Nitrogen removal performance and bacterial communities in zeolite trickling filter under different influent C/N ratios

Can natural zeolite improve the removal of micropollutants in a nitrifying sequencing batch reactor? Insights on bioreactor performance, kinetics, and microbial community using Ibuprofen and Diclofenac as model micropollutants

This study presents the effect of natural zeolite (NZ) on a nitrifying sequencing batch reactor for removing ibuprofen (IBP) and diclofenac (DFC) in the long term, including kinetics and microbial community. The research was conducted in two 2 L liquid-volume bioreactors, one with 5 g/L of NZ. Nitrogen load rates ranging between 5.8 and 8.5 mg N/L h were studied. Bioreactors were operated for 217 days, with IBP and DFC concentrations ranging between 20 and 2000 μg/L. The results showed that using NZ in a nitrifying SBR only improves IBP removal at low concentrations (40 μg/L). IBP and DFC do not affect the nitrification efficiency or kinetic of ammonia removal. In the presence of IBP and DFC, NZ also favored a higher relative abundance in the genus Nitrosomonas and the Bradyrhizobiaceae family (responsible for nitrite-oxidizing activity), allowing higher IBP degradations at low IBP concentrations. Finally, IBP and DFC stimulated heterotrophic nitrification.

Changing the order and ratio of substrate filling reduced CH4 and N2O emissions from the aerated constructed wetlands

Constructed wetlands (CWs) have been used to enhance pollutant removal by filling several types of material as substrates. However, research on substrate filling order remains still limited, particularly regarding the effects of greenhouse gas (GHG) emissions. In this study, six CWs were constructed using zeolite and ferric‑carbon micro-electrolysis (Fe-C) fillers to evaluate the effect of changing the filling order and ratio on pollutant removal, GHGs emissions, and associated microbial structure. The results showed that the order of substrate filling significantly impacted pollutant removal performance on CWs. Specifically, CWs filled with zeolite in the top layer exhibited superior NH4+-N removal compared to those filled in the lower layer. Moreover, the highest NH4+-N removal (95.0 % ± 1.9 %) was observed in CWs with a zeolite to Fe-C volume ratio of 8:2 (CWZe-1). Moreover, zeolite-filled at the top had lower GHGs emissions, with the lowest CH4 (0.22 ± 0.10 mg m-2 h-1) and N2O (167.03 ± 61.40 μg m-2 h-1) fluxes in the CWZe-1. In addition, it is worth noting that N2O is the major contributor to integrated global warming potential (GWP) in the six CWs, accounting for 81.7 %-90.8 %. The upper layer of CWs filled with zeolite exhibited higher abundances of nirK, nirS and nosZ genes. The order in which the substrate was filled affected the microbial community structure and the upper layer of CWs filled with zeolite had higher relative abundance of nitrifying genera (Nitrobacter, Nitrosomonas) and denitrifying genera (Zoogloea, Denitratisoma). Additionally, N2O emission was reduced by approximately 41.2 %-64.4 % when the location of the aeration of the CWs was changed from the bottom to the middle. This study showed that both the order of filling the substrate and the aeration position significantly affected the GHGs emissions from CWs, and that CWs had lower GHGs emissions when zeolites were filled in the upper layer and the aeration position was in the middle.

Ecological filter walls for efficient pollutant removal from urban surface water

Urban surface water pollution poses significant threats to aquatic ecosystems and human health. Conventional nitrogen removal technologies used in urban surface water exhibit drawbacks such as high consumption of carbon sources, high sludge production, and focus on dissolved oxygen (DO) concentration while neglecting the impact of DO gradients. Here, we show an ecological filter walls (EFW) that removes pollutants from urban surface water. We utilized a polymer-based three-dimensional matrix to enhance water permeability, and emergent plants were integrated into the EFW to facilitate biofilm formation. We observed that varying aeration intensities within the EFW's aerobic zone resulted in distinct DO gradients, with an optimal DO control at 3.19 ± 0.2 mg L-1 achieving superior nitrogen removal efficiencies. Specifically, the removal efficiencies of total organic carbon, total nitrogen, ammonia, and nitrate were 79.4%, 81.3%, 99.6%, and 79.1%, respectively. Microbial community analysis under a 3 mg L-1 DO condition revealed a shift in microbial composition and abundance, with genera such as Dechloromonas, Acinetobacter, unclassified_f__Comamonadaceae, SM1A02 and Pseudomonas playing pivotal roles in carbon and nitrogen elimination. Notably, the EFW facilitated shortcut nitrification-denitrification processes, predominantly contributing to nitrogen removal. Considering low manufacturing cost, flexible application, small artificial trace, and good pollutant removal ability, EFW has promising potential as an innovative approach to urban surface water treatment.

Feast/famine ratio regulates the succession of heterotrophic nitrification-aerobic denitrification and autotrophic ammonia oxidizing bacteria in halophilic aerobic granular sludge treating saline wastewater

Heterotrophic nitrification-aerobic denitrification (HN-AD) shows innovation potential of wastewater treatment process in a single tank. However, how to enrich HN-AD bacteria in activated sludge to enhance their contribution remained unknown. This study explored the impact of the feast/famine (F/F) ratio on the succession of autotrophic ammonia oxidizing bacteria (AOB) and HN-AD bacteria in a halophilic aerobic granular sludge (HAGS) system. As the F/F ratio decreased from 1/9 to 1/15, the total inorganic nitrogen (TIN) removal performance significantly decreased. The proportion of heterotrophic bacteria was dropped from 79.0 % to 33 %. Accordingly, the relative abundance of Paracoccus decreased from 70.8 % to 25.4 %, and the copy number of the napA gene was reduced from 2.2 × 1010 copies/g HAGS to 8.1 × 109 copies/g HAGS. It found the F/F ratio regulated the population succession of autotrophic AOB and HN-AD bacteria, thereby providing a solution to achieve the enrichment of HN-AD bacteria in HAGS.

Treatment of high-phosphorus load wastewater by column packed with non-burning compound filler/gravel/ceramsite: evaluation of performance and microorganism community

Cost-effective and environmental-friendly substrates are essential for the constructed wetlands (CWs). In this study, the column test was used to explore the differences in pollutant purification performance, microbial community structure and abundance between non-burning compound filler and conventional CWs substrates (i.e. gravel and ceramsite) at low temperature (0-15℃). It was found that the maximum phosphorus removal efficiency of compound filler (99%) was better than gravel (18%) and ceramsite (21%). Besides, the proportion of aerobic heterotrophic bacteria capable of ammonium oxidation, nitrification and denitrification (i.e. Pseudomonas, Acinetobacter, and Acetoanaerobium) was enhanced by compound filler, which has an excellent potential for nitrogen removal in the subsequent purification process. These results demonstrated that the self-made non-burning compound filler was a potential substrate for CWs, which was of great significance for the resource utilization of solid wastes such as polyaluminum chloride residue.

Optimization of synthetic domestic wastewater treatment performance in anoxic/aerobic sequencing batch reactor with zeolite addition

In this study, treatment performance was investigated based on chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total inorganic nitrogen (TIN) and simultaneous nitrification and denitrification (SND) parameters in a zeolite-added anoxic/aerobic sequencing batch reactor. Response surface methodology (RSM) was used to model treatment performance, determine the impact of operating conditions, and optimize them. The effect of zeolite size, dosage and COD/NH4+-N (C/N) ratio as operating parameters were evaluated in the central composite design (CCD). Variance analysis (ANOVA) results of the quadratic model, high coefficients of determination and low values of the root mean square error (RMSE) for dependent variables indicated the validity of the model in predicting experimental results. The desirability function showed that optimum conditions were 0.80 mm for zeolite size, 3.05 g/L for zeolite dosage and 9.8 for C/N. Under these conditions, the maximum COD, NH4+-N, TIN removal efficiencies and SND efficiency were 92.85%, 93.3%, 77.33% and 82.96%, respectively. The results of the study showed that the most effective independent variable on dependent variables was the C/N ratio.

Effects of combined pollution of organic pollutants and heavy metals on biodiversity and soil multifunctionality in e-waste contaminated soil

Electronic waste (e-waste) is increasing globally, but the impact of this source of combined pollution on soil biodiversity and multiple soil functions (i.e., ecosystem multifunctionality) remains unclear. Here, we evaluated the effects of combined pollution on the biodiversity and soil multifunctionality using samples collected from upland and paddy soils chronically contaminated with e-waste. Overall biodiversity, as well as the relative abundance and biodiversity of key ecological clusters, as combined pollution concentrations increased in upland soil, while the opposite was true in paddy soil. Soil multifunctionality followed the same trend. Organic pollutants had significant negative effects on soil multifunctionality and were the main influencing factors in upland soil. Heavy metals had significant positive effects on soil multifunctionality in paddy soil. Moreover, driving soil multifunctionality was overall biodiversity in upland soil but key biodiversity in paddy soil. Importantly, a strong positive association between key organism biodiversity and soil multifunctionality was found in soil with low contamination. However, the relationship between key organism biodiversity and soil multifunctionality weakened or disappeared in highly contaminated soil, whereas overall biodiversity was significantly and positively correlated with multifunctionality. Our results emphasized that severe e-waste contamination would reduce soil biodiversity and soil multifunctionality and warrants high attention.

Application of low-intensity ultrasound to enhance simultaneous nitrification/iron-based autotrophic denitrification

Intermittent ultrasound with an intensity of 0.2 W/ml was applied during simultaneous nitrification/iron-based autotrophic denitrification to evaluate its impacts on total nitrogen (TN) removal efficiency and microbial characteristics during low carbon/nitrogen ratio (C/N) wastewater treatment. At an optimal dissolved oxygen (DO) concentration of 1.2 mg/L, the TN removal rate was 91 ± 4%, and the TN concentration in the effluent decreased by 31% owing to the ultrasound treatment. In addition, the number of iron-compounds that formed in the sludge and wastewater increased by 55% and 37%, respectively. Low-intensity ultrasound caused a substantial increase in ammonia monooxygenase activity. Moreover, when the DO concentration increased to 1.2 mg/L, the activities of nitrate reductase and nitrite reductase, both of which are associated with denitrification, were effectively maintained. High-throughput sequencing indicated that low-intensity ultrasound enriched ammonium oxidising bacteria (Nitrosomonas) and suppressed the growth of heterotrophic denitrifying bacteria (Zoogloea and Simplicispira). These changes benefited simultaneous nitrification and autotrophic denitrification. Thus, low-intensity ultrasound promoted the simultaneous nitrification/iron-based autotrophic denitrification process during low C/N wastewater treatment.

The intrinsic relevance of nitrogen removal pathway to varying nitrate loading rate in a polycaprolactone-supported denitrification system

Up to date, the intrinsic association of nitrate loading rate (NLR) with treatment performance of solid-phase denitrification (SPD) systems is still ambiguous. To address this issue, three continuous up-flow bioreactors were configured. They were packed with polycaprolactone (PCL) under a filling ratio of 30%, 60% or 90% and were operated under a varying NLR of 0.34 ± 0.01-3.99 ± 0.12 gN/(L·d). Results showed that the denitrification efficiency was high (RE > 96%) and stable except the case with the highest NLR, which was mainly attributed to the lack of available carbon sources. At the phylum or genus level, most of the detected dominant bacterial taxa were either associated with organics degradation or nitrogen metabolism. The difference in bacterial community structure among the three stages was mainly caused by NLR rather than the filling ratio. Moreover, as the NLR got higher, the Bray-Curtis distance between samples from the same stage became shorter. By the results of gene or enzyme prediction performed in PICRUSt2, the main nitrogen metabolism pathways in these reactors were denitrification, dissimilatory nitrate reduction to ammonium (DNRA), assimilatory nitrate reduction to ammonium (ANRA) and nitrogen fixation. Moreover, aerobic and anaerobic nitrate dissimilation coexisted in the systems with the latter playing a dominant role. Finally, denitrification and DNRA occurred under both high and low NLR conditions while nitrogen fixation and ANRA preferred to occur under low NLR environments. These findings might help guide practical applications.

Efficient nitrogen removal from stormwater runoff by bioretention system: The construction of plant carbon source-based heterotrophic and sulfur autotrophic denitrification process

The plant carbon source and sulfur were selected as the denitrification electron donors and filled in the internal water storage zone (IWSZ) of bioretention system to establish excellent mixotrophic denitrification system, which was beneficial to waste recycling and showed very high nitrate nitrogen removal efficiency (approximately 94%). The ammonia nitrogen, total nitrogen, and chemical oxygen demand removal efficiencies could reach 79.41%, 85.89%, and 74.07%, respectively. Mechanism study revealed the synergistic degradation effect was existed between acetic acid released from plant carbon source and the generated sulfate, which improved the S/CH₃COOH mediated nitrate nitrogen removal reactions. Autotrophic denitrification occurred mainly in the upper layer of IWSZ, and the dominant bacteria were Thiobacillus. While in the lower layer, the dominant bacteria were mainly related to organic matter utilization and heterotrophic denitrification. The abundance of narG, nirK, nirS, and nosZ functional genes in the upper layer was significantly higher than the lower layers.

Purification of Micro-Polluted Lake Water by Biofortification of Vertical Subsurface Flow Constructed Wetlands in Low-Temperature Season

In this study, a novel lab-scale biofortification-combination system (BCS) of Oenanthe javanica and Bacillus series was developed to improve the treatment ability of vertical subsurface flow constructed wetlands (VSFCW) at low temperatures (0–10 °C). The results showed that BCS-VSFCW overcame the adverse effects of low temperature and achieved the deep removal of nutrients. In addition, the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) by BCS-VSFCW were 38.65%, 28.20%, 18.82%, and 14.57% higher than those of blank control, respectively. During the experiment, Oenanthe javanica and low temperature tolerant Bacillus complemented each other in terms of microbial activity and plant uptake. Therefore, VSFCW combined with Oenanthe javanica and low temperature tolerant Bacillus has a promising future in low temperature (<10 °C) areas of northern China.

Shifts in enzymatic activities and microbial community structures in the bioenhanced treatment of ship domestic sewage under microaerobic conditions

A bioenhancement strategy for improving the anaerobic degradation efficiency of ship domestic sewage under microaerobic conditions was proposed in this study. Strains Stenotrophomonas sp. MSPP05 and Prevotella sp. MSPP07 with high organic-degrading efficiency and extracellular hydrolase yield were used for the bioenhancement of activated sludge. In batch experiments, the removal rates of chemical oxygen demand and total nitrogen reached 94.5% and 66.9% after 72 h of degradation. The activities of dehydrogenase, extracellular amylase, and protease in the treatment group were 1.2, 1.4, and 2.0 times higher than those in the control group. Microbial community analysis showed that exogenous enhanced strains competed with original microorganisms and became dominant. One-stage continuous stirred tank reactor with bioenhanced activated sludge ran steadily for 90 days with average effluent COD and TN concentrations of 87.5 and 14.6 mg/L. The feasibility of improving organic-degrading efficiency through bioenhancement by using exogenous hydrolase-producing strains was confirmed under microaerobic conditions. This work provided a theoretical basis for improving treatment effects and developing a new technique for ship domestic sewage treatment.