Thomas D. DiStefano

Reductive dehalogenation of chlorinated ethenes and halogenated ethanes by a high-rate anaerobic enrichment culture.

An anaerobic enrichment culture, using CH 3 OH as an electron donor, dechlorinated tetrachloroethene (PCN, 55 μmol added/100 mL of culture) nearly stoichiometrically to vinyl chloride (VC) in 20 h with negligible buildup of other intermediates and at a maximum rate of 4.6±0.4 μmol of PCN transformed/mg of volatile suspended solids per day. Appreciable conversion of VC to NTH occurred only after the PCN was nearly depleted, suggesting the inhibition of VC dechlorination by PCN. PCN, trichloroethene, cis-1,2-dichloroethene (DCN), and 1,1-DCN were all rapidly metabolized to VC with near zero-order kinetics and apparently inhibited subsequent VC dechlorination

Characterization of the curing process from high-solids anaerobic digestion.

A laboratory-scale study was completed to simulate aerobic curing of solid-phase residue (digestate) from an anaerobic reactor fed a mixture of food and landscape wastes. The degree of organic stabilization was determined through routine analysis of oxygen uptake rates, percent O(2), temperature, volatile solids, and Solvita Maturity Index; measurements of ammonia and volatile fatty acid (VFA) concentrations served as indicators of phytotoxicity. Results suggest that stabilization of organics and elimination of phytotoxic compounds from anaerobic digestate preceded significant reduction of each volatile sulfur compound (VSC) detected (hydrogen sulfide, methanethiol, and dimethyl sulfide). Within 10-15 days of curing, stabilization of organics was achieved and phytotoxic compounds were eliminated, whereas reduction of VSCs to low levels required 15-20 days of curing. Based on these results, incomplete curing and anaerobic microenvironments within a curing facility may increase odor potential via formation of VSCs, whereas sufficiently cured digestate will resist VSC formation, despite the onset of anaerobic conditions.

Effect of anaerobic reactor process configuration on useful energy production

The effect of reactor process configuration on anaerobic production of useful energy (hydrogen and methane) from a complex substrate was investigated for the following reactor systems: suspended growth, two-phase mixed, two-stage mixed, upflow anaerobic sludge blanket (UASB) reactor, and two-phase UASB. The mixed two-phase and two-stage configurations yielded the highest specific energy productions of 13.3 and 13.4 kJ/g COD fed, respectively. Reactor process configuration influenced microbial pathways in acidogenic reactors in that butyrate was the predominant volatile acid in phased configurations, whereas acetate was predominant in the staged configuration. The UASB reactor achieved the highest average daily energy production per reactor volume of 101 kJ/L reactor-d. All reactor configurations achieved high COD removals on the order of 99%. However, hydrogen represented only 3% of the total energy produced by the two-phase mixed and two-phase UASB configurations. Theoretical analysis revealed that the maximum specific energy production by the two-phase suspended-growth configuration is only 9% higher than that for a single-stage mixed reactor. Consequently, the production of hydrogen from complex substrates in these process configurations does not seem to be justifiable solely from an energy point of view. Instead, it is suggested that phased anaerobic systems should be considered primarily for improved process stability whereas resultant hydrogen production is of secondary benefit.

Life-Cycle Analysis of Energy and Greenhouse Gas Emissions from Anaerobic Biodegradation of Municipal Solid Waste

Energy requirements and greenhouse gas (GHG) emissions for current landfilling of municipal solid waste (MSW) was compared to potential biodegradation of MSW in anaerobic digesters (AD) throughout the United States. A hybrid life-cycle analysis was completed to assess the potential for anaerobic biodegradation of MSW to methane, a valuable energy source. Conversion of MSW to methane in AD would generate a form of renewable energy, reduce GHG emissions, and save landfill space for nonbiodegradable materials. Based on laboratory- and pilot-scale studies conducted in the United States, full-scale data from facilities in Europe, and economic input-output life-cycle analysis, the annual 127 million t of MSW landfilled in the United States could be biologically converted to 5.9 billion m 3 of methane. Net methane production would have an estimated value of

High solids co-digestion of food and landscape waste and the potential for ammonia toxicity.

1.5 billion/year when converted to an equivalent amount of electricity at an assumed value of

A comparison of complex electron donors for anaerobic dechlorination of PCE

0.1/kWh. The 15 billion kWh/year of renewable energy released through the biodegradation process is estimated to satisfy the annual consumption of 1.3 million United States households. The analysis also suggests that diversion of MSW from landfills to AD systems would result in GHG emissions reductions of 146 million t CO 2 e per year, due to decreased landfill activity and use of biogenic methane instead of fossil fuel for electricity production. This represents a reduction in total emissions of 1.9% compared to U.S. GHG emissions in 2006. Nationwide AD systems are projected to reduce cumulative energy consumption by nearly 15 million TJ and reduce GHG emissions by 7.2 billion t CO 2 e, over a 50-year period. Logistics and capital costs of developing a nationwide reactor-based system for MSW management are considerable. Development of appropriate national policy and incentives would be needed to stimulate such a transition from the current landfill-based system that currently exists. It is estimated that a carbon emissions credit on the order of

Reductive dechlorination of high concentrations of tetrachloroethene to ethene by an anaerobic enrichment culture in the absence of methanogenesis.

30 to

Hydrogen as an electron donor for dechlorination of tetrachloroethene by an anaerobic mixed culture.

60/t CO 2 e would facilitate break-even economics for nationwide implementation of AD systems. Alternatively, renewable energy credits would enhance the value of electricity produced from AD biogas. Carbon emissions taxes on landfills would further improve the economics of AD systems.

The effect of tetrachloroethene on biological dechlorination of vinyl chloride: potential implication for natural bioattenuation

A pilot-scale study was completed to determine the feasibility of high-solids anaerobic digestion (HSAD) of a mixture of food and landscape wastes at a university in central Pennsylvania (USA). HSAD was stable at low loadings (2g COD/L-day), but developed inhibitory ammonia concentrations at high loadings (15 g COD/L-day). At low loadings, methane yields were 232 L CH4/kg COD fed and 229 L CH4/kg VS fed, and at high loadings yields were 211 L CH4/kg COD fed and 272 L CH4/kg VS fed. Based on characterization and biodegradability studies, food waste appears to be a good candidate for HSAD at low organic loading rates; however, the development of ammonia inhibition at high loading rates suggests that the C:N ratio is too low for use as a single substrate. The relatively low biodegradability of landscape waste as reported herein made it an unsuitable substrate to increase the C:N ratio. Codigestion of food waste with a substrate high in bioavailable carbon is recommended to increase the C:N ratio sufficiently to allow HSAD at loading rates of 15 g COD/L-day.

The role of process configuration in the performance of anaerobic systems

The potential of sugar, flour, corn steep liquor, molasses, non-fat milk, and whey to serve as electron donors for anaerobic dechlorination of tetrachloroethene (PCE) was examined. The electron donors were compared based on acclimation time, the extent of PCE dechlorination achieved, the minimum electron donor dose necessary to achieve PCE removal, and unit cost. The time required to achieve routine dechlorination of PCE (to any daughter product) for each donor was (in days): corn steep liquor (10), milk (10), whey (10), methanol (12), molasses (14), sugar (26), flour (30). Ethene production was achieved by milk-, whey-, and methanol-fed cultures, whereas the other donors did not facilitate ethene production over a 135-day period. Corn steep liquor-, whey-, molasses-, and sugar-fed cultures needed five times the stoichiometric amount (e.g., donor per eq PCE to ethene) to facilitate PCE conversion to dichloroethene (DCE). Cultures fed milk and flour needed 20 times the stoichiometric amount, and methanol-fed cultures required 50 times the stoichiometric amount, perhaps due to competition from methanogenic organisms. Minimum laboratory-scale electron donor costs to achieve stoichiometric conversion of PCE to DCE are (