Influence of Plants and Organic Matter on the Nitrogen Removal in Laboratory-Scale Model Subsurface Flow Constructed Wetlands Inoculated with Anaerobic Ammonium Oxidizing Bacteria

Nitrogen transformations in constructed wetlands: A closer look at plant-soil interactions using chemical imaging

Constructed wetlands have long been used for domestic wastewater treatment. Despite the widespread application of constructed wetlands for wastewater remediation, they are still regarded as a black box in terms of the complex biogeochemical processes occurring internally, particularly with respect to plant-soil (and nitrogen) interactions. Additionally, many critical processes pertaining to nitrogen transformations in constructed wetlands are thought to occur in microzones within the rhizosphere, highlighting the need for studies with sub-cm spatial resolution. In this study we coupled nitrogen porewater measurements with chemical imaging to determine spatio-temporal patterns in porewater O₂ and pH to assess the extent of plant-induced changes in soil redox dynamics that influence nitrogen biogeochemical cycling during dosed application of nitrogen-rich artificial wastewater. Planar optode imaging revealed extensive O₂ fluxes to otherwise anoxic sediment via radial oxygen loss (ROL) from Typha latifolia roots. The contribution of photosynthetic O₂ from this plant species was minimal as a strong oxic signal persisted in darkness (diel cycles). NH₄⁺ and NO_x^- removal were strongly correlated with the extent of oxic and anoxic areas, a function largely attributed to the presence of plants and the associated enhanced microbial communities supported. The distribution of nitrogen species within the Typha rhizosphere exhibited reproducible trends as a function of distance from roots, with concentrations highest close to roots (1-5 mm from root surface) and subsequently decreasing at greater distances. Microscale spatio-temporal redox heterogeneity within the rhizosphere due to ROL imposed by plants promoted nitrogen removal likely by stimulating the coupling between nitrification and denitrification in these systems. Collectively, this study highlights the profound importance of plants in exerting controls on soil conditions and nitrogen cycling in constructed wetland systems. With careful considerations, constructed wetlands designed to promote wetland plants' functions may enhance nitrogen removal and mitigate nitrogen pollution.

From Laboratory Tests to the Ecoremedial System: The Importance of Microorganisms in the Recovery of PPCPs-Disturbed Ecosystems

The presence of a wide variety of emerging pollutants in natural water resources is an important global water quality challenge. Pharmaceuticals and personal care products (PPCPs) are known as emerging contaminants, widely used by modern society. This objective ensures availability and sustainable management of water and sanitation for all, according to the 2030 Agenda. Wastewater treatment plants (WWTP) do not always mitigate the presence of these emerging contaminants in effluents discharged into the environment, although the removal efficiency of WWTP varies based on the techniques used. This main subject is framed within a broader environmental paradigm, such as the transition to a circular economy. The research and innovation within the WWTP will play a key role in improving the water resource management and its surrounding industrial and natural ecosystems. Even though bioremediation is a green technology, its integration into the bio-economy strategy, which improves the quality of the environment, is surprisingly rare if we compare to other corrective techniques (physical and chemical). This work carries out a bibliographic review, since the beginning of the 21st century, on the biological remediation of some PPCPs, focusing on organisms (or their by-products) used at the scale of laboratory or scale-up. PPCPs have been selected on the basics of their occurrence in water resources. The data reveal that, despite the advantages that are associated with bioremediation, it is not the first option in the case of the recovery of systems contaminated with PPCPs. The results also show that fungi and bacteria are the most frequently studied microorganisms, with the latter being more easily implanted in complex biotechnological systems (78% of bacterial manuscripts vs. 40% fungi). A total of 52 works has been published while using microalgae and only in 7% of them, these organisms were used on a large scale. Special emphasis is made on the advantages that are provided by biotechnological systems in series, as well as on the need for eco-toxicological control that is associated with any process of recovery of contaminated systems.

Modeling BOD and COD removal from Palm Oil Mill Secondary Effluent in floating wetland by Chrysopogon zizanioides (L.) using response surface methodology

While the oil palm industry has been recognized for its contribution towards economic growth and rapid development, it has also contributed to environmental pollution due to the production of huge quantities of by-products from the oil extraction process. A phytoremediation technique (floating Vetiver system) was used to treat Palm Oil Mill Secondary Effluent (POMSE). A batch study using 40 L treatment tanks was carried out under different conditions and Response Surface Methodology (RSM) was applied to optimize the treatment process. A three factor central composite design (CCD) was used to predict the experimental variables (POMSE concentration, Vetiver plant density and time). An extraordinary decrease in organic matter as measured by BOD and COD (96% and 94% respectively) was recorded during the experimental duration of 4 weeks using a density of 30 Vetiver plants. The best and lowest final BOD of 2 mg/L was obtained when using 15 Vetiver plants after 13 days for low concentration POMSE (initial BOD = 50 mg/L). The next best result of BOD at 32 mg/L was obtained when using 30 Vetiver plants after 24 days for medium concentration POMSE (initial BOD = 175 mg/L). These results confirmed the validity of the model, and the experimental value was determined to be quite close to the predicted value, implying that the empirical model derived from RSM experimental design can be used to adequately describe the relationship between the independent variables and response. The study showed that the Vetiver system is an effective method of treating POMSE.

Simultaneous anammox and denitrification (SAD) process in sequencing batch reactors

This study investigated nitrogen removal by the simultaneous anaerobic ammonium oxidation (anammox) and heterotrophic denitrification (SAD) process in a sequencing batch reactor (SBR) inoculated with suspended activated sludge and immobilized anammox sludge at various total organic carbon/nitrate (C/N) ratios. Synthetic wastewater containing nitrate 100mg-NL(-1), ammonium 70mg-NL(-1), and acetate 50-250mg-CL(-1) was fed to the SBR. Nitrite reduced from nitrate by heterotrophic denitrification was accumulated and removed with ammonium in each cycle operation of the SBR. The SAD process removed nitrate and ammonium effectively (T-N removal, 58-94%) by the high anammox contribution (ca. 80-100%) under low C/N ratios (0.5-1.0). At high C/N ratios of 1.2-2.5, the SAD process maintained T-N removal 67-79% with predominance of heterotrophic denitrification instead of anammox reaction. Results demonstrated that the SAD process performs high nitrogen removal effectively from wastewater with widely different C/N ratios.

Influence of season and plant species on the abundance and diversity of sulfate reducing bacteria and ammonia oxidizing bacteria in constructed wetland microcosms

Constructed wetlands offer an effective means for treatment of wastewater from a variety of sources. An understanding of the microbial ecology controlling nitrogen, carbon and sulfur cycles in constructed wetlands has been identified as the greatest gap for optimizing performance of these promising treatment systems. It is suspected that operational factors such as plant types and hydraulic operation influence the subsurface wetland environment, especially redox, and that the observed variation in effluent quality is due to shifts in the microbial populations and/or their activity. This study investigated the biofilm associated sulfate reducing bacteria and ammonia oxidizing bacteria (using the dsrB and amoA genes, respectively) by examining a variety of surfaces within a model wetland (gravel, thick roots, fine roots, effluent), and the changes in activity (gene abundance) of these functional groups as influenced by plant species and season. Molecular techniques were used including quantitative PCR and denaturing gradient gel electrophoresis (DGGE), both with and without propidium monoazide (PMA) treatment. PMA treatment is a method for excluding from further analysis those cells with compromised membranes. Rigorous statistical analysis showed an interaction between the abundance of these two functional groups with the type of plant and season (p < 0.05). The richness of the sulfate reducing bacterial community, as indicated by DGGE profiles, increased in planted vs. unplanted microcosms. For ammonia oxidizing bacteria, season had the greatest impact on gene abundance and diversity (higher in summer than in winter). Overall, the primary influence of plant presence is believed to be related to root oxygen loss and its effect on rhizosphere redox.

A review on nitrogen and organics removal mechanisms in subsurface flow constructed wetlands: dependency on environmental parameters, operating conditions and supporting media

With the unique advantages of lower operational and maintenance cost, the applications of subsurface flow constructed wetlands for the treatment of wastewater have been increasing rapidly throughout the world. The removal of nitrogen and organics by such systems has gained substantial attention in recent years. In subsurface flow wetlands, the removal of pollutants often relies on a diverse range of co-existing physical, chemical and biological routes, which are vitally dependent on numerous environmental and operational parameters. This paper provides a comprehensive review of wetland structures, classic and novel nitrogen and organics removal mechanisms along with the key environmental parameters and operational conditions that enhance removal in subsurface flow wetland systems. The critical exploration identifies the major environmental parameters such as: pH, DO, and temperature, operational factors i.e. organic carbon availability, loading, feed mode, retention time, recirculation, harvesting, and the complex role (of both parameters) on classical nitrogen and organics removal pathways. Subsequently, the necessity of further extensive research on such factors, for promoting novel nitrogen removal routes in wetland systems has also been highlighted. The expansion of the review on the influence of the unconventional wetland matrix indicates that, the structural differences and inherent properties of these media can support substantial nitrogen and organics removal from wastewater, under optimal operating conditions. Overall, the critical review illustrates the necessity of a profound knowledge on the complicated inter-relationship between nitrogen and organics removal routes, governing environmental and operational parameters, and wetland matrix for improving the treatment performances of subsurface flow wetlands.

Effects of pH and seasonal temperature variation on simultaneous partial nitrification and anammox in free-water surface wetlands

Design considerations to enhance simultaneous partial nitrification and anammox in constructed wetlands are largely unknown. This study examined the effects of pH and seasonal temperature variation on simultaneous partial nitrification and anammox in two free-water surface wetlands. In order to enhance partial nitrification and inhibit nitrite oxidation, furnace slag was placed on the rooting substrate to maintain different pH levels in the wetland water. The wetlands were batch operated for dairy wastewater treatment under oxygen-limited conditions at a cycle time of 7 d. Fluorescence in situ hybridization analysis found that aerobic ammonium oxidizing bacteria and anammox bacteria accounted for 42-73% of the bacterial populations in the wetlands, which was the highest relative abundance of ammonium oxidizing and anammox bacteria in constructed wetlands enhancing simultaneous partial nitrification and anammox. The two wetlands removed total inorganic nitrogen efficiently, 3.36-3.38 g/m(2)/d in the warm season with water temperatures at 18.9-24.9 °C and 1.09-1.50 g/m(2)/d in the cool season at 13.8-18.9 °C. Plant uptake contributed 2-45% to the total inorganic nitrogen removal in the growing season. A seasonal temperature variation of more than 6 °C would affect simultaneous partial nitrification and anammox significantly. Significant pH effects were identified only when the temperatures were below 18.9 °C. Anammox was the limiting stage of simultaneous partial nitrification and anammox in the wetlands. Water pH should be controlled along with influent ammonium concentration and temperature to avoid toxicity of free ammonia to anammox bacteria.

Effect of Nitrate on Sulphur Transformations Depending on Carbon Load in Laboratory-Scale Wetlands Treating Artificial Sewage

Two laboratory-scale constructed wetlands planted with Juncus effusus were used to investigate the dynamics of sulphur transformations under varying nitrate and organic carbon loads as well as its interactions with microbial carbon and nitrogen transformations. The removal of dissolved organic carbon was obtained to be around 65-87% with specific removal load of 1.40-2.63 g/m2 d. 94% of nitrate removal (under inflow concentration of 15 mg/L) irrespective of organic carbon loads indicated a highly active denitrification process in wetlands. Sulphate reduction was performed at a high level of 83% in a low redox potential (about -300 mV) under condition of inflow organic carbon concentration of 50 mg/L. The dosage of nitrate in the inflow can strongly hinder the process ofdissimilatory microbial sulphate. The coexist of sulphide with concentration of 1.65-2.65 mg/L and elemental sulphur of 0.17-2.18 mg/L in the pore water of wetlands demonstrated a simultaneous occurrence of microbial sulphate reduction and sulphide oxidation. A lower ammonium oxidation removal was initiated, which was probably caused by the toxic effect of sulphide with concentration of about 3 mg/L in the pore water. The sulphide concentration in the pore water was highly exponentially correlated with the redox potential, indicating the control of sulphide in wetlands could be performed by the adjustment of redox potential via aeration and/or nitrate dosage.

Anammox bacterial abundance, biodiversity and activity in a constructed wetland

An integrated approach to document high anammox activity and biodiversity in a constructed wetland (CW) was performed and showed that substantial anammox activity could mitigate undesirable N(2)O emission. The enhanced anammox bacterial abundance, biodiversity and activity were achieved by supplementing activated sludge to the CW. Up to 3.38 × 10(7) gene copies g(-1) dry soil of anammox bacteria were enriched in the CW. The activity measured by isotope pairing technique increased from 1.6 nmol N g(-1) sludge h(-1) in the original activated sludge to 18 nmol N g(-1) soil h(-1) in the CW, with the specific cellular activity increased from 5.1 to 12.8 fmol cell(-1) d(-1). Up to 33% of produced N(2) could be attributed to anammox process in the CW, with the remainder being due to denitrification. Phylogenetic analysis of anammox bacterial 16S rRNA genes indicated a shift of community from single Candidatus "Brocadia fulgida" in sludge to multiple "Jettenia", "Brocadia", and "Anammoxoglobus" species in the CW. With static chambers and control experiments, the CW with supplemented sludge had a 30% reduced N(2)O emission flux compared with the tests without adding biomass during an 8 month testing period.

Enhanced denitrification and organics removal in hybrid wetland columns: comparative experiments

This study investigated three lab-scale hybrid wetland systems with traditional (gravel) and alternative substrates (wood mulch and zeolite) for removing organic, inorganic pollutants and coliforms from a synthetic wastewater, in order to investigate the efficiency of alternative substrates, and monitor the stability of system performance. The hybrid systems were operated under controlled variations of hydraulic load (q, 0.3-0.9 m3/m2 d), influent ammoniacal nitrogen (NH4-N, 22.0-80.0 mg/L), total nitrogen (TN, 24.0-84.0 mg/L) and biodegradable organics concentration (BOD5, 14.5-102.0 mg/L). Overall, mulch and zeolite showed promising prospect as wetland substrates, as both media enhanced the removal of nitrogen and organics. Average NH4-N, TN and BOD5 removal percentages were over 99%, 72% and 97%, respectively, across all three systems, indicating stable removal performances regardless of variable operating conditions. Higher Escherichia coli removal efficiencies (99.9%) were observed across the three systems, probably due to dominancy of aerobic conditions in vertical wetland columns of the hybrid systems.