Anaerobic Digestion (AD) typically stabilizes 40-60% of influent wastewater sludge. Improving the methane yield in wastewater may produce enough energy to power some wastewater treatment processes, while the production of volatile-fatty acids (VFAs) generates economic incentives for yard waste pre-fermentation. In this research, pre-fermenters consisting of inocula composed of media; cellulose, lantana, or grass; and rabbit cecotrope were fed various concentrations of plant matter. The contents of these pre-fermenters were the influent for respective anaerobic digesters. The microbial consortium derived for the lignocellulosic pretreatment with common yard waste in Arizona successfully increased methane production in AD, while producing additional VFAs during pretreatment in all systems. The performance of the system appeared to depend on plant matter loading and operating time, with a higher plant loading increasing the VFA production and a longer operating time increasing soluble chemical oxygen demand (COD) in pre-fermentation, and therefore the methane production in AD increased. The pre-fermenter with the highest plant matter loading and longest operating time –1.44 g plant matter per day at a 9.6% influent concentration and 193 days of total operating time– produced 10,000 mg COD/L of VFA, and its reactor produced about 460 mL methane (CH4) per day, which was almost twice the production of the control AD at 250 mL CH4 per day. This research uses yard waste that would previously be disposed of in landfill to increase valuable product production in AD. The potential value added to wastewater treatment plant (WWTP) processes by these methods could incentivize the expansion of wastewater treatment, thereby increasing sanitation access. The use of net-neutral biogas as a fuel source for WWTPs is additionally an incremental solution for reducing carbon equivalents present in the atmosphere, thereby reducing the greenhouse gas effect.

Methane (CH4) is a prominent greenhouse gas that contributes to the negative impacts of global warming and climate change, whose emissions have more than doubled since the Industrial Revolution primarily due to anthropogenic sources. The main pathways in which methane moves through the environment are methanogenesis and methanotrophy. Methane is primarily generated by acetoclastic methanogenesis in wetlands while it can be oxidized both aerobically and anaerobically. Wetlands are important methane emission sources at 177 - 284 Tg CH4 year-1. The Tres Rios Wetland (TRW) is a constructed facility to complete nutrient removal of treated municipal wastewater, and has shown low emissions of methane. Whether such low emissions could be achieved through active anaerobic oxidation of methane (AOM) is not known, and the main objective of this work is to evaluate the rates of AOM in TRW. In this study an isotopic method and a mass balance method were utilized to determine the rate of AOM from top sediments found at Tres Rios at various locations and in two sets of sampling. The results showed that evidence of AOM occurred in the sediments of both sampling events conducted. The first sampling set showed evidence of AOM at all locations along a transect, showing that oxidation of methane is indeed occurring in Tres Rios sediments. Evidence from both methodologies suggested that high methanogenesis rates occurred at the outside location closest to the water. The second sampling set showed that the highest rate of AOM occurred at the outlet location, with the lowest rate occurring in the middle location. DNA extractions and PCR images resulted in a poor DNA yield, and inability to extract DNA. It was determined that the isotopic approach was less accurate than the mass balance approach due to unexpected delta CH4 values. It was determined that dilutions of CH4 ppm lead to less accurate isotopic measurements needed to estimate AOM rates using a 13C pulse technique. Literature review suggests that factors including water presence, temperature, redox potential, and plant presence can be influential in the oxidation of methane. This AOM assay can be beneficial in better understanding how methane cycles at Tres Rios, and can provide opportunities for future research in determining which factors influence the oxidation of methane in different locations throughout wetlands.

In order for microalgae to be a cost-effective renewable energy source, a high CO2-transfer efficiency (CTE) is necessary. Using hollow-fiber membranes (HFM), membrane carbonation (MC) in microalgal cultivation can be used to achieve a CTE near 100%. Due to the diurnal cycle in outdoor algal cultivation, an inconsistent CO2 demand with temperature fluctuations can cause pore wetting of the inner and outer fiber layers in composite HFMs. In addition, the presence of supersaturated O2 during high algal growth may change the gas transfer dynamics of the fibers, which can be critical when trying to selectively remove CO2 from a valuable gas such as biogas. This study evaluated fiber performance under conditions that mimic these effects by analyzing the carbon transfer efficiency (CTE), CO2 flux (JCO2), and outlet CO2 concentration compared to baseline values. Wetting of the interior fiber macropores resulted in an average 32% ± 8.3% decrease in flux, which was greater than for flooding of the outer macropores, which showed no significant change. All tests resulted in a decrease in CTE and an increase in outlet CO2. The presence of elevated O2 levels did not decrease the CO2 flux compared to baseline values, but it increased the O2 concentration and decreased the CH4 concentration at the distal end of the fibers. These findings highlight that liquid accumulation can decrease HFM performance during MC for microalgal cultivation, while the presence of supersaturated O2 can reduce separation efficiency.

Cyanobacteria and microalgae help reduce the environmental impact of human energy consumption by playing a vital role in carbon and nitrogen cycling. They are also used in various applications like biofuel production, food, medicine, and bioremediation. Understanding how these organisms respond to stress is important for efficient recovery strategies and sustainable outcomes. This study investigated the effects of low-level bleaching and thermal stress on cyanobacteria and microalgae, specifically Synechocystis, Chlorella, and Scenedesmus. The role of ferroptosis, an iron-dependent form of cell death, in the degradation of cellular components under these stressors was examined. Flow cytometry and spectrophotometry were used to measure changes in cellular health and viability. The results showed that temperature influences the type of cell death mechanism and can impact photosynthetic organisms. When treated with Liproxstatin-1, an inhibitor of ferroptosis, both Synechocystis and Chlorella experienced a decrease in oxidative damage, suggesting a potential protective role for the compound. Further investigation into ferroptosis and other forms of cell death, as well as identifying additional inhibitory molecules, could lead to strategies for mitigating oxidative stress and enhancing the resilience of cyanobacteria and microalgae.