Effects of scale-up on a hybrid moving bed biofilm reactor – membrane bioreactor for treating urban wastewater

Optimization of moving bed biofilm reactors for the treatment of municipal wastewater

The properties of biocarriers significantly influence the performance of a moving bed-biofilm reactor (MBBR). This study aimed to assess the impact of media type, filling ratio, and hydraulic retention time (HRT) on biofilm formation and MBBR performance in both batch and continuous setups using real municipal wastewater. Two different media, high-density polyethylene (HDPE) and polypropylene (PPE), with varying surface area and properties were used. Biofilm growth and MBBR performance were monitored and optimized using response surface methodology. The effect of different media was investigated for three filling ratios of 20%, 40% and 60% and HRT of 4, 6 and 8 h. Results depicted a better biofilm growth on HDPE media in comparison to PPE carriers due to difference in media structure and surface properties. At all the conditions tested, HDPE media showed comparatively better performance for the removal of organic matter and nutrients than PPE media. The maximum organic matter removal efficiency was found as 77% and 75% at an HRT of 6 h and filling ratio of 40% for HDPE and PPE media, respectively. The ammonia removal was also found better for HDPE media due to its geometry and structure favoring the anoxic conditions with maximum removal of 89% achieved at 6-h HRT and 40% filling ratio. Overall, the system with HDPE media indicated more stability in terms of reactor performance than PPE carriers with variations in the operating conditions.

Prolonging the Life Span of Membrane in Submerged MBR by the Application of Different Anti-Biofouling Techniques

The membrane bioreactor (MBR) is an efficient technology for the treatment of municipal and industrial wastewater for the last two decades. It is a single stage process with smaller footprints and a higher removal efficiency of organic compounds compared with the conventional activated sludge process. However, the major drawback of the MBR is membrane biofouling which decreases the life span of the membrane and automatically increases the operational cost. This review is exploring different anti-biofouling techniques of the state-of-the-art, i.e., quorum quenching (QQ) and model-based approaches. The former is a relatively recent strategy used to mitigate biofouling. It disrupts the cell-to-cell communication of bacteria responsible for biofouling in the sludge. For example, the two strains of bacteria Rhodococcus sp. BH4 and Pseudomonas putida are very effective in the disruption of quorum sensing (QS). Thus, they are recognized as useful QQ bacteria. Furthermore, the model-based anti-fouling strategies are also very promising in preventing biofouling at very early stages of initialization. Nevertheless, biofouling is an extremely complex phenomenon and the influence of various parameters whether physical or biological on its development is not completely understood. Advancing digital technologies, combined with novel Big Data analytics and optimization techniques offer great opportunities for creating intelligent systems that can effectively address the challenges of MBR biofouling.

Evaluation of a Hybrid Moving Bed Biofilm Membrane Bioreactor and a Direct Contact Membrane Distillation System for Purification of Industrial Wastewater

Integrated wastewater treatment processes are accepted as the best option for sustainable and unrestricted onsite water reuse. In this study, moving bed biofilm reactor (MBBR), membrane bioreactor (MBR), and direct contact membrane distillation (DCMD) treatment steps were integrated successively to obtain the combined advantages of these processes for industrial wastewater treatment. The MBBR step acts as the first step in the biological treatment and also mitigates foulant load on the MBR. Similarly, MBR acts as the second step in the biological treatment and serves as a pretreatment prior to the DCMD step. The latter acts as a final treatment to produce high-quality water. A laboratory scale integrated MBBR/MBR/DCMD experimental system was used for assessing the treatment efficiency of primary treated (PTIWW) and secondary treated (STIWW) industrial wastewater in terms of permeate water flux, effluent quality, and membrane fouling. The removal efficiency of total dissolved solids (TDS) and effluent permeate flux of the three-step process (MBBR/MBR/DCMD) were better than the two-step (MBR/DCMD) process. In the three-step process, the average removal efficiency of TDS was 99.85% and 98.16% when treating STIWW and PTIWW, respectively. While in the case of the two-step process, the average removal efficiency of TDS was 93.83% when treating STIWW. Similar trends were observed for effluent permeate flux values which were found, in the case of the three-step process, 62.6% higher than the two-step process, when treating STIWW in both cases. Moreover, the comparison of the quality of the effluents obtained with the analysed configurations with that obtained by Jeddah Industrial Wastewater Treatment Plant proved the higher performance of the proposed membrane processes.

Can a compact biological system be used for real hydraulic fracturing wastewater treatment?

Hydraulic fracturing wastewater (HFW), a byproduct of hydraulic fracturing oil extraction, contains a complex mixture of oil, aldehydes, and benzene compounds. Efficient and eco-friendly HFW treatment means are critical for the oil extraction industry, particularly in developing countries. In this study, two biological processes namely an anaerobic/anoxic/moving bed biofilm reactor (A²-MBBR) and an A²-MBBR with a microfiltration membrane (A²-MFMBBR) were established, and assessed for the real HFW treatment. Removal efficiencies of chemical oxygen demand (COD) and NH₄⁺-N were over 92% and 95%, respectively, in both processes with a hydraulic retention time of 72 h. The majority of organic compounds in both systems identified by GC-MS were degraded in the anaerobic units. In comparison, A²-MFMBBR demonstrated higher removal efficiencies for oil, total suspended solids, and complex compounds. The average relative abundances of refractory compound degrading bacteria were 43.4% and 51.6% in the A²-MBBR and A²-MFMBBR, respectively, which was consistent with the COD and oil removal, and suggested that the MBR could maintain a high diversity of microorganisms and contribute to deep recalcitrant organics degradation. This study sheds light on the potential of using a compact biological process for the real HFW treatment.

Bacterial biofilm and extracellular polymeric substances in the moving bed biofilm reactor for wastewater treatment: A review

Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacteriumsp. andRhodobactersp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH₄⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.

Treatment of landfill leachate using single-stage anoxic moving bed biofilm reactor and aerobic membrane reactor

Landfill leachate (LFL) is one of the most serious environmental problems due to the high concentrations of toxic and hazardous matters. Although several physical, chemical, methods have been tested, biological processes and single or multiple-stage combinations of them have been receiving more attention due to their cost-effective and environmentally-friendly manner. The present work recommended coupling of conventional single-stage A/O with moving bed biofilm reactor and membrane bioreactor (AnoxMBBR/AeMBR) for LFL treatment. The system performance was evaluated for 233 d under varying nitrate concentrations (100-1000 mgNO₃^--N/L), sludge retention time (SRT) (30-90 d), and HRT (24-48 h) in AnoxMBBR, and constant SRT (infinite) and HRT (48 h) in the AeMBR. The best system performances were observed at 1000 mgNO₃^--N/L concentration, SRT of 90 d and HRT of 48 h, and the average removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and nitrate‑nitrogen (NO₃^-N) were 74.2%, 99.7%, and 89.1%, respectively. Besides, the AeMBR was achieved above 99% NH₄⁺-N removal and not adversely affected by varying operation conditions of AnoxMBBR. A slight increase in selected phthalic acid ester (PAE) concentrations (diethyl phthalate (DEP), di (2-Ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP)) was detected in the AnoxMBR, and complete PAEs removal was attained in the AeMBR. Mg, Al, Si, Na, Fe was detected by SEM-EDX analyses in both biofilm of AnoxMBBR and the cake layers of AeMBR. Nitrobacter and Nitratireductor which showed a relatively high abundance played an important role in the removal of NH₄⁺-N and COD in LFL. The results confirmed that the proposed sequence is efficient for COD removal, nitrogen removal, and PAEs being an acceptable treatment for landfill leachates.

Recent progress in integrated fixed-film activated sludge process for wastewater treatment: A review

Integrated fixed-film activated sludge (IFAS) process is considered as one of the leading-edge processes that provides a sustainable solution for wastewater treatment. IFAS was introduced as an advancement of the moving bed biofilm reactor by integrating the attached and the suspended growth systems. IFAS offers advantages over the conventional activated sludge process such as reduced footprint, enhanced nutrient removal, complete nitrification, longer solids retention time and better removal of anthropogenic composites. IFAS has been recognized as an attractive option as stated from the results of many pilot and full scales studies. Generally, IFAS achieves >90% removals for combined chemical oxygen demand and ammonia, improves sludge settling properties and enhances operational stability. Recently developed IFAS reactors incorporate frameworks for either methane production, energy generation through algae, or microbial fuel cells. This review details the recent development in IFAS with the focus on the pilot and full-scale applications. The microbial community analyses of IFAS biofilm and floc are underlined along with the special emphasis on organics and nitrogen removals, as well as the future research perspectives.

Investigating the most appropriate methods for attached solids determination in moving-bed biofilm reactors

Moving-bed biofilm reactors (MBBR) have been employed worldwide as an efficient technology for the treatment of a diverse set of wastewaters. Although the attached biomass represents the major fraction of solids in MBBR systems, there is still no standard for its reliable quantification. An extensive literature review indicated that several methods for attached biomass assessment are applied, hindering the comparability of results issued from different studies. Therefore, the most reported methods for biofilm quantification in the MBBR literature were compared using three different carriers. The results revealed that the performance of each method was biased depending on the carrier type and shape. Moreover, differences in total attached solids (TAS) concentrations varied from 13% up to more than 90%, depending on the employed method for a given carrier. Overall, direct weighing of the carrier containing the biofilm, accounting for the clean carrier weight, and manual extraction of the biofilm, preceded or not by sonication for at least 15 min, were the most suitable techniques for assessing TAS and the volatile/total solids ratio in non-porous medias, respectively. The results here presented may be used as a frame of reference for standardization of the methods for assessing the biofilm mass in MBBR carriers.

Steady-state modeling of the biodegradation performance of a multistage moving bed biofilm reactor (MBBR) used for on-site greywater treatment

In this study, the Activated Sludge Model No. 3 (ASM3) was applied for the simulation of the removal of organics and nitrogen in a multistage moving bed biofilm reactor (MBBR) used for biological greywater treatment. The data related to the characterization of the greywater were collected over a period of 5 months to be investigated in the model. The reactor showed a high performance for the removal of chemical oxygen demand (COD), dissolved organic carbon (DOC), biological oxygen demand (BOD₅), ammonia (NH₄-N), and total nitrogen (TN) with a removal efficiency of 93%, 80.7%, 99%, 89%, and 77%, respectively. The results of modeling showed a good correlation between simulated and experimental concentrations of COD issued from different reactors of the MBBR system. The adaptability of the ASM3 model to fit other parameters such as TN, NH₄-N, total suspended solids (TSS), and the dissolved oxygen (DO) was also investigated for two selected reactors: reactor (R1) and the reactor (R5). The simulation results showed an acceptable correlation regarding the evolution of the investigated parameters in R1 and R5 and in the effluent except for total nitrogen TN. The adjustment of the stoichiometric parameters led to a satisfactory simulation of TN concentrations.

Optimisation of a modified submerged bed biofilm reactor for biological oleochemical wastewater treatment

Oleochemicals industry effluence mainly contains a high chemical oxygen demand (COD) in a range of 6000-20,000 ppm. An effective biological wastewater treatment process must be carried out before wastewater is discharged into the environment. In this study, a submerged bed biofilm reactor (SBBR) was adapted to the biological oleochemical wastewater treatment plant observed in the present study. The effect of wastewater flow rate (100-300 mL/min), Cosmoball^® percentage in the SBBR system (25-75%), and percentage of activated sludge (0-50%) were investigated in terms of COD reduction. The Box-Behnken design was used for response surface methodology (RSM) and to create a set of 18 experimental runs, which was needed for optimising the biological oleochemical wastewater treatment. A quadratic polynomial model with estimated coefficients was developed to describe COD reduction patterns. The analysis of variance (ANOVA) shows that the wastewater flow rate was the most effective factor in reducing COD, followed by activated sludge percentage and Cosmoball^® carrier percentage. Under the optimum conditions (i.e., a wastewater flow rate of 103.25 mL/min a Cosmoball^® carrier percentage of 71.94%, and an activated sludge percentage of 40.50%) a COD reduction of 98% was achieved. Thus, under optimum conditions, as suggested by the BBD, SBBR systems can be used as a viable means of biological wastewater treatment in the oleochemicals industry.

Influence of temperature on the start-up of membrane bioreactor: kinetic study

The start-up phase of a membrane bioreactor (MBR) for municipal wastewater treatment was studied to determine the effect of temperature on the organic matter removal and heterotrophic kinetics. The MBR system was analyzed during four start-up phases with values of hydraulic retention time (HRT) of 6 h and 10 h, mixed liquor suspended solids (MLSS) concentrations of 4,000 mg L^-1 and 7,000 mg L^-1 in the steady state, and temperature values of 11.5, 14.2, 22.9 and 30.1 °C. The influence of temperature on the biological process of organic matter removal was determined through the Arrhenius equation and Monod model. At the most favorable operation conditions of HRT (10 h) and MLSS (7,000 mg L^-1) corresponding to phase 4, the effect of these variables dominated over the temperature. Heterotrophic biomass from phase 2 (HRT = 10 h, MLSS = 4,000 mg L^-1 and T = 30.1 °C) had the highest values of chemical oxygen demand (COD) degradation rate (r_su,H), implying less time to remove organic matter and shorter duration of the start-up phase.

Essential factors of an integrated moving bed biofilm reactor-membrane bioreactor: Adhesion characteristics and microbial community of the biofilm

This work aims at revealing the adhesion characteristics and microbial community of the biofilm in an integrated moving bed biofilm reactor-membrane bioreactor, and further evaluating their variations over time. With multiple methods, the adhesion characteristics and microbial community of the biofilm on the carriers were comprehensively illuminated, which showed their dynamic variation along with the operational time. Results indicated that: (1) the roughness of biofilm on the carriers increased very quickly to a maximum value at the start-up stage, then, decreased to become a flat curve, which indicated a layer of smooth biofilm formed on the surface; (2) the tightly-bound protein and polysaccharide was the most important factor influencing the stability of biofilm; (3) the development of biofilm could be divided into three stages, and Gammaproteobacteria were the most dominant microbial species in class level at the last stage, which occupied the largest ratio (51.48%) among all microbes.

Meso and micro-scale response of post carbon removal nitrifying MBBR biofilm across carrier type and loading

This study investigates the effects of three specific moving bed biofilm reactor (MBBR) carrier types and two surface area loading rates on biofilm thickness, morphology and bacterial community structure of post carbon removal nitrifying MBBR systems along with the effects of carrier type and loading on ammonia removal rates and effluent solids settleability. The meso and micro analyses show that the AOB kinetics vary based on loading condition, but irrespective of carrier type. The meso-scale response to increases in loading was shown to be an increase in biofilm thickness with higher surface area carriers being more inclined to develop and maintain thicker biofilms. The pore spaces of these higher surface area to volume carriers also demonstrated the potential to become clogged at higher loading conditions. Although the biofilm thickness increased during higher loading conditions, the relative percentages of both the embedded viable and non-viable cells at high and conventional loading conditions remained stable; indicating that the reduced ammonia removal kinetics observed during carrier clogging events is likely due to the observed reduction in the surface area of the attached biofilm. Microbial community analyses demonstrated that the dominant ammonia oxidizing bacteria for all carriers is Nitrosomonas while the dominant nitrite oxidizing bacteria is Nitrospira. The research showed that filamentous species were abundant under high loading conditions, which likely resulted in the observed reduction in effluent solids settleability at high loading conditions as opposed to conventional loading conditions. Although the settleability of the effluent solids was correlated to increases in abundances of filamentous organisms in the biofilm, analyzed using next generation sequencing, the ammonia removal rate was not shown to be directly correlated to specific meso or micro-scale characteristics. Instead post carbon removal MBBR ammonia removal kinetics were shown to be related to the viable AOB cell coverage of the carriers; which was calculated by normalizing the surface area removal rate by the biofilm thickness, the bacterial percent abundance of ammonia oxidizing bacteria and the percentage of viable cells.