Jan A. Oleszkiewicz

Sulfide inhibition of anaerobic degradation of lactate and acetate

Abstract Bench-scale batch anaerobic degradation of lactate and acetate was investigated using three sets of serum bottles. All serum bottles were fed 1g 1−1 COD and 15.6 mM (1.5 g 1−1) SO42− at the start of the experiment. Set one (SL) used lactic acid, set two (SA) used acetic acid, and set three (SM) used a 1:1 mixture on a COD basis of the two organic acids. Each set consisted of 10 serum bottles of which 5 were started at a pH of 7 and 5 at a pH of 8. Each pH subset reactor had a different initial total sulfide (TS) concentration, which varied from 3.13 to 31.3 mM (100–1000 mg 1−1). Acetate removal followed first order reaction kinetics and proceeded without any significant sulfate reduction. Inhibition of acetate removal by aqueous hydrogen sulfide (H2S) was modeled using an exponential function. Both propionate removal and sulfate reduction were inhibited proportionally to the concentration of TS. This suggests a crucial role for the sulfate reducing bacteria in mediating propionate degradation to acetate. In the low pH subset of SM, complete inhibition of sulfate reduction occurred at only 17% inhibition of methanogenesis. Complete COD removal occurred in all the serum bottles of the high pH subsets, indicating the important role of H2S in sulfide inhibition.

Anaerobic co‐composting of municipal solid waste and waste sludge at hlgh total solids levels

Abstract The feasibility of anaerobic co‐composting of waste activated sludge (WSS) and simulated organic fraction of typical North‐American municipal solid waste (NA‐MSW), rich in lignocellulosics, at high total solids (TS) content, was examined. Sixteen semicontinuous reactors were run, at 4 levels of TS (25, 30, 35 and 40%), 2 levels of retention time (15 and 21 days), 2 temperature regimes (mesophilic at 39°C and thermophilic at 53°C), and 2 ratios of MSW‐to‐WSS (1: 1 and 2: 1 on total weight basis). Reactors operated at 35% TS and 21 days gave the best organic matter removal efficiencies (up to 44% and 53% on volatile solids basis, for mesophilic and thermophilic regimes respectively) and highest biogas productivities (up to 6 L kg‐1 reactor content day‐1). The methane concentration in biogas was between 55 and 60%. Successful thermophilic reactors generated 15 to 30% more biogas than the corresponding mesophilic digesters. Instability and failure of some thermophilic reactors at 15 days retention ti...

Importance of the operating pH in maintaining the stability of anoxic ammonium oxidation (anammox) activity in moving bed biofilm reactors

Two bench-scale parallel moving bed biofilm reactors (MBBR) were operated to assess pH-associated anammox activity changes during long term treatment of anaerobically digested sludge centrate pre-treated in a suspended growth partial nitrification reactor. The pH was maintained at 6.5 in reactor R1, while it was allowed to vary naturally between 7.5 and 8.1 in reactor R2. At high nitrogen loads reactor R2 had a 61% lower volumetric specific nitrogen removal rate than reactor R1. The low pH and the associated low free ammonia (FA) concentrations were found to be critical to stable anammox activity in the MBBR. Nitrite enhanced the nitrogen removal rate in the conditions of low pH, all the way up to the investigated level of 50mg NO(2)-N/L. At low FA levels nitrite concentrations up to 250 mg NO(2)-N/L did not cause inactivation of anammox consortia over a 2-days exposure time.

Effects of predation and ORP conditions on the performance of nitrifiers in activated sludge systems.

Effects of changing oxidation-reduction potential (ORP) and grazing of protozoa on nitrifiers in activated sludge systems was investigated. This study used sequencing batch reactors which were acclimated under aerobic and alternating anoxic/aerobic conditions, with and without inhibition of protozoa, the predatory microorganisms. The feed used was a synthetic wastewater containing beef and yeast extracts as a carbon source. It was found that the biomass, determined by mixed liquor volatile suspended solids (MLVSS) in the reactors, was significantly affected by predation while ORP (aerobic and alternating anoxic/aerobic conditions) has no impact on the MLVSS regardless of the presence or absence of predation. However, the nitrification rates in the reactors show completely different trends indicating that the ORP of the system has a significant impact on the rates while predation does not. It was found that nitrification rates in alternating reactors were almost double the rates in the aerobic reactors, both with and without predatory inhibition. The decay rate of autotrophic bacteria (b(A)) in aerobic reactors was determined by tracking the decrease of the maximum nitrification rate under both anoxic and aerobic starvation conditions. The b(A) in alternating anoxic/aerobic reactors was also determined under alternating starvation conditions. It was found that, in any case, the alternating anoxic/aerobic autotrophic biomass b(A) was much smaller that the b(A) of aerobic biomass determined under aerobic and anoxic starvation conditions. The alternating anoxic/aerobic b(A) was 62.1% less than the aerobic biomass b(A) under aerobic starvation and 40.2% less for the aerobic biomass starved under anoxic conditions. No statistically significant differences in b(A) were observed between reactors with or without the inhibition of predators.

VFA generation from waste activated sludge: Effect of temperature and mixing

The success of enhanced biological phosphorus removal (EBPR) depends on the constant availability of volatile fatty acids (VFAs). To reduce costs, waste streams would be a preferred source. Since VFAs were shown to vary in the incoming sewage and fermentate from primary sludge the next available source is waste activated sludge (WAS). The opportunity is particularly good in plants where WAS is stored before shipment. Little information is however available on the rate of VFA release from such sludge, especially at the lower temperatures and under the storage conditions typically found in colder climates. Bench-scale batch tests were performed to investigate the effect of temperature and requirement for mixing on VFA generation from WAS generated in full scale non-EBPR wastewater treatment plant. WAS fermentation was found highly temperature-dependent. Hydrolysis rate constant (k(h)) values of 0.17, 0.08 and 0.04 d⁻¹ at 24.6, 14 and 4°C were obtained, respectively. Arrhenius temperature coefficient was calculated to be 1.07. It took 5 d to complete hydrolysis at 24.6°C, 7 d at 14°C, and 9 d at 4°C. The fermentation lasted for 20 d. At 24.6°C the mixed reactor reached 84% of the overall VFA production only in 5 d. When temperature dropped to 14 and 4°C, the ratio of VFA production at day 10 to overall VFA production in the mixed reactor were 62% and 48%, respectively. The overall VFA-COD concentration in the non-mixed reactors was much lower than the mixed reactors. The information is important for the designer as there was uncertainty with the effect of temperature and mixing on sludge fermentation.

Impact of shear force on the biofilm structure and performance of a membrane biofilm reactor for tertiary hydrogen-driven denitrification of municipal wastewater

Hydrogen-driven denitrification using a hollow-fiber membrane biofilm reactor (MBfR) was evaluated for operation in tertiary wastewater treatment. Specific objectives were to evaluate the impact of different levels of shearing stress caused by mixing and nitrogen sparging on the biofilm structure and denitrification rates. Applying high shear force proved to be effective in improving denitrification rates by reducing the thickness of the biofilm. With intensive mixing a biofilm thickness of approximately 800 microm was maintained, while additional nitrogen sparging could further reduce the biofilm thickness to approximately 300 microm. The highest denitrification rates of 0.93 gN/m(2)d were obtained when biofilm thickness was lower than 500 microm. Lower extracellular polymeric substances (EPS) accumulation and carbohydrates to protein ratio observed in thinner biofilms allowed for higher nitrate removal in the system. No significant sloughing of biomass or change in total and soluble COD in the final effluent was observed under steady-state conditions.

Effects of pH on sulfide toxicity to anaerobic processes

Abstract Effects of sulfide on anaerobic degradation of lactate, butyrate, propionate (Pr) and acetate (Ac) were studied in batch serum bottles. Maintenance of higher pH = 7.7–7.9 allowed for tolerance of much higher concentrations of sulfide pointing to un‐ionized H2S as the inhibitory sulfide species. Concentration thresholds of 50% inhibition by total and un‐ionized sulfide were determined. Lactate utilization was the least affected while propionate degradation was the most affected by sulfide. Data analysis using semi‐log graphs of substrate utilization rates vs. sulfide produced retardation coefficients (k) of 0.6 L mg−1 for acetate and 1.2 L mg−1 for propionate. Retardation was more pronounced in a mixed Ac/Pr run than in pure Ac and Pr runs.

Influence of electric current on bacterial viability in wastewater treatment.

Minimizing the influence of electric current on bacterial viability in the electro-technologies such as electrophoresis and electrocoagulation is crucial in designing and operating the electric hybrid wastewater treatment system. In this study the biomass from a membrane bioreactor (MBR) was subjected to constant direct current and the bacterial viability was monitored against electrical intensity, duration as well as the spatial vicinity related to the electrodes. It was found that the bacterial viability was not significantly affected (less than 10% of death percentage) when the applied electric current density (CD) was less than 6.2 A/m2 after 4 h. The percentage of live cell dropped by 15% and 29% at CD of 12.3 A/m2 and 24.7 A/m2, respectively. The pH of electrolytic biomass fluid has shifted to alkaline (from nearly neutral to around pH 10) at CD above 12.3 A/m2, which could have been the contributing factor for the bacterial inactivation. The temperature change in the electrolytic media at all current densities during 4 h of experiment was less than 2 °C, thus temperature effects were negligible. Bacteria experienced different micro-environments in the electrochemical reactor. Bacterial cells on the cathode surface exhibited highest death rate, whereas bacteria outside the space between electrodes were the least affected. It was concluded that in an electro-technology integrated wastewater treatment process, sufficient mixing should be used to avoid localized inactivation of bacterial cells.

Impact of free ammonia on anammox rates (anoxic ammonium oxidation) in a moving bed biofilm reactor

Using a bench scale moving bed bioreactor (MBBR), the effect of free ammonia (FA, NH(3), the un-ionized form of ammonium NH(4)(+)) concentration on anoxic ammonium oxidation (anammox) was evaluated based on the volumetric nitrogen removal rate (NRR). Although, a detailed microbial analysis was not conducted, the major NRR observed was assumed to be by anammox, based on the nitrogen conversion ratios of nitrite to ammonium and nitrate to ammonium. Since the concentration of free ammonia as a proportion of the total ammonia concentration is pH-dependent, the impact of changing the operating pH from 6.9 to 8.2, was investigated under constant nitrogen loading conditions during continuous reactor operation. Furthermore, the effect of sudden nitrogen load changes was investigated under constant pH conditions. Batch tests were conducted to determine the immediate response of the anammox consortium to shifts in pH and FA concentrations. It was found that FA was inhibiting NRR at concentrations exceeding 2 mg N L(-1). In the pH range 7-8, the decrease in anammox activity was independent of pH and related only to the concentration of FA. Nitrite concentrations of up to 120 mg N L(-1) did not negatively affect NRR for up to 3.5 h. It was concluded that a stable NRR in a moving bed biofilm reactor depended on maintaining FA concentrations below 2 mg N L(-1) when the pH was maintained between 7 and 8.

Correlations between trans-membrane pressure (TMP) and sludge properties in submerged membrane electro-bioreactor (SMEBR) and conventional membrane bioreactor (MBR)

The influence of sludge properties in SMEBR and conventional MBR pilot systems on membrane fouling was investigated. Generated data were analyzed using statistical analysis Pearsons product momentum correlation coefficient (r(p)). Analysis showed that TMP had strong direct (r(p)=0.9182) and inverse (r(p)=-0.9205) correlations to mean particle size diameter in MBR and SMEBR, respectively. TMP in SMEBR had a strong direct correlation to the sludge mixed liquor suspended solids concentration (MLSS) (r(p)=0.7757) while a weak direct correlation (r(p)=0.1940) was observed in MBR. SMEBR showed a moderate inverse correlation (r(p)=-0.6118) between TMP and soluble carbohydrates (EPS(c)) and a very weak direct correlation (r(p)=0.3448) to soluble proteins (EPS(p)). Conversely, EPS(p) in MBR had more significant impact (r(p)=0.4856) on membrane fouling than EPS(c) (r(p)=0.3051). The results provide insight into optimization of operational conditions in SMEBR system to overcome membrane fouling.