N-removal with low carbon and phosphorus levels

The efficiency and technological reliability of biogenic compounds removal during long-term operation of a one-stage subsurface horizontal flow constructed wetland

Nutrient removal performance from agricultural drainage by strengthening ecological ditches in hilly areas

Enhanced total nitrogen removal performance in a full scale Orbal oxidation ditch by a novel step aeration mode

Batch experiments were conducted to study the short-term biological effects of rare earth ions (La3+, Ce3+) and their mixture on the nitrogen removal in a sequencing batch reactor (SBR). The data showed that higher NH4+-N removal rate, total inorganic nitrogen removal efficiency, and denitrification efficiency were achieved at lower concentrations of rare earth elements (REEs) (<1 mg/L). In the first hour of the aeration stage of SBR, the presence of REEs increased the total inorganic nitrogen removal efficiency and NH4+-N removal efficiency by 15.7% and 10%–15%, respectively. When the concentrations of REEs were higher than 1 mg/L, the total inorganic nitrogen removal efficiency decreased, and nitrate was found to accumulate in the effluent. When the concentrations of REEs was up to 50.0 mg/L, the total inorganic nitrogen removal efficiency was less than 30% of the control efficiency with a high level of nitrate. Lower concentrations of REEs were found to accelerate the nitrogen conversion and removal in SBR.

A pilot-scale multistage constructed wetland-pond (MCWP) system with a "pre-ecological oxidation pond, two-stage horizontal subsurface flow constructed wetland (HSCW) and surface flow constructed wetland (SFCW) as the core and postsubmerged plant pond" as the process was used to treat actual polluted river water in the field, and the variation in nitrogen removal from summer to winter was investigated. The results showed that the average total nitrogen (TN) removal efficiency in the MCWP was approximately 40.74%. The significant positive correlation between the daily highest temperature and the TN removal efficiency of the whole system was fitted with a nonlinear curve (R2 = 0.7192). The TN removal load rate in the HSCWs was 2.7–3.7 times that in the SFCW. The SFCW, which had high-density plants (35 plants/m2), increased the proportion of nitrogen removed by plant harvesting and microbial function. The TN transformed by Iris pseudacorus L. accounted for 54.53% in the SFCW. Furthermore, bacteria completed the nitrogen cycle in the SFCW through a variety of nitrogen removal pathways. This research not only investigated the TN removal performance in an MCWP system but also made it possible to predict the TN removal efficiency according to the daily highest temperature from summer to winter in the field.

A post-denitrification membrane bioreactor (MBR) system was developed to simultaneously remove organics and nitrogen from domestic wastewater. From a long-term experimental investigation, more than 96% organics could be degraded biologically and the effluent Chemical Oxygen Demand (COD) was below 10.5 mg/L. With a Hydraulic Retention Time (HRT) of 13.6 h and a total recirculation ratio of 8×Q, the MBR system could obtain a stably high Total Nitrogen (TN) removal efficiency of up to 92.4%, resulted in an effluent TN content of as low as 2.80 mg/L. Effects of operating parameters, including HRT, Sludge Retention Time (SRT), recirculation ratio and influent C/N, onto the system treatment performance were evaluated. It was revealed that HRT and recirculation ratio had significant impacts onto TN removal efficiency, reflected by that a reduced HRT to 9 h and a lower recirculation of 6×Q induced to 78.2% TN removal and an effluent TN of about 14 mg/L. A proper SRT and C/N ranged from 12 to 40 days, and from 8:1 to 13.5:1, respectively, have insignificant impacts onto the organic degradation and ammonia-N removal. Nevertheless, TN removal was highly inhibited by low SRT and C/N ratios. MBR combination with post-denitrification helps to enhance the organic and nitrogen removal compared with conventional activated sludge process, as it ensured a high biomass level in the treatment system. Keywords: Biological nitrogen removal, membrane bioreactor (MBR), nitrogen gas, organic degradation, post-denitrification, wastewater treatment.

A biological nitrogen removal model was established by AQUASIM software to model the autotrophic nitrogen removal performance of membrane aerated biofilm (MAB). The effects of biofilm thickness, hydraulic retention time (HRT) and influent ammonia concentration on microbial community and total nitrogen (TN) removal efficiency were investigated. The results show that the large biofilm thickness of counter-diffusion MAB contributed to the small proportion of AOB and low TN removal efficiency. It is worth noting that the TN removal efficiency reached 84% when the membrane thickness was 500 μm. Regarding with the HRT and influent ammonia nitrogen concentration, the low influent ammonia nitrogen concentration and HRT resulted in the high TN removal efficiency. The influent ammonia nitrogen concentration of 450 mg/L and HRT of 5.5 days contributed to the highest TN removal efficiency of 87%.

Biyolojik azot giderimi gerçekleştirilen atıksu arıtma proseslerinin (AO prosesi) modellenmesi amacıyla Aktif Çamur Modeli No. 1 (ASM1) kullanılagelmişse de bu modelde ihtiyaç duyulan girdi parametrelerinin tahmin edilmesi çok zaman almaktadır. Bu çalışma kapsamında, ASM1 kadar detaylı girdi verisi gerektirmeyen geri beslemeli yapay sinir ağlarının (BPANN) AO proseslerindeki kimyasal oksijen ihtiyacı (KOİ), toplam Kjeldahl azotu (TKN) ve toplam azot (TN) giderim verimlerinin tahminindeki performansı test edilmiştir. Bu amaçla BPANN’de dört farklı aktivasyon fonksiyonu kullanılmıştır. Elde edilen sonuçlar, AO proseslerindeki KOİ, TKN ve TN giderim verimlerinin BPANN ile yüksek doğrulukta tahmin edilebildiğini göstermiş; en iyi öğrenme ve tahmin yeteneği ise Sinc fonksiyonu ile elde edilmiştir. Sinc-BPANN ile elde edilen ortalama kare hatalar KOİ giderim verimi için 2,50 × 10 -4 , TKN giderim verimi için 4,15 × 10 -4 , TN giderim verimi için ise 2,65 × 10 -4 olarak hesaplanmıştır. Buna göre Sinc-BPANN AO proseslerindeki KOİ, TKN ve TN giderim verimlerinin doğrusal olmayan doğasını ASM1’e nazaran çok daha az girdi parametresiyle açıklayabilmektedir.

Membrane distillation as post-treatment for anaerobic fluidized bed membrane bioreactor for organic and nitrogen removal

Perfluorooctanoic acid (PFOA), an emerging organic contaminant frequently detected in wastewater, inhibits biological nitrogen removal processes, posing challenges to sustainable wastewater treatment. Mitigating the adverse effects of PFOA while enhancing total nitrogen (TN) removal efficiency remains a critical concern. In this study, three sequencing batch biofilm reactors (SBBRs) were operated under low-oxygen conditions with a C/N ratio of 4.0 to investigate enhanced nitrogen removal under PFOA stress using biochar. Compared to the 78.1% TN removal efficiency in the control reactor (SBBR-0) with an initial TN concentration of 50 mg/L, the addition of PFOA decreased TN removal by 2.3% in SBBR-1, while the combined addition of PFOA and biochar increased it by 3.2% in SBBR-2. Biochar, acting through its electron-donating surface functional groups, mitigated PFOA-induced reactive oxygen species accumulation and increased adenosine triphosphate production. These effects promoted the generation of quorum sensing (QS) signaling molecules, facilitating microbial communication and cooperation. Consequently, the relative abundance of key nitrogen-removing bacteria, such as Thauera (from 7.90% to 9.92%) and Nitrosomonas (from 1.42% to 5.75%), increased, leading to enhanced nitrogen removal efficiency. A metagenomic analysis revealed that biochar significantly reduced the production of antibiotic resistance genes without promoting their dissemination. These findings provide new insights into mitigating the negative effects of PFOA and improving TN removal through QS promotion, offering a potential approach for enhancing the sustainability of wastewater treatment systems.

A novel post-denitrification system fed by carbon source from primary sludge (PS) was used for enhancing biological nitrogen removal (BNR) of low C/N wastewater. This system included one anoxic/oxic (AO) reactor and a special reactor for simultaneous sludge fermentation and denitrification (Sifeden). Ammonia was nitrified to nitrate in AO and then the nitrate was reduced to dinitrogen in Sifeden , into which PS was added intermittently. Results showed that this system had high performance on nitrogen removal. Total nitrogen (TN) removal efficiency was higher than 85% and the effluent TN≤10mg/L in the condition of influent C/N≤2. In Sifeden, volatile fatty acid (VFA) produced from PS fermentation provided electron donor for nitrate reduction, and PS was preliminarily stabilized simultaneously. Oxidation-Reduction Potential (ORP) had a significant correlation with the denitrification performance. TN removal efficiency could be further improved if adopting proper PS addition strategy according to the ORP profiles.

Heterotrophic activity compromises autotrophic nitrogen removal in membrane-aerated biofilms: Results of a modeling study

This study investigated the effect of low and high chemical oxygen demand (COD):N ratios on biological nitrogen removal and microbial distributions in full-scale step-feed (SF) municipal wastewater treatment plants (WWTPs) in Thailand (SF1) and Taiwan (SF2). The SF1 WWTP had a low COD:N (4:1) ratio, a long solids retention time (SRT) (> 60 d), and low dissolved oxygen (DO) conditions (0.2 mg L− 1 in anoxic tank and 0.9 mg L− 1 in aerobic tank). The total nitrogen (TN) removal efficiency was 48%. The SF2 WWTP had a high COD:N (10:1) ratio, a short SRT (7 d), and high DO (0.6 mg L− 1 in anoxic tank and 1.8 mg L− 1 in aerobic tank). The TN removal efficiency was 61%. The nitrification and denitrification rates from these two plants were inadequate. Using a quantitative polymerase chain reaction (qPCR) technique, the populations of ammonium oxidizing bacteria (AOB) and ammonium oxidizing archaea were quantified. Measurement of ammonia monooxygenase (amoA) gene abundances identified these AOB: Nitrosomonas sp., Nitrosospira sp., Nitrosoccus sp. and Zoogloea sp. Higher amounts of the archaeal-amoA gene were found with long SRT, lower DO and COD:N ratios. Abundance of Nitrobacter sp. was slightly higher than Nitrospira sp. at the SF1, while abundance of Nitrobacter sp. was two orders of magnitude greater than Nitrospira sp. at the SF2. More denitrifying bacteria were of the nirS-type than the nirK-type, especially at higher COD:N ratio. Most bacteria belong to the phyla Acidobacteria, Actinobacteria Bacteroidetes, Chloroflexi, Proteobacteria. The results from this work showed that insufficient carbon sources at the SF1 and high DO concentration in anoxic tank of SF2 adversely affected nitrogen removal efficiencies. In further research work, advanced techniques on the next generation sequencing with different variable regions should be recommended in full-scale WWTPs.

To investigate the long-term nitrogen treatment efficiency in vertical-flow (VF)-horizontal-flow (HF) hybrid constructed wetlands (CWs), the nitrogen removal efficiency under different seasons, N loads, and three operating stages (representing age of the wetland) were evaluated over a 12-year period. The average total nitrogen (TN) removal efficiencies in the effluent during the operation period were in the following order: summer (75.2%) > spring (73.4%) ≒ autumn (72.6%) > winter (66.4%). The removal efficiencies of TN in summer, autumn, and spring were generally higher than those in winter. At different stages of operation (years), the average TN removal rates in the effluent were in the following order: middle stage (73.4%; years 2006-2009) > last stage (72.0%; years 2010-2013) > beginning stage (70.1%; years 2002-2005). In VF-HF CWs, the amount of average TN removal (mg N m(-2) day(-1)) over the 12-year period was in the order of summer (5.5) ≒ autumn (5.1) > spring (4.3) ≒ winter (4.2) for the VF bed and in the order of summer (3.5) ≒ spring (3.5) ≒ autumn (3.3) > winter (2.7) for the HF bed, showing that the amount of TN removal per unit area (m(2)) in summer was slightly greater than that in other seasons. The amount of TN removal in the VF bed was slightly greater than that in the HF bed. Using three-dimensional simulation graphs, the maximum TN removal rate was at inflow N loads below 2.7 g m(-2) day(-1) in the summer season, whereas the minimum TN removal rate was at inflow N loads below 1.4 g m(-2) day(-1) in the winter season. Consequently, the TN removal efficiency was very stable over the 12 years of operation in VF-HF hybrid CWs. Results demonstrate that the VF-HF hybrid CWs possess good buffer capacity for treating TN from domestic sewage for extended periods of time.

Enhancing the total nitrogen removal efficiency of anaerobic ammonium oxidation (anammox) with two types of biochars