Research of Environmental Technology

Environmental Technology (ETE) develops and evaluates innovative environmental technologies and concepts based on processes from nature, to recover and reuse essential components and maintain and create a viable environment.

• Removal of micropollutants and pathogens
• Resource quality in circular systems
• Open culture bio-conversions
• Biocrystallisation
• Urban infrastructure
• Membranes and (bio)electrochemistry
• Environmental solutions
• Industrial water management
• Closing nutrient and carbon cycles

The use of electricity allows the growth of specific microorganism on electrodes, providing a specific advantage for certain desired chemical conversions, while energy use is low, compared to traditional treatment methods. Possible applications for bio-electrochemical based water treatment methods are numerous.

One example of such an application concerns mercaptans. This smelly organosulfur compounds are released from decaying organic matter and are present, among others, in wastewater treatment plants and natural gas. Burning gas containing mercaptans results in the formation of sulfur dioxide (SO₂), that causes environmental damage due to acidification. Mercaptans can be removed by chemical oxidation, but this method is rather costly and inefficient. The application of bio-electrochemical technologies, might provide a more efficient and cost-effective treatment method. Furthermore, the recovery of nutrients from waste streams, like manure, can become more efficient by using bio-electrochemical treatment.

The most important Environmental Technology research areas and projects where (bio)-electrochemical technologies are used include:  

• Electrodialysis and capacitive deionization for desalination and recovery of nutrients This research focuses on using mathematical models to tune and optimize the removal and recovery of components, like sodium (Na⁺, desalination) or nutrients, like phosphate, from wastewater and manure.
• Producing so-called ‘green oxidants’ Electrochemical processes in combination with membranes are used to produce hydrogen peroxide (H₂O₂) from water. This green oxidant can be used to disinfect industrial pipes and equipment.
• Mercaptan removal from industrial gas streams using electricity and microorganisms, mercaptans are converted into hydrogen sulfide (H₂S). Using traditional processes, hydrogen sulfide can easily be further treated and converted into valuable elemental? sulfur that can be reused in, for example, agriculture.
• Ammonium removal from wastewater By applying electrochemistry in combination with microorganisms and membranes, ammonium is removed from waste streams and recovered as a liquid ammonium fertilizer, such as ammonium nitrate.

We use a combination of the following technologies:

• (Bio-)electrochemical systems to treat wastewater and recover resources
• Membrane-based technologies
• Reactor design and engineering improvements to increase the effectivity of the system, based on: 1) Modelling complex transport processes and chemical reactions at the electrodes and 2) Physical-chemical principles.
• Manipulating the microorganism species composition to promote specific chemical conversions, by controlling the electric current.

In this research theme, researchers aim for recovery and synthesis of valuable components from waste streams using controlled microbial communities, for optimal utilization of waste while closing the carbon cycle.    

At Environmental Technology, scientists recognise the immense potential of collaborating microbial communities in the synthesis of valuable chemicals from waste. By manipulating reactor conditions, for example temperature, pH, flow rate, and nutrients, the bacterial species composition can be controlled, promoting the formation of different chemicals. Environmental Technology scientists are focusing on selecting those microbial populations that are capable of synthesizing the desired chemical while treating the waste-stream. At the same time, research focuses on eliminating polluting substances, like pharmaceutical residues and pathogens, to increase the quality and application of the recovered resources.

The most important research areas contributing to synthesis and recovery of valuable chemical from waste streams are:

• Recovery of polymers from industrial waste water. Some polymers can be applied as flocculants in the dredging industry: they help to precipitate clay particles from sludge, resulting in a separation of water and clay.
• Synthesis of fatty acids from diverse organic waste streams. These fatty acids can be applied as feed supplements for cattle and thereby suppress pathogens present in the intestines of these animals. As a result, the need to use antibiotics can be reduced.
• Solid residue recovery of organic household waste The solids of organic residues originating from households can be modified to be better suited for use as soil conditioner in agriculture. If the microorganisms can deal with relatively high temperatures, the conditioning process can be accompanied by disinfection.

We use a combination of the following technologies:

• Anaerobic and aerobic recovery technologies: influencing the species composition of microorganisms in open culture bioreactors to promote the synthesis of high-quality components from waste
• Advanced chemical analyses and identification methods (HPLC, GC, NMR, Raman Spectroscopy) to quantify and characterize chemical components
• Microbial community analysis to identify the important species and their role in the process

An effective way to recover metals and minerals is by stimulating the crystallisation of these resources. Crystals have several important benefits. They are pure, relatively easy to separate from the waste stream and suitable for recycling. This reduces the need for mining and the inevitable environmental damage, and eliminates the need for costly waste management.

The Biocrystallisation theme of ETE uses biological processes, using microorganisms present in nature, to enhance resource crystallization. This has the advantage that no extra chemicals are needed and the reaction can usually be carried out at lower temperatures and pressure than chemical processes.

• Recovering metals from waste water by crystallisation, using sulfur. At high temperature (80 °C) and low pH (< 3) microorganisms convert sulfur into hydrogen sulfide (H₂S). This chemical may efficiently form a crystal with different metals, including copper, zinc, lead, and cadmium. These crystals consequently precipitate and can be retrieved.
• Sulfur recovery from biogas. In biogas, hydrogen sulfide (H₂S) is efficiently converted into sulfur by bacteria. However, the sulfur crystals formed are very small, and therefore difficult to recover. This research aims to increase crystal size by changing process conditions, like microorganisms and gas flow rate.
• Bio-recovery of selenium from wastewater. Selenium is present in several waste streams from the industry, for example in emission gases from coal plants. These gases are washed before release, and as a result, selenium ends up in waste water. Its toxicity requires removal. This research aims to develop a biological process to recover selenium from waste water. Challenges are to produce crystalline selenium that is pure and suitable for reuse. In addition, recovery should be efficient, with residual selenium concentrations in wastewater being extremely low, in the microgram per litre range.

We use a combination of the following technologies:

• X-ray diffraction to identify crystals
• Scanning electron microscopy (SEM) to visually evaluate the crystals, regarding size and shape
• Particle size distribution, important for crystal settling after formation and for re-use options
• Micro-CT scanning, allowing to follow crystal growth in three dimensions

Even in a water-rich country like the Netherlands, there is a local shortage of fresh water. For example, in the Province of Zeeland, in some areas fresh water has to be imported due to a lack of fresh ground water due to salt water intrusion. This worldwide problem, is quite common in cities close to the coast, where the use of fresh ground water leads to the replacement of fresh by salt water.

Environmental Technology aims to manage supply and demand of fresh water by developing modelling scenarios and implementing water treatment technologies to reuse or safely discard industrial wastewater. Since water scarcity is expected to increase in the future, technologies are more focused towards recycling and reusing wastewater. In addition, technologies to treat and clean historical polluted ground water are developed to prevent that the pollution reaches fresh water resources.

• Water Nexus. This project aims to better deal with salt water when fresh water is scarce. It’s slogan: ‘salt water when possible, fresh water when needed’, is translated into better fresh water management, developing better desalination technologies, while integrating sustainable and cost-effective methods. In addition, (biological) treatment technologies enabling the use of salt water by only removing those substances that hinder use of saline water (some salts and pesticides) and maintaining those that are beneficial to the end use (nutrients). Finally, models are used to optimally manage and control freshwater and saline water quantities and qualities.
• Optimizing the use of constructed wetlands for removing chemicals from cooling tower water, particularly in winter, when the biological processes are slow.
• Using the right microorganisms for cleaning historically polluted sites of DSM, where polluted groundwater flows towards the Muse river. Finding the right microbiota, while optimizing the environmental conditions for a more efficient biodegradation is a crucial part of this project.

We use a combination of the following technologies:

• Bacterial degradation of chemicals present in ground and industrial water
• Constructed wetlands, where biological and physical-chemical pollutant degradation processes are combined
• Mathematical models to improve water management, based on water availability, use and water quality needs
• Advanced water treatment technologies, like electrically driven, and membrane-based desalination technologies or oxidation

Wastewater treatment plants are not designed to remove micropollutants and pathogens and pathogens sufficiently, they enter surface waters, affecting the aquatic ecosystem. For example, the presence of estrogen-related compounds has been associated with feminization of fish, while antibiotic residues may lead to antibiotic resistance in microorganisms. If these waters are used to produce drinking water, the elimination of these micropollutants is even more important and poses additional challenges.

Therefore, in ETE’s Reusable Water Theme several research projects focus on the removal of these contaminants during wastewater treatment to obtain clean effluent as well as drinking water production, to obtain clean drinking water.

Numerous physical or chemical treatment technologies for the removal of micropollutants are currently available, like oxidation and membrane technologies. At ETE, we focus on developing novel technologies that are more effective, have lower costs, and have smaller energy requirements to fit the needs of the water and soil sectors.

• We apply three major water treatment technologies:
• Constructed wetlands. These man-made, natural-looking, wetlands originally used for the removal of nutrients can be adapted for the removal of micropollutants through natural processes, like sorption to soil, microbial degradation, uptake and transformation by plants, and light (UV) degradation. Continuing research focuses on a better understanding of different removal pathways to optimize and improve the system.
• Natural biofilms Biofilms are densely-packed microorganisms, that grow naturally on different surfaces and may degrade micropollutants. ETEs research focuses on their possible role in micropollutant removal in wastewater treatment and drinking water production. Current research is aimed to better understand the environmental conditions favoring specific bacterial communities for optimal micropollutant degradation in:
  • Groundwater biofilms to remove micropollutants prior to drinking water production.
  • Filtration systems in drinking water treatment plants containing either biofilm-coated sand or activated carbon.
• Combined treatment technologies. ETE aims at novel combinations of physical, chemical and biological treatment processes to develop technologies suited to degrade micropollutants.

We use a mixture of the following technologies:

• A combination of physical, chemical and biological treatments to remove micropollutants
• Advanced chemical assays to measure low micropollutant concentrations
• Bio-assays to assess the effect of micropollutant toxicity on growth of algae and bacteria
• Biomolecular analyses to assess microbial community composition and pathogen abundance

Resource quality can limit reuse of the resource for a particular application. For example, wastewater contains valuable components, like phosphorous, nitrogen and water, but also pollutants. Depending on the reuse, different quality standards for recovered resources apply. Recycled water aimed for irrigation or industrial purposes has different quality requirements than drinking water. Thus, to maximize efficiency, resource quality supply should match resource quality demand.

At Environmental Technology, different research projects focus on the development, application and adaptation of treatment technologies for the recovery of resources. In the theme Resource Quality in the Circular Economy, researchers focus especially on which quality requirements are needed to reuse resources in different applications. The research aims at determining the quality of resources that can be supplied using the available or adapted technologies, and matching this to reuse applications. For example, the theme contributes to circular agricultural systems by developing technologies to meet the quality standards to reuse recovered products from wastewater like nutrients and organics.

• The most important research areas from ETE contributing to the circular economy are:
• Circular water systems: This research focuses on the removal of contaminants from wastewater to produce water of sufficient quality for different applications (industry, agriculture, drinking water). Existing treatment methods are combined, while novel technologies are developed.
• Circular Agriculture Systems: Here, technology is developed to ensure the quality of recovered nutrients, like phosphorous and nitrogen, and organic compounds from waste and wastewater for reuse in agricultural systems.
• Circular urban water systems: ETE’s urban water research focuses on designing safe water cycles for sustainable cities of the future. To meet the challenge of the complex water systems in cities, research focuses on assessing urban water quality, developing technologies to treat water locally, and matching water quality with specific uses, like irrigation or recreation.

We use a combination of the following technologies:

• A combination of physical, chemical and biological treatments to remove pollutants from waste streams
• Advanced chemical assays to measure pollutants and pathogens
• Modelling and assessments to match supply and demand for recovered resources from different qualities

This transition requires better engineering and a more decentralized design to fit in an already-crowded and busy urban setting. This allows to process waste quicker than in current systems and avoids the formation of dangerous gases like hydrogen sulfide (H₂S) and methane (CH₄) in transport lines that are too long.

At ETE, scientists are engineering decentralized solutions for waste treatment systems and design how to fit them into an urban environment. There are specific requirements for such in-city systems. For example, the technology has to be scaled down, so it fits into a limited space, the release of dangerous gases and pathogens has to be avoided, the design has to blend in with the environment, and it needs an efficient transport network that allows to trace the origin of the resource for ensuring sufficient quality for reuse.

The most important research areas and projects contributing to the infrastructure transitions are:

• Designing a sewer system suitable for an urban environment, including a bio-electrochemical system, avoiding the formation of H₂S and CH₄, while conserving the potential to recover energy.
• Bio-oxidation of wood waste and source-separated urine to generate heat and compost for agriculture.
• Greenfood 5.0. Use track and trace life cycle data from an organic food certification system to design the circular use of food by-products at regional or national scale. For example, in China, canned peach production results in peach peel waste. This can be used to brew beer.
• DecentWater. The decentralized implementation of sanitation infrastructure in cities. In water-rich case cities like Amsterdam in The Netherlands and Suzhou in China, decentralized sanitation has been tested and scientists aim at assessing possibilities to upscale the technology in these two cities.

We use the following technologies:

• Urban data analyses on quality and quantity of urban waste(water)
• Geo-information modelling of the current and future sanitary infrastructure settings for a circular economy and climate mitigation and adaptation
• Environmental impact assessment at metropolitan scale, using for example life cycle assessment (LCA)
• Creation of quality indicators to assess the reuse potential of different resources
• Embed treatment capacity in the waste collection infrastructure, to avoid the formation of hazardous gases during waste transport and collection

In this research theme we aim to develop concepts and technologies for circular, resource-oriented management of wastewater and solid waste (residues), tailored for specific situations in emerging economies, like Southern-East Asia and Sub-Saharan Africa.

To deal with water shortage problems, ETE scientists specialized in urban engineering, assess water quantity and quality. This information is subsequently used to develop sustainable, more circular strategies and technologies. Examples are water saving, water treatment for recovery and reuse, adding alternative water sources (multi-sourcing) and cascading: recycling used water directly for another specific use. In example is using shower water to flush the toilet. However, implementation of these solutions can be complicated by a lack of (economical) resources, climate and local regulations. A similar approach and technologies are used to recover nutrients and organic matter from urban and agricultural residues for reuse in agriculture.

The most important research areas and projects contributing to circular management of waste water and waste, while recovering valuable resources are:

• In LOTUSHR different research institutes from The Netherlands and India collaborate to develop universal water management and risk assessment strategies that are applicable for megacities all around the world. Water treatment, including resource recovery, is performed using a chain of technologies. For example, anaerobic digestion, vital urban filters and micro algae. Efficient treatment and reuse can be achieved by applying these technologies separately or in combination to produce different qualities of water, for agricultural, industrial or urban reuse.
• ENTIRE project aims for circular use of water in the urbanized and industrialized deltas of countries like Vietnam, Bangladesh and Indonesia. Depending on reuse, customized solutions are provided using high-tech physical chemical treatment, but also nature-based technologies.
• Bangladesh delta project (Water4Rice) develops safe water reuse plans for peri-urban areas of the delta region.

We use a combination of the following technologies:

• Traditional mechanized waste water treatment like physical-biological reactors, with resource recovery
• Nature-based and low-cost solutions for treatment and recovery of nutrients from wastewater and residues, like improved septic tanks, digestors, modified constructed wetlands, sand filtration and crystallization processes
• Urban system engineering to match supply and demand for organic matter and nutrients for reuse in local agriculture

Although nutrients are not limiting yet, some have finite reserves for example phosphorus. Nitrogen is not limiting and sufficiently present in air. But synthesizing nitrogen, suitable for agriculture, costs a lot of energy. To prevent carbon shortages in agriculture, and deal with nutrients efficiently, carbon and nutrients present in waste streams should be recovered for reuse in agriculture. However, currently organic carbon nor nutrients are hardly recovered from waste for reuse.

To close carbon and nutrients cycles, ETE scientists develop strategies and technologies to preserve and recover these elements from waste streams. In addition, they evaluate the most efficient and effective methods to nourish soils using these ingredients: what is the best method to make the most suitable compost? How to prevent nutrient flushing from soils and how can emissions like CO₂ be minimized?

The most important research areas contributing to closing carbon and nutrient cycles, and nourishing agricultural soil most effectively are:

• Closing organic carbon and nutrient cycles at a regional level. The potential to recycle organic carbon and nutrients on a local scale is largely unexplored, while it offers the advantage of minimized transport. The potential of this decentralized recycling is investigated by modelling the agro-food-waste system, including the implementation of innovative technologies for increased recycling
• In the Resource Dynamo project, spatial and temporal nutrient cycles, are modelled. In a circular system, the supply and demand of nutrients need to be balanced in space and time. In this research area, we explore how this can be achieved with the highest resolution and precision, by taking nutrient supplies from buildings and specific geographical locations into account, as well as the nutrient demand from individual agricultural fields

We use a combination of the following technologies and approaches:

• Modelling more efficient organic waste collection scenarios
• Sustainability analysis of cycling scenario’s
• Biological treatment of organic residues, for example anaerobic digestion at different temperatures, to optimize the recovery of organic matter and nutrients