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

Current Research Projects

Compost Science & Utilization, (2009), Vol. 17, No. 4, 208
Materials and Methods

Impact of contaminants on potentially toxic element content of MSW compost
Investigators: Daryl McCartney, Weixing Chen, Shouhai Yu, Lixian Zhou, Department of Civil & Environmental Engineering, University of Alberta; Salim Abboud, Alberta Research Council, Edmonton, Alberta, Canada
Objectives: To develop a method to quantify the mass transfer rate of potentially toxic elements (PTE) from contaminants to the bulk compost

matrix. Contaminants tested included electronic cables, copper wires, Zn-plated screws, galvanized nails and Ni-Cd and alkaline batteries. The metal contaminants were mixed with a synthetic feedstock and composted at a low pH (5) and a high pH (8) for three-weeks at thermophilic temperatures in 1 m3 reactors. The mass loss of each contaminant was quantified using the corrosion weight loss method, i.e. the loss of mass per unit surface area of the contaminant was determined. The characterization of corrosion products and the corrosion condition was achieved by applying Scanning Electron Microscope (SEM-EDX), X-ray Diffractometer (XRD), Gas Chromatography (GC) and Ion-chromatography (IC) techniques. The results of the study were used to calculate the number of contaminant pieces per compost mass, e.g. number of batteries per kg dry compost, which would cause an exceedance of guidelines for PTEs in the final compost product. Transfer of PTEs was significantly higher in the low pH environment. The contaminants of most concern were Zn-coated nails and screws which would cause Zn guideline exceedances with as little as three pieces per dry kg of compost. Light bulb tails were found to have the least significance; 765 tails were required to cause a Pb guideline exceedance. Further work will be completed to attempt to balance the PTE loss from the surface of the contaminant with the bulk PTE mass found in the bulk composting matrix. This work should be completed by February 2010.

The role of aeration intensity, temperature regimes and composting mixture on gaseous emission during composting
Investigators: Jan Habart, Pavel Tlustos, Ales Hanc, Pavel Svehla, Jaroslav Vána, Petr Tluka, Frantisek Jelínek, Department of Agrochemistry and Plant Nutrition, Czech University of Agriculture, Prague – Suchdol, Czech Republic
Objectives: To compare production of N2O during composting with different temperature regimes, different aeration intensity and different input mixture. Two different mixtures of organic material with three levels of aeration underwent composting process in two temperature regimes. Mixture A contained woodchips, separated pick slurry, fresh grass and tree leaves; mixture B contained woodchips, tree leaves, grass and urea to optimize C:N ratio. Experiment has been carried out in 70 liters specially designed fermentors. Oxygen and nitrous oxide were monitored in the exhaust air as well as pH, NO3- and NH4+ and temperature of solid material. Mixture with urea additive showed high N2O production when kept under low temperature; when the same mixture was kept in higher temperature, production of N2O were 3 fold lower. However mixture without urea addition kept in high temperature showed almost no N2O production. Production of N2O was highest when nitrates concentration increase. Production of N2O is perhaps by-product of nitrification, but also other pathways may contribute.

Effect of municipal solid waste compost on mine soils as evaluated by plant growth, trace element leachability, ecotoxicity of leachates, and biological and biochemical properties of soils
Investigators: C. Cunha-Queda, A. Nobre and A. de Varennes, Department of Agricultural and Environmental Chemistry, Instituto Superior de Agronomia, Technical University of Lisbon, Lisboa, Portugal; P. Alvarenga, Department of Environmental Sciences, Escola Superior Agrária de Beja, Beja, Portugal
Objectives: To investigate whether compost from mixed municipal solid waste (MSW) could be used to remediate two soils from a mine contaminated with trace elements. Compost is increasingly used in land rehabilitation because they can improve soil quality and reduce the need for inorganic fertilizers. Their use contributes to an integrated approach to waste management by promoting recycling of nutrients and minimizing final disposal of organic residues that, due to their composition, can pose problems to agricultural soils. One of the soils was less acidic and had a greater content of Cu and Zn while the other had more Pb and a lower pH. The effect of MSW was evaluated by plant growth, trace element leachability, ecotoxicity of soil leachates, and biological and biochemical properties of soils. Growth of perennial ryegrass (Lolium perenne L. cv. Victorian) was stimulated in the MSW compost-amended soils compared with respective controls or with acidic soil when limed. After ryegrass had been growing for 119 days, the amount of water-extractable Zn was lower in MSW compost-amended soils, while the opposite was true for water-extractable Cu. Water-extractable Pb increased following MSW compost application to one soil and decreased in the other. The greatest dehydrogenase activity was obtained in amended limed soil, while the number of culturable bacteria and fungi and the activities of cellulase and b-glucosidase were similar in soil that was limed or following MSW compost application. In contrast, urease activity was repressed in limed or MSW compost-amended soils. Leachates from unamended soils were toxic towards Daphnia magna. Liming the very acidic soil led to a decrease in the toxicity of the leachate, but it was only in MSW compost-amended soils that ecotoxicity was no longer detected.