Mix and match to investigate sustainable solutions for environmental challenges

ABOUT THIS PLATFORM

The Modular Bioreactor Platform consists of different types of bioreactors that can be used in sequential and/or parallel configuration. The platform is specifically suitable for investigating sustainable solutions for environmental challenges, such as degradation of (micro)pollutants, sustainable energy generation, and recovery of resources from complex waste streams.

KEY SPECIFICATIONS
Location
Wageningen University & Research
Features
sustainable solutions, micropollutants removal, outdoor constructed wetlands, bio-electrochemical systems, high pressure, high temperature reactors
Contact person

TECHNICAL DETAILS

The Modular Bioreactor Platform is specifically suitable for investigating sustainable solutions for environmental challenges, such as degradation of (micro)pollutants, sustainable energy generation and recovery of resources from complex waste streams. This platform allows investigation of undefined complex waste streams with undefined microbial communities in defined reactors. The Modular Bioreactor Platform consists of multiple units of different types of bioreactors that can be used in a cascaded set-up as sequential reactors (technology trains) and/or in parallel configuration to allow for the direct comparison of different reactor systems.

Platform benefits

The flexible arrangement of automatic sampling and analytical equipment enables the investigation of a number of environmental conditions (redox, temperature, pressure, pH), and identification of the compounds transformed and produced by the present microbial community. High resolution experiments are facilitated with non-defined microbial communities (reductionist enrichment approach) as well as defined mixtures of microorganisms (synthetic ecology approach), that can be established in the Biodiscovery Platform. To our knowledge there is worldwide no other platform that enables the study of combinations of reactor types, whereas the added value is obvious; study processes in different reactor types (sequential or parallel) and analysis of mixed microbial community functioning at the scale and resolution of the UNLOCK Modular Bioreactor Platform.

Experimental units

The different reactor configurations that all can be used in sequential and parallel configurations are described in detail below:

Standard bioreactors (10 L, eight units). These bioreactors are used to study oligotrophic ecosystems, i.e. ecosystems with low content of nutrients or carbon sources for microbial growth, e.g. groundwater systems or wastewater treatment system effluent. For example, the most suitable technology for micropollutants removal from wastewater has not been identified yet, and sequences of reactor configurations are proposed (Gadipelly et al, 2014). In UNLOCK, combinations of reactor configurations can be tested sequentially or in parallel in custom-made systems, increasing the efficiency and reproducibility of the treatment technologies. Identifying the involved microbial processes (e.g. metabolic or co-metabolic processes) enables the development of sustainable treatment systems. In addition, by linking to the existing facilities at WU-Environmental Technology (WU-ETE), combinations with physical/chemical technologies (e.g. ozonation, activated carbon, membrane filtration) can also be studied at lab scale in the Modular Bioreactor platform. 

Outdoor constructed wetlands (12 m3, two units). Constructed wetlands (CWs) are designed to mimic natural processes that use plants and soil to treat wastewater in a controlled environment. Compared to other tertiary treatments, operation and maintenance of CWs are affordable and sustainable, and therefore extensively investigated as a tertiary treatment, for example to remove low concentrations of micropollutants from wastewater effluent. CWs are often approached as ‘black box’ systems, and the removal efficiency of a CW is determined by comparing influent and effluent concentrations (Wagner et al, 2018). Dominant contaminant removal processes in CWs are aerobic and anaerobic biodegradation, photodegradation, plant uptake and further transformation by plants, and sorption to the sediment. Especially aerobic and anaerobic biodegradation by undefined microbial communities, attached to the sediment and plants and present in biofilms, is a key removal mechanism for compounds in CWs. Determining the dominant microbial removal mechanisms for specific compounds in CWs allows the prediction of removal efficiency and the formation of possible toxic transformation products. This is necessary to design a CW adjusted to the compounds that need to be removed, and identify if pre- or post-treatment in other treatment units is needed, e.g. photooxidation as pre-treatment or biological polishing as post treatment. These sequential combinations are also part of the Modular Bioreactor platform.

Bio-electrochemical systems (BES, four units). BESs are an emerging biologically driven technologies that have the potential for clean and efficient conversions. Up to now, the potential of BESs is widely acknowledged; our current challenge is to scale-up and develop these systems towards a mature technology. Several companies have built BESs at pilot scale, and practical application has until now not been successful at an industrial scale. The main bottleneck for implementation of these BESs is the limited understanding of the key mechanisms and the fate of electrons. Understanding the key mechanisms is essential, especially since mixed microbial communities are present in the systems. Strategies are thus required to get insight in the microbial community, as this influences the selectivity of conversions, and with that the electron efficiency. For example, intermittent exposure to different redox conditions stimulates the production of polymers that act as energy storage component. However, little is known about its relation to electron storage in electro-active biofilms, or electron storage in biocathodes. Insights in dominant charge storage mechanisms and the involved microbial population, is essential for better understanding of the energy production from complex waste streams.

High pressure, high temperature reactors (two units). Anaerobic conversion of organic residues provides the means to efficiently produce renewable chemicals. However, the characteristics of biogas produced by anaerobic digestion do not meet the requirements for injection in existing gas distribution systems and other applications, and biogas upgrading units are necessary for injection into the natural gas grid.  A possibility to overcome this limitation is the production of high-grade biogas from slurries and waste water at high pressure. At such conditions, the different solubility at increasing pressure between CH4 and CO2 results in biogas that meets the quality of our Synthetic Natural Gas (SNG), or “green-gas”. Insight in the mixed microbial community that is able to withstand high pressures, will result in more robust conversion processes.

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OTHER PLATFORMS

The modular bioreactor platform consists of different types of bioreactors that can be used in sequential and/or parallel configuration. The platform is specifically suitable for investigating sustainable solutions for environmental challenges, such as sustainable energy generation, recovery of resources from complex waste streams, and degradation of (micro)pollutants. These micropollutants are observed at trace concentration (ng/L to µg/L) in the aquatic environment (Fig 1) in the last decades. 

Figure 1. Distribution of micropollutants in the environment through various processes (http://www.eusem.org)

These compounds are a potential hazard to environmental and human health and are found in important resources, such as water used for drinking water production. The concerns of the presence of these micropollutants in the environment indicates the importance of understanding the fate and transformation of these compounds and designing technologies for their removal throughout the water cycle. Combinations of microbial, chemical and physical processes in innovative reactors are needed, and these systems need to be designed, developed and validated. Two examples of the application of hybrid systems for the treatment of micropollutant contaminated water are given below.

Case 1  Pilot-scale hybrid constructed wetlands 

Hybrid-constructed wetlands (CWs) with three CW water flow types in different combinations were installed; (1) vertical subsurface flow CW, (2) horizontal subsurface flow CW, and (3) surface flow CW. In total, six different hybrid CWs were installed, allowing to test all the possible sequences with the 3 CW types. The CWs consisted of sand and gravel, and were planted with Phragmites australis. They were fed with a synthetic medium at a flow rate of 140 L/d, resulting in an HRT of 7.5 days. Removal of phosphate, benzoic acid, and benzotriazole was studied in these systems.

Figure 2. Outdoor pilot-scale hybrid constructed wetlands at WUR-ETE

The CWs were operated for a full year, and the removal of the various compounds is summarized below. 

Figure 3. The highest removal efficiency was observed in the vertical flow CWs, and no removal was seen in the surface flow CWs. benzoic acid, nitrate, bentriazole, and TOC were removed by biodegradation, whereas phosphate and benzotriazole were removed by adsorption
Figure 4. In autumn, the plants were removed, which resulted in less input of oxygen and nutrients for microbial processes. As a consequence, lower removal of compounds that rely on microbial degradation was observed in the horizontal flow CW: benzoic acid, benzotriazole, nitrate. The vertical flow CW performs similarly as in summer
Figure 5. The surface flow CW was frozen during winter, and no operation of the hybrid-CWs was possible. When not frozen, the low temperatures and absence of plants resulted in a low microbial activity, especially in the horizontal flow CWs. The vertical flow CWs still perform better. However, the overall performance of the wetlands depended on the figuration (the used sequences) tested.

The surface flow CW was frozen during winter, and no operation of the hybrid-CWs was possible. When not frozen, the low temperatures and absence of plants resulted in a low microbial activity, especially in the horizontal flow CWs. The vertical flow CWs still perform better.

However, the overall performance of the wetlands depended on the figuration (the used sequences) tested.

Case 2  Hybrid reactor system BO3B (bio-ozone-bio) reactor

This modular system (Figure 6) combines the efficiency of biological removal and the power of ozonation to remove a broad range of micropollutants, while also providing a sustainable and cost effective technology. Wastewater treatment plant (WWTP) effluent is fed into the first reactor (bio), where DOC is removed to reduce the required ozone dose in the second reactor (ozone). In the third reactor (bio), potentially toxic ozonized transformation products are further broken down by microorganisms.

Figure 6. Schematic overview of the BO3B system

First, the removal capacity at different loading rates and ozone dosage is tested, resulting in an optimal HRT of 88 min, and an ozone dose of 0.2 g O3/g TOC (Fig 7).

Figure 7. Overview of pharmaceutical removal

In addition to the modular BO3B reactor, different modules or the first biological reactor are tested in parallel, to identify the optimal configuration. (Fig 8)

Figure 8. Picture of BR1 selection experiment BO3B system; Granular Activated Carbon, Moving Bed Biofilm or Sandfilter.

This shows the variability that can be tested in the modular reactor platform of UNLOCK.