Thomas D. Glanville

Laboratory scale evaluation of volatile organic compound emissions as indication of swine carcass degradation inside biosecure composting units.

Biosecure livestock mortality composting systems have been used to dispose of diseased livestock mortalities. In those types of system, visual inspection of carcass degradation is not possible and monitoring VOCs (volatile organic compounds) released by carcasses is a new approach to assess progress of the composting process. In this study, field-scale livestock mortality composting systems were simulated and a laboratory scale composting system with aerobic and anaerobic test units was designed to collect VOC samples from the headspace of decaying plant materials (70 g dry weight) and swine tissues (70 g dry weight) at controlled operating temperatures. Headspace samples were collected with SPME (solid phase microextraction) and analyzed by a GC-MS (gas chromatography-mass spectrometry) system. Among the 43 VOCs identified, dimethyl disulfide, dimethyl trisulfide, and pyrimidine were found to be marker compounds of the mortality composting process. These compounds were only found to be produced by decaying swine tissues but not produced by decaying plant materials. The highest marker VOC emissions were measured during the first three weeks, and VOCs were not detected after the 6th week of the process, which indicates degradation processes were completed and compost materials microbially stabilized (no additional VOC production). Results of respiration tests also showed that compost materials were stabilized. Results of this study can be useful for field-scale composting operations but more studies are needed to show the effects of size and aeration rate of the composting units.

Determination of thermal properties of composting bulking materials

Thermal properties of compost bulking materials affect temperature and biodegradation during the composting process. Well determined thermal properties of compost feedstocks will therefore contribute to practical thermodynamic approaches. Thermal conductivity, thermal diffusivity, and volumetric heat capacity of 12 compost bulking materials were determined in this study. Thermal properties were determined at varying bulk densities (1, 1.3, 1.7, 2.5, and 5 times uncompacted bulk density), particle sizes (ground and bulk), and water contents (0, 20, 50, 80% of water holding capacity and saturated condition). For the water content at 80% of water holding capacity, saw dust, soil compost blend, beef manure, and turkey litter showed the highest thermal conductivity (K) and volumetric heat capacity (C) (K: 0.12-0.81 W/m degrees C and C: 1.36-4.08 MJ/m(3) degrees C). Silage showed medium values at the same water content (K: 0.09-0.47 W/m degrees C and C: 0.93-3.09 MJ/m(3) degrees C). Wheat straw, oat straw, soybean straw, cornstalks, alfalfa hay, and wood shavings produced the lowest K and C values (K: 0.03-0.30 W/m degrees C and C: 0.26-3.45 MJ/m(3) degrees C). Thermal conductivity and volumetric heat capacity showed a linear relationship with moisture content and bulk density, while thermal diffusivity showed a nonlinear relationship. Since the water, air, and solid materials have their own specific thermal property values, thermal properties of compost bulking materials vary with the rate of those three components by changing water content, bulk density, and particle size. The degree of saturation was used to represent the interaction between volumes of water, air, and solids under the various combinations of moisture content, bulk density, and particle size. The first order regression models developed in this paper represent the relationship between degree of saturation and volumetric heat capacity (r=0.95-0.99) and thermal conductivity (r=0.84-0.99) well. Improved knowledge of the thermal properties of compost bulking materials can contribute to improved thermodynamic modeling and heat management of composting processes.

Environmental Effects of Applying Composted Organics to New Highway Embankments: Part 1. Interrill Runoff and Erosion

Construction of new highways can lead to challenges when attempting to re-establish vegetation on right-of-ways. Lack of vegetation can leave soil exposed and subject to increased runoff and soil erosion. Therefore, the Iowa Department of Transportation and the Iowa Department of Natural Resources sponsored a study to evaluate the use of composts applied as mulch blankets to decrease runoff and erosion. This article evaluates interrill runoff and erosion between three types of compost (biosolids, yard waste, and bio-industrial byproducts) and two soil conditions (existing compacted subsoil (control) and imported topsoil) on a 3:1 highway embankment. Composts were applied as 5 and 10 cm blankets on the surface of the control, and topsoil was placed on the surface of the control at a depth of 15 cm. Treatments were replicated six times over a two-year period for both bare soil and six weeks following planting of an Iowa DOT-specified cover crop. Rainfall was applied at an average intensity of 95 mm h-1 using a rainfall simulator, and sampling was conducted for 1 h after runoff began. All compost treatments were effective at reducing interrill erosion rates under the conditions simulated in this study. In addition, the three compost media required 30 min or longer to produce runoff, while the two conventional soils produced runoff within the first 8 min. The depth of compost application was only a factor for the runoff rate on unvegetated treatments. In this case, the 5 cm depth had a significantly greater runoff rate than the 10 cm depth. Both 5 and 10 cm compost applications had similar effects on interrill erosion rates. Although the steady-state interrill erosion rates of all three composts were 3% to 24% of the steady-state interrill erosion rates of the two soils on unvegetated treatments, and 0.1% to 30% of the steady-state interrill erosion rates of the two soils on vegetated treatments, the type of compost was also a factor in interrill erosion control. The yard waste compost was the coarsest of the three compost materials, and on unvegetated plots had a steady-state interrill erosion rate that was 17% and 33% of the steady-state interrill erosion rates of biosolids and bio-industrial compost, respectively. Interrill erodibility factors were calculated for all treatments and fell within the range of experimental rangeland values (10,000 to 2,000,000 kg sec/m4) that are used in the Water Erosion Prediction Project.

Environmental Effects of Applying Composted Organics to New Highway Embankments: Part 2. Water Quality

An oversupply of composted organics, and imposition of new federal regulations governing stormwater discharges from construction sites, motivated the Iowa Department of Natural Resources (IDNR), and the Iowa Department of Transportation (Iowa DOT) to sponsor a study of the potential water quality impacts of using compost to control runoff and erosion on highway construction sites. Test areas treated with 5 and 10 cm deep blankets (unincorporated) of three types of compost (biosolids, yard waste, and bio-industrial byproducts) were constructed on a new highway embankment with a 3:1 sideslope and subjected to simulated rainfall intensity of approximately 100 mm h-1. Concentrations and total masses of N, P, K, and nine metals in runoff from compost-treated areas were compared to those in runoff from embankment areas receiving two conventional runoff and erosion control methods typically used by the Iowa DOT (light tillage and seeding of native embankment soil, or application of 15 cm of imported topsoil followed by seeding). Simulations were replicated six times under both vegetated and unvegetated conditions, and the first hour of runoff was sampled to determine concentrations and total masses of soluble and adsorbed nutrient and metals. The applied composts generally contained much greater pollutant concentrations than either of the two soils used in the conventional treatments, and runoff from unvegetated plots treated with compost also contained significantly greater concentrations of soluble and adsorbed Zn, P, and K, and adsorbed Cr and Cu, than runoff from the two conventional treatments. In accordance with previously reported soil erosion research, runoff from all test plots was sampled periodically during the first hour of runoff. Due to their significantly greater infiltration capacity, however, compost-treated areas required significantly greater amounts of rainfall than conventionally treated areas to produce 1 h of runoff. In light of this significant difference in the amount of rain applied, the total mass of pollutants contained in runoff generated by equal amounts of rainfall was judged a more equitable basis for comparing the treatments. Runoff samples collected during the first 30 min of rainfall (equivalent to a 25-year return period storm at the applied intensity of 100 mm h-1) were used for this purpose, and the resulting total masses of individual quantifiable soluble and adsorbed contaminants in runoff from conventionally treated areas were at least 5 and 33 times, respectively, those in runoff from compost-treated areas. Based on these results, blanket applications of compost can be used to reduce runoff and erosion from construction sites without increasing nutrients and metals in stormwater runoff.

Air Sampling and Analysis Method for Volatile Organic Compounds (VOCs) Related to Field-Scale Mortality Composting Operations

In biosecure composting, animal mortalities are so completely isolated during the degradation process that visual inspection cannot be used to monitor progress or the process status. One novel approach is to monitor the volatile organic compounds (VOCs) released by decaying mortalities and to use them as biomarkers of the process status. A new method was developed to quantitatively analyze potential biomarkers--dimethyl disulfide, dimethyl trisulfide, pyrimidine, acetic acid, propanoic acid, 3-methylbutanoic acid, pentanoic acid, and hexanoic acid--from field-scale biosecure mortality composting units. This method was based on collection of air samples from the inside of biosecure composting units using portable pumps and solid phase microextraction (SPME). Among four SPME fiber coatings, 85 microm CAR/PDMS was shown to extract the greatest amount of target analytes during a 1 h sampling time. The calibration curves had high correlation coefficients, ranging from 96 to 99%. Differences between the theoretical concentrations and those estimated from the calibration curves ranged from 1.47 to 20.96%. Method detection limits of the biomarkers were between 11 pptv and 572 ppbv. The applicability of the prepared calibration curves was tested for air samples drawn from field-scale swine mortality composting test units. Results show that the prepared calibration curves were applicable to the concentration ranges of potential biomaker compounds in a biosecure animal mortality composting unit.

Environmental Impacts & Bio-security of Composting for Emergency Disposal of Livestock Mortalities

Carcass degradation rate, environmental impacts, and bio-security of windrow-type composting test units were monitored in replicated seasonal trials to assess the feasibility of using composting for emergency disposal of cattle and other large livestock carcasses. Internal temperatures were highest in test units constructed with corn silage. Test units constructed with ground cornstalks or straw and manure were generally 10-20 °C cooler. O2 concentrations in the core of ground cornstalk test units typically exceeded 15%, while those in corn silage and straw/manure test units were in the 5-10% range during the initial weeks of the trials. Despite differences in core temperature and O2 concentration, soft tissue degradation rates were the same in all test units, taking 4-6 months in units constructed during warm weather, and 8-10 months during cold-weather. It is believed that the less favorable (lower) temperatures in the cornstalks may have been offset by significantly higher O2 concentrations which favor rapid aerobic decomposition. Thirty to 45 cm of cover material proved effective in absorbing and retaining odorous gases and leachate. Odors samples collected from the surface of the mortality composting piles typically had low threshold values (< 1500) that differed little from odors emitted by stockpiles of the cover material alone. Leachate volumes were <2% of the precipitation falling on the test units, and preliminary analyses of 1.2 m soil cores show only slight increases in total C and N concentrations in the top 45 cm. Biosecurity tests indicated that pathogens were effectively retained and inactivated: vaccine strains of two avian viruses were inactivated in <21 days; and <2% of sentinel poultry located near the test units exhibited an immune system response to these viruses.

Field scale evaluation of volatile organic compound production inside biosecure swine mortality composts

Emergency mortality composting associated with a disease outbreak has special requirements to reduce the risks of pathogen survival and disease transmission. The most important requirements are to cover mortalities with biosecure barriers and avoid turning compost piles until the pathogens are inactivated. Temperature is the most commonly used parameter for assessing success of a biosecure composting process, but a decline in compost core temperature does not necessarily signify completion of the degradation process. In this study, gas concentrations of volatile organic compounds (VOCs) produced inside biosecure swine mortality composting units filled with six different cover/plant materials were monitored to test the state and completion of the process. Among the 55 compounds identified, dimethyl disulfide, dimethyl trisulfide, and pyrimidine were found to be marker compounds of the process. Temperature at the end of eight weeks was not found as an indicator of swine carcass degradation. However, gas concentrations of the marker compounds at the end of eight weeks were found to be related to carcass degradation. The highest gas concentrations of the marker compounds were measured for the test units with the lowest degradation (highest respiration rates). Dimethyl disulfide was found to be the most robust marker compound as it was detected from all composting units in the eighth week of the trial. Concentration of dimethyl disulfide decreased from a range of 290-4340 ppmv to 6-160 ppbv. Dimethyl trisulfide concentrations decreased to a range of below detection limit to 430 ppbv while pyrimidine concentrations decreased to a range of below detection limit to 13 ppbv.

Evaluation of the biodegradability of animal carcasses in passively aerated bio-secure composting system

Composting livestock carcasses is a viable method for on-site treatment and disposal. Properly estimated carcass biodegradability is valuable for designing and controlling animal mortality composting systems. However, it is still difficult to assess the biodegradability inside composts. In this study, approximately 250kg of swine carcasses were composted in each of nine 2m X 2m weighable composting test units using three different envelope materials: corn silage, ground cornstalks, and ground oat straw. Total weight of compost material was measured monthly to observe the carcass decomposition trend with composting time. The most significant weight loss occurred during the first 6 weeks of composting. Biodegradability of the swine carcasses was estimated by comparing the mass of carcass remains after 16 weeks composting with the total carcass weight placed in the pile during the time of construction. Based on these results the influence of envelope material type on the biodegradability of swine carcasses was evaluated. The carcass decomposition within silage test units was only 66% of the initial carcass mass, while carcasses in cornstalk and oat straw test units decomposed 86% and 79% respectively.

Cover Crop Production and Weed Control on Highway Right-of-Ways Using Composted Organics

Compost mulch has been compared with topsoil and subsoil as a media for crop growth and weed suppression during revegetation of highway right-of-ways. In this study compost was shown to be as effective as topsoil and subsoil controls for crop growth, while significantly reducing growth of weed species. There were no significant differences between 5 and 10 cm depths of compost application, indicating that the shallower depth would be adequate for most situations. Compost mulches offer promising opportunities for crop and weed management during revegetation of roadsides and other disturbed landscapes.

Impacts of Compost Application on Highway Construction Sites in Iowa

Runoff, interrill erosion, and growth of erosion control vegetation and weeds were measured on conventionally treated portions (control) of newly constructed roadway embankments, and on areas pretreated with topsoil or one of three different types of composted organics. Runoff rates and interrill erosion rates from the control and topsoil-treated plots were highest. Runoff rates from the three compost media (biosolids, yard waste, bio-industrial waste) used were statistically lower than the control. Runoff from plots treated with yard waste and bio-industrial waste composts were statistically lower from plots treated with topsoil. Interrill erosion rates from topsoil-treated plots were significantly higher than from compost-treated or control plots. The amounts of planted cover crop grown on all treatments were statistically indistinguishable. Mean values for weed growth on the control and topsoil plots are statistically indistinguishable, and all compost treatments except biosolids-10 cm and yard waste-5 cm produced significantly lower weed growth than either the topsoil or control plots.