Performance and sustainability of short-rotation energy crops treated with municipal and industrial residues

Dimitriou, Ioannis (2005) Performance and sustainability of short-rotation energy crops treated with municipal and industrial residues. Doctoral diss. Dept. of Short Rotation Forestry, SLU. Acta Universitatis agriculturae Sueciae vol. 2005:44.

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Abstract

The sustainability of short-rotation willow coppice (SRWC) as a multifunctional system for phytoremediation—the use of plants for treatment of contaminated air, soil or water—and for producing energy biomass, was studied. SRWC is grown commercially in Sweden to produce energy biomass, nutrient-rich residues being applied as cost-efficient fertiliser to increase production. The principal residues used are municipal wastewater, landfill leachate, industrial wastewater (e.g. log-yard runoff), sewage sludge and wood-ash. Small- and large-scale experiments with residues aimed to quantify the extent of potential hazards and the performance of SRWC in reducing them.

Lysimeter experiments with willow plants, intensively irrigated with N-rich municipal wastewater, showed that N-leaching is a potential threat when high N loads are applied. Experimental data from SRWC fields irrigated with municipal wastewater in central Sweden suggest that in practice, N-leaching is significantly lower, even when the N load applied is greater than the N requirements of SRWC. Growth of willow plants of five different clones in pot experiments irrigated with landfill leachate was reduced by comparison with that of control plants. The reduction was attributed to saline stress or P deficiency, and indicates that, when hazardous compounds are present in wastewater, irrigation rates should be adjusted to avoid growth reduction. Genetic differences were observed between willow clones in salt tolerance and growth performance. The careful selection of clones to suit specific situations is therefore recommended. Leaf length can be used for rapid diagnosis of stress, to permit adjustment of the irrigation rate, and thus to avoid growth reduction. Phytoremedial efficiency of SRWC is satisfactory when the concentration of hazardous compounds in wastewaters is low, as in log-yard runoff, and depends on irrigation intensity. Application of sludge–ash mixtures to SRWC is not a substantial threat to sustainability, in terms of heavy metals. Total Cd in the soil is expected to decrease after harvest, but other metals and P loads, must also be considered.

Any decision concerning residue application must take into account factors such as residue composition, soil type, climate, and species or clone characteristics, if both a high growth rate of SRWC and sustainability are to be attained.