Simultaneous nitrification, denitrification, and phosphorus removal from municipal wastewater at low temperature

A novel simultaneous short-course nitrification, denitrification and fermentation process: bio-enhanced phenol degradation and denitrification in a single reactor

The feasibility of a simultaneous nitrification, denitrification and fermentation process (SNDF) under electric stirrer agitation conditions was verified in a single reactor. Enhanced activated sludge for phenol degradation and denitrification in pharmaceutical phenol-containing wastewater under low dissolved oxygen conditions, additional inoculation with Comamonas sp. BGH and optimisation of co-metabolites were investigated. At a hydraulic residence time (HRT) of 28 h, 15 mg/L of substrate as strain BGH co-metabolised substrate degraded 650 ± 50 mg/L phenol almost completely and was accompanied by an incremental increase in the quantity of strain BGH. Strain BGH showed enhanced phenol degradation. Under trisodium citrate co-metabolism, strain BGH combined with activated sludge treated phenol wastewater and degraded NO2--N from 50 ± 5 to 0 mg/L in only 7 h. The removal efficiency of this group for phenol, chemical oxygen demand (COD) and TN was 99.67%, 90.25% and 98.71%, respectively, at an HRT of 32 h. The bioaugmentation effect not only promotes the degradation of pollutants, but also increases the abundance of dominant bacteria in activated sludge. Illumina MiSeq sequencing research showed that strain BGH promoted the growth of dominant genera (Acidaminobacter, Raineyella, Pseudarcobacter) and increased their relative abundance in the activated sludge system. These genera are resistant to toxicity and organic matter degradation. This paper provides some reference for the activated sludge to degrade high phenol pharmaceutical wastewater under the action of biological enhancement.

Microplastics shaped performance, microbial ecology and community assembly in simultaneous nitrification, denitrification and phosphorus removal process

The widespread use of microplastics (MPs) has led to an increase in their discharge to wastewater treatment plants. However, the knowledge of impact of MPs on macro-performance and micro-ecology in simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) systems is limited, hampering the understanding of potential risks posed by MPs. This study firstly comprehensively investigated the performance, species interactions, and community assembly under polystyrene (PS) and polyvinyl chloride (PVC) exposure in SNDPR systems. The results showed under PS (1, 10 mg/L) and PVC (1, 10 mg/L) exposure, total nitrogen removal was reduced by 3.38-10.15 %. PS and PVC restrained the specific rates of nitrite and nitrate reduction (SNIRR, SNRR), as well as the activities of nitrite and nitrate reductase enzymes (NIR, NR). The specific ammonia oxidation rate (SAOR) and activity of ammonia oxidase enzyme (AMO) were reduced only at 10 mg/L PVC. PS and PVC enhanced the size of co-occurrence networks, niche breadth, and number of key species while decreasing microbial cooperation by 5.85-13.48 %. Heterogeneous selection dominated microbial community assembly, and PS and PVC strengthened the contribution of stochastic processes. PICRUSt prediction further revealed some important pathways were blocked by PS and PVC. Together, the reduced TN removal under PS and PVC exposure can be attributed to the inhibition of SAOR, SNRR, and SNIRR, the restrained activities of NIR, NR, and AMO, the changes in species interactions and community assembly mechanisms, and the suppression of some essential metabolic pathways. This paper offers a new perspective on comprehending the effects of MPs on SNDPR systems.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

Robustness of the anammox process at low temperatures and low dissolved oxygen for low C/N municipal wastewater treatment

Low water temperatures and ammonium concentrations pose challenges for anammox applications in the treatment of low C/N municipal wastewater. In this study, a 10 L-water bath sequencing batch reactor combing biofilm and suspended sludge was designed for low C/N municipal wastewater treatment. The nitrogen removal performance via partial nitrification anammox-(endogenous) denitrification anammox process was investigated with anaerobic-aerobic-anoxic mode at low temperatures and dissolved oxygen (DO). The results showed that with the decrease of temperature from 30 to 15℃, the influent and effluent nitrogen concentrations and nitrogen removal efficiencies were 73.7 ± 6.5 mg/L, 7.8 ± 2.8 mg/L, and 89.4 %, respectively, with aerobic hydraulic retention time of only 6 h and DO concentration of 0.2-0.5 mg/L. Among that, the stable anammox process compensated for the inhibitory effects of the low temperatures on the nitrification and denitrification processes. Notably, from 30 to 15℃, the anammox activity and relative abundance of the dominant Brocadia genus were increased from 39.7 to 45.5 mgN/gVSS/d and 7.3 to 12.0 %, respectively; the single gene expression level of the biofilm increased 9.0 times. The anammox bacteria showed a good adaptation to temperatures reduction. However, nitrogen removal by anammox was not improved by increasing DO (≥ 4 mg/L) at 8-4℃. Overall, the results of this study demonstrate the feasibility of the mainstream anammox process at low temperatures.

Constructed wetlands with recycled concrete for wastewater treatment in cold climate: Performance and life cycle assessment

This study investigated the technical, environmental, and economic feasibility of using recycled construction material (concrete) as substrate in constructed wetlands for cold climate decentralized domestic wastewater treatment. The wastewater treatment efficiency was examined, and life cycle assessment (LCA) and cost benefit analysis were performed. The technical feasibility was assessed in lab-scale two-stage wetland systems with recycled concrete or lava stone as substrates, which were operated at 22 °C and 5 °C with local wild plants and vegetables. The wetlands removed ∼85 % and ∼51 % of organics and ∼67 % and ∼34 % TN at 22 °C and 5 °C, respectively; no significant difference was found between concrete and lava stone. The heavy metal contents in the cultivated vegetables met WHO standards for human consumption, showing the feasibility of nutrient recovery from the treated wastewater. A comparative LCA of septic tank standalone, septic tank + constructed wetland (with recycled concrete), and gravity-driven ceramic membrane (GDCM) system was performed. This aims to illustrate the benefits of intensifying the existing treatment process (i.e., septic tank) with the constructed wetland, with an alternative membrane-based treatment technique as benchmark. The LCA results revealed that using waste materials as the substrate in constructed wetlands could reduce the environmental impact of wetlands. Installation of the wetland as posttreatment of the septic tank (1) could reduce ∼50 % of eutrophication potential without increasing global warming impact compared to the septic tank alone; (2) had ∼90 % higher global warming impact and ∼40 % lower eutrophication impact compared to GDCM. Economic analysis revealed that the total cost of septic tank + constructed wetland (0.143 €/m3) was comparable to the septic tank alone (merely 3.5 % difference), and 49 % lower than that of GDCM (with recycled membranes). Therefore, the septic tank + constructed wetland scenario could be favorable for sensitive areas with eutrophication potential regarding its technical, economical, and environmental feasibility.

Microplastics perturb nitrogen removal, microbial community and metabolism mechanism in biofilm system

Microplastics (MPs) are a significant component of global pollution and cause widespread concern, particularly in wastewater treatment plants. While understanding the impact of MPs on nutrient removal and potential metabolism in biofilm systems is limited. This work investigated the impact of polystyrene (PS) and polyethylene terephthalate (PET) on the performance of biofilm systems. The results revealed that at concentrations of 100 and 1000 μg/L, both PS and PET had almost no effect on the removal of ammonia nitrogen, phosphorus, and chemical oxygen demand, but reduced the removal of total nitrogen by 7.40-16.6%. PS and PET caused cell and membrane damage, as evidenced by increases in reactive oxygen species and lactate dehydrogenase to 136-355% and 144-207% of the control group. Besides, metagenomic analysis demonstrated both PS and PET changed the microbial structure and caused functional differences. Some important genes in nitrite oxidation (e.g. nxrA), denitrification (e.g. narB, nirABD, norB, and nosZ), and electron production process (e.g. mqo, sdh, and mdh) were restrained, meanwhile, species contribution to nitrogen-conversion genes was altered, therefore disturbing nitrogen-conversion metabolism. This work contributes to evaluating the potential risks of biofilm systems exposed to PS and PET, maintaining high nitrogen removal and system stability.

Mechanisms of persistence and impact of ordinary heterotrophic organisms in aerobic granular sludge

The stability of granules, contaminant removal and microbial structure of an aerobic granular sludge (AGS) process were investigated with a focus on ordinary heterotrophic organisms (OHOs). Long-term stable granules and high removals of COD (97 %), NH₄⁺ (98 %), P (85 %) and total N (77 %) were achieved. Sequencing analyses identified 6.6 % of phosphorus-accumulating organisms in the sludge, concordant with the observed bio-P removal capacity. However, OHOs were the most abundant bacteria in the sludge (70-93 %) without resulting in unstable aggregates. Under current dogmas of microbial competition in activated sludge, it seemed contradictory that OHOs could persist in the long term in the AGS where COD was depleted beginning in the anaerobic phase. Microbial analyses showed that OHOs could survive in granules by micropredation, proteolysis, fermentation and EPS consumption. Heterotrophic-nitrification/ aerobic-denitrification was an active pathway in the AGS. These findings contribute to a better understanding of microbial competition in AGS and its stability.

Performance of anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal system overwhelmingly dominated by Candidatus_Competibacter: Effect of aeration time

The anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal process (AOA-SNDPR) is a promising technology for enhanced biological wastewater treatment and in situ sludge reduction. Herein, the effects of aeration time (90, 75, 60, 45, and 30 min, respectively) on AOA-SNDPR were evaluated including simultaneous nutrients removal, sludge characteristics, and microbial community evolution, where the role of a denitrifying glycogen accumulating organisms, Candidatus_Competibacter, was re-explored given its overwhelming dominance. Results revealed that nitrogen removal was more vulnerable, and a moderate aeration period of 45-60 min mostly favored nutrients removal. Low observed sludge yields (Y_obs) were obtained with decreased aeration (as low as 0.02 g MLSS/g COD), while MLVSS/MLSS got increased. The dominance of Candidatus_Competibacter was proven to be the key to endogenous denitrifying and in situ sludge reduction. This study would aid the more carbon- and energy-efficient aeration strategy for AOA-SNDPR systems treating low-strength municipal wastewater.