Session- Air Emissions
Ammonia Emissions and Pathogen Inactivation During Composting
CRONJE, ANGELA (1), Barker, Andrew J. (2), Guy, Stuart (2), Turner, Claire (1), Williams, Adrian G. (1)
(1) Silsoe Research Institute, Wrest Park, Silsoe, Befordshire, MK45 4HS, UK, (2) School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingahm, B15 2TT, UK
The composting of pig manure and straw was investigated using 3 cylindrical reactors operated under controlled conditions, each with a working capacity of approximately 210 litres. They were used to investigate the effects of carbon to nitrogen ratio (C:N) and pH on ammonia emisions and pathogen inactivation. Heat losses from the reactors were compensated for with external heat sources. A heating cable, coiled around each reactor body, balanced and, hence, minimised lateral heat losses in response to the difference between centre and side temperatures. The vertical temperature gradient was reduced by heating the top and base surfaces of the reactor, which also prevented condensation. The conditions inside, therefore, resembled those experienced at the core of a composting heap. The off-gas was analysed for ammonia, using acid traps, and oxygen and carbon dioxide, using a combined gas analyser. Microbial heat can generate temperatures of above 55 C, which, when held for several hours, causes the thermal inactivation of pathogenic organisms. The total viable bacterial counts in the feed and composted material were compared to estimate the extent of inactivation. Respirometry experiments with pig manure showed that maximum aerobic activity occurs at 60 C. The core temperature was prevented from rising above 60 C by increasing the airflow to dissipate the surplus heat, and so prolong the period of maximum microbial activity. Preliminary results show the temperature difference across the bed was maintained at 1 C. Maximum temperatures of between 55 and 60 C lasted for at least 5 days in each reactor. Results of the experiments will be used to test and refine of a simulation model of the compost system. The model was formulated to predict the temperature change and the ammonia volatilised from input values of; the biodegradable fraction of the substrate, air flow rate through the bed, thermal properties of the substrate, initial pH and ammoniacal nitrogen and moisture content of the feed.
Public and Worker Health: Pathogens, Bioaerosols, and Odors
EPSTEIN, ELIOT (1)
(1) Tetra Tech, Inc., USA
Public and worker health concerns related to composting operations primarily relate to pathogens, bioaerosols, and odors. Most composting feedstocks can contain pathogens. Biosolids, municipal solid waste (MSW), manures, food waste, and yard waste contain bacteria, viruses, and parasites. In biosolids and MSW, the primary source of pathogens is humans, whereas in food waste, manures, and yard waste, the primary source of pathogens is animals. Composting is an excellent method for the destruction of pathogens. The potential public exposure is principally from use of improperly prepared compost products. Providing correct time-temperature relationships are maintained during the composting process, excellent disinfection will occur. Data will be provided to show the effectiveness of good composting practices on product disinfection. Bioaerosols are airborne materials comprised of organisms or biological agents that may affect humans through infectivity, allergenicity, toxicity, or other means. These bioaerosols can contain living organisms, including bacteria, fungi, actinomycetes, arthropods, and protozoa as well as microbial products, such as endotoxin, microbial enzymes, B-1,3glucans, and mycotoxins. Organic dust may contain bioaerosols, such as endotoxin, fungi, and other materials, which can result in a pathogenic condition termed "organic dust toxic syndrome." Workers are the principal individuals exposed to bioaerosols. The public can be protected through facility design and operations. Data on bioaerosols at composting facilities and a discussion of mitigation measures and controls will be provided. Odors have been a major concern for composting operations. In the past, odors had been considered only a nuisance. More recently, there has been considerable attention by the regulatory community in considering and evaluating odors as a potential health issue. Data from large animal operations as well as several industrials have shown that odors have resulted in health issues such as nausea, headaches, irritation, stress, and other effects. The relation of odors and health will be discussed.
Effect of Carbon Availability On Greenhouse Gases Emissions and Nitrogen Conservation During High Rate Composting.
LEMUS, GLADIS R., and Lau, Anthony K.
Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia, Canada
The value of compost as fertilizer is mainly based on its nitrogen content, however nitrogen might be lost during the process, resulting in poor nutrient content in the finished product, and important greenhouse gas emissions. Biological transformation of the nitrogen present in organic wastes is strongly linked to the carbon content, particularly to its availability.Organic wastes rich in lipidic compounds are not typically composted. However, fats, oils & grease (FOGs) residues have a high concentration of readily available carbon, and a high energy content that makes them ideal candidates for aerobic composting. The aim of this project is to evaluate the effect of composting substrate carbon availability on (1) nitrogen content in compost product, and (2) greenhouse gas emissions, particularly nitrous oxide, carbon dioxide and methane. A series of lab scale tests have been performed using lipid-rich wastes as a source of easily degradable carbon. Two different substrates were used: yard waste (grass clippings, wood shavings and wood chips), and synthetic food waste (dry dog food). Preliminary results show a 4-fold reduction in ammonia losses whenever easily degradable carbon was added. Lipid concentration was reduced by 50% in average, with a maximum of 80%. Volatile solids content changed by 15-20% for the up to 10 days composting period. Thermophilic temperatures were readily achieved without any external heat addition, with peak temperatures around 70 C. Analysis of greenhouse gases, and compost product nutrient content are currently in progress. By adding an easily degradable source of carbon to the composting substrate is expected that more nitrogen will be metabolized, thus resulting in improved product quality, and less atmospheric emissions. The present study is one more step in the search for sustainable ways to recycle organic wastes.