Effects of high interstitial velocity on nitrification in horizontal flow wetlands for tertiary wastewater treatment

This thesis describes in detail the background, methods, results, and conclusions of a three-year PhD research project - “subsurface flow constructed wetlands for the treatment of domestic wastewater”, which was undertaken at Monash University between April 2008 and December 2010. The overall objective of the research was to discover the efficiencies of key pollutant removals (organics, nutrients, solids, and coliforms), when a medium-strength wastewater is treated in different types of subsurface flow wetlands, and how the pollutant removal should be modelled to reflect the biodegradation kinetics of the pollutants. The research was designed and carried out in four phases: In phase 1, a comparative experiment was carried out to understand how wetland media may affect the removal of organics and nitrogen; special focus was on studying the nitrification-denitrification process in hybrid wetland systems with an unconventional organic-containing wetland media (wood-mulch). The results indicated simultaneous nitrification-denitrification in vertical flow wetlands with organic mulch media, primarily due to greater oxygen flux in the wetland matrix and the supply of organic carbon from the media. In contrast, this unconventional media was found to be inefficient when it is applied in horizontal flow wetlands, as anoxic conditions caused excessive leaching of organics from the media. The monitoring of the performances of different wetland units, during this phase, allowed the selection of an effective hybrid wetland system for further experiments, to monitor pollutant removal stability in the next phase. In phase 2, experiments were carried out in three hybrid wetland systems that had identical configurations, plants (Phragmites australis), and media (including gravel, wood-mulch, and zeolite). The three systems were operated under different pollutant and hydraulic loadings, to monitor the removal of nitrogen and organics. The results demonstrated stable nitrogen and organics removal efficiencies within the range of hydraulic and pollutant loading variations. The media of wood-mulch and zeolite were found, or further confirmed, to enhance nitrogen removal in vertical flow wetlands, by enhancing simultaneous nitrification-denitrification and adsorption of ammonia. Horizontal flow wetlands with the traditional gravel media showed abilities to remove nitrate and the excess organics that was leached into the wastewater from wood-mulch media and, within the experiment range, the mass removals of nitrate and COD in the horizontal flow wetlands were found to increase with their loadings. In phase 3, kinetic models were developed to describe the biodegradation of nitrogen and organics removal in wetland systems. Reaction kinetics that were considered in the model development included first-order, Monod and multiple-Monod-kinetics; these kinetics were combined with continuous-stirred tank reactor (CSTR) or plug-flow pattern, to produce equations that link the inlet and outlet concentrations of each key pollutants across a single wetland. Using three statistical parameters, a critical evaluation was made to evaluate the suitability of five potential models for describing pollutant removals in vertical and horizontal flow wetlands. The results recommended the models that were derived from Monod kinetics for nitrogen and organics removal in both vertical and horizontal flow wetland systems. Finally, in phase 4 a simple MATLAB programme was established, based on the model studies in the previous phase, to provide a potential design tool for determining the surface area of a single subsurface (vertical or horizontal) flow wetland, when it is required to achieve a given pollutant removal target. The MATLAB programme can also be used to predict the performances of existing wetland systems. In order to assist readers to track the results of four phases of this research in its logic sequence, the thesis has been arranged to contain seven chapters. Chapters 1-2 describe the scope and objectives of the research and a literature survey on the technical development of subsurface flow wetlands for wastewater treatment. Chapters 3-6 describe in sequence the detailed methods and results of the four phases of the research. Overall conclusions are presented in Chapter 7. Four publications, including three ISI journal papers and one international conference paper, have been produced as a direct result of the research. The papers are attached in Appendix I, and all the original experiment records are attached in Appendix II. Overall, this research improved the current understanding of the removal of ammonia, nitrate, COD and BOD in vertical and horizontal flow wetlands. In addition, it produced kinetic models to describe the removal of these pollutants, potentially allowing model-based design of vertical and horizontal flow constructed wetlands for the direct treatment and reclamation of medium-strength wastewater.

Mass transfer approach and the designing of horizontal subsurface flow constructed wetland systems treating waste stabilisation pond effluent.

Rapid urbanisation, water pollution, and infrastructure development are increasingly facing challenges in water management and sanitation in urban areas. Conventional gray infrastructure such as centralised treatment plants and extensive drainage networks, while effective in certain contexts, often remains costly, energy-intensive, and environmentally unsustainable. Traditional infrastructure can cause environmental degradation and public health risks when managing wastewater and stormwater. Therefore, Nature-based Solutions (NbS) emerge as a sustainable alternative to address these challenges. The main objective of the research was to assess the feasibility of implementing NbS to create more resilient, sustainable, and liveable urban water systems. Specific objectives included identifying the most suitable NbS for urban residential wastewater management, evaluating their performance in terms of pollutant removal, and designing context-appropriate systems for a selected study area. Parliament Lake sub-catchment 1 in Sri Lanka, one of the most urbanised and heavily polluted areas in the country, was selected as the study area for this research. A methodological framework was developed comprising terrain and hydrological analysis, land-use compatibility assessment, and ecological enhancement potential. After investigating the applicability of various types of NbS for this sub-catchment, constructed wetlands (CWs) were selected based on the existing needs and requirements of water management and sanitation. This study specifically targeted two sites within the Parliament Lake sub-catchment. Location 1 consisted of three houses, and Location 2 consisted of seven houses, both of which contribute domestic wastewater to the sub-catchment. Based on site suitability and functional requirements, hybrid constructed wetlands combining Horizontal Flow (HF) and Vertical Flow (VF) systems were selected for application. At Location 1, a HF wetland of 30.4 m² and a VF wetland of 22.8 m² were proposed, while at Location 2, larger units of 70.8 m² (HF) and 53.1 m² (VF) were designed. HF wetlands were selected to efficiently remove Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and suspended solids, while VF wetlands were designed to target ammonia removal. The hybrid system combining HF and VF wetlands provides a comprehensive approach to treating complex wastewater streams. It was found that scaling up CWs within the available land space of the selected sub-catchment was practical and feasible. Beyond wastewater treatment, CWs offer co-benefits including urban cooling, biodiversity conservation, flood control, and opportunities for safe water reuse in non-potable applications. However, successful implementation requires attention to long-term maintenance, institutional coordination, and community engagement to ensure sustained functionality.

Nutrient removal efficiency and resource economics of vertical flow and horizontal flow constructed wetlands

Constructed wetlands for grey water treatment

Resilience of carbon and nitrogen removal due to aeration interruption in aerated treatment wetlands

Organic matter and nutrients removal in hybrid constructed wetlands: Influence of saturation

Constructed wetlands (CWs) are simple low-cost wastewater treatment units that use natural process to improve the effluent water quality and make it possible for its reuse.in this study used the horizontal flow system for the tertiary treatment of wastewater effluent from secondary basins at Al-Rustamiya wastewater treatment plant / old project / Baghdad / Iraq. the Phragmites Australis plant was used for wastewater treatment and the horizontal subsurface flow system was applied. the experimental study was carried out in February 2020 to October 2020. the parameters were monitored for a period of five weeks, Concentration-based average removal efficiencies for HSSF-CW were COD,53% [NO]_3,41.3% [PO]_4,52% and TSS, 54.2%. Thus, constructed wetland can be considered as a sustainable alternative to the tertiary conventional treatment of wastewater, thus making it possible for reuse..

Specific (nitrifying, denitrifying, and methanogenic) microbial activities were measured in simplified down-flow lab-scale columns simulating subsurface horizontal flow (HF) and vertical flow (VF) constructed wetlands (CWs). Extractable volatile solid (EVS) was 6.5-fold higher in VF system than in HF system. Potential nitrification rate was similar in both systems (2.6–3.2 g N/m2 day), while specific nitrifying activities were higher in the HF system (29–48 mg N/g EVS day) than in VF system (3.9–4.7 mg N/g EVS day), indicating a higher relative abundance of nitrifying bacteria in HF biofilm. Potential denitrification rates were 13–19 (HF) and 1–4 (VF) g N/m2 day and specific denitrifying activities were 178–195 (HF) and 2.3–5.6 (VF) mg N/g EVS day. However, VF units exploited better the potential nitrification and denitrification rates by removing significant amounts of nitrogen. Specific methanogenic activity was null in VF units but high (0.13–0.20 g COD-CH4/g EVS day) in HF units.

Attenuation of emerging organic contaminants in a hybrid constructed wetland system under different hydraulic loading rates and their associated toxicological effects in wastewater

Investigations on phosphorus retention in subsurface flow constructed wetlands

Thirty years of constructed wetlands for municipal wastewater treatment in the Czech Republic

A comparative study on the removal of nutrients and organic matter in wetland reactors employing organic media

Industrial wastewater treatment in constructed wetlands packed with construction materials and agricultural by-products

Stress detection by laser-induced fluorescence in Zantedeschia aethiopica planted in subsurface-flow treatment wetlands