Compost Science Complete scientific data on compost process control and end product quality

CURRENT RESEARCH

Compost Science & Utilization, (2008), Vol. 16, No. 2, 72

Materials and Methods
Quantifying water extractable contaminants from composted food waste and biosolids blends
Investigators: K.C. Das and J.T. Kirkland, Department of Biological and Agricultural Engineering, The University of Georgia, Athens, Georgia
Objectives: To report maximum water extractable nutrients, pathogens, and regulated metals from

biosolids and food waste composts as measured from a snapshot sampling of windrows at different stages of stabilization at a commercial operation at a single point in time. Results show that unstable composts released larger amounts of fecal 00form (13,100 to 19,000 Most Probable Number per g of sample, MPN g-1) than stable composts (6 to 7 MPN g-1). Maximum water extractable C was 4690 and 5990 mg kg-1 in food waste and biosolids composts, respectively. In both composts, extractable amounts of C decreased with increased stability of compost, but was not so for extractable N or P. Significantly greater P was extractable from food waste (9.7 to 12.5% of total P) than biosolids composts (2.8 to 3.9%). Heavy metal extractability was highest for Ni (5.3 to 13.4% of total present) and Cd (8.5 to 29%). Since rainfall runoff and leachate from windrows composting organic wastes carry nutrients and pathogen, it is important to assess water extractability of contaminants in compost, which impacts the design of runoff treatment systems.

Compost Curing Reduces Suppression of Plant Diseases
Investigators: Sharon Zmora-Nahum, Yona Chen, Department of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot, The Hebrew University of Jerusalem, Israel; Michael Danon, Yitzhak Hadar, Department of Plant Pathology and Microbiology, Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot. The Hebrew University of Jerusalem, Israel
Objectives: To demonstrate that similar effects of prolonged curing may be exhibited by additional types of composts and pathosystems, following a previous study that demonstrated prolonged curing of compost reduces risks of phytotoxicity, but may also have an undesirable effect on suppressiveness against soil-borne diseases. In this previous study, this was demonstrated for a compost produced from a mixture of yard waste and biosolids, against Sclerotium rolfsii. Therefore, the effect of curing of three types of composts against S. rolfsii and Pythium aphanidermatum were investigated. These plant pathogens were subjected to different suppression mechanisms. The prolonged curing was characterized and validated by measurements of a range of chemical and spectroscopic parameters. All three composts from different source materials were suppressive against both diseases before curing. At high inoculum levels, suppression against P. aphanidermatum was lost for the cured biosolids and straw and manure based compost. Loss of suppression was associated with a decrease in basal and substrate induced respiration. For S. rolfsii suppression was lost with curing for all three composts and was associated with a decrease in dissolved organic carbon and NH4+ concentration, a decrease in pH and an increase in NO3- concentration.

Soil Improvement
Emission Of N2O From Polycyclic Aromatic Hydrocarbons (PAHs) Contaminated Soil
Investigators: Dioselina Álvarez-Bernal, Silvia M. Contreras-Ramos, Joaquín A. Montes-Molina and Oswald Luc Dendooven, Laboratory of Soil Ecology, Dept. Biotechnology and Bioengineering, Instituto Politécnico Nacional, México; Van Cleemput, Faculty of Bioscience Engineering, Laboratory of Applied Physical Chemistry-ISOFYS, Ghent University, Gent, Belgium
Objectives: Addition of vermicompost increased production of CO2 and N2O. Addition of PAHs increased production of CO2 when water content of soil at 60%WHC and production of N2O when water content of soil at 80%WHC. Addition of PAHs induced immobilization of inorganic N and inhibited nitrification as the concentration of NH4+ and NO2- in soil contaminated with PAHs was larger than in unamended soil while the concentration of NO3- was lower. It was found that contamination of soil with PAHs increased emissions of N2O and CO2 and biostimulation of autochthonous microflora with organic material to remediate those soils further increases production of N2O and CO2. These findings indicate that trace gas emissions should be included in estimations of the environmental impact of contamination of soil and their subsequent bioremediation.

Relative Efficiency Of Substrates In Raising Earthworms
Investigators: D. Chakrabarty, Department of Zoology, Krishnagar Government College, Krishnagar, Nadia, India, S. K. Das, Waste Management Cell, West Bengal Pollution Control Board, Kolkata, India; M. K. Das, Department of Zoology, Krishnagar Government College, Krishnagar, Nadia, India.
Objectives: 300 adult healthy earthworms (Eudrillus euginae) of (weight 1.6-3.0 g, mean 2.55±1.1 g; length 14-29 cm, mean 21.5±6.8 cm) were cultured in three different substrates for 70 days. The substrates were soil alone (control) [T-1], cow dung and water hyacinth (1:1) [T-2] and partially dried neem leaves with kitchen waste (1:1) [T-3]. The earthworms were subjected to monitoring for various growth patterns (length, biomass, number) at fortnightly (5 observations) interval. The observation showed that T-2 was the best among the three treatments employed.