Abstract

This paper deals with environmental effects of producing and combusting energy forest fuel. Energy forest means in the following short rotation willow (Salix). Supposed effects of sewage sludge application are discussed as well. Rules and regulations are dealt with in the chapters about sludge and combustion. Energy forestry on agricultural land implies both advantages and disadvantages for the environment. Leaf litter (humified leaves) increases the humus content in the top soil. The soil fauna is also positively affected. Until now performed studies about nitrogen leakage from fields cultivated with energy forest (Salix), have not given any distinct results. A retarded drainage within energy forest fields is on the other hand noticed. While the root system of Salix is active during a long period of the year, the nitrogen leakage become less compared to traditional cultivation. The use of pesticides are estimated to be reduced by a changeover to energy forestry on previous grain growned land. The content of plant nutrients and organic matter in sewage sludge make a resource that can be useful for agricultural purposes, especially for energy forest cultivation. The quality of sewage sludge is however not only positive. The content of heavy metals and organic emissions contradicts sludge application to agricultural land. Sewage sludge with todays quality increases somewhat the content of heavy metals in the soil. This condition can be counteracted to a certain extent by growing energy forest. It has been established that Salix has high ability to heavy metal uptake, especially cadmium. Sludge dumping will end in the long run. Landdisposal and/or combustion will thereafter be the methods of treatment. Sewage sludge application to farm land is economic according to an investigation done by the Swedish University of Agricultural sciences. The character of the landscape changes when growing energy forest. Before the plantation is cut, it has reached a hight of 5 to 7 meters. This fact can be negatively experienced. Within some areas, for example in flat country, Salix can give positive effects. It promotes a more varied landscape. Growing energy forest on drained farm land is connected with a risk for root penetration into the drainage system. With enough water and plant nutrients in the top soil the risk is reduced. Shallow depth of the pipes increases the risk. Combustion of wood chips from energy forests (and other types of biomass) gives especially two advantages. It does not give any net contribution of carbon dioxide to the atmosphere. The sulphur discharge will be minimal since the sulphur content in wood fuel is low. Discharge of nitrogen oxide and hydrocarbons may give some problems. These problems can be reduced by technological measures when combusting.

Keywords

biobränsle; bioenergi; energi; energiskog; salix; slam; rötslam

Published in

Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
1992,
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet

Permanent link to this page (URI)

https://res.slu.se/id/publ/125604