MBBR System Research Articles

The inhibitory effects of reject water on nitrifying populations grown at different biofilm thickness

Suppression of nitrite oxidizing bacteria (NOB) is of vital importance to achieve successful, energy efficient, mainstream anammox processes for wastewater treatment. In this study, biofilm carriers from a fully nitrifying MBBR system, fed with mainstream wastewater, were temporarily exposed to reject water from sludge dewatering, to evaluate this as a possible strategy to inhibit NOB and achieve nitrite production under realistic conditions. Two different carrier types were compared, in which biofilm thickness was maintained at approximately 400 and 50 μm, respectively, and reject treatment was tested at different exposure time and loading rates. Reject exposure almost always resulted in an increased nitrite production in the thinner biofilm, and overall, nitrifiers growing in the thin biofilm were more sensitive than those grown in the thicker biofilm. The effect from reject exposure remained in the systems for four days after returning to mainstream operation, with nitrite production gradually increasing for three days. Increased concentrations of free ammonia correlated with reject exposure and may be the cause of inhibition, although other factors cannot be excluded.

Hybrid Moving Bed Biofilm Reactor for the biodegradation of benzotriazoles and hydroxy-benzothiazole in wastewater

A laboratory scale Hybrid Moving Bed Biofilm Reactor (HMBBR) was used to study the removal of five benzotriazoles and one benzothiazole from municipal wastewater. The HMBBR system consisted of two serially connected fully aerated bioreactors that contained activated sludge (AS) and K3-biocarriers and a settling tank. The average removal of target compounds ranged between 41% (4-methyl-1H-benzotriazole; 4TTR) and 88% (2-hydroxybenzothiazole; OHBTH). Except for 4TTR, degradation mainly occurred in the first bioreactor. Calculation of biodegradation constants in batch experiments and application of a model for describing micropollutants removal in the examined system showed that AS is mainly involved in biodegradation of OHBTH, 1H-benzotriazole (BTR) and xylytriazole (XTR), carriers contribute significantly on 4TTR biodegradation, while both types of biomass participate on elimination of 5-chlorobenzotriazole (CBTR) and 5-methyl-1H-benzotriazole (5TTR). Comparison of the HMBBR system with MBBR or AS systems from literature showed that the HMBBR system was more efficient for the biodegradation of the investigated chemicals. Biotransformation products of target compounds were identified using ultra high-performance liquid chromatography, coupled with a quadrupole-time-of-flight high-resolution mass spectrometer (UHPLC-QToF-MS). Twenty two biotransformation products were tentatively identified, while retention time denoted the formation of more polar transformation products than the parent compounds.

Interpreting the effect of increasing COD loading rates on the performance of a pre-anoxic MBBR system: implications on the attached and suspended biomass dynamics and nitrification-denitrification activity.

A pre-anoxic MBBR system was subjected to increasing organic loading rates up to 18gCOD/(m(2)day). At 3gCOD/(m(2)day), most of the incoming organic matter was removed via denitrification. However, at higher loads, anoxic COD removal became limited by the nitrite/nitrate supply from the aerobic reactor, which assumed an important role in this conversion. Despite the application of low dissolved oxygen (DO) levels (<2mg/L) in this tank, nitrification was observed to be nearly complete until 8gCOD/(m(2)day). As the organic input was increased, the maximum specific nitrifying activity gradually declined. Activity tests suggested that an oxygen-limited environment was established in the biofilm. At lower loads [3-8gCOD/(m(2)day)], the nitrification product obtained was affected by the DO concentration, whereas from 16 to 21gCOD/(m(2)day), nitrite/nitrate profiles were likely associated with microbial stratification in the biofilm. The results also indicated that the role of the suspended biomass in the overall nitrification and denitrification can be very significant in high loaded MBBRs and should not be neglected, even at low HRTs.

Combined organic matter and nitrogen removal from a chemical industry wastewater in a two-stage MBBR system

Pesticide-producing factories generate highly polluting wastewaters containing toxic and hazardous compounds which should be reduced to acceptable levels before discharge. In this study, a chemical industry wastewater was treated in a pre-denitrification moving-bed biofilm reactor system subjected to an increasing internal mixed liquor recycle ratio from 2 to 4. Although the influent wastewater characteristics substantially varied over time, the removal of chemical oxygen demand (COD) and dissolved organic carbon was quite stable and mostly higher than 90%. The highest fraction of the incoming organic matter was removed anoxically, favouring a low COD/N environment in the subsequent aerobic nitrifying tank and thus ensuring stable ammonium removal (90–95%). However, during pH and salt shock periods, nitrifiers were severely inhibited but gradually restored their full nitrifying capability as non-stressing conditions were reestablished. Besides promoting an increase in the maximum nitrification potential of the aerobic attached biomass from 0.34 to 0.63 mg , the increase in the internal recycle ratio was accompanied by an increase in nitrogen removal (60–78%) and maximum specific denitrification rate (2.7–3.3 mg ). Total polysaccharides (PS) and protein (PT) concentrations of attached biomass were observed to be directly influenced by the influent organic loading rate, while the PS/PT ratio mainly ranged from 0.3 to 0.5. Results of Microtox tests showed that no toxicity was found in the effluent of both the anoxic and aerobic reactors, indicating that the biological process was effective in removing residual substances which might adversely affect the receiving waters' ecosystem.

Biodegradation of Polychlorinated Biphenyls Using a Moving‐Bed Biofilm Reactor

As persistent organic pollutants, polychlorinated biphenyls (PCBs) are rarely degraded in nature environment. Biodegradation is an effective method for the removal of PCBs from contaminated wastewater. In this study, an assessment of the performance of a combined moving‐bed biofilm reactor and a membrane filtration system (MBBR‐MF) for the treatment of PCB‐containing wastewater was performed. Simulated wastewater containing PCB77 was treated in an MBBR system. PCB removal efficiency was investigated at different sections of the combined MBBR‐MF system. The results showed that the removal efficiencies for PCB77 in the anaerobic MBBR were 73 and 84.4% in the aerobic section. The possible biodegradation products were investigated. The results of gas chromatography–mass spectrometry indicate that the PCBs were converted into small molecules that were easily mineralized under aerobic conditions. Thus, the MBBR technology could have potential for biodegradation use of PCB‐contaminated wastewater.

Mass Transfer Characteristics of Floating Media in MBBR and IFAS Fixed-Film Systems

The goals of this project were to establish a standard protocol for measuring mass transfer rates in biofilm media, and to use the resulting data to develop and calibrate an empirical model. Two laboratory-scale continuous flow reactors were loaded with MBBR media donated from two manufacturers, and fed a synthetic wastewater free of organic carbon, but rich in ammonia. The reactors were aerated using coarse-bubble aeration, and operated at two different temperatures for one year. The continuous system was periodically halted to allow for batch testing of the media within each reactor. A total of 200 batch tests were conducted, at varying mixing rates, temperatures, bulk phase dissolved oxygen and ammonia concentrations. Data from the batch tests were used to develop an empirical model of ammonia mass transfer. The model includes half-order terms for bulk phase dissolved oxygen (DO) concentration and the mixing rate (expressed in terms of the velocity gradient), and an Arrhenius-type temperature dependence. A reasonable fit was obtained through non-linear regression, with an average root-mean-squared-error of less than 10% between model and observed ammonia flux rates. The protocol and resulting model were successfully used to compare the two media, and to project mass transfer within a nitrifying system. This title belongs to WERF Research Report Series ISBN: 9781780407050 (eBook)

Microbial Community Composition and Dynamics of Moving Bed Biofilm Reactor Systems Treating Municipal Sewage

Moving bed biofilm reactor (MBBR) systems are increasingly used for municipal and industrial wastewater treatment, yet in contrast to activated sludge (AS) systems, little is known about their constituent microbial communities. This study investigated the community composition of two municipal MBBR wastewater treatment plants (WWTPs) in Wellington, New Zealand. Monthly samples comprising biofilm and suspended biomass were collected over a 12-month period. Bacterial and archaeal community composition was determined using a full-cycle community approach, including analysis of 16S rRNA gene libraries, fluorescence in situ hybridization (FISH) and automated ribosomal intergenic spacer analysis (ARISA). Differences in microbial community structure and abundance were observed between the two WWTPs and between biofilm and suspended biomass. Biofilms from both plants were dominated by Clostridia and sulfate-reducing members of the Deltaproteobacteria (SRBs). FISH analyses indicated morphological differences in the Deltaproteobacteria detected at the two plants and also revealed distinctive clustering between SRBs and members of the Methanosarcinales, which were the only Archaea detected and were present in low abundance (<5%). Biovolume estimates of the SRBs were higher in biofilm samples from one of the WWTPs which receives both domestic and industrial waste and is influenced by seawater infiltration. The suspended communities from both plants were diverse and dominated by aerobic members of the Gammaproteobacteria and Betaproteobacteria. This study represents the first detailed analysis of microbial communities in full-scale MBBR systems and indicates that this process selects for distinctive biofilm and planktonic communities, both of which differ from those found in conventional AS systems.

Systematic evaluation of biofilm models for engineering practice: components and critical assumptions

Biofilm models are valuable tools for the design and evaluation of biofilm-based processes despite several uncertainties including the dynamics and rate of biofilm detachment, concentration gradients external to the biofilm surface, and undefined biofilm reactor model calibration protocol. The present investigation serves to (1) systematically evaluate critical biofilm model assumptions and components and (2) conduct a sensitivity analysis with the aim of identifying parameter subsets for biofilm reactor model calibration. AQUASIM was used to describe submerged-completely mixed combined carbon oxidation and nitrification IFAS and MBBR systems, and tertiary nitrification and denitrification MBBRs. The influence of uncertainties in model parameters on relevant model outputs was determined for simulated scenarios by means of a local sensitivity analysis. To obtain reasonable simulation results for partially penetrated biofilms that accumulated a substantial thickness in the modelled biofilm reactor (e.g. 1,000 microm), an appropriate biofilm discretization was applied to properly model soluble substrate concentration gradients and, consistent with the assumed mechanism for describing biofilm biomass distribution, biofilm biomass spatial variability. The MTBL thickness had a significant impact on model results for each of the modelled reactor configurations. Further research is needed to develop a mathematical description (empirical or otherwise) of the MTBL thickness that is relevant to modern biofilm reactors. No simple recommendations for a generally applicable calibration protocol are provided, but sensitivity analysis has been proven to be a powerful tool for the identification of highly sensitive parameter subsets for biofilm (reactor) model calibration.

Respirometry as a Simple Operational Tool for Monitoring of MBBR and IFAS Biofilm Systems

Respirometry as a Simple Operational Tool for Monitoring of MBBR and IFAS Biofilm Systems

Modelling of hybrid moving bed biofilm reactors: a pilot plant experiment

In recent years there has been an increasing interest in the development of hybrid biofilm reactors, especially in the upgrading of existing WWTP that are no longer able to respect concentration limits. In fact, today's challenge is the achievement of a good aquatic state for the receiving water bodies according to the Water Framework Directive requirements, which indeed limit even more the continuous emissions, i.e. coming from WWTP. This paper presents the setting up of a mathematical model for the simulation of a hybrid MBBR system; the model calibration/validation has been carried out considering a field gathering campaign on an experimental pilot plant. The main goal is to gain insight about MBBR processes attempting to overcome main shortcomings in particular referring to the modelling aspects. The model is made up of two connected sub-models for the simulation of the suspended and attached biomass. The model is mainly based on the concepts of the activated sludge model No. 1 (ASM1) for the description of the biokinetic process both for the suspended and for the attached biomass. The results show a good agreement between predicted and observed values both for the attached and for the suspended biomass moreover they are encouraging for further researches.

UNDERSTANDING THE IMPORTANCE OF AEROBIC MIXING, BIOFILM THICKNESS CONTROL AND MODELING ON THE SUCCESS OR FAILURE OF IFAS SYSTEMS FOR BIOLOGICAL NUTRIENT REMOVAL

Research was conducted in IFAS systems to identify problems that arose with the biofilm when the intensity of mixing and aeration fall below or rise above certain thresholds. The types of IFAS media evaluated include fixed bed cord media (Ringlace and Bioweb), moving bed sponge (sponge media – Linpor and Captor; and plastic media – Kaldnes) and RBC media. An aeration process design model and operating strategies have been developed to address these problems. This paper presents the IFAS and MBBR design methodology and aeration process design component of the Aquifas Unified Model for Activated Sludge, IFAS and MBBR systems. The paper references specific instances in full-scale IFAS plants where problems occurred because of insufficient or improper mixing patterns and documents how they were resolved. The problems observed included nuisance predator development and plugging of media and screens. The IFAS model was upgraded to incorporate computation of biofilm thickness and the impact of the increase in biofilm thickness on the reduction in effective surface area available on a various types of media. Effective surface area is the m 2 of biofilm surface per m 3 of tank volume. The model uses the effective surface area and the amount of media in the tank to compute the substrate (COD, NH4N and Oxidized-N) profiles. Additional research is being conducted to establish certain thresholds for mixing necessary above and beyond the aeration requirements to maintain a thin biofilm. The paper shows how the process design model is applied to improve the design of IFAS and MBBR systems. In instances where the aeration requirement to satisfy the DO set-point is satisfied but the mixing is below the threshold to maintain a thin biofilm, the media fill volume fraction in an aerobic cell can be increased and the fraction of tank volume occupied by the aerobic cell can be increased. By increasing the media fill volume fraction in a situation where the biofilm in an aerobic cell is too thick, the total amount of biofilm surface area present in the aerobic cell is increased and the soluble COD concentration is decreased. This decreases the biofilm thickness observed for the same intensity of mixing and increases the effective surface area of biofilm. This improves the performance of the system. When the media fill volume fraction is increased, the air flow per unit of reactor volume has to be increased to satisfy the additional oxygen demand. This increase in air flow helps satisfy the mixing requirements to mix the media and induce the requisite amount of biofilm shear. In some instances with fixed bed media, supplemental aeration system is installed below the frames to increase the air flow during diurnal peak load hours and thin out the biofilm.