Influence of Carrier Filling Ratio on the Advanced Nitrogen Removal from Wastewater Treatment Plant Effluent by Denitrifying MBBR

Biofilm formation and microbial interactions in moving bed-biofilm reactors treating wastewater containing pharmaceuticals and personal care products: A review

The risk of pharmaceuticals and personal care products (PPCPs) has been paid more attention after the outbreak of COVID-19, threatening the ecology and human health resulted from the massive use of drugs and disinfectants. Wastewater treatment plants are considered the final stop to restrict PPCPs from wide spreading into the environment, but the performance of conventional treatment is limited due to their concentrations and characteristics. Previous studies have shown the unreplaceable capability of moving bed-biofilm reactor (MBBR) as a cost-effective method with layered microbial structure for treating wastewater even with toxic compounds. The biofilm community and microbial interactions are essential for the MBBR process in completely degrading or converting types of PPCPs to secondary metabolites, which still need further investigation. This review starts with discussing the initiation of MBBR formation and its influencing parameters according to the research on MBBRs in the recent years. Then the efficiency of MBBRs and the response of biofilm after exposure to PPCPs are further addressed, followed by the bottlenecks proposed in this field. Some critical approaches are also recommended for mitigating the deficiencies of MBBRs based on the recently published publications to reduce the environmental risk of PPCPs. Finally, this review provides fundamental information on PPCPs removal by MBBRs with the main focus on microbial interactions, promoting the MBBRs to practical application in the real world of wastewater treatment.

Performance evaluation of a new sponge-based moving bed biofilm reactor for the removal of pharmaceutical pollutants from real wastewater

Pharmaceutical pollutants, a group of emerging contaminants, have attracted outstanding attention in recent years, and their removal from aquatic environments has been addressed. In the current study, a new sponge-based moving bed biofilm reactor (MBBR) was developed to remove chemical oxygen demand (COD) and the pharmaceutical compound Ibuprofen (IBU). A 30-L pilot scale MBBR was constructed, which was continuously fed from the effluent of the first clarifier of the Southern Tehran wastewater treatment plant. The controlled operational parameters were pH in the natural range, Dissolved Oxygen of 1.5-2 mg/L, average suspended mixed liquor suspended solids (MLSS), and mixed liquor volatile suspended solids (MLVSS) of 1.68 ± 0.1 g/L and 1.48 ± 0.1 g/L, respectively. The effect of hydraulic retention time (HRT) (5 h, 10 h, 15 h), filling ratio (10%, 20%, 30%), and initial IBU concentration (2 mg/L, 5 mg/L, 10 mg/L) on removal efficiencies was assessed. The findings of this study revealed a COD removal efficiency ranging from 48.9 to 96.7%, with the best removal efficiency observed at an HRT of 10 h, a filling ratio of 20%, and an initial IBU concentration of 2 mg/L. Simultaneously, the IBU removal rate ranged from 25 to 92.7%, with the highest removal efficiency observed under the same HRT and filling ratio, albeit with an initial IBU concentration of 5 mg/L. An extension of HRT from 5 to 10 h significantly improved both COD and IBU removal. However, further extension from 10 to 15 h slightly enhanced the removal efficiency of COD and IBU, and even in some cases, removal efficiency decreased. Based on the obtained results, 20% of the filling ratio was chosen as the optimum state. Increasing the initial concentration of IBU from 2 to 5 mg/L generally improved COD and IBU removal, whereas an increase from 5 to 10 mg/L caused a decline in COD and IBU removal. This study also optimized the reactor's efficiency for COD and IBU removal by using response surface methodology (RSM) with independent variables of HRT, filling ratio, and initial IBU concentration. In this regard, the quadratic model was found to be significant. Utilizing the central composite design (CCD), the optimal operating parameters at an HRT of 10 h, a filling ratio of 21%, and an initial IBU concentration of 3 mg/L were pinpointed, achieving the highest COD and IBU removal efficiencies. The present study demonstrated that sponge-based MBBR stands out as a promising technology for COD and IBU removal.

Investigation of the performance of the combined moving bed bioreactor-membrane bioreactor (MBBR-MBR) for textile wastewater treatment

The present study focused on the investigation of the performance of a Moving Bed Bioreactor coupled with a Membrane Bioreactor (MBBR-MBR) on a small scale for textile wastewater treatment. The parameters examined in this study included the removal efficiency of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), turbidity, color, and heavy metals (HM). The two reactors were operated consecutively and maintained aerobic conditions. The idea is to reduce the pollutant load significantly through the activity of microorganism attached to the biofilm covered carriers in MBBR and successive membrane filtration. The system demonstrated a favorable outcome even in a smaller hydraulic retention time (HRT) of 1 day, which presents a significant advantage in terms of cost and space saving. The removal effectiveness of COD attained a maximum of 92 %, BOD reached a maximum of 95 %, and the color removal performance obtained a removal efficiency of 87 %. Furthermore, the treatment showed remarkable efficiency in removing up to 100 % of TSS and 96 % of turbidity. Additionally, an evaluation was conducted on the elimination of heavy metals, including Zinc (Zn), Lead (Pb), Chromium (Cr), and Iron (Fe). The efficacy of removing these HMs was found to exceed 85 %. All these favorable outcomes contribute to the improvement of effluent quality, mitigation of contamination hazards, and fouling reduction.

Metagenomic insights into the effects of various biocarriers on moving bed biofilm reactors for municipal wastewater treatment

Preferable biocarrier is vital for start-up and operation of moving bed biofilm reactor (MBBR). Effects of three separate biocarriers - PPC, PU, and PP on MBBRs were systematically investigated including nutrients removal performances, biomass attachment, microbial community, and relevant functional genes. Results showed that three biocarriers achieved similar removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP), though much higher biomasses were found attached onto PPC and PU carriers. PPC and PU performed better than PP for ammonia nitrogen (NH₄⁺-N) removal. However, PPC exhibited the greatest and most reliable denitrifying efficiency, mainly due to stronger simultaneous nitrification and denitrification during better micro-anoxic-environment created within PPC carriers than others. Further studies by 16S rRNA gene and metagenomic sequencing analysis uncovered the bacterial diversity and structures, and relevant functional genes for nitrogen-transformation and pathways of nitrogen metabolisms, which laid the biological basis for the best performances via biocarrier PPC. This study inspired a feasible approach for municipal wastewater treatment through PPC filled MBBR.

The Changing and Distribution Laws of Oxygen Transfer Efficiency in the Full-Scale IFAS Process

The integrated fixed-film activated sludge (IFAS) process has been widely used in the upgrading of wastewater treatment plants (WWTPs). The oxygen transfer efficiency (αOTE) is of great significance to the design and operation of the IFAS process. The carrier filling ratio (CFR) and aeration type are two critical factors affecting αOTE and standard oxygen transfer efficiency (αSOTE). However, the distribution and changing laws of αOTE and αSOTE in the full-scale IFAS process areunclear. To optimize the operation of a WWTP and to improve the αOTE of the aeration systems, several off-gas tests were conducted under different aeration types and different CFRs. The results show that for the aerobic tank investigated (the ratio of length and width was 8:1), the αOTE and the αSOTE of the middle of the aeration systems were higher than those of the other two sides. However, the reason for the low αOTE at the beginning and the end of the tank may be different. Coarse-bubble aeration systems had a lower αOTE and almost the same oxygenation capacity (αSOTE) as the fine-bubble aeration systems under constant CFR (43%). The average αSOTE (18.7–28.9%) of the hybrid aeration systems increased with increasing CFR (7.7–57.7%), and different locations exhibited different degrees of change. The results reveal the distribution and changing law of the αOTE of aeration systems in the IFAS process, and attention should be paid to the improvement of the OTE of the plug-flow IFAS process.

Numerical study of hydrodynamic characteristics in a moving bed biofilm reactor

The moving bed biofilm reactor (MBBR) has certain advantages, such as high wastewater treatment efficiency, low maintenance and operating costs, and simple operation. It has emerged as a valuable option for small decentralized facilities. The filling ratio, aeration mode and aeration intensity are the main factors that affect the performance of MBBRs in wastewater treatment. However, the information that concerns the used criteria that pertain to the process design for the MBBR is not adequate. In this study, a three dimensional computational fluid dynamics (CFD) model was constructed and the maximum error was only 1.98%, which was much smaller than the traditional 2D-CFD model. The filling ratio, aeration mode and aeration intensity of MBBR were optimized by CFD model from the point of view of fluid mechanics. The results show that the fluidization performance of the filling is the best under the one-side aeration mode with 30% filling ratio. The cost-performance ratio of the reactor with 30% filling ratio was 1.53, 25% and 35% filling ratio were only 1.17 and 1.14 respectively. Increasing the aeration intensity could improve the fluidization performance. However, the effect of high aeration intensity on the fluidization performance of the carrier was limited and the energy consumption increased greatly. The results revealed that when the aeration intensity increased from 0.07 min^-1 to 0.13 min^-1, the proportion of the carrier area increased by 16.56%. The proportion of the carrier area with an aeration rate of 0.20 min^-1 was only 4.23%, which is higher than 0.13 min^-1. The main factors that control the fluidization of the carrier were the range of the flow zone and the flow velocity of the liquid. Increasing the range of the flow zone could facilitate the flow of the carriers. The critical value of the flow velocity of the liquid in the flow zone was 0.04 m/s. These results could guide the optimization design of the filling ratio and the aeration conditions and provide a theoretical basis for the application of MBBR.

Release Mechanism, Secondary Pollutants and Denitrification Performance Comparison of Six Kinds of Agricultural Wastes as Solid Carbon Sources for Nitrate Removal

Agricultural wastes used as denitrification carbon sources have some drawbacks such as excessive organic carbon release and unclear release characteristics of nitrogen, phosphorus, and chromatic substances, which can cause adverse effects on the effluent quality during the denitrification process. The composition and surface characteristics, carbon release mechanisms, and secondary pollutant release properties of six kinds of agricultural wastes, i.e., rice straw (RS), wheat straw (WS), corn stalk (CS), corncob (CC), soybean stalk (SS), and soybean hull (SH) were studied and analyzed in this research. The denitrification performance of these agricultural wastes was also investigated extensively by batch experiments. The results showed that the carbon release basically followed the second-order reaction kinetic equation and Ritger-Peppas equation in the 120 h reaction, and it was mainly controlled by the diffusion process. The kinetic equation fitting results and bioavailability test suggested that the potential risk of excessive effluent COD of CC was the lowest due to the appropriate amount and degradability of its released carbon. The NH₄⁺-N, TN, and TP in the leachate of RS were higher than those of the other five agriculture wastes, and the chroma in the leachate of WS and CS was heavier than that of the others. CC released the lowest pollutants, which resulted in slight fluctuations of effluent quality in the start-up period (1-11 d), and it had the best nitrogen removal capacity in the denitrification experiment. The average NO₃^--N removal of CC was 5.12 mg for each batch in the stable period (11-27 d), which was higher than that of others, and less NO₂^--N, NH₄⁺-N, and COD were accumulated in the CC effluent during the whole denitrification process.

Assessment of the aerobic glass beads fixed biofilm reactor (GBs-FBR) for the treatment of simulated methylene blue wastewater

The present research is focused on the application of glass beads (GBs) in fixed biofilm reactor (FBR) for the treatment of simulated methylene blue (MB) wastewater for 9 weeks under aerobic conditions. The COD of MB wastewater showed a reduction of 86.48% from 2000 to 270.4 mg/L, and BOD was declined up to 97.7% from 1095.5 to 25.03 mg/L. A drastic increase in the pH was observed until the 3rd week (8.5 to 8.28), and later, marginal changes between 8.30 ± 0.02 were noticed. A dramatic fluctuation was observed in ammonia concentration which increased (74.25 mg/L) up till the 2nd week, and from the 3rd week it started declining. In the 9th week, the ammonia concentration dropped to 16.5 mg/L. The color intensity increased significantly up till the 2nd week (259,237.46 Pt/Co) of the experiment and started decreasing slowly thereafter. The SEM-EDX analysis has shown the maximum quantity of carbon content in the GBs without biofilm, and then in the GB samples of 1st, and 9th-week old aerobic biofilms. Furthermore, Raman spectroscopy results revealed that the 9th-week GBs has a fine and strong MB peak and matched with that of the MB stock solution. Overall, the results have shown that the GBs filter media were suitable for the development of active biofilm communities for the treatment of dye wastewater. Thus, GBs-FBR system can be used for wastewater treatment to solve the current problem of industrial pollution in many countries and to protect the aquatic environment from dye pollution caused by the textile industry.

Comparative Study of Denitrifying-MBBRs with Different Polyethylene Carriers for Advanced Nitrogen Removal of Real Reverse Osmosis Concentrate

Nitrogen (N) remains a great challenge in wastewater treatment while attempts to remove N has continuously been a research point for decades. In this study, the long-term performance of four identical-shape denitrification MBBRs (moving bed biofilm reactors) with four different configurations of cylindrical polyethylene as carriers (Φ25 × 12, Φ25 × 4, Φ15 × 15, and Φ10 × 7 mm) for advanced N removal of real reverse osmosis concentrate was investigated in great detail. The N of the real concentrate can be effectively removed by denitrification MBBRs when the pH, temperature, hydraulic retention time (HRT), C/N ratio, and filling rate are 7.50–8.10, 24~26 °C, 12 hours, 6.6, and 50%, respectively. The results showed that the MBBR with the Φ15 × 15 poly-carrier had the best removal efficiency on NO₃^-–N (78.0 ± 15.8%), NO₂^-–N (43.79 ± 9.30%), NH₄⁺–N (55.56 ± 22.28%), and TN (68.9 ± 12.4%). The highest biomass of 2.13 mg/g-carrier was in the Φ15 × 15 poly-carrier was compared with the other three carriers, while the genes of the Φ15 × 15 poly-carrier reactor were also the most abundant. Proteobacteria was the most abundant phylum in the system followed by Bacteroidetes and then Firmicutes. The entire experiment with various parameter examination supported that Φ15 × 15 poly-carrier MBBR was a promising system for N removal in high strength concentrate. Despite the lab-scale trial, the successful treatment of high strength real reverse osmosis concentrate demonstrated the reality of the treated effluent as possible reclaimed water, thus providing a good showcase of N-rich reverse osmosis concentrate purification in practical application.