Constructed Wetlands as a Sustainable Wastewater Treatment Method in Communities

Does a scaling exist in urban ecological infrastructure? A case for sustainability trade-off in China

So far, urban scaling theory has proven that urban area, infrastructure, and economic output have a scaling relation with population. But if we consider ecological space as a part of urban infrastructure, would the same scaling characteristics exist? What is the scaling relationship between ecological spaces and economic social development in different stages of urbanization? This paper is based on this question and explores the trade-off between social economic system and ecosystem in 370 cities of China. The results show that the relationship between population and urban ecological space generally follows the scaling theory in terms of different types of ecological spaces and ecosystem services. For every 10-fold increase in population size, the total area of ecological space and ecosystem services increase by approximately 4 times. The manifestation of ecological space following the scaling laws is the aggregation behavior of better network connectivity. There is a trade-off between urban ecological space and socioeconomic development, with flow equilibrium reached at a population of 2 million and efficiency equilibrium reached at a population of 1 million. Starting from type I and type II megapolis, urban development gradually tends to stabilize, and there may even be a trend of slow decline in urban development potential. In the absence of ecological space, virtual network space can serve as a substitute for ecological space. The driving factors affect scaling behavior of ecological space, including connectivity of ecological space, spatial heterogeneity of natural conditions, and disturbance of economic and social activities. This research can help city to expand ecological space, promoting the added value of urban ecological assets and keeping the urban development potential within the optimal threshold range continuously.

The Role of Wetland Plants on Wastewater Treatment and Electricity Generation in Constructed Wetland Coupled with Microbial Fuel Cell

CWMFC is a novel technology that has been used for almost a decade for concurrent wastewater treatment and electricity generation in varying scopes of domestic, municipal, and industrial applications since its implementation in 2012. Its advantage of low-cost enhanced wastewater treatment and sustainable bioelectricity generation has gained considerable attention. Nevertheless, the overall efficiency of this novel technology is inclined by several operating factors and configuration strands, such as pH, sewage composition, organic loading, electrode material, filter media, electrogens, hydraulic retention time, and macrophytes. Here, we investigate the effect of the wetland plant component on the overall performance of CWMFCs. The macrophyte’s involvement in the oxygen input, nutrient uptake, and direct degradation of pollutants for the required treatment effect and bioelectricity production are discussed in more detail. The review identifies and compares planted and unplanted CWMFC with their efficiency on COD removal and electricity generation based on previous and recent studies.

Circling the drain: A systems analysis of opportunities for enhanced sewer self-purification technologies in wastewater management

The shift of discussions on wastewater management to realize a circular water economy requires rethinking of how the existing systems are managed. The collection system, a physical infrastructure that collects and transports wastewater, is often overlooked in innovation studies in wastewater management. Hence, a review of the collection system is required to realize overlooked innovation points, especially those of its functions and configurations. In this paper, we highlight the possibility of the collection system to contribute to wastewater management, not only to collect and transport wastewater, but to treat wastewater through enhancing sewer self-purification. To realize this, a systems analysis of the forms and functions of the collection system was first conducted to see how the collection system supports different wastewater management systems. It was found that emphasis on the collection system's function to treat wastewater is beneficial because of the transition of wastewater management towards a circular water economy. Second, a scenario analysis of applying enhanced sewer self-purification technologies was conducted to determine communities which would most benefit from using the collection system to treat wastewater. The findings highlight that communities with as much as 100 cap ha-1, typical of urban peripheries, could have their pollutant load reduced to about half if the pipe length per capita is 5 m. It was seen in this study that while the collection system supports wastewater management by functioning to collect and transport wastewater, it can further be elevated into a treatment technology within appropriate localities and thus, contribute to a circular water economy.

Modelling faecal pathogen flows and health risks in urban Bangladesh: Implications for sanitation decision making

Faecal-oral infections are a major component of the disease burden in low-income contexts, with inadequate sanitation seen as a contributing factor. However, demonstrating health effects of sanitation interventions - particularly in urban areas - has proved challenging and there is limited empirical evidence to support sanitation decisions that maximise health gains. This study aimed to develop, apply and validate a systems modelling approach to inform sanitation infrastructure and service decision-making in urban environments by examining enteric pathogen inputs, transport and reduction by various sanitation systems, and estimating corresponding exposure and public health impacts. The health effects of eight sanitation options were assessed in a low-income area in Dhaka, Bangladesh, with a focus on five target pathogens (Shigella, Vibrio cholerae, Salmonella Typhi, norovirus GII and Giardia). Relative to the sanitation base case in the study site (24% septic tanks, 5% holding tanks and 71% toilets discharging directly to open drains), comprehensive coverage of septic tanks was estimated to reduce the disease burden in disability-adjusted life years (DALYs) by 48-72%, while complete coverage of communal scale anaerobic baffled reactors was estimated to reduce DALYs by 67-81%. Despite these improvements, a concerning health risk persists with these systems as a result of effluent discharge to open drains, particularly when the systems are poorly managed. Other sanitation options, including use of constructed wetlands and small bore sewerage, demonstrated further reductions in local health risk, though several still exported pathogens into neighbouring areas, simply transferring risk to downstream communities. The study revealed sensitivity to and a requirement for further evidence on log reduction values for different sanitation systems under varying performance conditions, pathogen flows under flooding conditions as well as pathogen shedding and human exposure in typical low-income urban settings. Notwithstanding variability and uncertainties in input parameters, systems modelling can be a feasible and customisable approach to consider the relative health impact of different sanitation options across various contexts, and stands as a valuable tool to guide urban sanitation decision-making.

Knowledge Production for Resilient Landscapes: Experiences from Multi-Stakeholder Dialogues on Water, Food, Forests, and Landscapes

Landscape-wide approaches integrating agriculture, forestry, energy, and water are considered key to address complex environmental problems and to avoid trade-offs. The objective of this paper is to analyse how knowledge production through multi-stakeholder dialogues on water, landscapes, forests, and agriculture can inform governance and the management of landscapes. Multi-stakeholder learning dialogues and platforms (MSPs) were established related to water and natural resources management, complemented by targeted reviews, to establish a shared understanding of the drivers of change and impacts on the hydrology of landscapes and ecosystem services. The MSP dialogues illustrate the need to address water as an integral part of landscape management and governance to achieve the wide range of the Sustainable Development Goals related to water and food security, climate action, life on land, as well as sustainable production and consumption, equality, and strong institutions. The co-production of knowledge through MSPs contributes to continuous learning that informs adaptive management of water flows in landscapes, above and below ground, as well as in the atmosphere. It helps to build a shared understanding of system dynamics and integrate knowledge about hydrology and water flows into policy recommendations. Co-production of knowledge also contributes to stakeholder participation at different levels, inclusiveness, and transparency, and to water stewardship.

Mathematical Modeling of a Domestic Wastewater Treatment System Combining a Septic Tank, an Up Flow Anaerobic Filter, and a Constructed Wetland

Systems combining anaerobic bioreactors with constructed wetlands (CW) have proven to be adequate and efficient for wastewater treatment. Detailed knowledge of removal dynamics of contaminants can ensure positive results for engineering and design. Mathematical modeling is a useful approach to studying the dynamics of contaminant removal in wastewater. In this study, water quality monitoring was performed in a system composed of a septic tank (ST), an up flow anaerobic filter (UAF), and a horizontal flow constructed wetland (HFCW). Biological oxygen demand (BOD5), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), NH3, organic nitrogen (ON), total suspended solids (TSS), NO2−, and NO3− were measured biweekly during a 3-month period. First-order kinetics, multiple linear regression, and mass balance models were applied for data adjustment. First-order models were useful to predict the outlet concentration of pollutants (R2 > 0.87). Relevant multiple linear regression models were found, which could be applied to facilitate the system’s monitoring and provide valuable information to control and improve biological and physical processes necessary for wastewater treatment. Finally, the values of important parameters (μmax, Ks,  and Yx/s) in mass-balance models were determined with the aid of a differential neural network (DNN) and an optimization algorithm. The estimated parameters indicated the high robustness of the treatment system since performance stability was found despite variations in wastewater composition.

Environmental performance of building integrated grey water reuse systems based on Life-Cycle Assessment: A systematic and bibliographic analysis

The increasing demand for fresh water has been a global concern for decades. Desalination and water transportation systems consume an ample amount of energy, which also adds to the environmental pollution. This has led to a constant look-out for more viable options to conserve freshwater resources without compromising the environmental quality. The building sectors are remarkably the largest consumers of fresh water in the world; thus, the reclamation and reuse of greywater for non-potable purposes helps to reduce a significant amount of water consumed within a building. This study critically reviews the environmental performance of building-integrated greywater treatment systems compared to the conventional treatment systems deployed. Life-Cycle Assessment (LCA) is the method used to identify the environmental impacts associated with both the systems during their entire life span. The greywater treatment techniques and the guidelines for its reuse are also investigated. The bibliographic analysis was systematic, and the resources for this study were chosen after three stages of quality assessment. The study found physical and biological treatment techniques to be beneficial as they produce excellent quality of treated greywater for reuse. The environmental assessment by various studies prefers the reuse of greywater over its disposal. Guidelines for the reuse of treated greywater have recently been proposed by various countries and building rating systems. This study aims to address the policymakers, governmental and environmental organizations, mainly situated in the water-stressed areas such as the Middle East and North Africa (MENA) region, to raise awareness and initiate greywater reuse techniques within residential and commercial building sectors.

Assessment of a batch-flow free water surface constructed wetland planted with Rhynchospora corymbosa (L.) Britton for campus greywater treatment

A pilot-scale batch-flow free water surface (FWS) constructed wetland (CW) system planted with Rhynchospora corymbosa (L.) Britton was developed with a hydraulic retention time (HRT) of 2.5 days. The average porosity of the substrate was 0.55 and calculated hydraulic loading rate (HLR) was 3.96 (g BOD/m²-day). Quantitative and qualitative characterization of the greywater were done. The concentrations of pollutants in the greywater before and after it was fed into the FWS CWs were measured using standard sampling and analyses methods. The average daily per capita water use estimated was 162 L, out of which 72.5 L was greywater. The mean removal efficiencies (RE) of the CWs were 81% COD, 85% TN, 82% TK, 10% TP, 0.2% pH, 81% TSS, Zn 91%, 81% Al, 94% Mg, and 90% Fe. It was observed that the FWS with batch-flow configuration tested in the study was slightly different in terms of results reported on the conventional continuous flow system. R. corymbosa as a macrophyte has roots that can provide a surface area for microbial growth and oxygen exchange and can be used as emergent macrophytes in phytoremediation of greywater. The result provided information on the performance and pollutant removal efficiency of a batch-operated FWS CW system planted with R. corymbosa.

The Role of Constructed Wetlands as Green Infrastructure for Sustainable Urban Water Management

Nowadays, it is better understood that the benefits of green infrastructure include a series of ecosystem services, such as cooling, water storage and management, recreation and landscaping, among others. Green technologies are still developing to provide sustainable solutions to the problems that modern cities and peri-urban areas face at an ever-increasing rate and intensity. Constructed wetlands technology is an established green multi-purpose option for water management and wastewater treatment, with numerous effectively proven applications around the world and multiple environmental and economic advantages. These systems can function as water treatment plants, habitat creation sites, urban wildlife refuges, recreational or educational facilities, landscape engineering and ecological art areas. The aim of this article is to highlight the synergies between this green technology and urban areas in order to reconnect cities with nature, to promote circularity in the urban context and to apply innovative wetland designs as landscape infrastructure and water treatment solutions. This approach could be a step further in the effort to mitigate the current degradation process of the urban landscape. Following the concept of green infrastructure, the article presents and suggests ways to integrate wetland technology in the urban environment, namely: (i) stormwater and urban runoff management (storage and treatment of water during storm events) to provide protection from flood incidents, especially considering climate change, (ii) innovative low-impact infrastructure and design solutions for urban wastewater treatment, and (iii) wetland technology for habitat creation and ecosystem services provision.

Bio-Capture of Solid Pollutants by Vegetation Canopy Cave in Shallow Water Flow

Vegetation has already been acknowledged to have the ability to remove fine solid pollutants by retention and absorption, and is widely used in the biorestoration engineering of natural shallow water flow. Vegetation usually takes a long time to obtain the expected removal rate. Therefore, vegetation is not applicable for some urgent or pressing situations. In addition, in traditional biorestoration engineering, solid pollutants usually deposit in the soil of flow bed, which infiltrates into the far-field and accumulates in crops to threaten human health. Herein, we propose a new biotechnique of foliage capture by designing a cave on the top of a vegetation canopy, which is aimed to enhance the removal efficiency (i.e., achieve quick removal) and avoid the soil deposition of pollutants. The effectiveness and efficiency of this new design were validated by a set of indoor water flume experiments, with one flat canopy top configuration serving as the model of a traditional bioretention system and three cave configurations of differing aspect ratios. The results showed that compared with that of the flat canopy top, the total amount of foliage-captured solid particles for the three caved canopies increased by 3.8, 7.3, and 12.2 times. Further, we found that the foliage-capture efficiency depended on the aspect ratio of the canopy cave. The results revealed that the effectiveness of foliage capture and the enhanced efficiency were mainly from three hydrodynamic mechanisms: (i) as flow penetrated the cave boundary from the above-canopy region to the within-canopy region, it entrained solid pollutants to collide with the foliage and increased their fate of capture; (ii) the large eddy vortices of turbulence broke due to the increasing canopy resistance, which resulted in enhanced mixing dynamics for fine, suspended, solid pollutants to collide into foliage; and (iii) the flow shear along the cave boundary decreased, which provided a reduced lift force for solid pollutants to suspend or resuspend. Comparisons between the flat canopy and caved canopies of three aspect ratios showed that the design of the canopy cave is highly significant for capture efficiency.

Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 10⁹ and 3.2 × 10⁸ copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

The Effects of Plants on Pollutant Removal, Clogging, and Bacterial Community Structure in Palm Mulch-Based Vertical Flow Constructed Wetlands

In this study, the effects of plants on the performance and bacterial community structure of palm mulch-based vertical flow constructed wetlands was studied. The wetlands were built in August 2013; one of them was planted with Canna indica and Xanthosoma sp., and the other one was not planted and used as a control. The experimental period started in September 2014 and finished in June 2015. The influent was domestic wastewater, and the average hydraulic surface loading was 208 L/m2d, and those of COD, BOD, and TSS were 77, 57, and 19 g/m2d, respectively. Although the bed without plants initially performed better, the first symptoms of clogging appeared in December 2014, and then, its performance started to fail. Afterwards, the wetland with plants provided better removals. The terminal restriction fragment length polymorphism (T-RFLP) analysis of Enterococci and Escherichia coli in the effluents suggests that a reduction in their biodiversity was caused by the presence of the plants. Thus, it can be concluded that the plants helped achieve better removals, delay clogging, and reduce Enterococci and E. coli biodiversity in the effluents.

A full-scale comparison of two hybrid constructed wetlands treating domestic wastewater in Pakistan

Objective of the current work was to monitor the year-round response of full-scale hybrid constructed-wetlands (CWs) treating domestic wastewater under variable continuous flow. Two systems were evaluated: system-I consisted of an anaerobic baffled reactor (ABR) followed by a saturated vertical subsurface-flow (VSSF) CW and a free-water-surface (FWS) CW as a tertiary treatment; system-II consisted of an ABR followed by a horizontal subsurface-flow (HSSF) CW and FWS. Maximum reduction of 80 and 78%, 81 and 82%, 63 and 69%, 79 and 89% for chemical oxygen demand (COD), biological oxygen demand (BOD), total kjeldahl nitrogen (TKN) and total suspended solids (TSS) was achieved in Systems I and II respectively. There was also effective removal (94% and 93%) of the bacterial population in both systems while more than 94% of pathogenic microorganisms were removed. Data from both systems were further used to compute the first-order rate constants for the k-C* model commonly used in CW design. The treatment performance was confirmed to follow a first-order reaction rate, in which the k₂₀ values of chemical oxygen demand (COD), biological oxygen demand (BOD), total kjeldahl nitrogen (TKN), total phosphorus (TP) and total suspended solids were calculated as 165, 117, 133, 7.5 and 78 m yr^-1 respectively for VSSF and 226, 134, 199, 22 and 73 m yr^-1 respectively for HSSF. A positive correlation with temperature was discovered for all parameters in both systems.