Moving bed biofilm reactor for blackwater treatment: insights into pollutant removal, microbial communities, and water quality prediction through machine learning

Abstract

Effective treatment of blackwater is critical for sustainable water management and environmental protection. This study investigated the performance of a novel two-stage anoxic-oxic moving bed biofilm reactor (A/O-MBBR) over an operational period of 82 d to enhance the treatment efficiency of blackwater. With an HRT of 25.5 h, the MBBR achieved removal rates of 94.4% for COD, 99.7% for NH₃-N, 84.0% for TN, and 74.6% for TP. Even at reduced HRT, the system maintained consistently high removal efficiencies for both COD and TN, highlighting its robust performance under varying operational conditions. This study underscored the superior nitrification activity of attached biofilm compared to the suspended biomass. Predominant microbial genera identified within the biofilm included Thiothrix, Azospira, Acinetobacter, and Thauera genera, which played a critical role in nutrient removal processes. Notably, at low operational temperatures ranging from 8 to 15 °C, facultative anaerobic species contributed significantly to sustaining nitrogen removal efficiencies, hence demonstrating the adaptability of the microbial community to varied environmental conditions. Furthermore, an advanced machine learning model, eXtreme Gradient Boosting (XGBoost), was developed and applied to predict pollutant concentrations across different A/O-MBBR chambers. The model exhibited exceptional predictive accuracy, highlighting the potential of integrating computational intelligence with biological treatment systems to optimize wastewater treatment processes.

Graphical abstract

Keywords

Blackwater / MBBR / Nitrification / Microbial analysis / Machine learning

Highlight

	● A novel two-stage A/O-MBBR was established to enhance blackwater treatment.
	● The excellent pollutant removal rates were achieved when the HRT was 25.5 h.
	● The attached biofilm was found to play a crucial role in removal of nitrogen.
	● The system has superior robustness to shortened HRT and low temperature.
	● Precise prediction by ML model supported the refinement of blackwater treatment.

References

[1] Ashkanani A, Almomani F, Khraisheh M, Bhosale R, Tawalbeh M, Aljaml K. (2019). Bio-carrier and operating temperature effect on ammonia removal from secondary wastewater effluents using moving bed biofilm reactor (MBBR). Science of the Total Environment, 693: 133425

[2] Bian W, Zhang S, Zhang Y, Li W, Kan R, Wang W, Zheng Z, Li J. (2017). Achieving nitritation in a continuous moving bed biofilm reactor at different temperatures through ratio control. Bioresource Technology, 226: 73–79

[3] Boiocchi R, Zhang Q, Gao M, Liu Y. (2022). Modeling and optimization of an upflow anaerobic sludge blanket (UASB) system treating blackwaters. Journal of Environmental Chemical Engineering, 10(3): 107614

[4] Chen X, Xu P, Yang C, Wang S, Lu Q, Sun X. (2021a). Study of enhanced nitrogen removal efficiency and microbial characteristics of an improved two-stage A/O process. Environmental Technology, 42(27): 4306–4316

[5] Chen X, Zhang Q, Zhu Y, Zhao T. (2021b). Response of wastewater treatment performance, microbial composition and functional genes to different C/N ratios and carrier types in MBBR inoculated with heterotrophic nitrification-aerobic denitrification bacteria. Bioresource Technology, 336: 125339

[6] Deaver J A, Popat S C. (2025). Effect of hydraulic retention time on microbial electrolysis cell treatment of high-strength primary sludge-based blackwater. Process Biochemistry, 151: 65–73

[7] Deng M, Li L, Dai Z, Senbati Y, Song K, He X. (2020). Aerobic denitrification affects gaseous nitrogen loss in biofloc-based recirculating aquaculture system. Aquaculture, 529: 735686

[8] Fanta A B, Sægrov S, Azrague K, Østerhus S W. (2024). Experimental investigation of simultaneous nitrification-denitrification and phosphorus removal in pilot-scale sequencing batch moving bed biofilm reactors (SB-MBBRs). Water Resources and Industry, 31: 100258

[9] Han N N, Wang X P, Yang J H, Fan N S, Jin R C. (2024). Biofilm-induced heterogeneity toward anammox bacteria distribution and metabolome. Chemical Engineering Journal, 498: 155535

[10] He Q, Xie Z, Fu Z, Wang M, Xu P, Yu J, Ma J, Gao S, Chen L, Zhang W. . (2021). Interaction and removal of oxytetracycline with aerobic granular sludge. Bioresource Technology, 320: 124358

[11] Jiang H, Wen Y, Qian R, Liu S, Tang X, Huang W, Chen H. (2022). Novel insights into aerobic duration control-based partial nitritation in source-separated blackwater treatment: growth type, inoculation source, and comammox threat. Journal of Environmental Management, 324: 116319

[12] Jiang K, Gao Q, Feng J, Zhu S, Zhai W, Wu D, Zhang H, Zhang W, Liu X, Zhang J. . (2024). Impact of phenolic-formaldehyde resin microplastics on anaerobic granular sludge: EPS interaction mechanisms and impacts on reactor performance. Journal of Hazardous Materials, 480: 136308

[13] José Carlos de M J, Patrícia Camara De B, Ribeiro R P, Kligerman D C, Oliveira J L M. (2024). Nitrogen removal and nitrous oxide emission from moving bed biofilm reactor (MBBR) under different loads and airflow. Journal of Environmental Chemical Engineering, 12(3): 112574

[14] Lee I S, Parameswaran P, Rittmann B E. (2011). Effects of solids retention time on methanogenesis in anaerobic digestion of thickened mixed sludge. Bioresource Technology, 102(22): 10266–10272

[15] Li J, Du Z, Liu J, Xu L, He L P, Gu L, Cheng H, He Q. (2024). Analysis of factors influencing the energy efficiency in Chinese wastewater treatment plants through machine learning and SHapley additive explanations. Science of the Total Environment, 920: 171033

[16] Niazkar M, Menapace A, Brentan B, Piraei R, Jimenez D, Dhawan P, Righetti M. (2024). Applications of XGBoost in water resources engineering: a systematic literature review (Dec 2018–May 2023). Environmental Modelling & Software, 174: 105971

[17] Oduah U I, Ogunye E B. (2023). A smart solution for preventing environmental pollution caused by overflowing onsite sewage septic tank. Heliyon, 9(4): e14925

[18] Pan D, Shao S, Zhong J, Wang M, Wu X. (2022a). Performance and mechanism of simultaneous nitrification–denitrification and denitrifying phosphorus removal in long-term moving bed biofilm reactor (MBBR). Bioresource Technology, 348: 126726

[19] Pan W, Ouyang H, Tan X, Deng R, Gu L, He Q. (2022b). Anaerobic dynamic membrane bioreactors for synthetic blackwater treatment under room temperature and mesophilic conditions. Bioresource Technology, 355: 127295

[20] Pan Y, Sun R Z, Wang Y, Chen G L, Fu Y Y, Yu H Q. (2023). Carbon source shaped microbial ecology, metabolism and performance in denitrification systems. Water Research, 243: 120330

[21] Pechaud Y, Peyre Lavigne M, Bessiere Y, Ochoa J C, Queinnec I, Paul E. (2022). Influence of shear stress, organic loading rate and hydraulic retention time on the biofilm structure and on the competition between different biological aggregate morphotypes. Journal of Environmental Chemical Engineering, 10(3): 107597

[22] SEPA (2002). Water and Wastewater Monitoring and Analysis Method. 4th Edition. Beijing: China Environmental Science Press (in Chinese)

[23] Singh N K, Yadav M, Singh V, Padhiyar H, Kumar V, Bhatia S K, Show P L. (2023). Artificial intelligence and machine learning-based monitoring and design of biological wastewater treatment systems. Bioresource Technology, 369: 128486

[24] Singh R P, Kun W, Fu D. (2019). Designing process and operational effect of modified septic tank for the pre-treatment of rural domestic sewage. Journal of Environmental Management, 251: 109552

[25] StatisticsN B O (2024). China Statistical Yearbook. Beijing: China Statistics Press (in Chinese)

[26] Sui Q, Di F, Zhang J, Chen M, Wei Y. (2024). A single-stage membrane aerated biofilm reactor achieving the combination of partial nitritation/anammox and enhanced biological phosphorus removal. Journal of Water Process Engineering, 58: 104933

[27] Todt D, Heistad A, Jenssen P D. (2015). Load and distribution of organic matter and nutrients in a separated household wastewater stream. Environmental Technology, 36(12): 1584–1593

[28] Wang Y, Wang D, Liu Y, Wang Q, Chen F, Yang Q, Li X, Zeng G, Li H. (2017). Triclocarban enhances short-chain fatty acids production from anaerobic fermentation of waste activated sludge. Water Research, 127: 150–161

[29] Wei R, Hu Y, Yu K, Zhang L, Liu G, Hu C, Qu S, Qu J. (2024). Assessing the determinants of scale effects on carbon efficiency in China’s wastewater treatment plants using causal machine learning. Resources, Conservation and Recycling, 203: 107432

[30] Wen C, Dai Z, Dai H, Zha X, Cheng F, Cheng H, Cai Q, Lu X. (2024). Enhancing energy recovery and microbial stability in blackwater anaerobic digestion with graphite felt. Journal of Water Process Engineering, 58: 104808

[31] Wu H, Bai X, Li L, Li Z, Wang M, Zhang Z, Zhu C, Xu Y, Xiong H, Xie X. . (2024). Two-stage partial nitrification-denitrification and anammox process for nitrogen removal in vacuum collected toilet wastewater at ambient temperature. Environmental Research, 262: 119917

[32] Xiao W, Meng G, Meng C, Sun R, Hu S, Yi M, Bai X, Lv C, Wu Y. (2024). New insights into microbial community for simultaneous removal of carbon and nitrogen via heterotrophic nitrification aerobic denitrification process. Journal of Environmental Chemical Engineering, 12(3): 112896

[33] Xing X, Yuan X, Zhang Y, Men C, Zhang Z, Zheng X, Ni D, Xi H, Zuo J. (2023). Enhanced denitrification of the AO-MBBR system used for expressway service area sewage treatment: a new perspective on decentralized wastewater treatment. Journal of Environmental Management, 345: 118763

[34] Yang Y, Zang Y, Hu Y, Wang X C, Ngo H H. (2020). Upflow anaerobic dynamic membrane bioreactor (AnDMBR) for wastewater treatment at room temperature and short HRTs: process characteristics and practical applicability. Chemical Engineering Journal, 383: 123186

[35] Yu Z, Chu H, Zhang W, Gao K, Yang L, Zhang Y, Zhou X. (2021). Multi-dimensional in-depth dissection the algae-related membrane fouling in heterotrophic microalgae harvesting: deposition dynamics, algae cake formation, and interaction force analysis. Journal of Membrane Science, 635: 119501

[36] Zhang W, Chu H, Yang L, You X, Yu Z, Zhang Y, Zhou X. (2023). Technologies for pollutant removal and resource recovery from blackwater: a review. Frontiers of Environmental Science & Engineering, 17(7): 83

[37] Zhao W, Peng Y, Wang M, Huang Y, Li X. (2019). Nutrient removal and microbial community structure variation in the two-sludge system treating low carbon/nitrogen domestic wastewater. Bioresource Technology, 294: 122161

[38] Zheng H, Chai H, Zhao L, Liao Y, Cao X, Feng L, Ji F. (2023). Pretreatment of septic tank wastewater by packed anaerobic baffled reactor: pollutant degradation and microbial community succession in different compartments. Environmental Research, 223: 115475

[39] Zhou X, Bi X, Fan X, Yang T, Wang X, Chen S, Cheng L, Zhang Y, Zhao W, Zhao F. . (2022). Performance and bacterial community analysis of a two-stage A/O-MBBR system with multiple chambers for biological nitrogen removal. Chemosphere, 303: 135195

[40] Zhou X, Jiang Z, Gu J, Bi X, Liu J, Wang X, Yang T, Shi X, Cheng L, Huang S. . (2023). Performance characteristics and bacterial community analysis of a novel two-step-feed three-stage A/O-MBBR system for nitrogen removal in municipal wastewater. Journal of Water Process Engineering, 52: 103513

[41] Zhou X, Zhang Q, Sun H, Zhao Q. (2019). Efficient nitrogen removal from synthetic domestic wastewater in a novel step-feed three-stage integrated anoxic/oxic biological aerated filter process through optimizing influent flow distribution ratio. Journal of Environmental Management, 231: 1277–1282

[42] Zhou Y, Guo B, Zhang L, Zou X, Yang S, Zhang H, Xia S, Liu Y. (2020). Anaerobically digested blackwater treatment by simultaneous denitrification and anammox processes: feeding loading affects reactor performance and microbial community succession. Chemosphere, 241: 125101

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