High concentration powder carrier bio-fluidized bed process: A new perspective for domestic wastewater treatment

Ciprofloxacin affects nutrient removal in manganese ore-based constructed wetlands: Adaptive responses of macrophytes and microbes

Ciprofloxacin (CIP) has received considerable attention in recent decades due to its high ecological risk. However, little is known about the potential response of macrophytes and microbes to varying levels of CIP exposure in constructed wetlands. Therefore, lab-scale manganese ore-based tidal flow constructed wetlands (MO-TFCWs) were operated to evaluate the responses of macrophytes and microbes to CIP over the long term. The results indicated that total nitrogen removal improved from 79.93% to 87.06% as CIP rose from 0 to 4 mg L-1. The chlorophyll content and antioxidant enzyme activities in macrophytes were enhanced under CIP exposure, but plant growth was not inhibited. Importantly, CIP exposure caused a marked evolution of the substrate microbial community, with increased microbial diversity, expanded niche breadth and enhanced cooperation among the top 50 genera, compared to the control (no CIP). Co-occurrence network also indicated that microorganisms may be more inclined to co-operate than compete. The abundance of the keystone bacterium (involved in nitrogen transformation) norank_f__A0839 increased from 0.746% to 3.405%. The null model revealed drift processes (83.33%) dominated the community assembly with no CIP and 4 mg L-1 CIP. Functional predictions indicated that microbial carbon metabolism, electron transfer and ATP metabolism activities were enhanced under prolonged CIP exposure, which may contribute to nitrogen removal. This study provides valuable insights that will help achieve stable nitrogen removal from wastewater containing antibiotic in MO-TFCWs.

New insights into substrates shaped nutrients removal, species interactions and community assembly mechanisms in tidal flow constructed wetlands treating low carbon-to-nitrogen rural wastewater

A limited understanding of microbial interactions and community assembly mechanisms in constructed wetlands (CWs), particularly with different substrates, has hampered the establishment of ecological connections between micro-level interactions and macro-level wetland performance. In this study, CWs with distinct substrates (zeolite, CW_A; manganese ore, CW_B) were constructed to investigate the nutrient removal efficiency, microbial interactions, metabolic mechanisms, and ecological assembly for treating rural sewage with a low carbon-to-nitrogen ratio. CW_B showed higher removal of ammonia nitrogen and total nitrogen by about 1.75-6.75 % and 3.42-5.18 %, respectively, compared to CW_A. Candidatus_Competibacter (denitrifying glycogen-accumulating bacteria) was the dominant microbial genus in CW_A, whereas unclassified_f_Blastocatellaceae (involved in carbon and nitrogen transformation) dominated in CW_B. The null model revealed that stochastic processes (drift) dominated community assembly in both CWs; however, deterministic selection accounted for a higher proportion in CW_B. Compared to those in CW_A, the interactions between microbes in CW_B were more complex, with more key microbes involved in carbon, nitrogen, and phosphorus conversion; the synergistic cooperation of functional bacteria facilitated simultaneous nitrification-denitrification. Manganese ores favour biofilm formation, increase the activity of the electron transport system, and enhance ammonia oxidation and nitrate reduction. These results elucidated the ecological patterns exhibited by microbes under different substrate conditions thereby contributing to our understanding of how substrates shape distinct microcosms in CW systems. This study provides valuable insights for guiding the future construction and management of CWs.

A novel process based on powder carriers demonstrates robustness in nitrogen and phosphorus removal from real municipal wastewater

The development of efficient and low-consumption wastewater upgrading process is currently at the forefront of the wastewater treatment field. In this study, a novel wastewater treatment process based on powder carriers was proposed. Three systems, namely the activated sludge (AS) system, powder carrier (PC) system, and moving bed biofilm reactor (MBBR) system, were established and operated for over 140 days to treat real municipal wastewater. The characteristics and differences between the three systems were comprehensively investigated. The results suggested that the PC system exhibited notable advantages in nitrogen and phosphorus removal, especially under high influent load and low aeration conditions. The PC system, characterized by a higher nitrification rate compared to the MBBR system and a higher denitrification rate compared to the AS system, contributed to the stable nitrogen removal performance. The particle size of the zoogloea increased under the linkage of the powder carriers, and the mean size of micro-granules reached 170.88 μm. Large number of hydrophobic functional groups on sludge surface, coupled with increased protein content in EPS, further promoted sludge aggregation. Micro-granules formation improved settling performance and enhanced the abundance and activity of functional microbes. A significant enrichment in denitrifying bacteria and denitrifying phosphorus accumulating bacteria was observed in PC system. Up-regulation of the napA, narG, and nosZ genes was responsible for efficient nitrogen removal of the PC system. Moreover, a higher abundance in polyphosphate phosphotransferase (2.11 %) was found in PC system compared with AS and MBBR systems. The increase in the enzymes associated with poly-β-hydroxybutyrate (PHB) synthesis metabolism in PC system provided the energy for denitrification and phosphorus removal processes.

Enhanced biological phosphorus removal by high concentration powder carrier bio-fluidized bed (HPB): Phosphorus distribution, cyclone separation, and metagenomics

This study provides a comparative investigation of phosphorus removal between anaerobic-anoxic-oxic (AAO) and high-concentration powder carrier bio-fluidized bed (HPB) in the same full-scale wastewater treatment plant. The results showed that the total phosphorus removal of HPB was 71.45%-96.71%. Compared with AAO, the total phosphorus removal of HPB can be increased by a maximum of 15.73%. The mechanisms of enhanced phosphorus removal by HPB include the followings. Biological phosphorus removal was significant. The anaerobic phosphorus release capacity of HPB was enhanced and polyphosphate (Poly-P) in the excess sludge of HPB was 1.5 times higher than that of AAO. The relative abundance of Candidatus Accumulibacter was 5 times higher than that of AAO, and oxidative phosphorylation and butanoate metabolism were enhanced. The analysis of phosphorus distribution showed that cyclone separation increased the chemical phosphorus precipitation (Chem-P) in the excess sludge by 16.96% to avoid accumulation in the biochemical tank. The phosphorus adsorbed by extracellular polymeric substance (EPS) in the recycled sludge was stripped, and the EPS bound-P in the excess sludge increased by 1.5 times. This study demonstrated the feasibility of HPB to improve the phosphorus removal efficiency for domestic wastewater.

Enhanced sludge settlement of two stage PN/Anammox for reject water treatment with respective diatomite addition

The present study investigated the potential of diatomite addition in enhancing sludge settlement of two-stage PN/Anammox for real reject water treatment, with a focus on sludge settling velocity, nitrogen removal capacity, sludge morphological features, and microbial community changes. The study found that diatomite addition significantly improved the sludge settleability of the two-stage PN/A process, resulting in a decrease in sludge volume index (SVI) from 70 to 80 mL/g to about 20-30 mL/g for both PN and Anammox sludge, although the sludge-diatomite interaction differed between the two types of sludge. In the PN sludge, diatomite acted as a carrier, while in the Anammox sludge, it acted as micro-nuclei. The addition of diatomite also increased the biomass amounts in the PN reactor, with a 5-29 % improvement attributed to its role as a biofilm carrier. The effects of diatomite addition on sludge settleability were more prominent at high mixed liquor suspended solids (MLSS), where sludge characteristics were deteriorated. Furthermore, the settling rate of the experimental group consistently exceeded that of the blank group after diatomite addition, with a significant decrease in SV. The relative abundance of Anammox bacteria was improved, and sludge particle size decreased in the diatomite-added Anammox reactor. Diatomite was effectively retained in both reactors, with less loss observed for Anammox than PN due to its more tightly wrapped structure, resulting in a stronger sludge-diatomite interaction. Overall, the results of this study suggest that diatomite addition has potential in enhancing the settling properties and performance of two-stage PN/Anammox for real reject water treatment.

Enhanced biological phosphorus and nitrogen removal by high-concentration powder carriers: extracellular polymeric substance, microbial communities, and metabolic pathways

In this study, diatomite, activated carbon, and iron-carbon (Fe-C) were used as biological carriers for the integrated fixed-film activated sludge process. Biomass, pollutant removal efficiency, and extracellular polymer were tested, and the effect of nitrogen and phosphorus removal, enzyme activity, and microbial diversity were studied after the sludge retention time was changed. The mechanism of carrier enriching microorganism and promoting pollutant degradation was studied. The results showed that the addition of these three carriers contributed to the enrichment of nitrifying bacteria in the system, and the NH₄⁺-N removal efficiency was above 98%. Diatomite and Fe-C could improve pollutant removal by increasing the activity of the electron transfer system. The abundance of denitrogenation-related reductases and the enzymes synthesizing poly-β-hydroxybutyrate was increased in activated carbon. The addition of Fe-C increased the abundance of denitrifying phosphate-accumulating organisms by approximately 25% and the removal efficiency of total phosphorus by 12.61-14.88% at the end of the long-term operation.

Metagenomics reveals a full-scale modified integrated fixed-film activated sludge process: Enhanced nitrogen removal and reduced sludge production

This study provides a side-by-side comparative investigation between the full-scale conventional activated sludge (CAS) and the high-concentration powder carrier bio-fluidized bed (HPB) processes. The results showed that the HPB total nitrogen removal efficiency increased by 10.86 % more than CAS. The anammox pathway increased by 6.92 %, while the simultaneous nitrification-denitrification pathway increased by 4.27 %. Also, the effluent's total nitrogen of the HPB process was stabilized below 10 mg/L, which can withstand the impact of industrial wastewater better. More energy and substance (protein) were consumed to attach to the carriers and resist external selective pressure to produce extracellular polymeric substance rather than sludge production in the HPB process. For a 10,000 m³/d HPB wastewater treatment plant, lowering the total nitrogen and sludge production saved $110,369.64 in annual operating costs.

Rapidly recovering and maintaining simultaneous partial nitrification, denitrification and anammox process through hydroxylamine addition to advance nitrogen removal from domestic sewage

The collapse of simultaneous partial nitrification, denitrification and anammox (SPNDA) system, caused by the destruction of partial nitrification (PN), is the most likely phenomenon to occur. Therefore, recovering the process quickly and maintaining efficient nitrogen removal is a valuable topic for research. In the anaerobic/aerobic/anoxic operation mode, SPNDA process was used to treat domestic sewage in a sequencing batch biofilm reactor. After the deterioration of PN effect, with the addition of hydroxylamine, the activity of ammonia-oxidizing bacteria in the nitrobacteria increased (61.0-91.3 %), whereas the accumulation of nitrite quickly recovered to 90.4 % within 5 days. Meanwhile, the nitrogen removal efficiency improved (61.8-95.6 %) and the effluent TN was 2.1 mg/L. Furthermore, Candidatus Brocadia was enriched (0.50-1.82 %) in the system. The results indicated that the addition of hydroxylamine was an effective strategy to recover and economically maintain the SPNDA process for advanced nitrogen removal from domestic sewage.