Evaluating organics removal performance from lagoon-pretreated swine wastewater in pilot-scale three-stage surface flow constructed wetlands

Assessment of wetland ecosystem health in Rarh Region, India through P-S-R (pressure-state-response) model

The current study attempted to assess wetland ecosystem health (EH) in the Murshidabad district's Rarh tract using the P-S-R (Pressure-State-Response) model and machine learning (ML) algorithms and validated it with a field-based validation approach as well as conventional validation approaches. To assess the ecosystem's health, 27 metrics were used to monitor the wetlands' pressure, state, and response. All of the models found that 46.1 % of wetlands in strong EH zones have transformed to 11.41 % in relatively fragile EH zones during the previous thirty years, demonstrating a progressive loss of EH quality throughout larger wetland areas. All of the applied models were deemed to be acceptable based on the results of the model validation process, however, the Random Forest (RF) model performed exceptionally well. The deterioration of EH in the wetlands happened due to the rapid expansion of settlement areas and agricultural land. So, the findings of the study deepen our knowledge about EH in the Rarh tract's wetlands, assisting decision-makers in creating sustainable wetland management strategies.

Analysis of ammonia-nitrogen removal kinetics by stage in pilot scale vertical flow wetlands treating landfill leachate in series

This study explored the effect stage number and plant type have on ammonia-nitrogen (NH3-N) removal kinetics in a two-stage pilot-scale vertical flow constructed wetland (VFCW) system treating landfill leachate. Half of the VFCW columns were planted with Typha latifolia and the other half Scirpus californicus, and half of the columns were loaded with municipal solid waste landfill leachate (diluted to 1 part leachate to 2 parts total) with the effluent from these columns was collected in two separate barrels. The remaining columns were loaded with the effluent collected from the first columns, creating a two-stage VFCW system with four unique pairs to be tested. The leachate used here experienced no prior pre-treatment, and average influent concentrations of NH3-N for the first- and second-stage VFCWs were 508 and 321 mg L-1, respectively- much higher than many other VFCW treatment systems. Some reduction in chemical oxygen demand was observed, as well as generation of nitrate and nitrite, evidence of nitrification. No apparent correlation between aboveground biomass and removal of NH3-N was observed. Overall removal efficiency of NH3-N through two stages of VFCWs was 53.7% for columns planted with T. latifolia and 58.3% for those planted with S. Californicus. Average NH3-N removal efficiencies for the first stage VFCWs were 32.7% and 34.3%, while those in the second stage were 31.3% and 36.5%; no significant difference was observed between the first and second stage, suggesting that stage number does not have a significant effect on the removal efficiency of NH3-N in the primary treatment of landfill leachate via VFCWs. However, average mass removal rates of NH3-N in the first stage were 166 and 175 mg L-1 d-1; the second stage was significantly lower at 99.4 and 112 mg L-1 d-1, indicating that the first stage removed more pollutants overall.

Meta-analysis review for pilot and large-scale constructed wetlands: Design parameters, treatment performance, and influencing factors

Despite their longstanding use in environmental remediation, constructed wetlands (CWs) are still topical due to their sustainable and nature-based approach. While research and review publications have grown annually by 7.5 % and 37.6 %, respectively, from 2018 to 2022, a quantitative meta-analysis employing advanced statistics and machine learning to assess CWs has not yet been conducted. Further, traditional statistics of mean ± standard deviation could not convey the extent of confidence or uncertainty in results from CW studies. This study employed a 95 % bootstrap-based confidence interval and out-of-bag Random Forest-based driver analysis on data from 55 studies, totaling 163 cases of pilot and full-scale CWs. The study recommends, with 95 % confidence, median surface hydraulic loading rates (HLR) of 0.14 [0.11, 0.17] m/d for vertical flow-CWs (VF) and 0.13 [0.07, 0.22] m/d for horizontal flow-CWs (HF), and hydraulic retention time (HRT) of 125.14 [48.0, 189.6] h for VF, 72.00 [42.00, 86.28] h for HF, as practical for new CW design. Permutation importance results indicate influent COD impacted primarily on COD removal rate at 21.58 %, followed by HLR (16.03 %), HRT (12.12 %), and substrate height (H) (10.90 %). For TN treatment, influent TN and COD were the most significant contributors at 12.89 % and 10.01 %, respectively, while H (9.76 %), HRT (9.72 %), and HLR (5.87 %) had lower impacts. Surprisingly, while HRT and H had a limited effect on COD removal, they substantially influenced TN. This study sheds light on CWs' performance, design, and control factors, guiding their operation and optimization.

Effect of plant-self debris on nitrogen removal, transformation and microbial community in mesocosm constructed wetlands planted with Myriophyllum aquaticum

Aquatic macrophytes debris decomposition could release pollutants and nutrients into the water of constructed wetlands (CWs), but their role in nitrogen removal and transformation remains poorly understood. The present study investigated the effects of plant-self debris on nitrogen removal and microbial communities in mesocosm CWs planted with Myriophyllum aquaticum. During the 68-day operation, the plant debris addition did not change the mean removal efficiency of ammonium (NH₄⁺-N) and total nitrogen (TN) of CWs but showed significant differences over the operation time. The NH₄⁺-N and organic nitrogen released from the plant debris decomposition affected the nitrogen removal. The plant debris decreased the effluent nitrate concentration and N₂O emission fluxes of the CWs with the increased abundance of denitrifying bacterial genera, indicating that plant debris decomposition increased the denitrification activities via dissolved organic carbon release. High-throughput sequencing indicated that the plant debris altered the distribution and composition of the microbial community in the sediments. Proteobacteria was the dominant phylum (28-52%), and the relative abundance of denitrifying bacteria genera was significantly higher in the sediments with debris addition (37-40%) than in the non-addition (6.6-7.7%). The present study provided new insights into the role of macrophytes in pollutant removal and the plant management strategy of CWs.

Transcriptomics Insights into Phosphorus Stress Response of Myriophyllum aquaticum

Through excellent absorption and transformation, the macrophyte Myriophyllum (M.) aquaticum can considerably remove phosphorus from wastewater. The results of changes in growth rate, chlorophyll content, and roots number and length showed that M. aquaticum could cope better with high phosphorus stress compared with low phosphorus stress. Transcriptome and differentially expressed genes (DEGs) analyses revealed that, when exposed to phosphorus stresses at various concentrations, the roots were more active than the leaves, with more DEGs regulated. M. aquaticum also showed different gene expression and pathway regulatory patterns when exposed to low phosphorus and high phosphorus stresses. M. aquaticum's capacity to cope with phosphorus stress was maybe due to its improved ability to regulate metabolic pathways such as photosynthesis, oxidative stress reduction, phosphorus metabolism, signal transduction, secondary metabolites biosynthesis, and energy metabolism. In general, M. aquaticum has a complex and interconnected regulatory network that deals efficiently with phosphorus stress to varying degrees. This is the first time that the mechanisms of M. aquaticum in sustaining phosphorus stress have been fully examined at the transcriptome level using high-throughput sequencing analysis, which may indicate the direction of follow-up research and have some guiding value for its future applications.

Fermented Myriophyllum aquaticum and Lactobacillus plantarum Affect the Distribution of Intestinal Microbial Communities and Metabolic Profile in Mice

This research explores the effects of fermented Myriophyllum aquaticum (F) and Lactobacillus plantarum BW2013 (G) as new feed additives on the gut microbiota composition and metabolic profile of mice. Crude protein (p = 0.045), lipid (p = 0.000), and ash (p = 0.006) contents in Myriophyllum aquaticum (N) were improved, whereas raw fiber (p = 0.031) content was decreased after solid-state fermentation by G. Mice were fed with no additive control (CK), 10%N (N), 10%N + G (NG), 10%F (F), and 10%F + G (FG). High-throughput sequencing results showed that, compared with the CK group, Parabacteroides goldsteinii was increased in treatment groups and that Lactobacillus delbrueckii, Bacteroides vulgatus, and Bacteroides coprocola were increased in the F and FG groups. Bacteroides vulgatus and Bacteroides coprocola were increased in the F group compared with the N group. Metabolomic results showed that vitamin A, myricetin, gallic acid, and luteolin were increased in the F group compared with the N group. Reduction in LPG 18:1 concentration in the N and F groups could be attenuated or even abolished by supplementation with G. Furthermore, 9-oxo-ODA was upregulated in the FG group compared with the F group. Collectively, N, F, and G have beneficial effects on gut microbiota and metabolic profile in mice, especially intake of FG.

Effects of substrate type on variation of sludge organic compounds, bioelectric production and microbial community structure in bioelectrochemically-assisted sludge treatment wetland

A bioelectrochemical assisted sludge treatment wetland (BE-STW) is a promising technology used in the elimination of organic compounds and recovery of bio-energy. In this study, four BE-STW systems were constructed to investigate the effects of some substrates (i.e. graphite particles, zeolite, ceramsite, and gravel) on organic compounds biodegradation and transformation, electricity production, and anodic bacterial community. The maximum output voltages were 0.939, 0.870, 0.741 and 0.835 V, and the maximum power densities were 0.467, 0.143, 0.110, and 0.131 W/m³ for the graphite particles (BS-GP), zeolite (BS-Z), ceramsite (BS-C), and gravel (BS-G) systems, respectively. Also, the dissolved organic carbon (DOC) removal rates were 61.84%, 28.54%, 25.56%, and 18.34% in BS-GP, BS-G, BS-Z, and BS-C, respectively. The degradation of aromatic compounds in sludge extracellular biological organic matter (EBOM) was mainly due to the decrease of hydrophilic fraction (HPI) and transphilic acid fraction (TPI-A) contents. Moreover, aromatic proteins were preferentially removed in BS-Z. For BS-C, the tyrosine-like proteins and humic acid-like substances in TPI-A were totally removed. An excitation-emission matrix (EEM) analysis showed that the fluorescent intensity of the humic acid-like substances was the lowest in BS-GP, and no fluorescence peaks of fulvic acid-like substances were observed. Finally, at the genus level, Longilinea, Terrimonas, Ottowia, and Saccharibacteria_genera_incertae_sedis were the dominant bacteria in BE-STW, and Methylophilus was also only detected in BS-GP. These results confirmed that substrate materials have a significant impact on the preferentially degraded organic matter in BE-STWs, which can provide a theoretical basis for the practical application of STW in the future.

Unveiling the role of sediments in phosphorus removal in pilot-scale constructed wetlands for swine wastewater treatment

The accumulation rate, fractions, and sorption capacity of phosphorus in sediments determine the removal efficiency and service life of constructed wetlands (CWs). Nine pilot-scale three-stage surface flow CWs were constructed to treat three loading rates of lagoon-pretreated swine wastewater, and surface sediment samples at initial and one-year treatment were collected to analyze the phosphorus fractions and sorption capacity. After one-year treatment, concentration of total phosphorus (TP) in sediments increased for high loading rates of wastewater, but remained stable for low loading rates. The annual accumulation rate of TP in sediments (M_a) was -43-445 mg kg^-1 yr^-1 at surface loading rate (SLR) of 36-355 g P m^-2 yr^-1. Their association could be described well using a sigmoid model, i.e., M_a = -23 + 538/(1 + exp.(-(SLR-262)/48)) (R²_adj = 0.897, RMSE = 40.8, p < 0.01), indicating that the phosphorus accumulation rates in sediments were loading rate-dependent. The sum of inorganic phosphorus fractions contributed to 80-100% of the TP concentration, and accumulation of aluminum-bound phosphorus (AlP) and iron-bound phosphorus (FeP) was responsible for variability of TP concentration in sediments. Phosphorus sorption capacity of CW1 sediments increased by 1.3-1.8 times, attributed to increased pH, and concentrations of ammonium oxalate-extractable aluminum and iron in sediments due to the wastewater input. Selecting iron and aluminum-rich materials preferentially as substrates and regulating the ratio of metal ions to phosphorus in wastewater should be alternative enhancement strategies of CWs for phosphorus removal.

Phyco-remediation of swine wastewater as a sustainable model based on circular economy

Pork production has expanded in the world in recent years. This growth has caused a significant increase in waste from this industry, especially of wastewater. Although there has been an increase in wastewater treatment, there is a lack of useful technologies for the treatment of wastewater from the pork industry. Swine farms generate high amounts of organic pollution, with large amounts of nitrogen and phosphorus with final destination into water bodies. Sadly, little attention has been devoted to animal wastes, which are currently treated in simple systems, such as stabilization ponds or just discharged to the environment without previous treatment. This uncontrolled release of swine wastewater is a major cause of eutrophication processes. Among the possible treatments, phyco-remediation seems to be a sustainable and environmentally friendly option of removing compounds from wastewater such as nitrogen, phosphorus, and some metal ions. Several studies have demonstrated the feasibility of treating swine wastewater using different microalgae species. Nevertheless, the practicability of applying this procedure at pilot-scale has not been explored before as an integrated process. This work presents an overview of the technological applications of microalgae for the treatment of wastewater from swine farms and the by-products (pigments, polysaccharides, lipids, proteins) and services of commercial interest (biodiesel, biohydrogen, bioelectricity, biogas) generated during this process. Furthermore, the environmental benefits while applying microalgae technologies are discussed.

Sustainable livestock wastewater treatment via phytoremediation: Current status and future perspectives

Phytoremediation, the application of vegetation and microorganisms for recovery of nutrients and decontamination of the environment, has emerged as a low-cost, eco-friendly, and sustainable approach compared to traditional biological and physico-chemical processes. Livestock wastewater is one of the most severe pollution sources to the environment and water resources. When properly handled, livestock wastewater could be an important alternative water resource in water-scarce regions. This review discussed the characteristics and hazards of different types of livestock wastewater and available methods for the treatment. Meanwhile, the current status of investigations on phytoremediation of livestock wastewater via different hydrophyte systems such as microalgae, duckweed, water hyacinth, constructed wetlands, and other hydrophytes is reviewed, and the utilization of hydrophytes after management is also discussed. Furthermore, advantages and limitations on livestock wastewater management via phytotechnologies are emphasized. At last, future research needs are also proposed.

Effect of ammonia stress on carbon metabolism in tolerant aquatic plant-Myriophyllum aquaticum

In this study, the tips of Myriophyllum aquaticum (M. aquaticum) plants were planted in open-top plastic bins and treated by simulated wastewater with various ammonium-N concentrations for three weeks. The contents of related carbohydrates and key enzyme activities of carbon metabolism were measured, and the mechanisms of carbon metabolism regulation of the ammonia tolerant plant M. aquaticum under different ammonium-N levels were investigated. The decrease in total nonstructural carbohydrates, soluble sugars, sucrose, fructose, reducing sugar and starch content of M. aquaticum were induced after treatment with ammonium-N during the entire stress process. This finding showed that M. aquaticum consumed a lot of carbohydrates to provide energy during the detoxification process of ammonia nitrogen. Moreover, ammonia-N treatment led to the increase in the activitives of invertase (INV) and sucrose synthase (SS), which contributed to breaking down more sucrose to provide substance and energy for plant cells. Meanwhile, the sucrose phosphate synthase (SPS) activity was also enhanced under stress of high concentrations of ammonium-N, especially on day 21. The result indicated that under high-concentration ammonium-N stress, SPS activity can be significantly stimulated by regulating carbon metabolism of M. aquaticum, thereby accumulating sucrose in the plant body. Taken together, M. aquaticum can regulate the transformation of related carbohydrates in vivo by highly efficient expression of INV, SPS and SS, and effectively regulate the osmotic potential, thereby delaying the toxicity of ammonia nitrogen and improving the resistance to stress. It is very important to study carbon metabolism under ammonia stress to understand the ammonia nitrogen tolerance mechanism of M. aquaticum.

Principal component analysis as a criterion for monitoring variable organic load of swine wastewater in integrated biological reactors UASB, SABF and HSSF-CW

The multivariate analysis to optimize the parameters of wastewater is essential to reduce costs. The aim of this study was to evaluate the use of multivariate and conventional analysis in biological system composed by upflow anaerobic sludge blanket (UASB), submerged aerated biological filters (SABF) and horizontal subsurface flow constructed wetland (HSSF-CW) reactors in the organic stabilization of swine wastewater (SW). Four loads were used in the system with alteration by COD concentration of untreated SW, and the data were evaluated by principal components (PCA). The average efficiency of COD and BOD removal increased from 45% in phase I to 67% in phase IV in the UASB, SABF and HSSF-CW reactors. The principal component analysis promoted the reduction of 13 original variables to 5, 8 and 5 principal components in the UASB, SABF and HSSF-CW reactors, respectively, optimizing the dynamics of interpretation of the data that influenced the most the stability of the wastewater system across the four phases. There was a strong negative effect of oxygen concentrations in the SABF reactor in relation to organic variables, optimizing the biological mechanisms of the HSSF-CW and, therefore, enabling better decision making and cost reduction with analysis at treatment plants.

Nitrogen removal performance and needed area estimation of surface-flow constructed wetlands using a probabilistic approach

Pollutant concentrations in influents into constructed wetlands (CWs) are highly fluctuating and may vary over several orders of magnitude, leading to large uncertainties in removal performance assessment when using pollutant concentrations in the influent and effluent directly. Incorporating a probabilistic approach into removal performance assessment and needed area estimation of CWs could advantage decision making regarding wastewater treatment and engineering applications. A series of three-stage surface-flow CWs (SFCWs) were constructed for treating ammonium-rich swine wastewater. The surface removal rate and removal efficiency of ammonium nitrogen in the SFCWs using the probabilistic approach were 0.27-3.23 g m^-2 d^-1 and 43.0-99.9% (95% confidence interval (CI)), which were consistent with the deterministic approach (95% CI: 0.24-3.18 g m^-2 d^-1 and 70.4-99.9%). The needed SFCW area was estimated as 6.6 (95% CI: 1.4-17.8) to 29.7 (95% CI: 6.4-80.1) m² for required removal efficiency from 40% to 90% for 0.18 m³ d^-1 swine wastewater with different strengthens. For specific removal efficiency of 90%, the needed CW areas was 13.9 (95%CI: 4.9-42.7), 25.1 (95%CI: 5.9-66.0), 33.5 (95%CI: 13.5-87.1), and 40.8 (95%CI: 16.2-89.4) m² for influent ammonium loading rate of 0.18-2.7, 2.7-14.4, 14.4-36, and 36-60 g d^-1, respectively. The first-order removal constant of ammonium nitrogen decreased logarithmically with increasing influent and effluent concentration/loading rate in the SFCW units (p < 0.001), which was responsible for the needed SFCW areas covering a wide range. The reliability analysis confirmed the results from the probabilistic approach were appropriate. The present study shed new lights on the performance evaluation and design of CWs for treating wastewater with highly-fluctuating concentrations using a probabilistic approach.

Does rice straw application reduce N2O emissions from surface flow constructed wetlands for swine wastewater treatment?

Rice straw was applied often as a carbon source to improve nitrogen removal; however, few studies have considered the effect of rice straw on nitrous oxide (N₂O) emission during nitrogen removal in constructed wetlands (CWs). We constructed eighteen combined systems, consisting of rice straw ponds and surface flow CWs to investigate the effect of rice straw application on N₂O emission in three strengths of swine wastewater treatments. The results showed rice straw (RS) treatment increased 131.5% of N₂O emission factor from low strength CWs, but decreased 37.2-43.7% of N₂O emission factors for medium and high strengths compared with no rice straw (NRS) treatment. The RS application led to an average 10.7% increase in the potential denitrification rate, and simultaneously enhanced gene abundances of the total bacteria (16S rRNA), ammonia-oxidising archaea, ammonia-oxidising bacteria, nitrate reductase, and N₂O reductase (nosZ) for all strengths CWs. The multiple regression model revealed N₂O emissions were strongly related to water temperature, nitrate, chemical oxygen demand, and denitrification genes. The proportion of nosZ gene abundance in 16S rRNA was higher in RS (0.7-1.3%) than NRS (0.4-0.9%) for medium and high strengths, while an opposite trend was observed for low strength. The discrepancy was responsible for increasing or decreasing N₂O emission by RS application among different strengths. These findings indicated the effectiveness of RS application to control N₂O emissions from the surface flow CWs was related to the pollution level of wastewater.