Unraveling microbial characteristics of simultaneous nitrification, denitrification and phosphorus removal in a membrane-aerated biofilm reactor

Characterizing biofilm thickness, density, and microbial community composition in a full-scale hybrid membrane aerated biofilm reactor

This study examined biofilm thickness, density, and microbial composition in a full-scale MABR treating municipal wastewater, focusing on their spatial and operational variability. The MABR cassette arrangement created a thickness gradient, with biofilms in the front cassettes more than twice as thick as those at the back. Lower scouring intensity due to reduced airflow resulted in thicker biofilms. Microbial communities varied longitudinally and by operational phase, with thicker biofilms having a higher relative abundance of anaerobic microorganisms, such as fermenters and sulfur reducers, and fewer aerobic nitrifiers. Nitrosomonas were the main ammonia oxidizers, while Nitrospira and Ca. Nitrotoga dominated as nitrite oxidizers. The 16S RNA gene profiles showed strong correlations with biofilm thickness (R2 = 0.8) and nitrification rates (R2 = 0.4). Full-scale MABR biofilm characteristics have not been studied before. Study findings have practical implications for better modeling practices and improved design of future MABR facilities.

Decarburization, denitrification characteristics and microbial community analysis of a full-scale two-stage anoxic-oxic process for treating refractory coking wastewater

Coking wastewater is a representative intractable industrial wastewater, which contains plenty of organic pollutants and nutrient nitrogen and needs to be treated effectively. The decarburization, denitrification characteristics and microbial community composition and structure of coking wastewater treated by a full-scale two-stage anoxic-oxic (A/O) process were systematically investigated. The results showed that the full-scale two-stage A/O process exhibited outstanding decarburization and denitrification capability with a removal efficiency above 90% for chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), and total nitrogen (TN) in coking wastewater. Different biological reaction tanks in the two-stage A/O process played various roles in coking wastewater treatment. COD was mainly removed in the first stage anoxic tank (A1), TN was mainly removed in A1 and the second stage anoxic tank (A2), and NH4 +-N was mainly removed in the first stage oxic tank (O1). The function of different biological reaction tanks was highly associated with the composition and structure of the microbial community. The differential microorganisms in different biological reaction tanks were determined by multidimensional analysis. Thiobacillus, Thauera, Thioalkalispira, Pedomicrobium, Azoarcus, etc, were the key differential microorganisms in A1. Mycobacterium, Nitrospira, Acinetobacter, Pseudomonas, Nitrosomonas, etc, were the key differential microorganisms in O1. Bacillus, Thiobacillus, Mesorhizobium, Pusillimonas, etc, were the key differential microorganisms in A2. Truepera, Legionella, Sphingobium, Pseudomonas, etc, were the key differential microorganisms in the second stage oxic tank (O2). Augmenting the key microorganisms in different biological reaction tanks is crucial for boosting the treatment effect of actual coking wastewater.

Simultaneous carbon, nitrogen and phosphorus removal in sequencing batch membrane aerated biofilm reactor with biofilm thickness control via air scouring aided by computational fluid dynamics

Membrane aerated biofilm reactor (MABR) is challenged by biofilm thickness control and phosphorus removal. Air scouring aided by computational fluid dynamics (CFD) was employed to detach outer biofilm in sequencing batch MABR treating low C/N wastewater. Biofilm with 177-285 µm thickness in cycle 5-15 achieved over 85 % chemical oxygen demand (COD) and total inorganic nitrogen (TIN) removals at loading rate of 13.2 gCOD/m2/d and 2.64 gNH4+-N/m2/d. Biofilm rheology measurements in cycle 10-25 showed yield stress against detachment of 2.8-7.4 Pa, which were equal to CFD calculated shear stresses under air scouring flowrate of 3-9 L/min. Air scouring reduced effluent NH4+-N by 10 % and biofilm thickness by 78 µm. Intermittent aeration (4h off, 19.5h on) and air scouring (3 L/min, 30 s before settling) in one cycle achieved COD removal over 90 %, TIN and PO43--P removals over 80 %, showing great potential for simultaneous carbon, nitrogen and phosphorus removals.

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

Preparation of PDMS and PDMS-UiO-66 oxygen-rich membranes and modules for membrane-aerated biofilm reactors

A membrane-aerated biofilm reactor (MABR) combines membrane technology with biofilm processes and has unique advantages in the treatment of organic wastewater and volatile wastewater. The common membranes for MABR systems usually have relatively uneven pore structures and low bubble point pressure, resulting in unsatisfactory O2 utilization and wastewater treatment efficiency. In this work, polydimethylsiloxane (PDMS) and UiO-66 (a Zr-based metal organic framework) were coated on the surface of a commercial polypropylene (PP) hollow fiber membrane to prepare oxygen-rich MABR membranes and modules, which showed an attractive O2 utilization rate and wastewater treatment efficiency. The bubble points of the PDMS and PDMS-UiO-66 membranes were significantly higher than those of the PP membranes, and the PDMS-UiO-66 membranes had better oxygen enrichment capacity and biological affinity. The optimal PDMS-UiO-66 membrane modules had an O2 permeance of 31.65 GPU (1 GPU = 3.35 × 10-10 mol m-2 s-1 Pa-1), with O2/N2 selectivity of 2.21. The membrane hanging effect and processing capacity for domestic sewage were greatly improved. This study may provide insights and guidelines to fabricate porous mixed matrix membranes and modules in the industry for MABR. The developed products are expected to be applied in the actual separation process.