This study proposes the use of a cobalt-based Prussian blue analogue (Co-PBA; potassium cobalt hexacyanoferrate), as an adsorbent for the cost-effective recovery of aqueous ammonium ions. The characterization of Co-PBA involved various techniques, including Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, nitrogen adsorption-desorption analysis, and zeta potential. The prepared Co-PBA reached an adsorption equilibrium for ammonium ions within approximately 480 min, which involved both surface adsorption and subsequent diffusion into the interior. The isotherm experiment revealed a maximum adsorption capacity of 37.29 mg/g, with the Langmuir model indicating a predominance of chemical monolayer adsorption. Furthermore, the material consistently demonstrated adsorption efficiency across a range of pH conditions. Notably, adsorption was observed even when competing cations were present. Co-PBA emerges as a readily synthesized adsorbent, underscoring its efficacy in ammonium removal and selectivity toward ammonium.

As an alternative for energy intensive aerobic wastewater treatment system, development of sulfate reducing bacteria (SRB)-based domestic wastewater treatment system was researched. No requirement of aeration, fast substrate utilization and less sensitiveness of SRB are main factors for energy conservative wastewater treatment system. Sulfate for SRB’s synthesis could be supplied from SOx in industrial gas, thus the system also can contribute to the economical treatment of hazardous sulfur compound in the gas. With the dissolved sulfate as an electron acceptor, SRB degrade organic matters in wastewater and produce sulfide. This produced sulfide was used for electricity generation in sulfide fuel cell system connected to continuously operating UASB reactor. This study also focused on obtaining SRB dominant granule from methanogen dominant anaerobic granule in a competition between SRB and methanogens. As a strategy to increase SRB activity and to suppress methanogens, starvation was applied by not providing organic source but continuous supplying sulfate. Based on the well adopted hypothesis on the granule structure, methanogens located relatively inner core of a granule died out due to the lack of organic source, while SRB located at outer part of granule survived utilizing extracellular polymeric substance (EPS) or organic matters from died out microbes as an organic source. By eliminating the competition, the portion of organic matter degradation by SRB was increased from 19% before starvation to 93% after starvation, achieving 80% COD removal in total. In case of sulfate removal, 15% improvement was achieved compared to the control reactor. This effect of starvation on the granule characteristics were confirmed with scanning electron microscope (SEM) and transmission electron microscope (TEM). Not only wastewater treatment by SRB but also electricity generation with sulfide fuel cell system was studied. Several sets of batch tests were conducted and continuous operation was also carried out with effluent containing 80mg/L -100mg/L sulfide. Through the batch tests, hydraulic retention time (HRT) was optimized to 8 h, removing almost all of the sulfide from the effluent, having the highest power density of 0.033 mW/cm². With the optimized HRT, sulfide fuel cell connected to the UASBr was continuously operated for over 50 days. This newly developed wastewater treatment system with SRB integrated with electricity generating sulfide fuel cell system is believed to be a promising technology for more sustainable wastewater treatment system.

Waste activated sludge (WAS) and food waste (FW) are available year round at low cost and have the potential to promote synergism in anaerobic digestion (AD). The goal of this study was to clarify the synergism in co-digestion of WAS and FW. A slight amount of FW at various ratios was added to WAS as an auxiliary substrate, and anaerobic batch tests were performed under mesophilic conditions. By adding FW, total CH₄ produced was increased, where most of them were come from WAS, clearly suggesting synergism. Also, lag period was shortened and CH₄ production rate was increased by FW addition. It was hypothesized that enhanced performance was owing to the facilitated hydrolysis of WAS by FW addition, which was revealed by the increased activities of hydrolytic α-amylase and protease.