Carcass Composting for Management of Farm Mortalities: A Review

For the last two decades, carcass disposal by burial is being replaced with alternatives such as composting. Improper animal mortality disposal may generate various environmental and health hazards such as odor nuisance (resulting from the anaerobic breakdown of proteins) that can reduce the quality of life and decrease property values. Pathogens, which may still be present in the decomposed material, are capable of spreading diseases in soil, plants, animals and humans. The potential leaching of harmful nitrogen and sulfur compounds from animal mortalities to ground water is another concern. To control these side effects, compost facility operators need to know and understand the science and guidelines of carcass composting. While basic principles of carcass composting are similar to those for composting of organic materials, its management issues, including appropriate composting methods for large or small scale carcass composting, quantities and types of carbon sources, composting time, odor and leachate control, and equipment requirements differ from composting of organics. The purpose of this study is to review the previous works related to carcass composting and provide information on recent advances in small and large-scale carcass composting enabling higher decomposition rates, minimum usage of carbon source materials, easier and shorter management control strategies and reduced land requirement while producing a useful end product and avoiding negative impact on public safety and environmental parameters.     

Environmental Impacts of Farm-Scale Composting Practices

Because of its agronomic benefits, farm-scale composting is an efficient means of recycling agricultural waste. Composting process is an aerobic degradation of fresh organic matter in mature compost. Nevertheless, according to the literature, composting may induce some environmental problems. The environmental impacts of composting will be described, along with an assessment of farm-scale composting practices which play a major role in pollution. The main environmental components potentially affected by composting pollution are air and water. Various gases released by composting, such as NH₃, CH₄ and N₂O, can impact air quality and are therefore studied because they all have environmental impacts and can be controlled by composting management. The effect on water quality can be evaluated by considering loss of NO₃ ^-, NH₄ ⁺, organic compounds and PO₄ ^3-. Technical evaluation criteria for the impact of farm-scale composting on the air are determined from the physical and chemical characteristics of the raw materials, the use of additives, the turning method and frequency and the duration of the composting operations. Regarding water, the weather conditions at the beginning of the composting operation, the location of the heap, the protection against rain, the water addition during the process, the use of covers and the recovery of leaching and runoff water are also taken into account. The two main practices which control the air and water pollution from composting are: the choice of the raw material which influences gas emissions and the choice of composting location which have an high effect on losses by leaching and runoff.     

外源微生物对堆肥理化性质及酶活影响的研究

利用牛粪和稻草为原料进行堆肥实验,通过测定堆肥过程中的温度、含水率等物理、化学指标以及酶活性的变化,研究了接种外源微生物对堆肥过程的影响。结果表明,接种外源微生物比对照提前2d达到高温期,并且维持时间长。大肠杆菌数量及植物毒性比不接种大幅度降低,纤维素酶、脲酶、多酚氧化酶、过氧化氢酶均有所增加。说明接种外源微生物可以使堆肥中微生物数量增多,加速堆料中有机物的分解,加快堆肥腐熟,缩短堆肥反应的进程,对优化堆肥工艺具有重要的意义。     

Passively Aerated Composting of Straw-Rich Pig Manure: Effect of Compost Bed Porosity

Straw-rich manure from organic pig farming systems can be composted in passively aerated systems as the high application of straw results in a compost bed with good structure and porosity. The passively aerated composting process was simulated in one-dimensional reactors of 2 m³ for straw-rich manure with compost bed densities of 1100, 700 and 560 kg m^?3. Temperature profiles over the reactor height were monitored online and ammonia emissions were measured periodically. The composition of the compost bed over the reactor height was determined at the end of the composting process. The composting process strongly depends on the density of the compost bed. At a density of 1100 kg.m^?3, the porosity of the bed is too low to initiate natural convection, and aerobic degradation fails and anaerobic conditions may lead to emissions of methane and odorous compounds. At a density of 560 kg.m^?3, the porosity of the bed is high and the high rate of natural convection will keep the temperature low thereby preventing the removal of pathogens and weeds. Best results were observed at a density of 700 kg.m^?3 for which aerobic degradation and drying were adequate and temperatures were high enough to kill pathogens and weeds. On basis of the Ergun equation, which describes the airflow in porous media with internal heat generation, this corresponds to a compost bed permeability of 7×10^?8 m². It was also shown that it is possible to compost animal manures with a low C/N ratio without significant emissions of ammonia. This can be established by trapping the initial ammonia emissions in a straw filter, which is placed on top of the compost bed. Ammonia absorbed in the straw filter and in the compost bed were removed by nitrification and denitrification. The passively aerated composting system results in a compost bed which is highly heterogeneous with respect to temperature, oxygen level and its composition. It is proposed that in this way a highly diverse microbial community in the compost bed is established which can perform various microbial conversions. The extensive composting system is most promising for on-farm production of an organic fertilizer from straw-rich manure, since the costs of the process and the level of ammonia emissions were low.     

基于温度-时间的好氧堆肥通风控制系统的设计与运行效果

通风控制是强制通风静态好氧堆肥系统的技术关键。本研究开发了基于温度-时间的工业控制计算机好氧堆肥通风控制系统(TTime)，并实现了软硬件的配套。该文详细阐述了系统的设计思路、研究方法、功能和实现过程。运行试验表明，系统运行稳定、可靠，能保证堆肥过程的顺利进行，同时，加强了畜禽场废弃物堆肥过程的在线监控，降低了堆肥系统的运行费用，适合在大中型畜禽场推广应用。     

基于NIRS和Local PLS算法的堆肥关键参数实时动态分析

为对不同堆肥工艺堆肥全过程关键参数进行实时动态分析,该研究以牛粪便和玉米秸秆为原料,进行规模化槽式和膜覆盖好氧堆肥,采集堆肥全过程样本,分析了2种堆肥技术堆肥全过程中含水率、有机质含量和碳氮比等关键参数的变化,并结合Local PLS算法建立了2种堆肥技术堆肥全过程中上述参数的通用速测模型,得出以下结果:1)2种主要工艺关键参数数值及变化规律均不同,且在整个堆肥过程中有显著性变化(P0.05);2)所建立的Local PLS模型的RPD(Ratio of Prediction to Deviation)为4.47,RSD(Relative Standard Deviation)为3.37%,可达到很好的预测效果;有机质含量和碳氮比的R_P~2分别为0.74和0.77,RPD大于1.5,RSD小于10%,模型可用于定量预测;近红外预测值与实测值随堆肥时间的变化趋势具有较好的一致性,可实现规模化堆肥过程中关键参数的实时分析。     

Operational Parameters for Composting Night Soil in Korea

Recently composting of organic wastes started to gain popularity in Korea. The purpose of this study was to investigate the effect of operational parameters on night soil composting. Operational parameters investigated included compost recycle ratio and temperature control. Lab-scale composting reactors were used in this study. At the recycle ratio of 10 percent, reduction of both volatile solids and moisture content was greater than that at the recycle ratio of 0 percent and 30 percent. This result means that composting reaction was the most active at 10 percent recycle ratio. Temperature control played a important role in the night soil composting process. The greatest decrease in volatile solids was observed when the temperature of composting process was set below 60°C. Also, the amount of CO₂ evolved was the greatest when the maximum temperature was set below 60°C. Kinetic study indicated that first order kinetics described volatile solids reduction very well.     

Factors Affecting Air Pycnometer Performance For its Use in the Composting Process

Air filled porosity (AFP) is a crucial factor in composting to guarantee aerobic conditions inside the composting matrix. Among the different methods proposed to measure AFP in composting processes, air pycnometry is defined as the most adequate. There is a lack of a standard methodology for air pycnometry utilization for AFP determination in heterogeneous samples as those from composting materials. Air pycnometers currently used for this purpose are custom made instruments operating under different conditions (sample volume, initial pressure, etc.). All factors affecting air pycnometry accuracy in the composting process are related to the proper maintenance and handling of the air pycnometer and the composting sample. In this study, AFP measurements have been performed in more than 50 samples of a wide range of composting materials using two different custom made pycnometers, one of them coupled to a composting reactor allowing in situ AFP measurement. While temperature variation during AFP measurement has been discarded as an error source, the determination of the sample volume has been found to be a significant factor affecting the air filled porosity calculation. Regarding the initial pressure to use, a compromise between accuracy and practicality has to be established for each pycnometer design as AFP values obtained with diverse initial pressures (from 200 to 500 kPa gauge pressure) were found to present no statistical differences. An initial pressure in the range of 300-500 kPa (gauge pressure) is recommended. In conclusion, there is a need for a standard methodology for AFP determination or prediction at industrial scale. A complete procedure for air filled porosity determination by air pycnometry is also presented in this work.     

A Preliminary Comparative Study of Three Manure Composting Systems and their Influence on Process Parameters and Methane Emissions

Three cattle manure composting systems — windrowing, forced aeration with temperature feedback control and simple minimal intervention (manure stacks — “passive composting”) were compared with respect to specifically selected and operationally important process parameters including dry matter, moisture and volatile solids losses, volume reduction and bulk density changes. The windrowing method proved to be the most effective with respect to the above parameters. Preliminary investigations of methane from the three systems during processing showed that the minimal intervention method produced high levels of methane (> 4 percent) in the waste matrix. The intervention methods, of windrowing or forced aeration, drastically reduced methane output. The importance of animal manures in global agriculture, with reference to methane emissions and global warming, is briefly reviewed. The widespread reliance of manure disposal by the use of simple stacks, sometimes erroneously elevated to a processing status by use of the term “passive composting”, is questioned on ecological and environmental grounds. The data from this preliminary study shows the enormous impact that simple windrowing techniques can achieve in terms of organic waste conversion and product quality, concomittant with ecologically acceptable treatment routes.     

Developing nutrient profile models: a systematic approach

OBJECTIVE: Nutrient profiling can be defined as the 'the science of categorising foods according to their nutritional composition'. The purpose of the present paper is to describe a systematic and logical approach to nutrient profiling. DESIGN: A seven-stage decision-making process is proposed and, as an illustration of how the approach might operate in practice, the development of a nutrient profiling model for the purpose of highlighting breakfast cereals that are 'high in fat, sugar or salt' is described. RESULTS: The nutrient profile model developed for this paper calculates scores for foods using a simple equation. It enables breakfast cereals to be compared with each other and with other foods eaten at breakfast. CONCLUSION: Nutrient profiling is not new, but hitherto most nutrient profiling models have been developed in an unsystematic and illogical fashion. Different nutrient profiling models are needed for different purposes but a key requirement should be that they are developed using a systematic, transparent and logical process. This paper provides an example of such a process; approaches to validating nutrient profiling models are described elsewhere.     

A Quantitative Respirometric Method for Monitoring Compost Stability

Compost stability was quantified using dissolved oxygen (D. O.) respirometry during composting of municipal solid waste (MSW) in a pilot-scale system. Changes in stability of samples taken at various times during the composting process were verified with chemical and physical tests. Rates of change of oxygen level in air over a compost sample incubated in a flask at 37°C were converted to a rate of O₂ uptake/(g volatile solids · hour). Oxygen uptake, determined with D. O. respirometry and converted to rates of dry matter loss, was correlated with actual rates, calculated from energy balances observed in the pilot-scale system. The method can be used either as a simple quality control measure or in a more complex way to calculate rates so that efficiency within or among composting facilities can be compared.     

Greenhouse gas accounting for landfill diversion of food scraps and yard waste

Diverting organics from landfills to compost piles is generally recognized as a means to reduce greenhouse gas emissions. This article provides a detailed review of the Climate Action Reserve (CAR) and the U.S. EPA Waste Reduction Model (WARM) protocols on landfill diversion and composting for food scraps and yard waste. The primary benefits associated with diversion are methane avoidance. The equations used to quantify methane avoidance include first-order decay rate constants for different feedstocks to predict how quickly organics will decay. The total methane generation potential of the different feedstocks is also included. The equations include estimates of gas collection efficiencies in landfills. The decay rate constants have been determined from laboratory incubations and may not be representative of decomposition within a landfill. Estimates of gas capture efficiency have been improved and more closely reflect actual landfill conditions. Gas capture efficiency will vary based on landfill cover material, portion of the landfill where measurements take place, and whether the gas collection system is operational. Emissions during composting are included in these calculations. Only the WARM model includes a consideration of benefits for compost use. Nevertheless, significant benefits are recognized for landfill diversion of food scraps. The WARM model suggests that landfilling yard waste is superior to composting.     

Chemical Amendments and Process Controls To Reduce Ammonia Volatilization During In-House Composting

Composting inside high-rise, caged layer facilities can produce atmospheric ammonia (NH₃) concentrations exceeding standards for human and poultry health. Control measures that reduce NH₃ volatilization are necessary for in-house composting to be sustainable. Due to differences specific to in-house composting — low carbon to nitrogen ratios of composting material, continuous manure addition, and frequent turning — it is not known whether NH₃ control measures used previously for poultry manure will work. The objectives of this study were to evaluate various amendment and process controls on NH₃ produced during simulated in-house composting in the lab, and to evaluate select chemical control measures during composting inside a high-rise layer facility. Ten amendments (aluminum sulfate; chloride salts of aluminum, calcium, magnesium, and potassium; gypsum; sodium bisulfate; zeolite (clinoptilolite); straw; and cellulose) and four process controls (moisture; temperature; turning frequency; and particle size) were evaluated in lab incubations in 1 L vessels wherein samples of poultry manure compost were incubated to simulate composting. Vials of boric acid solution were used to capture NH₃ evolved during incubations. With the exception of zeolite and cellulose, all amendments reduced NH₃ capture. Low moisture and temperature also reduced NH₃ capture, although managing temperature and moisture to achieve low NH_g would adversely impact microbial activity and other desired benefits of composting. When evaluated inhouse, aluminum sulfate, calcium chloride and magnesium chloride did not reduce NH evolution from compost measured on three different dates with a gas sensor. Spatial variability along treated segments of windrow apparently masked amendment effects. At the end of a six-week composting cycle, total nitrogen content was higher in compost treated with aluminum sulfate than control or chloride salt treatments. Aluminum sulfate and process controls such as moisture content, carbon source and particle size have potential to reduce NH₃ loss from poultry manure composted inside high-rise layer structures. In-house compost management to reduce NH₃ volatilization must consider the cost of amendments, effectiveness, and impacts on the composting process.     

The Potential for Bioremediation of Soils Containing PAHs by Composting

? Environmental contamination by synthetic polynuclear aromatic hydrocarbons (PAHs) has become a major pollution problem. Plant tissues, lignin, soil humus constituents, some pesticides, and numerous commercial organic chemicals are also based upon aromatic building blocks. Many of these molecules are potentially toxic and carcinogenic. Some PAH compounds occur naturally at a low concentration in soils. Long exposure to naturally occurring hydrocarbons has enabled bacteria to evolve enzymes that degrade them.

Landfarming and incineration are the primary technologies used for removing PAH compounds from soils and groundwater. Recent data suggest that bioremediation by PAH composting can offer significant advantages to other treatment alternatives. Landfarming is a relatively uncontrolled method of reducing PAHs in residues. Composting is quicker, more controlled, and requires less space than landfarming. Although composting is slower and less complete than incineration, it is significantly more cost-effective.

This presentation deals with the feasibility of composting PAH contaminated soils and residues. Included will be methods for process evaluation and control, degradation potential of specific PAHs, and determining the application of composting to specific situations.     

Moisture Relationships in Composting Processes

Moisture is a key environmental factor that affects many aspects of the composting process. Biodegradation kinetics are affected by moisture through changes in oxygen diffusion, water potential and water activity, and microbial growth rates. These relationships are made more complex by the dynamic nature of the composting process, with changes in particle size and structure occurring over time. A deductive model of the effects of moisture on composting kinetics has defined these relationships based on fundamental physical properties and biological mechanisms. This study applies this model to experimental data from a manure and papermill sludge composting system. The results demonstrate that the optimum moisture content for biodegradation can vary widely for different compost mixtures and times in the composting process, ranging from near 50 to over 70% on a wet basis. While there is a significant reduction in biodegradation rate when operating outside the optimum range, the results also suggest opportunities to mitigate this effect through manipulation of substrate density and particle size. This framework for engineering analysis demonstrates the importance and challenges of maintaining optimum moisture content in dynamic composting systems, where biological drying, metabolic water production, and changes in compaction and porosity are all occurring over time.     

风干预处理对堆肥腐熟度及臭气排放量的影响

该研究以风干猪粪堆肥为处理,以新鲜猪粪堆肥为对照,在秸秆调理相同C/N基础上,对两个处理腐熟度和臭气排放进行比较分析。从温度、p H值、电导率和发芽率来看,利用新鲜猪粪和风干猪粪堆肥所得的产品均能达到腐熟和无害化标准;在硫化氢、羰基硫、二硫化碳、甲硫醚、乙硫醚、二甲二硫、甲硫醇和乙硫醇几种含硫臭气中,甲硫醚和二甲二硫占96%以上;风干猪粪堆肥比新鲜猪粪堆肥少排放71.09%的氨气,66.11%的甲硫醚和9.66%的二甲二硫。在不考虑风干环节存在的问题条件下,与新鲜猪粪堆肥相比,风干猪粪堆肥堆肥时间短,在堆肥品质提高的基础上,堆肥产品产量增加60%。通过降低水分和体积风干猪粪运输成本降低1/3,且对环境影响小,是远距离资源化处理畜禽粪便的较好途径。     

城市生活垃圾堆肥过程中腐熟度指标及控制参数

以日处理400 t经马家楼筛分处理后的15～60 mm生活垃圾的北京南宫堆肥厂垃圾堆肥过程为研究对象,对堆肥过程中垃圾的理化性质、腐熟度指标与控制参数进行了研究。结果表明,堆肥过程中水分含量是下降的;不同季节堆肥pH值的总体变化均呈上升趋势;电导率(EC)降到了作物受抑制的限定值以下,不会对作物产生盐分毒害;堆肥水浸提的腐殖酸E₄/E₆值随着垃圾堆肥腐熟度升高呈增加趋势;24 h和96 h的发芽率指数(GI)表明垃圾堆肥时间可以从8周缩短到5周;有机碳、总氮和C/N比随着堆肥时间的增加均呈下降趋势;C/N比与E₄/E₆值和GI(24 h和96 h)值呈显著负相关关系,EC值与E₄/E₆值和GI(24 h和96 h)值呈极显著负相关,而E₄/E₆值与GI(24 h和96 h)值呈极显著正相关。     

A Method for Determining the Ultimate Fate of Synthetic Chemicals during Composting

? Pollution control workers have proposed composting as a bioremediation method for the cleanup of contaminated soil and for the detoxification of hazardous organic chemicals. However, decomposition (mineralization to CO₂ and H₂O) may not always be enhanced by composting, and transformation products of unknown risk may accumulate during composting. This paper presents a scientifically based scheme to determine the ultimate fate of synthetic materials in a composting environment, and for studying factors that may control the degradation of specific chemicals including herbicides (e.g., substrate bioavailability, enzyme concentrations, environmental conditions).     

MSW Compost Reduces Nitrogen Volatilization During Dairy Manure Composting

Manures lose N through volatilization almost immediately after deposit. Attempts to control losses include the addition of a C source to stimulate nitrogen immobilization. Composting is a treatment process that recommends the addition of carbonaceous materials to achieve a C:N ratio of 30:1 to stimulate degradation and immobilize nitrogen. Dairies near cities may be able to reduce N loss from manures by composting with urban carbonaceous residues such as municipal solid waste (MSW) or MSW compost that, by themselves, have little agronomic value. Studies were conducted using a self-heating laboratory composter where dairy solids were mixed with MSW compost to determine the reduction of N loss during composting. One-to-one mixtures (v/v) of dairy manure solids and MSW compost were composted and NH₃ volatilization, CO₂ evolution and temperatures were compared to composting of manure alone. Addition of MSW compost resulted in increased CO₂ evolution and reduced N loss. Nitrogen loss from composting dairy manure alone was four to ten times greater than that from composting dairy manure mixed with MSW compost. Adjustment of the C:N ratio to 25 by adding MSW compost to manure appeared to be the major factor in reducing N losses.     

Using a Biocell to Measure Effect of Compressive Settlement on Free Air Space and Microbial Activity In Windrow Composting

This paper describes the first equipment developed to include compressive loads in a physical model of the composting environment. This new type of composting reactor was named a biological load cell, or biocell for short. Our hypothesis was that the exclusion of compressive settlement in existing physical models may lead to errors if the data is used to design full-scale windrow composting facilities. Municipal biosolids were mixed with three organic amendments (wood chips, straw, and leaves) to yield mixture moisture contents of 55%. Compressive settlement analyses were completed by subjecting the mixtures to loads of 0, 4.3, 8.6, and 12.9 kPa using biocells. The effect of compressive settlement on microbial activity was investigated using the biosolids:leaf mixture under loaded (12.9 kPa) and unloaded conditions. The settlement behavior of all three mixtures was found to fit established soil compaction equations and new equations were developed to represent the vertical free air space (FAS) and bulk density profiles in composting systems. The FAS profiles indicated that existing physical models do not simulate the FAS conditions within a composting matrix and significant differences in microbial activity were observed between loaded and unloaded biocells. The microbial activity differences were attributed to the reduced FAS within the loaded biocells, which, in consequence, lead to lower pore space oxygen concentrations. It proved difficult, however, to simulate the air flow regime within a windrow composting matrix. To further develop the biocells, there is a need to investigate the in-situ stress conditions and natural draft ventilation rates of full-scale windrow systems. While further work is required to perfect the biocells as a physical model of the windrow composting environment, it has demonstrated its potential use for FAS analysis and as a standard bulk density apparatus. Using biocells, it is recommended that FAS curves be developed for a wide range of feedstock recipes. The biocell apparatus could also be developed as a standard bulk density test apparatus. Other important conclusions drawn from the work include: leaves should not be used as a bulking agent; wood chips showed superior bulking properties and are recommended for use in very high (3.7 m) windrows; straw showed intermediate bulking properties and should not be used for high windrows without further investigation; for all materials, compaction occurred rapidly after each incremental load, suggesting that windrow turning will do little to alleviate a low FAS problem associated with an incorrect composting recipe.