PB389 Integrated Solid Waste Management Numfon Eaktasang, Ph.D. Thammasat University

Solid Waste Management generation Waste reduction and separation at the source Collection Transportation Separation, processing & transformation Disposal

Disposal Technology Dumping on land Burial Hog feeding Incineration Sanitary landfill Composting Biogas

What is composting? Compost Using the natural process of decay to change organic wastes into a valuable humus-like material called compost Compost

Biological conversion processes Major objectives of biological conversion processes = conversion of the organic matter in the waste to a stable end product Chemoheterotrophic organisms are of primary importance use organic compounds both energy and carbon sources Nutrients usually rich in MSW may need to be added in some commercial wastes Nitrogen

Types of Microorganisms Primary importance in biological conversion of the organic fraction of solid wastes Procaryotic groups (eubacteria and archaebacteria) generally referred to simply as bacteria Eucaryotes group fungi yeasts actinomycetes

Types of Microorganisms Bacteria found in aerobic and anaerobic environments wide variety of inorganic and organic compounds can be used

Types of Microorganisms Fungi ability to grow under low-moisture conditions tolerate relatively low pH optimum around 5.6, but the viable range is from 2 to 9 aerobic metabolism long filaments ability to degrade a wide variety of organic compounds

Types of Microorganisms Yeasts fungi that can not form filaments and are unicellular Actinomycetes intermediate properties between bacteria and fungi similar in form to fungi

Environmental requirements Temperature one of the important factor for survival and growth of microorganisms optimum growth condition occurs within a fairy narrow range can survive within much broader limits growth rates double with approximately every 10 degree-C increase until the optimum temperature is reached. Some typical temperature ranges for various bacteria Temperature, degree-C Type Range Optimum Psychrophilic Mesophilic Thermophilic -10 – 30 20 – 50 45 – 75 15 35 55

Types of biological transformations Aerobic process Organic matter + O2 + Nutrients  new cells + resistant organic matter + CO2 + H2O + NH3 + SO42- + ... + heat Anaerobic process Organic matter + H2O + Nutrients  new cells + resistant organic matter + CO2 + CH4 + NH3 + H2S + heat

Anaerobic biological transformations Lipids Polysaccharaides Protein Nucleic acids Hydrolysis Fatty acids Amino acids Purines & Pyrimidines Simple aromatics Monosaccharides Acidogenesis Other fermentation products (e.g. propionate, butyrate succinate, lactate ethanol) Methanogenic substrates H2, CO2, formate, methanol, methylamines, acetate Methanogenesis Methane + carbon dioxide Pathways leading to the production of methane and CO2 from the anaerobic digestion

Biological process selection Comparison of aerobic composting and anaerobic digestion processes for processing organic fraction of MSW Characteristic Aerobic processes Anaerobic processes Energy use Net energy user Net energy producer End products Humus, CO2, H2O Sludge, CO2, CH4 Volume reduction up to 50% Processing time 20 to 30 days 20 to 40 days Primary goal Energy production Secondary goal Compost production Waste stabilization Operation Relatively simple Relatively complex

Aerobic composting Aerobic composting Process description most commonly used biological process Application to yard waste, separated MSW, commingled MSW, and co-composting with wastewater sludge Process description 3 processes: preprocessing: removing contaminants, adjusting moisture content, C/N ratio aerobic decomposition product preparation and marketing: may include fine grinding, screening, air classification, blending with various additives, granulation, bagging, storage, shipping.

Aerobic composting Thermophilic Mesophilic Cooling Maturing

Aerobic composting Important process variables Composting techniques particle size and its distribution, seeding and mixing requirements, the required mixing/turning schedule, total oxygen requirements, moisture content, temperature and its control, carbon-nitrogen ratio, pH, degree of decomposition, respiratory quotient (RQ), and control of pathogens Composting techniques Agitated: the material to be composted is agitated periodically to introduce oxygen, to control the temperature, and to mix the material to obtain a more uniform product. Static: the material to be composted remains static and air is blown through the composting material.

Types of composting Windrow composting Aerated static pile composting In-vessel composting

Windrow composting Windrow composting One of the oldest methods Simplest form 8 to 10 ft high and 20 to 25 ft wide turned once per year need 3 to 5 years for complete degradation may cause odor problem High-rate form typically 6 to 7 ft high and 14 to 16 ft wide depend on type of equipment used to turn processed by shredding and screening to 1 to 3 inch Adjusted to 50 to 60 % of moisture content turned twice per week for 3 to 4 weeks after turning period, 3 or 4 weeks curing period without turning to allow further reduction of decomposable materials by fungi and actnomycetes keep temperature around 55 degree-C

Windrow composting

Aerated static pile composting similar to passively aerated windrows, force air into pile using pipes with blowers. allows for large piles and turning in not required.

Aerated static pile composting typically 2 to 2.5m height Air is introduced to provide the oxygen needed and to control the temperature within the pile Layer of screened compost: for insulation and odor control Material is composed for 3 to 4 weeks, followed by curing period Bulking agent: wood chips for dewatered wastewater treatment plant sludge to maintain the porosity of the composting material to absorb excess moisture

Aerated static pile composting

In-vessel composting In-vessel Confine composting materials within building, container, or vessel. Forced aeration and mechanical turning techniques are used to speed the process

In-vessel composting In-vessel composting Other composting systems accomplished inside an enclosed container or vessel Two major categories Plug flow: first-in first-out principle dynamic (agitated bed): mixed mechanically 1 to 2 weeks for detention time total system needs 4 to 12 weeks for whole process Popularity increase recently Easiness of process and odor control faster throughput and smaller area requirements lower labor costs Other composting systems Developed many composting systems and used in commercial basis

In-vessel composting

In-vessel composting

Aerobic composting Design and operational considerations Particle size Carbon to Nitrogen ratio (C/N ratio) Blending and seeding moisture content Mixing/turning Temperature Control of pathogens Air requirements pH control Degree of decomposition Land requirement

Aerobic composting Particle size C/N ratio influences the bulk density, internal frictions and flow characteristics Reduction of particle size increase the biochemical reaction rate should be between 25 and 75 mm C/N ratio Initial carbon to nitrogen ratios between 25 and 50. lower ratio: Release or inhibition of ammonia higher ratio: lack of nitrogen as a nutrient

Material Percent N C/N ratio Food processing wastes Fruit wastes Mixed slaughterhouse waste Manures Cow manure Pig manure Sludge Digested activated sludge Raw activated sludge Wood and straw Sawdust Wheat straw Wood (pine) Paper Mixed paper Newsprint Yard wastes Grass clippings Leaves Biomass Water hyacinth 1.52 7.0-10.0 1.7 3.75 1.88 5.6 0.10 0.3 0.07 0.25 0.05 2.15 0.5-1.0 1.96 34.8 2.0 18.0 20.0 15.7 6.3 200-500 128 723 173 983 20.1 40-80 20.9 Aerobic composting Nitrogen content and nominal C/N ratios of selected compostable materials (dry basis)

Aerobic composting Blending and seeding Moisture content Blending based on C/N ratio and moisture content Seeding involves the addition of a volume of microbial culture sufficiently large to effect the decomposition of the receiving material at a faster rate Moisture content should be between 50 and 60 Mixing/turning to prevent drying, caking and air channeling to achieve more uniform distribution of nutrients and microorganisms

Aerobic composting Temperature 50 to 55 degree C for first few days, 55 to 60 degree C in the remainder of the active composting period controlled by airflow turning frequency

Aerobic composting Control of pathogens Air requirements pH control Between 60 and 70 degree C for 24 hours are required to kill all the pathogens Required temperature and time is different in each pathogen Air requirements can estimate the theoretical quantity of oxygen required Air with at least 50 % of the initial oxygen concentration remaining should reach all parts of the composting material pH control should remain at 7 to 7.5 range should not rise above about 8.5 to avoid ammonia gas release.

Aerobic composting Degree of decomposition Control of odor can be estimated by measuring the final drop in temperature, degree of self heating capacity, amount of decomposable and resistant organic matter in the composted material, rise in the redox potential, oxygen uptake, growth of the fungus Chaetomium gracilis, starch-iodine test Control of odor mainly caused by organic acids, generated in a partially anaerobic condition enough oxygen supply, reduction of particle size, remove nonbiodegradable materials Land requirements 1.5 to 2.0 acres for 50 ton/d capacity

Aerobic composting Comparison of aerobic composting processes Item Windrow Aerated static pile In-vessel, forced aeration With agitation (dynamic) No agitation (plug flow) Capital costs Generally low Generally low in small systems, can become high in large systems Generally high Operating costs High (in sludge digestion) Land requirements High Low, but can increase if windrow drying or cutting required Control of air Limited unless forced aeration is used Complete Operational control Turning frequency, amendment, or compost recycle addition Airflow rate Airflow rate, agitation, amendment, or compost recycle addition Airflow rate, amendment, or compost recycle addition

Aerobic composting Comparison of aerobic composting processes, contd. Item Windrow Aerated static pile In-vessel, forced aeration With agitation (dynamic) No agitation (plug flow) Sensitivity to cold or wet weather Sensitivity unless in housing Demonstrated in cold and wet climates Control of odors Depends on feedstock, potential large-area source May be large-area source but can be controlled Potentially good Potential operating problems Susceptible to adverse weather Control of airflow rate is critical, potential for channeling or short-circuiting air supply High operational flexibility, system may be mechanically complex Potential for channeling or short circuiting of air supply, system may be mechanically complex

Aerobic composting Issues in the implementation of composting facilities Odor every existing facility has had an odor event facility siting, process design and biological odor management are of critical importance. Presence of pathogens Presence of heavy metals Contamination in shredding process Definition of what constitutes an acceptable compost

Composting of cow manure in Japan

Composting area in TU

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