The wastewater treatment is a critical but expensive component for forward operating bases (FOBs). Development of a self-sustaining wastewater treatment is urgently needed to sustain the FOBs. The goal of this project was to integrate solar, biological, and membrane technologies into wastewater treatment concept to create an energy-neutral small-scale wastewater treatment system that can significantly reduce mass of the wastewater, and simultaneously generate portable water for FOBs. The studied system includes four unit operations: solar energy generation, anaerobic digestion, electrocoagulation, and membrane filtration. Six specific objectives were carried out to develop the system: 1) designing a new solar-bio-hybrid power generation unit; 2) optimizing lab-scale upflow fixed-film anaerobic digestion on blackwater and food wastes; 3) studying electrocoagulation to reclaim the water; 4) investigating nano-filtration on potable water generation from the electrocoagulation (EC) solution; 5) establishing a pilot scale, self-sustaining system and evaluating its performance; and 6) conducting a detailed technical and economic analysis on the system. The project objectives were met and the technology was demonstrated under ESTCP.
Individual units in the integrated system was first investigated at bench scale to obtain the parameters for the system design and integration. Solar thermal and solar electricity approaches were studied to combine with methane from anaerobic digestion (AD) to power the entire system. An upflow fixed-film anaerobic digestion system was studied and designed to improve the efficiency of blackwater and food waste treatment in terms of reducing the footprint of digester, enhancing solid reduction, improving biogas production, and removing pathogens. The methane gas from the digester was studied to be used as a biochemical storage of solar energy to compensate unsteady solar heat and generate more energy. Electrocoagulation as a simple, efficient electric-chemical process was then studied to post-treat the effluent from the digester and reclaim the water. The electrocoagulation was designed to accommodate availability and amount of on-site energy sources (solar and methane energy) as well as the wastewater quality and quantity. A study of developing an anti-fouling nano-filtration was then conducted to turn the reclaimed water into potable water. Built up on the research outcomes from the studies on individual unit operations, a pilot scale system was then fabricated. Consequently, the system performance was evaluated and the detailed technical and economic analysis were conducted.
Two new solar thermal receivers using Fresnel lens as the collector of solar irradiation were concluded to be used to convert solar energy into high-quality thermal energy that is combined with biogas energy to efficiently and stably provide the required energy and power the treatment system. A high-efficiency upflow fixed-film digestion was developed to handle mixture of blackwater and food wastes, which had the methane productivity of 414 L/kg total solids (TS) loading and the TS reduction of 71%. The EC unit can remove approximately 99% of the TS in the AD effluent, and remove most total coliform. The combination of nano-filtration and reverse-osmosis filtration further turned the reclaimed water into clean water for potable uses. The technical and economic analysis further concluded that combining solar energy collection and biological methane generation provides sufficient and stable energy for small size wastewater treatment operations (fixed film anaerobic digestion, water reclamation, and nano-filtration of water purification), and overcomes the disadvantages of individual technologies such as unsteady energy flow for solar power generation, low efficiency of conventional anaerobic digestion, and higher energy requirement of water purification.
The research outcomes of this project clearly demonstrated a self-sustaining system that is not only a waste management tool but also an on-site renewable energy generation unit. Essentially, the technology developed by this project will advance military bases for their waste treatment and energy utilization, and significantly improve the sustainability of all FOBs, if fully deployed. In addition, the integrated solar-bio-nano concept also has a great potential to be applied by a wide range of waste treatment systems from agricultural wastewater to municipal wastewater treatment. The use of such novel technology will dramatically change the status of wastewater treatment. It will eventually turn the wastewater from an environmental liability into a public and private asset.