Resource recovery in self-driven bio-electrochemical systems
Date of Issue2019
Interdisciplinary Graduate School (IGS)
Nanyang Environment and Water Research Institute
There are many useful resources in the wastewater (WW) and wasted activated sludge, such as organic matters, phosphate, nitrogen, and precious metals. The cost of conventional technologies to recover them from wastewater and sludge can be very high and the efficiency is quite low. Bioelectrochemical system (BES) is considered an ideal treatment method to recover nutrients, while multiple pollutants can be degraded at the same time. Such approach can improve energy savings and reduce environmental stress, and also address the urgency to rely on fossil-fuel. Meantime, there are large amount of industrial wastewater discharged to the environment as well. Some wastewater contains pharmaceuticals and personal care products (PPCP) which are not easy to remove using conventional bioprocess. Again, BES was introduced in recent decades to handle recalcitrant or antibiotic compounds in the wastewater. There would be certain interaction between antibiotics and biofilm in the BES reactors. However, how the presence of antibiotics would affect the BES system and the mechanisms of potential effects are not clear. Two types of antibiotics of sulfamethoxazole (SMX) and chloramphenicol (CAP) were chosen in this thesis. The study on the effects of SMX for power generation in microbial fuel cell (MFC) was presented in Chapter 4. SMX was added in the anode to monitor the performance of power generation. We found out SMX was able to enhance the power generation as well as to extent energy duration. SMX was degraded within 36 hours operation. The degradation pathway was corresponding to the activity of three main exoelectrogenics. Meantime, SMX helped to remove competitive microorganisms in the anode and further contributed to the power generation and organic matter conversion. Notwithstanding the excellent energy recovery performance, the power produced from the MFC system cannot be collected. It would need to be utilized in-situ. In order to improve the efficiency of CAP removal, Chapter 5 compared three different cathode materials, i.e. carbon rod (CR), copper foam (Cu), and nickel foam (NF), for CAP removal in microbial electrolysis fuel cell (MEC). The results demonstrated that Cu was the most efficient cathode for CAP degradation. With Cu electrode under a higher applied voltage (0.5 V), CAP could be degraded to nitrobenzene within 24 h. The by-product has lower toxicity for microorganisms. Although MEC is efficient for CAP removal, it still needs external energy supply. Such energy supply can actually be provided by MFC system. In Chapter 6, a self-driven MFC-MEC system was attempted to utilize the energy generated by MFC to power MEC for CAP removal. At the same time, precious metal Ag from electroplating wastewater was also recovered in MFC cathode. Under the optimum condition, 99.8% and 98.8% of Ag(I) and CAP were recovered or removed, respectively. Scanning electron microscope (SEM), Energy Dispersive X-ray Detector (EDX) and X-ray photoelectron spectroscopy (XPS) results demonstrated the product on the electrode of MFC was pure silver. In most of previous BES study including the self-driven system reported above, researchers commonly use acetate simulated wastewater in the anode for power generation. Considering practical application, the organic matter can be replaced with real wastewater or other waste material that contains carbon source. Chapter 7 reported an integrated sludge treatment and resource recovery system for simultaneous energy and nutrients recovery. Sludge fermented liquor (FL) was used as feed for MFC, which provided a maximum voltage of 0.477 V and power density of 8.07 W m-3. A total 90.59% ammonium was removed and 42 % phosphorus was removed and stored in the biomass in the form of polyphosphate (poly-P). Nitrogen can then be recovered at the cathode and phosphorus can be recovered from the biomass in the anode.
Engineering::Environmental engineering::Water treatment