Achieving simultaneous nitrification, denitrification, and phosphorus removal in pilot-scale flow-through biofilm reactor with low dissolved oxygen concentrations: Performance and mechanisms

Stratified biofilm structure of MABR enabling efficient ammonia removal from aquaculture medicated bath wastewater

The presence of high concentrations of residual antibiotics in aquaculture medicated bath wastewater poses challenges to conventional biological nitrogen removal processes. Membrane aerated biofilm reactor (MABR), known for its energy efficiency and stratified biofilm structure that supports diverse ecological niches, was therefore introduced. Experimental results revealed that MABR achieved an exceptional NH4+-N removal efficiency of 98.2 ± 1.8 % even under high oxytetracycline exposure, attributed to the protective effects of the biofilm on functional bacteria colonized in the inner layer (e.g., ammonia- and nitrite-oxidizing bacteria). Genes mediating the nitrification process, such as amoA/B and nxrA, showed an overall upward trend, with the activation of efflux pumps synergistically constituting the microbial response. Conversely, total nitrogen removal efficiency decreased from 95.3 ± 2.5 % to 76.0 ± 8.8 %, despite enrichment of Denitratisoma oestradiolicum (14.5 %) and denitrifying bacterium clone NOA-1-C (41.7 %), likely due to limited expression of the narG gene. After ceasing oxytetracycline dosing and adjusting operational parameters, total nitrogen removal improved to 87.4 ± 5.8 %. The results of this study underscore the significance and resilience of MABR technology in the treatment of aquaculture medicated bath wastewater.

Profiling and metabolic analysis of microorganisms in bioretention cells vegetated with vetiver and cattail species treating nitrogen and phosphorous

Bioretention cells (BRCs) are increasingly used to treat nutrients in stormwater runoff, with plants known to enhance nitrogen (TN) and phosphorus (TP) uptake. This study investigated the role of rhizosphere microbial communities in TN, TP, and COD removal across three BRCs: an unvegetated control (CP), one vegetated with vetiver (P1), and another with cattail (P2). Detailed microbiome profiling revealed key taxa across phylum, family, and genus levels contributing to nutrient cycling, with P2 showing the highest species richness and diversity based on OTU counts and diversity indices. Proteobacteria, Acidobacteria, and Verrucomicrobiota were the most prominent phyla, aligning with their known roles in nutrient uptake. Key functional taxa included denitrifiers (e.g., Ramlibacter, TRA3-20), Ammonia Oxidizing Bacteria (AOBs) (e.g., MND1, Ellin 6067), and Phosphate Accumulating Organisms (PAOs) (e.g., Comamonadaceae, Vicinamibacteria), supporting TN (>79%) and TP (>84%) removal rates. Distinct microbial compositions between vegetated BRCs confirmed the role of root exudates in microbial selection and enhanced nutrient removal. These findings emphasize the importance of plant-specific rhizosphere effects and microbial selection in optimizing BRC design for stormwater treatment applications.

Purification of inorganic nitrogen from the mariculture tail water by anaerobic/anoxic/oxic (A2O) process

This study aims to address the suboptimal performance of conventional denitrifying strains in treating mariculture tail water (MTW) containing inorganic nitrogen (IN). The concentration of inorganic nitrogen in the mariculture tail water is about 5-20 mg·L-1. A biofilm treatment process was developed and evaluated using an anoxic-anoxic-aerobic biofilter composite system inoculated with the denitrifying strain Meyerozyma guilliermondii Y8. The removal effect of total nitrogen (TN), IN, and Chemical Oxygen Demand (CODMn) from MTW was investigated. The results indicate that the A2O composite biological filter has excellent pollutant removal efficiency within 25 days of operation, after the acclimation of the denitrifying microorganisms. The initial concentrations of TN, IN, and CODMn ranged between 10.24 and 12.89 mg·L-1, 7.84-10.49 mg·L-1, and 9.44-11.52 mg·L-1, respectively, and the removal rates of these indexes reached 38-68 %, 45-70 %, and 55-70 %, respectively. The experiments with different hydraulic retention times (HRT = 6 h, 8 h, 10 h) demonstrated that longer HRT was more conducive to the removal of inorganic nitrogen. Moreover, scanning electron microscopy observations revealed that the target strain successfully grew and attached to the filler in large quantities. The findings of this study provide practical guidance for the development of efficient biofilm processes for the treatment of MTW.

Oxygen affinity and light intensity induced robust phosphorus removal and fragile ammonia removal in a non-aerated bacteria-algae system

Non-aerated bacteria-algae system gaining O2 through photosynthesis presents an alternative for costly mechanical aeration. This study investigated oxygen supply and performance of nutrients removal at low and high light intensity (LL and HL). The results showed that P removal was high and robust (LL 97 ± 1.8 %, HL 95 % ± 2.9 %), while NH4+-N removal fluctuated dramatically (LL 66 ± 14.7 %, HL 84 ± 8.6 %). Oxygen generated at illumination of 200 μmol m-2 s-1, 6 h was sufficient to sustain aerobic phase for 2.25 g/L MLSS. However, O2 produced by algae was preferentially captured in the order of heterotrophic bacteria (HB), ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB). Oxygen affinity coupled with light intensity led to NOB suppression with stable nitrite accumulation ratio of 57 %. Free nitrous acid (FNA) and light stimulated the abundance of denitrifying polyphosphate accumulating organism (DPAO) of Flavobacterium, but with declined P-accumulating metabolism (PAM) of P release, P/C, K/P and Mg/P ratios. Flavobacterium and cyanobacteria Leptolyngbya, along with biologically induced CaP in extracellular polymeric substances was the key to robust P removal. AOB of Ellin6067 and DPAO of Flavobacteria offer a promising scenario for partial nitrification-denitrifying phosphorus removal.

Divalent manganese stimulates the removal of nitrate by anaerobic sludge

This study investigated the effect of different concentrations of Mn2+ on the removal of nitrate by anaerobic sludge and changes in the microbial communities through batch experiments. The results showed that the addition of Mn2+ promoted nitrate removal by anaerobic sludge; the nitrate was completely removed within 6 d in the treatment group with >5 mM Mn2+. With the increase in Mn2+, the concentration of nitrite and nitrous oxide increased in the first 4 d and then decreased to 0 μM after 8 d of incubation. The increasing tendency of ammonium increased firstly and then decreased with the addition of Mn2+ compared to A. Moreover, the Mn2+ removal efficiency gradually decreased with the increase of Mn2+ concentration. The changes of microflora structure in sludge before and after adding Mn2+ were analyzed, and the results revealed that the microbial communities in the sludge may have evolved towards an energy-efficient association of short-cut nitrification, denitrification, and anaerobic ammonia oxidation after adding Mn2+. Mn2+ stimulated the removal of nitrate by anaerobic sludge mainly by promoting the growth of PHOS-HE36.

Simultaneous nitrification, denitrification and phosphorus removal: What have we done so far and how do we need to do in the future?

Nitrogen and phosphorus contamination in wastewater is a serious environmental concern and poses a global threat to sustainable development. In this paper, a comprehensive review of the studies on simultaneous nitrogen and phosphorus removal (SNPR) during 1986-2022 (538 publications) was conducted using bibliometrics, which showed that simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) is the most promising process. To better understand SNDPR, the dissolved oxygen, carbon to nitrogen ratio, carbon source type, sludge retention time, Cu²⁺ and Fe³⁺, pH, salinity, electron acceptor type of denitrifying phosphorus-accumulating organisms (DPAOs), temperature, and other influencing factors were analyzed. Currently, SNDPR has been successfully implemented in activated sludge systems, aerobic granular sludge systems, biofilm systems, and constructed wetlands; sequential batch mode of operation is a common means to achieve this process. SNDPR exhibits a significant potential for phosphorus recovery. Future research needs to focus on: (1) balancing the competitiveness between denitrifying glycogen-accumulating organisms (DGAOs) and DPAOs, and countermeasures to deal with the effects of adverse conditions on SNDPR performance; (2) achieving SNDPR in continuous flow operation; and (3) maximizing the recovery of P during SNDPR to achieve resource sustainability. Overall, this study provides systematic and valuable information for deeper insights into SNDPR, which can help in further research.