Abstract
© Copyright © 2019 Cristiani, Gajda, Greenman, Pizza, Bonelli and Ieropoulos. In the present work different prototypes of floating MFCs have been tested in anoxic water environments of wastewater plants in Italy, over a period of 3 years. Several configurations of horizontal (flat) and vertical (tubular) MFCs were assembled, using low-cost and light-weight materials, such as plastic lunch boxes, polystyrene or wood to keep the systems afloat, and ceramics for the MFCs. Untreated carbon cloth or veil was used for both anode and cathode electrodes. Felt (flat MFCs) or clay (tubular MFCs) was used as the cation-exchange separator. Single flat MFCs generated power up to 12 mW/m2 while a 32 cylindrical MFC stack generated up to 18 mW/m2. The testing lasted for more than 2 years and there was no inoculation other than exposing the MFCs to the denitrification environment. The cathodes of the flat MFCs were spontaneously colonized by algae and plants, and this did not affect the stability of the systems. Natural light increased the power output of the flat MFCs which were smaller than 50 × 50 cm. Diurnal oscillation of temperature and periodic water flow did not significantly affect the performance of the MFCs. The largest flat MFC produced the highest absolute power, although in a disrupted way. A new, simple low-energy remote monitoring system, based on LoRa technology was used for data transmission over distances of >500 m. This is a piece of hardware that could potentially be suitable for remote monitoring as part of a network, as it can be directly powered by the deployed MFCs.
Highlights
The biotechnological purification of wastewater is based on complex and strictly interconnected physico-chemical and biological processes
Both the flat Microbial Fuel Cells (MFCs) and the tubular MFCs types were immersed in the denitrification tank without prior inoculation
In the case of the flat MFCs whose electrodes were separated though a porous PPE felt, without any electrolytic membrane, biofilm grew on the cathode sustaining the catalysis of the cathodic reaction
Summary
The biotechnological purification of wastewater is based on complex and strictly interconnected physico-chemical and biological processes. Regular measurement of physicochemical parameters such as temperature, water flow, dissolved oxygen, organic load is regularly carried out in wastewater treatment plants (WWTPs). The concentration of biodegradable organic matter is the most important parameter of the process, which would require closer monitoring. The frequency of analysis is governed by the instability of the system operation, which is normally more pronounced in smaller treatment plants where the demand for a greater number of controls is often challenged by the availability of resources (human and technical ones). On-line monitoring devices are often used in modern WWTPs, depending on their dimensions, practice and available resources (Bourgeois et al, 2001), whereas the strict control of the water treatment in emerging economies is often unsustainable, if at all supported. Sensing is becoming increasingly important as a function performed to protect and preserve natural ecosystems, whether in developed or emerging economies
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