The below videos showcase our lab facilities at USC (including the Water Lab) and include testimonials from our students.
Anaerobic biotechnologies, such as anaerobic membrane bioreactors (AnMBRs), are emerging as an eco-efficient strategy for domestic wastewater treatment. Unlike aerobic activated sludge systems, AnMBRs produce energy directly in the form of methane-rich biogas. We have demonstrated that AnMBRs are capable of matching the treatment performance of activated sludge systems even at low psychrophilic temperatures (see figure to the right). We found supporting biofilm development on the membrane surface to be a key strategy in maintaining effluent quality at such low temperatures. Microbial characterization of the biofilm showed that we were able to enrich for a community with highly active methanogens and syntrophic bacteria. However, methane generation in the biofilm resulted in significant dissolved methane oversaturation in the effluent, a potential concern for energy recovery and greenhouse gas emissions of treatment. Read the full paper here.
Evaluating new biotechnologies such as AnMBRs requires systems level thinking. We used process modeling and sustainability assessment methodology to perform a life cycle assessment of AnMBRs compared to conventional treatment approaches. Because AnMBRs are still in the early phases of development, we evaluated uncertainty at two levels: "today" based on reported values from bench- and pilot-scale systems and "future" based on developments that are likely to occur as AnMBR technology moves to full-scale implementation. We found that for AnMBRs to be competitive with conventional treatment systems, energy demands for fouling control need to be significantly reduced and effluent dissolved methane must be managed to reduce global warming potential (see figure to the left). Outputs of this work (e.g., design and operational targets) are being used to guide future experimental research to develop strategies to improve AnMBR energy recovery and limit greenhouse gas emissions. Read the full paper here.
Full-scale implementation of anaerobic bioprocesses requires that we assess emerging contaminants, improve the energy balance, better understand microbial community dynamics, mitigate effluent dissolved methane, and make advances in membrane development to reduce fouling. These areas are being explored in our current research described below.
Emerging biotechnologies to mitigate antibiotic resistance
Despite the longstanding benefits of antibiotics, their persistence in wastewater creates a selective pressure for development of antibiotic resistance in microbial communities found in engineered systems. Sensitive (non-resistant) bacteria can acquire resistance mechanisms from antibiotic resistant bacteria via the horizontal exchange of mobile genetic elements (MGEs) containing antibiotic resistance genes (ARGs). Wastewater treatment systems have a high density of microorganisms that promote antibiotic resistance proliferation via vertical and horizontal gene transfer when exposed to sublethal levels of antibiotics. Anaerobic membrane bioreactors (AnMBRs) are an emerging technology with the potential to improve energy efficiency and effluent reuse during mainstream wastewater treatment. However, their contribution to the proliferation of contaminants of emerging concern, such as antibiotic resistance genes (ARGs), remains largely unknown. Our lab explores ARG fate in AnMBRs, the distinct profiles of ARGs in biomass and effluents, impact of antibiotics on microbial community structure, and is exploring operational strategies and design elements that limit ARG abundance in effluents and biosolids. For more information on this topic and our most recent study concerning ARGs click here.
Energy recovery from food waste
There is an immediate need for fundamental and applied research on anaerobic treatment of food waste due to legislative pressures requiring food waste diversion from landfills. Although co-digestion with sewage sludge at wastewater treatment plants is an attractive management strategy, decentralized anaerobic treatment can utilize existing transportation routes in certain applications to reduce overall environmental impacts. AnMBRs are well-suited for this application given their enhanced energy recovery, improved effluent quality, reduced sludge production, and smaller footprint. Although substantial research has been done to-date on anaerobic digestion, AnMBRs are still an emerging technology with few full-scale installations worldwide. In particular, very few studies have evaluated AnMBRs for the sole treatment of food waste. Given the nature of food waste (i.e. highly complex organics with temporal variations in strength and composition), we hypothesize that a two-phase AnMBR equipped with ceramic membranes will provide the greatest economic and environmental benefits. Additional fundamental research is also needed to better understand the highly complex microbial communities driving anaerobic systems. A significant opportunity exists to apply advanced molecular microbiological methods such as high-throughput sequencing and provide a fundamental and mechanistic understanding linking microbial community structure and function in anaerobic systems. These knowledge gaps and the impending need to manage diverted food waste were explored in our research study (link).
Bioelectrochemical systems for dissolved methane handling
Microbial fuel cells, bioelectrochemical systems where microorganisms directly deposit electrons to an anode during oxidation of organic or inorganic compounds, have traditionally been studied for energy recovery directly from domestic wastewater and thus can be a competitor to mainstream anaerobic treatment. One of the drawbacks of anaerobic treatment is that it produces an effluent saturated with dissolved methane, dramatically increasing greenhouse gas emissions relative to aerobic treatment processes if this methane is released to the atmosphere. We evaluated dissolved methane removal efficiency of air-cathode MFCs and demonstrated up to 85% dissolved methane removal and multiple lines of evidence indicated a methanotroph-exoelectrogen interaction enabling energy recovery from dissolved methane. To find more about the exciting work performed click here.
Nanofiber and nanocomposite membrane development for MBRs and membrane distillation
Electrospinning is a process that utilizes a high voltage field to generate a nanofiber mat from polymers that acts as a microfiltration membrane. Certain polymers, such as PVDF, exhibit piezoelectric properties when electrospun. This capability offers and exciting possibility to manage membrane fouling by applying an electric field in situ resulting in material deformation (e.g., vibration) of the membranes. We explored this application in a recent publication (link). We are also evaluating nanocomposite membranes that utilize molybdenum disulfide nanoparticles on a functionalized nanofiltration membrane to improve water flux and lessen fouling propensity. Finally, we are exploring novel electrospun membranes for membrane distillation applications.