John M. Owens

STILLAGE CHARACTERIZATION AND ANAEROBIC TREATMENT OF ETHANOL STILLAGE FROM CONVENTIONAL AND CELLULOSIC FEEDSTOCKS

Abstract A technical evaluation of stillage characterization, treatment, and by-product recovery in the ethanol industry was performed through a review of the scientific literature, with particular emphasis on solutions pertinent to a cellulosic-based ethanol production system. This effort has generated substantial information supporting the viability of anaerobic digestion for stillage treatment followed by land application on biomass crops for nutrient recovery. Generally, the characteristics of stillage from cellulosic materials appear comparable to those of conventional sugar- and starch-based feedstocks. However, the data on cellulosic stillage characteristics and treatment parameters are extremely limited and highly variable. This has significant impacts on the capital costs and biogas recovery of anaerobic treatment systems predicted from these data. In addition, technical questions remain unanswered with regard to stillage toxicity from untested feedstocks and the impact of heavy metal leaching when acid hydrolysis reactors are fabricated from corrosion-resistant alloys. Thermophilic anaerobic digestion of ethanol stillage achieves similar treatment efficiencies and methane yields compared to mesophilic treatment, but at almost twice the organic loading rate. Therefore, application of thermophilic anaerobic digestion would improve process economics, since smaller digesters and less stillage cooling are required. Downstream processes for stillage utilization and by-product recovery considered worthy of continued investigation include the production of feed (from single cell protein and/or algae production), color removal, and production of calcium magnesium acetate. This study finds that sustainable and economically viable solutions are available for mitigating the environmental impacts which result from large-scale biomass-to-ethanol conversion facilities. However, further research in some areas is needed to facilitate successful implementation of appropriate technology options.

Renewable methane from anaerobic digestion of biomass

Production of methane via anaerobic digestion of energy crops and organic wastes would benefit society by providing a clean fuel from renewable feedstocks. This would replace fossil fuel-derived energy and reduce environmental impacts including global warming and acid rain. Although biomass energy is more costly than fossil fuel-derived energy, trends to limit carbon dioxide and other emissions through emission regulations, carbon taxes, and subsidies of biomass energy would make it cost competitive. Methane derived from anaerobic digestion is competitive in efficiencies and costs to other biomass energy forms including heat, synthesis gases, and ethanol.

Biochemical methane potential of biomass and waste feedstocks

Abstract The biochemical methane potential (BMP)) assay was evaluated in terms of inoculum (rumen versus primary sludge digester), inoculum-to-feed ratio, and particle size for analysis of extent and rate of conversion of biomass and waste feedstocks to methane. The rumen and sludge inocula exhibited similar solubilization of particulate matter. An inoculum-to-feed ratio of 2:1 was shown to give maximum conversion rates. Particle size did not influence rate in the range of 1–8 mm. An extensive data base on the biochemical methane potential of several biomass and waste feedstocks is presented, including freshwater, marine, herbaceous, and woody feedstocks and municipal wastes; data for plant parts are also included. In addition, the influence of several parameters on the BMP of feedstocks are presented, including growth and harvest conditions, and ensiling.

Anaerobic Digestion for Reduction and Stabilization of Organic Solid Wastes During Space Missions: Laboratory Studies

The technical feasibility of applying anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during space missions was investigated. This process has the advantages of not requiring oxygen or high temperature and pressure while producing methane, carbon dioxide, nutrients, and compost as valuable products. High-solids leachbed anaerobic digestion employed here involves a solidphase fermentation with leachate recycle between new and old reactors for inoculation, wetting, and removal of volatile organic acids during startup. After anaerobic conversion is complete, the compost bed may be used for biofiltration and plant growth medium. The nutrientrich leachate may also be used as a vehicle for nutrient recycle. Physical properties of representative waste feedstocks were determined to evaluate their space requirements and hydraulic leachability in the selected digester design. Anaerobic biochemical methane potential assays were run on several feedstocks to determine extent and rates of bioconversion. Modifications for operation of a leachbed anaerobic digestion process in space environments were incorporated into a modified design, including flooded operation to force leachate through feedstock beds and separation of biogas from leachate in a gas collection reservoir. The results of runs in a prototype laboratoryscale reactor system operated on simulated solid waste blends are presented.

Anaerobic Digestion for Reduction and Stabilization of Organic Solid Waste During Space Missions: Systems Analysis

High Solids Leachbed Anaerobic Digestion (HSLAD) is a biological waste treatment system that has been successfully demonstrated for solid waste treatment in terrestrial applications. The process involves a solid phase leachbed fermentation, employing leachate recycle between new and mature reactors for inoculation, wetting, and removal of volatile organic acids during startup. HSLAD also offers a potential option for treatment of biodegradable waste on long-duration space mission and for permanent planetary bases and would produce 1.5 kg of methane, 4.1 kg of carbon dioxide and 1.9 kg of compost daily from 7.5kg of biodegradable solid wastes generated daily from a crew of six. HSLAD can operate at low temperature and pressure and has the potential for being a net energy producer. A detailed analysis of this process was conducted to design the system size required for a space mission with a 6-person crew The mass, energy and water balance of the process and an equivalent system mass (ESM) analysis are presented.

NAD(P)H and F420 Fluorescence Monitoring in Anaerobic Digestion

Abstract Anaerobic digesters are frequently upset by changes in the feed strength, changes in environmental conditions and toxic feed components. These can cause reactor failures and lead to lengthy and costly start-ups. Real-time on-line measurements are needed to assess the state of the digester and guide effective process control strategies. This paper presents initial investigations of the response of fluorescence probes for the coenzymes NAD(P)H and F to common causes of digester upsets, namely an increase in loading, a decrease in loading, and toxin (phenol) addition.