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Co‐digestion of industrial and domestic wastewater.

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This study is part of an extensive project studying the possibility of co-digestion of industrial and domestic wastewater at Amanzimtoti Wastewater Treatment Plant in Durban, South Africa. The focus of this study was to develop a model-based procedure to dose the 2 000 m3 full-scale Amanzimtoti pilot co-digestion plant with expired fruit juice. Modelling and experiments were used to create a six-stage feedback control loop. Experiments were conducted in 6.5 L batch reactors in the laboratory and in the 2 000 m3 plant that was operated at room temperature with intermittent mixing. The laboratory reactors were used in the first stage loop for data acquisition at 35°C and 25°C with digester sludge from the 2 000 m3 plant and expired fruit juice. pH values and biogas flowrate were measured continuously for 24 h during the experiments. The experimental data collected was used to calibrate a model of the laboratory reactor in the second stage. The WEST modelling platform was used for all modelling activities. The model was a UCT adaptation of the ADM1 model, and it used glucose as a representative of expired fruit juice as indicated in earlier work. Extensive kinetic parameters from the second stage were used to develop a model of the 2 000 m3 plant in the third stage. Expired fruit juice was dosed into the 2 000 m3 plant, and pH data was collected continuously over 24 h in the fourth stage. The pH data was used in the fifth stage to calibrate the model of the 2000 m3 plant model to the dosing of expired fruit juice. Extensive kinetic parameters from the fifth stage were used to develop the 6.5 L batch reactor model in the sixth stage. The 35°C experimental data was successfully used in the development of the 2 000 m3 plant model. The feedback control loop can be used to guide how much expired fruit juice can be dosed in the 2 000 m3 plant. Although the feedback control loop was successful, various components of the 2 000 m3 digester were not functional, which resulted in the feedback control loop being completed only once.


Masters Degree. University of KwaZulu-Natal, Durban.