Effects of Sewage Sludge on Energy Content and Combustion Emissions of Energy Crops

Abstract

This study was conducted to investigate the energy crop production suitability of sewage sludge as well as pollutant transfer from sewage sludge to feedstock of Miscanthus x giganteus and Arundo donax, with a focus on ash constituents and exhaust gaseous emissions. Dewatered sludge and natural field soil were filled into pots, and seedlings produced from rhizomes were planted in the pots, which were arranged under a completely randomized design with four replications. The soil treatments were fertilized with conventional fertilizer, while no external fertilizer was supplied for sludge treatments. Harvested plant samples were subjected to characterization. Both crop species produced sufficient biomass yield on either soil or sludge treatments. High heating values measured for plants cultivated on soil and sludge were insignificant and in the range of 17.95-17.62 MJ kg(-1) and 17.31-18.05 MJ kg(-1) for M. x giganteus and A. donax, respectively. Sewage sludge significantly increased the plant macronutrients and heavy metal content of both species. Si was the dominant element in ash and was higher in A. donax plants. K and Ca were secondary high concentration elements, giving similar results for both plant species. Nitrogen concentrations in plant tissue provided by sewage sludge increased NOx emissions with a maximum increment observed at 10% with A. donax plants. SO2 emissions obtained were consistent with plant species but the emission concentrations were very small. The use of sewage sludge for energy crop cultivation confirmed that ash and air emissions hold great potential for both the energy crop production and waste minimizing alternative. (C) 2018 Friends Science Publishers