Evaluation of sensor techniques for detection of contaminants in greywater from showers

Abstract: This thesis has been made in collaboration with the company Orbital Systems. The aim has been to optimize their product the Orbital shower, which is a circulating shower system. The work evaluates different sensor techniques suitable for detection of contaminants in greywater. After a comprehensive literature study, three techniques; ultrasound, IR and impedance were further investigated and practically tested. Impedance values and IR absorbance were obtained from contaminants in still water, while the speed and frequency content of ultrasound was calculated using time of flight and FFT in both still and circulating water. Test solutions used to evaluate the sensor techniques consisted of personal care products (shampoo, body wash and conditioner), human body contaminants and calcium. Varying concentrations of sodium chloride and cattle blood was used to simulate body fluids. Calcium was used to modify the hardness of water. All three techniques were able to detect some contaminants and failed to detect others. The widest range of contaminants were detected when using a combination of IR and impedance. This combination did not only detect all test solutions but it could also to some extent quantify the contaminants. It is recommended that this combination should be investigated further. Technical parameters, advantages and limitations of each technique are discussed. Lastly, an extensive recommendation was presented to Orbital Systems regarding how future research on sensor techniques should be conducted.