Selection of Mediterranean plants biomass for the composting of pig slurry solids based on the heat production during aerobic degradation.

Heat recovery from composting processes and its use as a source of bioenergy have come into prominence in recent years. In this study, the selection of an adequate bulking agent for the composting of the solid fraction of pig slurry has been based on the heat produced by the microbial activity during aerobic degradation of the organic matter. Residues of five plant species typical of the Mediterranean area were mixed with the solid fraction of pig slurry, as bulking agents. The residues were: the prunings of three common cultivated tree species (orange, palm, and olive) and the biomass of two herbaceous species (milk thistle and sunflower). Self-heating tests were run for 18 days in thermally insulated laboratory-scale reactors; the energy released as heat was calculated from the temperature increase inside the reactors. The mixtures were sampled at the beginning and end of the experiment, and the microbial stability was evaluated by aerobic respiration tests. The heat energy produced was highest in the mixture with milk thistle (18.3 ± 1.78 MJ kg-1 of total solids -TS), followed by that with orange tree prunings (16.0 ± 1.094 MJ kg-1 TS), and was lowest with olive tree prunings (6.3 ± 0.23 MJ kg-1 TS). The microbial biodegradability of the mixtures and the physico-chemical characteristics (mainly the C/N ratio, cellulose concentration, and density) of the different bulking agents controlled the heat energy produced. The orange tree prunings were considered the most suitable bulking agent for composting of pig slurry solids as they showed high degradability and energy recovery potential.

Solidification/stabilization of landfill leachate concentrate using different aggregate materials.

The application of reverse osmosis for the treatment of landfill leachate is becoming widespread in Turkey as well as in Europe. A major drawback of this process is the production of concentrate, which could be as much as 30% of the feed stream, and high concentrations of salts and contaminants. The reverse osmosis concentrate is disposed of by using several methods including re-infiltration, drying, incineration and solidification/stabilization. In this study, solidification/stabilization (S/S) technology was studied for the treatment of reverse osmosis concentrate produced from landfill leachate. In order to benefit from its capability to absorb heavy metals, ammonia and some other pollutants, zeolite and different aggregate materials were used in solidification experiments. Main pollutants in the leachate concentrate, TOC, DOC, TDS and ammonia were successfully solidified and approximately 1% of TOC, DOC, TDS and ammonia remained in the eluate water. The results indicated that the landfill disposal limits could be attained by solidification/stabilization process.