MIKROPELLETS Phase 1 – Investigation of processes for integrated micropollutant elimination with aerobic granular sludge

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The project "MIKROPELLETS - Investigation of processes for integrated micropollutant elimination with aerobic granular sludge" aims to integrate micropollutant removal into innovative granular sludge technology in order to improve the condition of water bodies in North Rhineland-Westphalia. The main focus of phase 1 will be placed on the development, implementation and optimization of innovative, patent-free aerobic granular sludge processes in a Sequencing Batch Reactor (SBR) as well as in a continuous flow process. The aim is to gather previous knowledge on aerobic granular sludge and to investigate the operational stability and efficiency for municipal wastewater.

Due to aerobic, easily sedimentable biomass, aerobic granular sludge processes can achieve high conversion rates per volume, even with municipal wastewater. In addition, various biological processes, such as nitrification and denitrification, can take place simultaneously in the different functional layers of the granules. This allows smaller reactors to be realized with the same treatment capacity. In addition, energy-intensive system components such as recirculation are no longer required. Important advantages of the aerobic granular sludge technology compared to the conventional activated sludge process are therefore:

  • Energy saving
  • Cost reduction
  • Space optimization

Important parameters for the formation of aerobic granular sludge are short settling times within the reactors and therefore an associated selection pressure as well as a certain degree of hydrodynamic shear forces (Morgenroth et al., 1997; Liu and Tay, 2004).

The project is divided into two different phases of investigation. In the first phase of the project, ISA will develop a reactor design for an aerobic granular sludge reactor using the SBR process. The reactor will then be built and operated for at least one year at the HTK Neuss. The operation will be intensively accompanied by various analytics, such as wastewater-typical standard analyses and photographic monitoring of the granular sizes.

The first project phase is expected to be completed in November 2022. Currently, three SBRs are in operation with municipal wastewater and initial results have already been obtained. These result from several trial periods in which aspects such as granule formation and nutrient removal were monitored. In addition, various modifications have been investigated so far. These include the feed volume, the cycle settings and the aeration strategy, which should lead to an improvement of the reactor performance.

Granule formation without the use of inoculated sludge could already be achieved up to a granulation degree of 30 %. Overall, the operation of the reactors with inoculation shows a high potential in the removal of COD, nitrogen compounds and phosphorus. In comparison to a reference plant, a higher cleaning performance could also be observed during feed disturbances in the treatment plant, which suggest an increased process stability of the aerobic granular sludge reactors. However, some difficulties still have to be overcome due to different reactor geometries. In the course of the first project phase, further tests are therefore planned concerning the cycle settings, the aeration strategy and the filling of the reactors.

 
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During the start up of one of the reactors, it was also illustrated that the short settling time and the plug flow feed resulted in the selection of fast settling biomass.

In parallel with further experiments on the reactor design, targeted activity tests will be carried out in phase 1. These will allow the resistance of the granules to selected parameters to be tested and compared with reference sets.

The knowledge obtained will be used to develop practical recommendations for this novel process in terms of operation, design and construction. These recommendations then will be made available to the urban water sector.

In a planned second project phase, micropollutant removal processes will be integrated into the investigated aerobic granular sludge technology. The partners' experience in the field of micropollutant elimination using ozone or powdered activated carbon will be incorporated into the project.