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Master thesis

Wastewater treatment plant of the future: development of process for carbon capture and valorisation

Abstract : Wastewater treatment using activated sludge process is a mature technology and has been in use for over 100 years. It is an energy intensive process, requiring considerable electrical energy for aeration to eliminate organic pollutants. In addition to creating energy demand and contributing to carbon dioxide emissions, it represents a high operating cost for the plant operators. However, the organic pollutants represent a source of energy. Organic matter can be captured at the start of the treatment train and directed towards an anaerobic digester to considerably increase the biogas production. Innovative processes exist, which have to be tested in pilot scale before they are scaled up and implemented in existing WWTP. It can decrease the overall energy footprint of wastewater treatment and has the potential to be a source of energy. A variation on conventional activated sludge process, called A-B process is a promising process to capture the organic matter at the head of the WWTP. Different technologies exist for capturing this organic matter as the first unit operation in the treatment train, such as chemically enhanced primary treatment and high rate activated sludge. With this guiding principle, "CAPTURE" project was launched in which this internship work was conducted. The objective of this internship was to study the biological option to capture carbon by performing pilot scale experiments. A 3m3 bio-reactor present in Irstea's research platform was chosen for this study. This reactor was originally conceived to study extended aeration processes and hence needed considerable modification. The associated pumps and pipes were replaced to deliver high flowrates required. Its aeration system was tested In the absence of a suitable secondary clarifier, and to proceed during the delay in procuring one, the reactor run as a Sequencing Batch Reactor. The reactor was fed with raw wastewater under real conditions, and its performance was measured after 4 days of continuous functioning. Parameters of interest are the capacity of aeration, removal efficiency of the reactor and settling properties of the sludge. Firstly, the reactor's capacity to oxygenate was measured - i.e., its volumetric mass transfer coefficient (KLa) - as 7.9 g O2 / h for an air flow rate of 290 NL/min in fresh water. Performance of the reactor was measured as 37% of COD removal. Column settling experiments were performed with the mixed liqueur from the reactor to have data on the settling characteristics. This data is a key input in the design of a secondary clarifier. Overall, the performance of the reactor is not satisfactory as the react phase of the SBR cycle was not sufficiently long for expected levels of carbon capture to occur. Should the aeration time be increased, the overall rate of the system will diminish and will no longer represent a high rate system. With these learnings, the next phase of the project will test a continuous fed reactor with a dedicated clarifier.
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Master thesis
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Submitted on : Saturday, May 16, 2020 - 4:37:02 PM
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  • HAL Id : hal-02608656, version 1
  • IRSTEA : PUB00060175

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R.S. Guthi. Wastewater treatment plant of the future: development of process for carbon capture and valorisation. Environmental Sciences. 2018. ⟨hal-02608656⟩

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