Respirometric tests in a combined UASB-MBR system treating wastewater containing emerging contaminants at different OLRs and temperatures: Biokinetic analysis

This research focuses on the application of respirometric techniques to provide new insights into the biokinetic behaviour of bacterial species developed in an Upflow Anaerobic Sludge Blanked -UASB reactor combined with a membrane bioreactor -MBR, treating urban wastewater with emerging contaminants frequently found in this kind of effluents. The lab-scale pilot plant was operated at different metabolic and operational conditions by limiting the organic loading rate- OLR of the influent. In a first stage, the MBR was performed with suspended biomass, while in a second stage bio-supports were introduced to operate coexisting suspended and fixed biomass. From the results of the microscopic monitoring of sludge, it was concluded that the decrease in OLR resulted in a greater disintegration of the floc structure, more dispersed growth, and a low presence of inter-floccular bonds. However, no effect of toxicity or inhibition of microorganisms caused by the presence of emerging contaminants -ECs was determined. Kinetic modelling was carried out to study the behaviour of the system. The results showed a slowing down of biomass degradative capacity at low OLR stages and operating at low temperatures of mixed liquor. In addition, a decrease in oxygen consumption was observed with decreasing biodegradable substrate, resulting in lower degradation of organic matter. Mean values of specific oxygen uptake rate and heterotrophic biomass yield at low OLR were SOUR end = 1.49 and 1.15 mg O2· g MLVSS−1 h−1 and YH,MLSSV end = 0.48 and 0.28 mg MLVSS· mg COD−1substrate at stage 1 (suspended biomass) and stage 2 (suspended and supported biomass), respectively. From the analysis of the endogenous decomposition constant (kd), a higher cell lysis was determined operating with suspended biomass (kd = 0.03 d−1) in comparison to the operation coexisting suspended and supported biomass (kd = 0.01 d−1). Heterotrophic biomass yield values (YH, MLVSS = 0.48 ± 0.06, 0.40 ± 0.01 and 0.29 ± 0.01 mg MLVSS· mg COD−1substrate at high, medium and low OLR) showed lower sludge production at low OLR due to the influence of substrate limitation on cell growth.Spanish Ministry of Economy and Competitiveness through the projects “Combined System UASB + SMEBR + O3/AC (CTM 2016-76910-R)” and “Combined treatments for the degradation and/or elimination of emerging pollutants in water” (CTM 2013-46669-R) and University of Alicante

Integrated Fixed Film Activated Sludge (IFAS) membrane BioReactor: The influence of the operational parameters

The present paper investigated an Integrated Fixed Film Activated Sludge (IFAS) Membrane BioReactor (MBR) system monitored for 340 days. In particular, the short-term effects of some operational parameters variation was evaluated. Results showed a decrease of the removal rates under low C/N values. Respirometry results highlighted that activated sludge was more active in the organic carbon removal. Conversely, biofilm has a key role during nitrification. The major fouling mechanism was represented by the cake deposition (irreversible)

Biofilm Control in a Fludized Bed Bioreactor (FBBR) Treating Municipal Wastewater: Optimization, Modeling, and Nitrous Oxide (N2O) Emissions

Among the various biological wastewater treatment processes for industrial and municipal wastewater treatment, fluidized bed bioreactors (FBBR) demonstrate numerous advantages compared to suspended growth systems such as lower hydraulic retention time, high surface area and accordingly high biomass retention time, higher volumetric conversion rates, lower sensitivity to temperature, and less sludge production. Despite the numerous biofilm bioreactor configurations and system schemes that are currently available for a wide variety of environmental applications, the development and optimization of a stable biofilm that is capable of offering effective and integrated functions, i.e. biodegradation, biomass-liquid separation, and biomass retention along with a substantial reduction of nitrous oxide (N2O) emissions is still challenging. To achieve this goal, this work addresses four separate but interconnected projects with a focus on denitrifying biofilm in FBBR. First, biofilm morphology and structure was investigated by changing the media properties, i.e. sphericity, surface roughness, and specific surface area. Four different types of media (natural and artificial) were tested and it was found that particles with sphericity of 0.9 (multi-blast plastic (MB) and natural zeolite (NZ)) maintained a fluffy protruding biofilm and achieved slightly higher nutrient removal efficiencies as compared to particles with a sphericity of 0.5 (maxi-blast plastic (MX) and lava rock (LR)), which exhibited a patchy biofilm at low COD-to-nitrogen (COD/N) ratio. The second study explored influent wastewater characteristics to change and control the biofilm thickness, morphology, and structure in denitrifying FBBRs as well as enhance biofilm strength. The DFBBRs were operated on a synthetic municipal wastewater at five different characteristics at two different COD/N ratios of 5 and 3.5. The third study involved the use of the developed methodology to mitigate N2O emissions from denitrification processes. It was found that the N2O conversion rate at typical municipal wastewater was about 0.53% of the influent nitrogen loading, whereas the N2O conversion rates for R120,R180,and R240 were 0.34%, 0.42%, and 0.41%, respectively. At the higher nitrogen loading, the N2O conversion rate of R60 increased three folds to 1.57% of the influent nitrogen loading. Finally, a biofilm calibration protocol was developed for biofilm one-dimensional (1-D) fully dynamic and steady-state biofilm simulation models. The developed calibration protocol sets a complete strategy to model particulate biofilm reactors and proposes a method to collect the data and translate it to useful information. The detailed calibration procedures presented here will not only help the process engineers design and retrofit plants but also plan sampling and monitoring requirements for process optimization. Sensitivity analysis was also used to identify the most important biofilm parameters and guide experimental measurements

Application of a novel respirometric methodology to characterize mass transfer and activity of H2S-oxidizing biofilms in biotrickling filter beds

The elimination capacity of gaseous H2S biofiltration can be limited either by mass transfer or bioreaction in the biofilm. Assessment of the biological activity of immobilized cells (biofilm) usually implies morphological and physiological changes during the adaptation of cells to respirometric devices operated as suspended cultures. In this study, respirometry of heterogeneous media is advised as a valuable technique for characterizing mass transport and biological activity of H2S-oxidizing biofilms attached on two packing materials from operative biotrickling filters. Controlled flows of liquid and H2S-containing air were recirculated through a closed heterogeneous respirometer allowing a more realistic estimation of the biofilm activity by the experimental evaluation of the oxygen uptake rate (OUR). Specific maximum OUR of 23.0 and 38.5 mmol O-2 (g biomass min)(-1) were obtained for Pall rings and polyurethane foam, respectively. A mathematical model for the determination of kinetic-related parameters such as the maximum H2S elimination capacity and morphological properties of biofilm (i.e., thickness and fraction of wetted area of packing bed) was developed and calibrated. With the set of parameters obtained, the external oxygen mass transport to the wetted biofilm was found to limit the global H2S biofiltration capacity, whereas the non-wetted biofilm was the dominant route for the gaseous O-2 and H2S mass transfer to the biofilm. Oxygen diffusion rate was the limiting step in the case of very active biofilms.Peer ReviewedPostprint (author’s final draft

Microsieving as a Primary Treatment for Biological Nitrogen Removal from Municipal Wastewater

There has been an increased interest in alternative carbon diversion technologies in wastewater treatment to improve the efficiency and performance of primary treatment, increase treatment capacity, and minimize overall energy consumption, especially in geographies with limited space for expansion. Microsieving technologies like the rotating belt filters (RBFs) have emerged as a promising primary solids separation alternative to primary clarification. This research was conducted to study the implications of retrofitting existing wastewater treatment plants (without primary treatment) with RBF technology. In order to fully evaluate the impact of RBF in water resource recovery facilities, it is paramount to investigate the unique characteristics of the more fibrous material removed by microsieving, cellulose, mostly in the form of toilet paper, which is a major component of the particulates in raw municipal wastewater. To date, a validated method for cellulose quantification in wastewater and sludge matrices was unavailable. This research demonstrated that the Schweitzer-reagent method is a very robust and reliable cellulose quantification method in light of its reproducibility and accuracy. Sludge from the RBF was observed to contain 37±1 % cellulose (on dry basis), whereas primary clarifier sludge contained 18±0.2 % cellulose (on dry basis) which confirmed that the RBF captures the cellulose more efficiently than the primary clarifier. The contribution from this work would have great implications on wastewater research in understanding the fate of toilet-paper-cellulose, and its impact on biosolids management given the already emerging trend to increase sustainability and resource recovery. When looked in the context of the impact of the RBF on activated sludge processes, RBF effluent was compared with raw wastewater and primary clarifier effluent. This was accomplished using respirometric techniques to identify the most influential biokinetic parameters required for model simulations. The raw wastewater was predominantly biodegradable where 71% of the TCOD was observed to be biodegradable. Primary clarifier and RBF treatment increased the biodegradable fraction to 80% and 74%, respectively, by removing inert particulates by settling and microsieving, respectively. As expected, microsieving and settling do not impact the soluble components in the wastewaters. The fractionation of the particulate components was dictated by the primary treatment suspended solids removal efficiency and was observed to be comparable for the RBF effluent and the primary clarifier effluent. The implementation of different COD fractions and kinetic coefficients of the RBF effluent would improve the model simulations for design, control, and optimization of biological wastewater treatment processes employing RBF as a primary treatment. In addition, the results from this study established that the RBF offers an alternative level of treatment (to primary clarification), which removes particulate solids, without impacting nitrification and denitrification processes with total nitrogen removal efficiency ranging from 68%-73% for medium-strength wastewater. Upon modeling (using GPS-X) to predict performance for high-strength wastewater, it was observed that within the TSS removal of 27%-70% by the RBF, biological nitrogen removal was not adversely affected (79% total nitrogen removal). Moreover, the overall primary and biological sludge production by a wastewater resource recovery facility employing an RBF as primary treatment was found to be 9% lower than the one with primary clarification. Chemically-enhanced-RBF treatment was observed to be ideal for plants trying to achieve BOD and ammonia limits; however, excessive removal of carbon compromised nitrogen removal efficiency (30% total nitrogen removal), especially with low-strength wastewaters. The findings of this work would instigate further research on RBF technology for successful integration as a primary treatment alternative in wastewater resource recovery facilities

Experimental testing and modeling of partial nitrification at different temperatures

Nitrogen in wastewater treatment plant effluents has adverse environmental effects on aquatic systems. Excessive concentrations of nitrogen in water bodies can result in the depletion of dissolved oxygen, deterioration of water quality, and shifts of biotic community. Conventional biological nitrogen removal (BNR) processes consume high energy for nitrification and require external carbon for denitrification. Alternatively, partial nitrification is of interest as an emerging technology for its lower need of organic carbon addition and cost savings in aeration. In this study, the main objectives are: 1- developing a mathematical model involving operational parameters for the determination of successful partial nitrification conditions; 2- analyzing the factors affecting the performance of partial nitrification in a sequencing batch reactor (SBR) using kinetic models at 35oC; 3- investigating the effect of dissolved oxygen (DO) on nitrification in a sequencing batch reactor (SBR) treating low ammonia wastewater (40 mg N/L) at low temperature (14oC); 4- investigating the effect of nickel on nitrification in a sequencing batch reactor (SBR) treating low ammonia wastewater (40 mg N/L) at low temperature (10 oC). First, a mathematical model based on the minimum DO concentration (DOmin), minimum/maximum substrate concentration (Smin and Smax), was developed. The model evaluated the influence of pH (7-9), temperature (10oC-35oC), and solids retention time (SRT) (5days-infinity) on the minimum/maximum substrate concentration (MSC) values. In addition, specific application for shortcut nitrification-anammox process at 10oC was analyzed. Furthermore, experimental data from different literature studies was used for model simulation ii and the model prediction fitted experimental data well. The model provides a method to identify feasible combinations of pH, DO, total ammonium nitrogen (TAN), total nitrite nitrogen (TNN), and solids retention time (SRT) for successful shortcut nitrification. Second, to meet objective 2, a sequencing batch reactor (SBR) was operated at 35oC for over 4 months with dissolved oxygen (DO) and influent ammonia concentration as operating variables to evaluate nitrite accumulation. Stable partial nitrification was observed at two conditions, influent ammonia concentration of 190 mg N/L and a DO of 0.6-3.0 mg/L as well as influent ammonia concentration of 100 mg N/L and a DO of 0.15-2.0 mg/L with intermittent aeration. Kinetic parameters were determined or estimated with batch tests and model simulation. The kinetic model predicted the SBR performance well. Third, a sequencing batch reactor (SBR) treating low ammonia wastewater (40 mg N/L) at a low temperature (14 °C) was operated for 130 days. Three dissolved oxygen levels (5–6 mg O2/L, 2–3 mg O2/L, and 0.8–1.0 O2/L) were tested. Dissolved oxygen reduction resulted in lower ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) activity, with decreasing ammonia conversion ratio (ACR) and increasing nitrite accumulation ratio (NAR). The maximum growth rates of AOB and NOB determined in this study (0.28 and 0.38 d-1 ) were below the median literature values (0.47 and 0.62 d-1 ), whereas the oxygen half-saturation coefficients of AOB and NOB (1.36 and 2.79 mg/L) were higher than those found in the literature. The kinetic model explained the SBR performance well. Low dissolved oxygen, together with long solids retention time, was recommended for partial nitrification at a low temperature. Lastly, acute and chronic toxicity of nickel to nitrifiers was inverstigated. Chronic toxicity of nickel to nitrification of low ammonia synthetic wastewater was investigated at 10oC in two iii SBRs with 1 mg/L nickel dosing either from the beginning or after biomass concentration decreased to 300 mg/L. Significant nickel inhibition occurred at Ni/MLSS ratio of 2.7 mg Ni/ g MLSS. At a Ni/MLSS ratio of 4-7 mg Ni/g MLSS, ammonia oxidizing bacteria (AOB) activity was inhibited by 47%-58% after acclimatization. After long-term acclimatization to nickel at 10oC, high DO(~7mg/L) and SRT of 63-70 days, the µmax, b and Ko of AOB and NOB were determined as 0.16 d-1 , 0.098 d-1 and 2.08 mg O2/L, and 0.16 d-1 , 0.098 d-1 and 2.12 mg O2/L, respectively. Acute toxicity of nickel to nitrification at 10oC, 23oC, and 35oC was evaluated by short-term batch tests. The nickel inhibition constants based on a modified noncompetitive model for nitrification at 10oC, 23oC, and 35oC were determined. Long-term SBRs operation and short-term batch tests results were consistent. Short-term nickel inhibition of nitrifying bacteria was completely reversible

Generation of (synthetic) influent data for performing wastewater treatment modelling studies

The success of many modelling studies strongly depends on the availability of sufficiently long influent time series - the main disturbance of a typical wastewater treatment plant (WWTP) - representing the inherent natural variability at the plant inlet as accurately as possible. This is an important point since most modelling projects suffer from a lack of realistic data representing the influent wastewater dynamics. The objective of this paper is to show the advantages of creating synthetic data when performing modelling studies for WWTPs. This study reviews the different principles that influent generators can be based on, in order to create realistic influent time series. In addition, the paper summarizes the variables that those models can describe: influent flow rate, temperature and traditional/emerging pollution compounds, weather conditions (dry/wet) as well as their temporal resolution (from minutes to years). The importance of calibration/validation is addressed and the authors critically analyse the pros and cons of manual versus automatic and frequentistic vs Bayesian methods. The presentation will focus on potential engineering applications of influent generators, illustrating the different model concepts with case studies. The authors have significant experience using these types of tools and have worked on interesting case studies that they will share with the audience. Discussion with experts at the WWTmod seminar shall facilitate identifying critical knowledge gaps in current WWTP influent disturbance models. Finally, the outcome of these discussions will be used to define specific tasks that should be tackled in the near future to achieve more general acceptance and use of WWTP influent generators