Nutrient Removal Performance Research Articles

The exogenous compound bacteria alter microbial community and nutrients removal performance in the biofilm unit of the integrated aquaculture wastewater bioremediation systems

Integrated bioremediation systems are widely emerging treatment of mariculture wastewaters. The system consists of several units including the biofilm which is microbial consortium that help in removal of waste nutrients. However, a great performance would have been achieved if there was an addition of exogenous compound bacteria (ECB) in the biofilm unit. In this study, the ECB were added to the biofilm unit of an artificially created integrated mariculture wastewater system to explore their influence on the microbial community composition and structural diversity. A high-throughput amplicon of 16 S rRNA, PERMANOVA and LDA Effect Size (LEfSe) analyses were used to investigate the effects of ECB on the microbial community and nutrients removal performance in the biofilm unit of the integrated bioremediation systems of aquaculture wastewater (ISBAW). The results showed that the contents of total phosphorus (TP), chemical oxygen demand (CODMn), ammonia nitrogen (NH4+-N), and nitrate (NO3--N) decreased significantly after the treatment of ECB with the removal rates of 68%, 58%, 75% and 84%, respectively. The bacterial community in the water column has experienced three successional stages: the pretreatment, the middle and the late stage. The biofilm has gone through two successional stages: the pretreatment - early stage and the late stage. Bacillus became potential biomarker in the late water column and the pretreatment biofilm, respectively. Random processes were closed correlated with the community in the water column while deterministic processes were closely correlated to the biofilm’s component. Generally, the addition of ECB significantly affects the structural composition of bacterial communities on different media in the biofilm unit. The study provides basic information for understanding and development of efficient and optimized the IBSAW.

Effects of operational parameters on the performance of unialgal Oedogonium sp. filamentous algae nutrient scrubbers under controlled environmental conditions

Filamentous algae nutrient scrubber (FANS) operating parameters can strongly influence algal biomass productivity and nutrient removal. However, few studies to date have investigated the effects of FANS operating parameters such as initial standing crop, harvesting frequency and influent flow rate on biomass productivity and nutrient removal performance, especially for FANS that cultivate a single species of algae. Therefore, the overall aim of this study was to investigate how operating parameters affect the biomass productivity and nutrient removal performance of Oedogonium sp. - a promising species for unialgal FANS. The initial standing crop had a significant effect on biomass productivity, with productivities being highest (8.6 ± 0.5 g DW biomass m−2day−1) when the initial standing crop was 60–70 g DW m−2. However, the daily nutrient removal rate was highest (0.47 ± 0.06 g N m−2 day−1and 1.24 ± 0.13 g P m−2 day−1) at the highest initial standing crop (100–110 DW m−2). Biomass productivity was highest with a three-day growth period, regardless of size of the initial standing crop. Therefore, a four-day harvesting interval was selected as the optimal harvesting regime to promote exponential growth and high biomass production. Influent flow rate had a significant effect on biomass productivity, which was highest (9.3 ± 1.7 g DW m−2 day−1) for the 1 L min−1 flow rate. This flow rate also gave the highest instantaneous nutrient removal rate (0.05 ± 0.02 g N m−3 and 0.14 ± 0.05 g P m−3). Current results suggest that an optimum initial standing crop of 70–80 g DW m−2, harvesting frequency of four days and influent flow rate of 1 L min−1 (16.7 L min−1 m−1 width) were optimal for Oedogonium sp. cultivated on FANS to maximize their biomass production and nutrient removal under controlled laboratory conditions. These results contribute to understanding the impacts of operating parameters on optimizing unialgal Oedogonium sp. FANS biomass production and nutrient removal performance.

Energy efficiency and nutrient removal performance: comparison between several types of activated sludge process

The operation of a wastewater treatment plant entails a huge amount of electricity. The majority of energy inputs are consumed by aeration systems to support biological processes for treated wastewater. Urban wastewater treatment plants are energy-intensive facilities that consume significant amounts of energy. For conventional activated sludge systems, 25% to 60% of the operating costs are associated with energy use. Malaysia’s wastewater treatment plants have fallen short in terms of technological advancement in the sewerage industry. The goal of this research is to analyse and make a comparison of the capabilities of the sequencing batch reactor (SBR) and other activated sludge (AS) system treatment plants in Selangor, Malaysia. High energy electricity consumption was an important issue that affected the operational cost and development of wastewater treatment plants (WWTP). The result and discussion for the analysis had been presented into comparison result for each objective of this research studied which was to determine lowest energy efficiency, to assess highest nutrient removal efficiency and compliance rate for each WWTP process plant. This paper presents best practices that can be implemented and adapted by operators in their pursuit of energy and reduce cost or expenses in the sewage treatment plant.

Effect of horizontal-flow velocity on permeate flux and nutrient removal of the novel inclined-tube/oxidation-ditch membrane bioreactor for building wastewater recycling

A hybrid system of the inclined-tube/oxidation ditch-membrane bioreactor or IT/OD-MBR system was developed. While keeping hydraulic retention time (HRT) of 24 h, the system was operated with different horizontal flow velocities of 0.2,0.3 and 0.4 m/s. The performance and stability of the IT/OD-MBR system for biological nutrient removal and permeate flux was investigated. The results indicated that IT/OD-MBR system could achieve high performances for COD, ammonia and phosphorus removal efficiencies over 90%, 90% and 80%, respectively with the horizontal flow velocity at least 0.2 m/s. Moreover, the predominant foulant of microbial EPS was found to be lipid. For long-term system operation, the optimal horizontal flow velocity at least 0.3 m/s is recommended for the stable permeate flux and nutrient removal performance. High quality of treated effluent from the proposed hybrid IT/OD-MBR system could comply with the water reuse guideline for landscape and gardening purposes.

Nutrient Removal and Membrane Performance of an Algae Membrane Photobioreactor in Urban Wastewater Regeneration.

The increase in industry and population, together with the need for wastewater reuse, makes it necessary to implement new technologies in the circular economy framework. The aim of this research was to evaluate the quality of the effluent of an algae membrane photobioreactor for the treatment of the effluent of an urban wastewater treatment plant, to characterise the ultrafiltration membranes, to study the effectiveness of a proposed cleaning protocol, and to analyse the performance of the photobioreactor. The photobioreactor operated under two days of hydraulic retention times feed with the effluent from the Los Vados wastewater treatment plant (WWTP) (Granada, Spain). The microalgae community in the photobioreactor grew according to the pseudo-second-order model. The effluent obtained could be reused for different uses of diverse quality with the removal of total nitrogen and phosphorus of 56.3% and 64.27%, respectively. The fouling of the polyvinylidene difluoride ultrafiltration membrane after 80 days of operation was slight, increasing the total membrane resistance by approximately 22%. Moreover, the higher temperature of the medium was, the lower intrinsic resistance of the membrane. A total of 100% recovery of the membrane was obtained in the two-phase cleaning protocol, with 42% and 58%, respectively.

Performance assessment of normal and electrode-assisted floating wetlands: influence of input pollutant loads, surface area, and positioning of anode electrodes.

This study reports the design and development of microbial fuel cell (MFC) assisted floating wetlands and compares treatment removal performance with a normal (without electrodes) floating wetland. Both types of floating wetlands were planted with Phragmites plant and evaluated for real municipal wastewater treatment. The effective volume of each floating wetland was 0.5 m3. The floating wetlands were operated under variable hydraulic load rates, i.e., 20 and 60mm/day. Mean 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), ammoniacal nitrogen (NH4-N), total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), and coliform removal percentages ranged between 71 and 96%, 72 and 94%, 62 and 86%, 58 and 75%, 82 and 97%, 64 and 92%, and 72 and 93%, respectively within the normal and electrode-assisted MFC integrated floating wetlands. The electrode-integrated floating wetlands showed better pollutant removal performance than the normal system under unstable input pollutant loading conditions. Nitrogen and organic matter removals were achieved through both electrochemically active and inactive microbial removal routes. Physical separation processes, such as filtration and sedimentation, contributed to phosphorus, solids, and coliform removal. Plant uptake contributed to micro-scale nitrogen (≤ 1%) and phosphorus (≤ 0.1%) removal. Increment of hydraulic/pollutant load improved organic removal but decreased nutrient removal performance of the normal, electrode-integrated floating wetlands. The electrode-integrated floating wetlands produced power densities ranging between 0.7 and 1.4 mW/m3, and 0.2 and 2.3 mW/m3 during lower, upper input loading ranges, respectively. Bioenergy production of the electrode-integrated floating wetlands varied within the two operational periods due to a wider range of electrochemically inactive microbial populations in real wastewater that interfered with electrochemical organic matter oxidation. The positioning difference of the anode electrodes was a significant factor that improved pollutant removal within the electrode-integrated floating wetlands compared to the other variable, i.e., anode electrodes surface area.

Differences in Nitrogen and Phosphorus Removal under Different Temperatures in Oenanthe javanica Cultivars

Plant selection plays a critical role in phytoremediation. However, previous research has focused on comparing different plant species but has ignored different cultivars. Here, a laboratory experiment was performed to analyze the nitrogen (N) and phosphorus (P) removal performance of different cultivars of Oenanthe javanica, which are widely employed for phytoremediation in China. Seven cultivars were planted on simulated livestock wastewater with high N and P content prepared with compounds for 22 days in two artificial climate chambers with different temperatures. N and P contents were monitored to estimate the nutrient removal performance of the cultivars. ‘Suzhou Yuanye’ had the highest N removal ability at room temperature (45.33 ± 1.92%) and under cold stress (39.63 ± 2.15%) in 22 days, and it could also remove P effectively (99.32 ± 0.33% at room temperature and 77.50 ± 0.08% under cold stress). ‘Yixing Yuanye’ performed the best in P removal (97.90 ± 2.89% at room temperature and 99.57 ± 0.61% under cold stress). ‘Liyang Baiqin’ performed well in N removal only at room temperature (44.30 ± 1.03%). ‘Suqian Jianye’ had low removal efficiencies for both N and P. From the biomass and N content, we could conclude that the high N removal efficiency of ‘Suzhou Yuanye’ is due to high N assimilation of the plant. However, ‘Yixing Yuanye’ did not show higher P assimilation ability than other cultivars. Taken together, the selection of cultivars is important for phytoremediation projects using O. javanica, and ‘Suzhou Yuanye’ is much more suitable for phytoremediation than other cultivars.

Integration of silicate minerals for ammonium and phosphate removal with an on-site wastewater treatment prototype

Inadequately treated wastewater exiting from on-site water treatment systems (OWTS) contains high levels of ammonium and phosphate, which contribute to environmental nutrient pollution. Nutrient removal in small-scale OWTS can be challenging because the most effective known methods are designed for large-scale systems and rely on biological processes. This work focuses on the implementation of two natural silicate-based minerals, clinoptilolite and Polonite, as non-biological sorptive media for nutrient removal in an OWTS. Lab-scale batch sorption experiments showed that Polonite performance is maximized after suspended solids have been removed from blackwater via ultrafiltration. In contrast, clinoptilolite shows robust performance even with untreated blackwater. With both minerals installed in our full-scale OWTS prototype, nutrient removal performance increased from 47.5 ± 15.0% to 84.1 ± 6.3% removal for total N and from 32.3 ± 2.3% to 78.9 ± 5.9% removal for total P. Nevertheless, the target removal performance (>80%) for total P was only achieved with high Polonite loading, which increased effluent pH outside the target range of 6 < pH < 9. Additionally, no loss in nutrient removal performance was observed when the OWTS was restarted after a 150-day idle period. To investigate the potential for media reuse and nutrient recovery, various media regeneration solutions were evaluated. For clinoptilolite, 1 M HCl, NaCl, and KCl all showed good regeneration ability at 2 h contact time, with KCl showing the highest (>86%) ammonium recovery. For the first time, we demonstrated that a minor fraction (30–40%) of binding sites in Polonite can be regenerated using 1 M NaOH or KOH. We also found that the same 1 M HCl regeneration solution could be reused for four clinoptilolite regeneration cycles with no loss in performance. From these results, we discuss opportunities and limitations for implementing these materials in small-scale OWTS.

Modeling nutrient removal and energy consumption in an advanced activated sludge system under uncertainty

Activated sludge models are widely used to simulate, optimize and control performance of wastewater treatment plants (WWTP). For simulation of nutrient removal and energy consumption, kinetic parameters would need to be estimated, which requires an extensive measurement campaign. In this study, a novel methodology is proposed for modeling the performance and energy consumption of a biological nutrient removal activated sludge system under sensitivity and uncertainty. The actual data from the wastewater treatment plant in Slupsk (northern Poland) were used for the analysis. Global sensitivity analysis methods accounting for interactions between kinetic parameters were compared with the local sensitivity approach. An extensive procedure for estimation of kinetic parameters allowed to reduce the computational effort in the uncertainty analysis and improve the reliability of the computational results. Due to high costs of measurement campaigns for model calibration, a modification of the Generalized Likelihood Uncertainty method was applied considering the location of measurement points. The inclusion of nutrient measurements in the aerobic compartment in the uncertainty analysis resulted in percentages of ammonium, nitrate, ortho-phosphate measurements of 81%, 90%, 78%, respectively, in the 95% confidence interval. The additional inclusion of measurements in the anaerobic compartment resulted in an increase in the percentage of ortho-phosphate measurements in the aerobic compartment by 5% in the confidence interval.The developed procedure reduces computational and measurement efforts, while maintaining a high compatibility of the observed data and model predictions. This enables to implement activated sludge models also for the facilities with a limited availability of data.

Nutrient removal performance and microbial community analysis of amended bioretention column for rainwater runoff treatment

Bioretention is a promising approach for rainwater runoff treatment, while effective performances can hardly be expected from traditional systems. Several amended bioretention columns were configured for enhanced pollutants removal with different media designs and submerged depths. Results revealed that amended media largely stimulated simultaneous nutrients removals under different influent concentrations, with the highest removal rates by 90% traditional bioretention soil media +5% water treatment residuals +5% coconut coir. Further experiments showed that increase of submerged depth significantly improved the removal of nitrate and total nitrogen, though led to slight decrease of ammonia nitrogen, total phosphorus and chemical oxygen demand removals. HiSeq sequencing elucidated that the submerged depth altered the diversity and structure of the microbial community in the bioretention columns, as well as some putative bacteria for biological pollutants removal. This study might stimulate the cost-effective treatment of rainwater runoff by bioretention approaches.

La–Fe magnetic bentonite stimulated denitrifying phosphorus removal from low C/N wastewater in the A2/O process: Performance, microbial community, and potential mechanism

A novel process combined A2/O bioreactor with a millimeter-sized magnetic lanthanum-modified bentonite (La–Fe-MB) granules material (terms as A2/O–La–Fe-MB) was proposed for highly efficient phosphorus removal from municipal sewage. A series of experiments were carried out to explore the feasibility and suitability of using La–Fe-MB as a novel adsorbent. The performance of nutrient removal and microbial composition, and any adverse effect brought by dosing La–Fe-MB are of interests. The long-term operation (240 days) suggested that dosing La–Fe-MB in the A2/O bioreactor achieved a highly-efficient TP removal with average effluent TP concentrations for 0.22 mg/L by enhancing denitrifying phosphorus removal (DPR) and chemical precipitation. Based on the mass balance equations, La–Fe-MB contributed to ∼39.7% of TP removal via adsorption/precipitation in the anaerobic zone, 43.6% of TP was removed through anoxic DPR in the anoxic zone, and post-aerobic zone further reduced ∼14.4% of phosphorus. Moreover, an interesting synergic effect between the La–Fe-MB and functional bacteria was found in the combined process. La–Fe-MB addition not only have less effect on the removal of organic, nitrogen species, and functional bacteria (AOB, NOB, etc.,), but significantly facilitated the enrichment of denitrifying phosphorus accumulating organisms (DPAOs) via releasing traces of Fe (Fe(II)/Fe(III)) in bioreactor. Besides, DPAOs (1.7%), glycogen accumulating organisms (GAOs) (0.031%) and P-accumulating organisms (PAOs) (0.41%) co-existed in this combined system, potentially resulting in simultaneous denitrifying dephosphatation and aerobic phosphorus absorbing. The above results demonstrated that the novel A2/O–La–Fe-MB system is a promising technique for highly-efficient TP removal from wastewater.

The effect of PO43--P concentration on sludge settleability and nutrients removal performance.

In order to explore the effect of influent PO43--P concentration on the relationship of phosphorus remove performance and sludge settleability, three sequencing batch reactors (SBRs) operated as anaerobic/aerobic mode were used to treat wastewater with different PO43--P concentrations (same COD), and the organic loading rate (OLR) was changed through adjusting the anaerobic (aerobic) duration. The sludge settleability, nutrients removal, and microorganism species were investigated. The results showed that when the influent PO43--P were 4.3 mg·L-1 and 8.6 mg·L-1, increasing the OLR through decreasing aerobic duration could significantly improve sludge settleability, while decreasing anaerobic duration could not. It was found that increase the OLR could promote the denitrification compete for carbon sources with phosphorus release process by inhibiting the accumulation of NO2--N, leading to the decrease of phosphorus removal ability. When the influent PO43--P was 17.2 mg·L-1, sufficient nitrification was beneficial to enrich denitrifying phosphorus accumulating bacteria (DPAO), and the activities of Thauera and Flavobacterium (DPAO) were stronger. Therefore, increasing influent PO43--P concentration and reducing aerobic duration could help phosphorus accumulating bacteria (PAO) compete with denitrification for COD and enrich DPAO, thus reducing carbon source consumption.

Developing a Novel Alum Sludge-Based Floating Treatment Wetland for Natural Water Restoration

Novel alum sludge-based floating treatment wetland (FTW) was developed to enhance the purification performances of natural water bodies, i.e., rivers, lakes, and ponds. Polyurethane was applied to foam the lightweight alum sludge based-substrate (PU-AL) of FTW through the response surface method. Three FTWs configurations were created for a half-year lab-scale operation, and the PU-AL FTW presents the greatest purification performance in the removal rate of chemical oxygen demand (COD) of 62.58 ± 6.65%, total nitrogen (TN) of 53.31 ± 4.65%, and total phosphorus (TP) of 45.39 ± 4.69%. PU-AL substrate could enhance the nutrient removal performance of existing FTW by providing a proper media for microbial and plants’ growth. This study provides a good solution and showcase not only from a natural water restoration point of view but also from the waterworks sludge management view for a better understanding of FTWs and good applications in engineering practice.

Stable denitrification performance of a mesh rotating biological reactor treating municipal wastewater

The mesh rotating biological reactor (MRBR) is one of the advanced modifications of the rotating biological contactor. MRBRs have a high specific surface area for biomass in order to achieve efficient nutrient removal performance. This study evaluated the denitrification performance of an MRBR during municipal wastewater treatment. A laboratory-scale MRBR was continuously operated for approximately 550 days under ambient conditions, fed with actual sewage. Influent NO3−-N concentration was decreased from 27.8 ± 6.0 mg-N L−1 to an effluent value of 8.4 ± 4.8 mg-N L−1 at ≥20 ºC under 2 h of hydraulic retention time. The total nitrogen removal was 190 ± 130 g N m−3 d−1, compared to 860 ± 310 g N m−3 d−1 with added nitrate at ≥20 ºC and 100 ± 47 g N m−3d−1 compared to 830 ± 220 g-N m−3d−1 with added nitrate at ≤15 ºC. A batch test showed that soluble chemical and biological oxygen demand removal efficiencies were 87% and 93%, respectively, after 2 h of operation. While NO3−-N remained after 2 h, adding methanol to enhance denitrification resulted in 93% removal after 8 h. Microbial analysis was performed on samples taken from the surface and inside the mesh carrier. Comamonadaceae, Thiotrichaceae, and Rhodocyclaceae denitrifying bacteria dominated the bacterial community and accelerated the performance of the MRBR. The study revealed that water temperature changes have an insignificant effect on denitrification and that the process can be performed stably throughout the year.

Developing a 3D Hydrodynamic and Water Quality Model for Floating Treatment Wetlands to Study the Flow Structure and Nutrient Removal Performance of Different Configurations

Floating treatment wetlands (FTWs) are widely used in surface water. The nutrient removal performance depends on both physical processes and chemical/biological transformations in FTWs. However, research describing the coupling processes of hydrodynamic and water quality in the system remains limited. Therefore, a coupled three-dimensional model of hydrodynamic and water quality for FTWs was developed based on the Environmental Fluid Dynamics Code (EFDC). Additional plant drag terms were added to the momentum equations to simulate the suspended canopy effect, and the chemical/biological processes occurring in FTWs were integrated into the original water quality equations simultaneously. The fully calibrated model was used to compare the hydrodynamic characteristics and nutrient removal performance of seven FTW configurations. The modeling results showed that the main stream would turn to the bottom and side of the plant root zone because of the block in FTWs. The differences in the hydrodynamic characteristics among the seven configurations led to a difference in water quality improvement effects. Segmenting a single FTW into a pair of parallel FTWs could achieve the maximum nitrogen and phosphorus mass removal. The results of the study are useful for designing an optimal FTW configuration in surface water.

Unveiling significance of Ca2+ ion for start-up of aerobic granular sludge reactor by distinguishing its effects on physicochemical property and bioactivity of sludge

Almost all of the aerobic granular sludge (AGS) reactors were fed on certain amounts of Ca2+ ion, but whether and why it was necessary for reactor start-up remain unknown. Herein, this study conducted a set of comparative experiments in three AGS reactors, which were operated in parallel with Ca2+ addition in R3, hydroxyapatite (HAP) addition in R1, and without any forms of Ca addition in R2. Results showed that R3 not only achieved the complete granulation of sludge, but exhibited superior performance of COD and nutrient removal. In contrast, R1 had a slightly quicker granulation rate than R3 (R1: 0.07 day−1; R3: 0.06 day−1), but the formed granules could not efficiently degrade pollutants. In R2, both sludge granulation and pollutants removal did not proceed normally. Further investigations found that the Ca2+ ion acted in three ways: (1) it increased inorganic composition of sludge to promote granulation; (2) the transformed HAP strengthened stability of granular structure; (3) it ensured bioactivity of granules by driving enrichment of functional microbes and synthesis of metabolism enzymes. Overall, this study systemically proved significance of Ca2+ ion for the start-up of AGS reactors and its influencing mechanisms on different properties of granules.

A comprehensive evaluation of process kinetics: A plant-wide approach for nutrient removal and biogas production

The present study investigated the deviations of operational parameters of a large-scale wastewater treatment plant (WWTP) from design basis through combining dedicated batch experiments with full-scale dynamic modeling results. The long-term process performance of a full-scale biological nutrient removal (BNR) plant equipped with anaerobic sludge digestion system was monitored to evaluate the process kinetics of both carbon and nutrient removal and anaerobic sludge digestion. In this respect, plant-specific characterization; chemical oxygen demand (COD) fractionation, batch kinetic studies and sludge settling velocity tests were performed together with plant-wide SUMO model simulation. Results showed that nitrification and anaerobic hydrolysis were found to be 30% and 70% lower than literature values, respectively. The anaerobic digestion test coupled with plant-wide model calibration showed that anaerobic hydrolysis was the bottleneck in biogas production. Correspondingly, performance of the anaerobic digestion in the full-scale plant was poor as low biogas production yields were observed. In addition, the degradation rate via anaerobic hydrolysis of primary sludge was found to be higher (∼2-2.5) compared to anaerobic hydrolysis of biological sludge. The results of this study provide insight into model-based experimental characterization as well as plant-wide modeling approach. Coupling model-based batch experiments with full-scale modeling enabled to reduce the number of kinetic parameters to be fine-tuned. Moreover, the information gathered from kinetic batch tests to the simulation platform yielded a satisfying prediction of long-term performance of the plant operation.

Impact analysis of hydraulic loading rate on constructed wetland: Insight into the response of bulk substrate and root-associated microbiota

Constructed wetland (CW) is an environment-friendly and low-cost technology for nutrients removal from domestic wastewater. For a well-tuned CW, hydraulic loading rate (HLR) is one of the critical factors, particularly under the challenging circumstance of more frequent heavy rainfall events brought by global warming. In this study, a comprehensive investigation was conducted to explore the influence of different HLRs on the CW's bulk substrate and root-associated microbiota aiming to yield new insight for CW management from a hybrid perspective of environmental microbiology and engineering science. The response of the microbial community and associated nutrients removal performance under different HLR settings were analyzed after a one-year operation. Results showed that the bulk substrate and rhizosphere genera involved in desulfurization and denitrification, such as Ferritrophicum, Sulfurimonas, and Sulfurisoma, were enriched in the higher HLR condition and associated with the higher total nitrogen (TN) and nitrate nitrogen (NO3−-N) removal compared to the lower HLR condition. Co-occurrence network analysis demonstrated a more complex network under the higher HLR condition. Besides, it was observed that more stochastic in microbial assembly under the higher HLR condition. Surprisingly, zoonotic pathogens were observed and showed a greater prevalence under the higher HLR condition, indicating the potential correlation between HLR and pathogen intrusion. Collectively, this study revealed that the microbiota could be significantly altered under different HLR conditions, thereby resulting in differences in nutrients removal performance.

Optimizing floating treatment wetland and retention pond design through random forest: A meta-analysis of influential variables

Floating treatment wetlands (FTWs), artificial systems constructed from buoyant mats and planted with emergent macrophytes, represent a potential retrofit to enhance the dissolved nutrient removal performance of existing retention ponds. Treatment occurs as water flows through the dense network of roots suspended in the water column, providing opportunities for pollutants to be removed via filtration, sedimentation, plant uptake, and adsorption to biofilms in the root zone. Despite several recent review articles summarizing the growing body of research on FTWs, FTW design guidance and strategies to optimize their contributions to pollutant removal from stormwater are lacking, due in part to a lack of statistical analysis on FTW performance at the field scale. A meta-analysis of eight international FTW studies was performed to investigate the influence of retention pond, catchment, and FTW design characteristics on effluent concentrations of nutrients and total suspended solids (TSS). Random forest regression, a tree-based machine learning approach, was used to model complex interactions between a suite of predictor variables to identify design strategies for both retention ponds and FTWs to enhance treatment of nutrient and sediment. Results indicate that pond design features, especially loading ratio and pond depth (which should be limited to 200:1 and 1.75 m, respectively), are most influential to effluent water quality, while the benefits of FTWs were limited to improving mitigation of phosphorus species and TSS which was primarily influenced by FTW coverage and planting density. Findings from this work inform wet retention pond and FTW design, as well as guidance on scenarios where FTW implementation is most appropriate, to improve dissolved nutrient and sediment removal in urban runoff.

Enhanced nutrient removal from mainstream sewage via denitrifying dephosphatation, endogenous denitrification and anammox in a novel continuous flow process

It is a challenging subject to realize nitrogen and phosphorus elimination synchronously from limited-carbon sewage through conventional biological processes. Herein, a novel continuous flow anaerobic/oxic/anoxic/oxic (AOA-O) process, which integrated denitrifying dephosphatation, endogenous denitrification and anammox in the anoxic zone, was developed to enhance nutrient elimination from low carbon/nitrogen sewage (3.4 in average). After the long-term operation (280 days), a satisfactory nutrient removal performance (effluent PO43--P: 0.2 mg P/L, total inorganic nitrogen (TIN):8.9 mg N/L) was obtained. Mass balance indicated that anammox contributed to 26.1% TIN removal and denitrifying dephosphatation contributed to 25.6% phosphorus removal, respectively. The cooperation of anammox bacteria retained in biofilms and endogenous denitrifying bacteria in flocculent sludge was responsible for the enhanced nutrient removal in the anoxic zone. Dechloromonas carried out phosphorus uptake both under oxic conditions and anoxic conditions. This study can broaden the application prospect of mainstream anammox.