. Interpretation of experimental results by means of model simulation indicated competition and co-existence of PAOs and GAOs within the EBPR process, numerically assessing the composition of the microbial community sustained and identifying the respective role and function of PAOs and GAOs on the fate of glycogen and PHA.

Conventional Morphological and Functional Evaluation of the Microbial Populations in a Sequencing Batch Reactor Performing EBPR

Abstract To help confirm and interpret the Enhanced Biological Phosphorus Removal (EBPR) performance of the microbial populations in a laboratory-scale activated sludge (AS) system, conventional microscopic examinations were carried out. A lab-scale sequencing batch reactor (SBR), named ARC, was fed with acetate, as the sole carbon source, and operated for EBPR. Daily monitoring and cyclic behavior evaluation studies indicated that the system always worked for EBPR in the long run, with efficiencies depending on the influent characteristics and operational stability. Poly-P and PHB-staining experiments revealed that the enriched biomass of the reactor was quite diverse in terms of morphology, hosting populations of traditional rod-shaped PAOs, tetrad/sarcina-like cells (referred here as TFOs, rather than GAOs), diplococci-shaped cells, and staphylococci-like clustered populations, in addition to few filaments. Although the microscopic observations were qualitative, rather than quantitative, they seemed likely to correlate well to the biochemical performance of the reactor.

Effects of high-concentration influent suspended solids on aerobic granulation in pilot-scale sequencing batch reactors treating real domestic wastewater

The aim of this study was to investigate the effect of high-influent-concentration suspended solids (SS) on the cultivation, structure and long-term stability of aerobic granular sludge (AGS). Cultivation and long-term stability of AGS were monitored in two pilot-scale sequencing batch reactors fed with raw (R1) and settled (R2) domestic wastewater, representing high and medium SS content, respectively. The real domestic wastewater had high chemical oxygen demand (COD) content (1100 ± 270 mg COD L-1). Aerobic granular sludge was cultivated in 44 days (R1) and 25 days (R2) under the conditions of high settling velocity (18 m h-1) and high organic loading rate (OLR) (2.1-2.4 kg COD m3 day). The AGS in both reactors had similar structural properties during long-term operation and remained structurally and functionally stable during the last five months of operation. Comparative evaluation of the results indicated that the high influent SS content of the real domestic wastewater had a positive influence on maintaining significantly lower SVI30 and relatively lower effluent SS concentration. Moreover, a higher influent SS content resulted in smaller mature granules during the stable period. Microbial community analyses helped to understand the aerobic granular sludge structure and showed that the sludge retention time and OLR affected the granular sludge population. The high influent SS increased biomass detachment from the granular sludge surface and caused wash-out of some bacteria colonizing the exterior of the granular sludge.

Improving the settling properties of activated sludge by gradually decreasing the settling time

AbstractThe study aims at evaluating the impact of gradually decreasing the settling time on settling properties of activated sludge removing organic matter. For that, a lab-scale sequencing batch reactor (SBR), fed with soluble starch and acetate, was seeded with floccular biomass. As the selected strategy to washout slowly settling flocks and retain biomass with improved settling capacity, settling time (Ts) was decreased gradually from 45 to 30, 15, 5 and 1 min. Long-term monitoring showed that each time the Ts was decreased to the next lower level, there was biomass washout. Yet high amount of biomass (10 g MLVSS/L) with improved settling properties (sludge volume index ⩽ 16 mL/g) and high chemical oxygen demand (COD) removal performance (97%) was maintained with a Ts as low as 5 min. Further decreasing Ts to 1 min did not impose any negative effect. Biomass maintenance, settling properties, and COD removal performance of the system were comparable with those of aerobic granular biomass. Yet, minimum ...

Follow-up on Rubric-Based Assessment of Student Outcomes by Senior-Year Graduation Design Project and Continuing to Improve by Performance Indicator Breakdown-Based Assessment

The study is a follow-up on rubric-based assessment of level of attainment of Student Outcomes (SOs) in Environmental Engineering undergraduate education by the senior-year Graduation Design Project (GDP): the focal points are the process of and results from incorporation of additional assessment tools and implementation of “Performance Indicator (PI)-breakdown” to continue improving the SO Assessment and Evaluation (A&E) process. For several consecutive cycles, A&E to define attainment level of total of seven SOs by the GDP gave results below the set thresholds for some of them (SO1, 5, 8), which indicated a discrepancy and a need for improvement in the assessment tools and processes. Accordingly, two remedial actions were undertaken to meet those needs and the SOs were re-assessed. Results of the previous and improved SO A&E process revealed a clear progress in SO attainment addressed by the GDP, from 2014–15 to 2015–16, upon choice and addition of other tools. Yet, those still gave a general sense of deficiencies at SO-level. Therefore, some additional tools were added and the “PI-breakdown”-based approach was implemented. Those informative results are combined successfully with the formerly improved SO A&E process, facilitating attainment of more realistic results and further fine tuning of the SO A&E process.

The Effect of Sludge History on Aerobic Sludge Stabilization Efficiency

This paper evaluated the effect of sludge history on the efficiency of aerobic sludge stabilization. The fate of excess sludge in activated sludge systems is closely related to the nature of biomass sustained in the system. The composition of biomass greatly affects stabilization performance. In this study, the impact of sludge history was investigated for different sludge ages in the range of 1–35 days in a system treating typical domestic sewage. A biochemical model was adopted to define particulate COD components for selected sludge ages. For each selected sludge age, the progress of aerobic stabilization was evaluated in terms of the same parameters for a period of 30 days. Model simulation indicated that the active fraction of the biomass (X H ) varied between 0.13–0.40 depending on the sludge age of the systems at the beginning of the stabilization period. It also showed that the nature of the biomass corresponding to a selected sludge age was a key factor determining the stabilization efficiency.

Morphological and Physiological Features of an Aerobic Granular EBPR Biomass Fed with Propionate

The current study is an attempt to link the morphological and EBPR-related physiological traits of a propionate-fed aerobic granular biomass with the EBPR performance of the system. A lab-scale SBR was started up by the aerobic granular EBPR biomass taken from an acetate-fed SBR and the inoculum was acclimated to propionate as the sole C-source. Mechanical-mixing applied during 2-h of anaerobiosis at the head of the cycle was the main source of shear (v SMix; 7.6 cm/s), thus hydraulic selection pressure, and feeding the system under anaerobic conditions for 1 h at the head of the cycle, as well as supplying ortho-P in the influent (COD:P=12.8 mg COD/mgPO4-P) were the main metabolic-selection pressures ensuring the dynamic formation, maintenance, and stability of the aerobic semi-granular EBPR biomass (d gra; 1.41 mm) with superior settling properties and compactness (SVI≤50 mL/g), and promoting the selection of anaerobically C-storing (>95% anaerobic COD-removal), aerobically slowly growing and P-removing organisms –the PAOs- in the system, resulting in an acceptable level of EBPR performance (78% EBPR efficiency). The biomass was considerably diverse with various morphotypes being present (rods, filaments, tetrads/sarcina-like cells, coccoid-clusters, diplo-coccoids, and elongated rod-shaped cells unique for the system). Phenotypic characterization via chemical-staining and conventional light-microscopy revealed the presence of the PAOs cycling their intracellular poly-P and PHB inclusions between the anaerobic and aerobic phases. Tetrads/sarcina-like cells (TFOs) resembled the GAOs morphologically but not phenotypically. Elongated rod-shaped cells (PUBs), which had the ability to anaerobically utilize propionate and store it as PHB, were speculated to be either GAOs or functionally less efficient PAOs. Microbiological observations were qualitative, rather than quantitative, yet they found to correlate to an extend with the observed biochemical performance of the system.