Wetlands for wastewater treatment and Nature-Based solutions

The moderator of this session is: Huub Rijnaarts (Professor, Environmental Technology, Wageningen University and Research)

This session will include the speakers: Mireille Martens (Rietland bvba, Minderhout, Belgium and HZ University of Applied Sciences, Middelburg, The Netherlands), Thomas Wagner (Wageningen University & Research, Department of Environmental Technology) and Oscar A. Alvarado (The Hague Academy for Local Governance)

Take a look at the abstracts below: 

Aerated wetlands as innovative pretreatment for desalination plant for chemical industry 

Presenting author: Mireille Martens

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The growing world population leads to an increasing demand for food and water. Moreover, the depletion of resources and the consequences of climate change require industries to reduce their water footprint by using water more efficiently through innovative technologies. Dow Benelux is located in the water-stressed Southwestern Delta of the Netherlands (Terneuzen). Currently, Dow uses 22 million m³ of freshwater annually for the production of 800 different chemicals and plastics. Today, 75% of Dow’s water supply comes from renewable sources. By 2024, the last 4-5 mil m³/year of industrial water use should no longer compete with drinking water resources, making the river basin more resilient to water stress.  

One of the alternative local water sources combines i) rainwater collected from the Dow site and its periphery, ii) treated Dow wastewater and iii) treated municipal wastewater from the Terneuzen Waste Water Treatment Plant (WWTP). This water mixture is treated to the required industrial quality in a desalination plant (Ultrafiltration à Ion eXchange à Reverse Osmosis). To increase the efficiency of the desalination and reduce costs, a nature-based pre-treatment (wetland) is investigated with the objective to reduce biological fouling of the membranes with minimal use of energy and chemicals. To the authors’ best knowledge, this is the first study in which outdoor aerated wetlands are applied on such a large scale as pretreatment before a desalination plant. 

The pilot setup of wetlands was placed on the Dow/Evides site and is operational since April 2019. It consists of two aerated horizontal subsurface flow wetland cells, based on the Forced Bed AerationTM principle, 350 m² (28 m x 12.5 m x 1 m) each and fed with 10 m³/h municipal effluent from the Terneuzen WWTP and effluent from the Dow WWTP. Both pilot cells are filled with clay aggregates and are aerated in three separate zones by means of blowers, which are connected to aeration grids at the bottom of the wetland cells. The wetland is covered with common reed – Phragmites australis – and the hydraulic residence time in each wetland cell is 12 hours. 

After 18 months of research and a variety of settings, it can be concluded that aerated constructed wetlands can supply more biologically stable effluent to the desalination plant. Ammonium was completely removed in the wetlands. The incoming water mixture of the wetland consists of substances that are not easily biodegradable. However, the average low concentrations of COD and TN (25 mg/L and 10 mg/L respectively) are reduced about 25% in the wetland. There was a trade-off found between COD and TN removal, as an increase in the oxygen availability in the filter results in more COD removal and less TN removal. Seasonal variation only affects the removal of TN, where the removal efficiency for municipal wastewater was 38% during summer while being 24% during winter.  

These positive results pave the way towards full-scale implementation in the near future. 

Water Nexus – Saltwater when possible, fresh water when needed

Presenting author: Thomas Wagner

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Worldwide, delta areas are of immense economic importance because of its dense concentration of population, industry and agriculture. Half the world’s population will live in delta areas this century. The economy of delta areas relies on freshwater. Severe scarcity is imminent due to growing demand and saltwater intrusion. Good quality freshwater is essential for public health, food production and certain types of industry. Worldwide, freshwater scarcity is an immense problem, and rapidly increasing:

• For agriculture the shortage already is more than 100 billion m3/yr.

• For domestic use, a shortage of 50% is forecasted.

• For industry demand in 2025 is predicted to be at twice the level of the year 2000.

The pressure on fresh water resources from growing demand (and increasing pollution) is enhanced by changes in climate (extremes in drought and precipitation and rising sea levels) and soil subsidence (saltwater intrusion).

Present attempts to find solutions are fragmented (focusing on partial solutions) and are often connected with high costs and poor sustainability. Furthermore, it is clear that these solutions cannot create sufficient water quantities to really solve the scarcity. For a genuine breakthrough, a radically different approach is needed: integral water quantity and quality management. NWO-TTW funded research program Water Nexus developed a coherent set of technologies that will enable such a breakthrough. It focused on large volume sectors with a focus on industry, but in connection to agriculture, horticulture and ecosystems, with a high orientation on impact in solving scarcity.

Measuring and quantifying the benefits of nature-based
solutions in cities: case study of urban park in Amsterdam

Presenting author: Oscar A. Alvarado

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​​A comprehensive review of the many existing (and still under development) assessment frameworks and indicators for quantifying the multitude of benefits arising from nature-based solutions (NbS) in urban contexts. This includes an evaluation and cross-comparison of tools using multi-criteria analysis as well as the application of the highest-scoring tool on an urban NbS case study in the Netherlands. The focus of the study is primarily on water-related ecosystem services however additional biophysical benefits are also considered.

There are a growing number of tools that attempt to measure, quantify and valorise the well-being and that human societies receive from healthy and functioning ecosystems. However there has been limited adoption of these tools by decision makers and policy-makers, especially in urban settings, which can result in an underestimation of the ecosystem services and societal benefits that are being provided by nature-based solutions (NbS) in cities. In order to facilitate the use of empirical data for greater NbS implementation in urban contexts, it is important to understand the properties of each tool, their suitability for diverse urban environments, and the relationship between indicators that measure NbS ecosystem services with indicators that are intended to assess ecosystem properties (i.e. health, integrity, resilience).

This study first provides a thorough overview and comparison of the wide variety of available assessment tools in terms of their ability to measure ecosystem services delivered by urban NbS. Using criteria from the literature and practical perspectives, a multi-criteria analysis is used to identify suitable assessment tools that can capture NbS ecosystem services across different urban landscape domains and societal challenges. In the second part of this study, the effectiveness of a chosen assessment tool, i-Tree, is tested through its application to an urban park case study in Amsterdam. The aim of the study is to quantify and measure as many ecosystem services as possible from the urban park, which can then be presented as societal benefits within a business case proposal that uses non-technical language but is grounded in scientific evidence. Both the approach and applied tool of this study can be modified and replicated by a wide range of stakeholders to estimate and/or measure the benefits of integrating bluegreen solutions into urban spatial planning. These benefits include, but are not limited to, more resilient and adaptable infrastructure, reductions in flood risk, more efficient and multi-functional land use, and improved environmental quality. In particular, the i-Tree tool is well-positioned for use in citizen science projects.

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