Short Rotation Coppice

Short Rotation Coppice

For these plantations species like willows, poplars, eucalyptus or bamboo are used, since they are fast growing in their youth and can sprout again from their roots after harvesting. The plantations are arranged in a single or double row system. An average yield of 10 tons absolute dry wood per year and hectare can be expected. This has the energy content equivalent to 5,000 L heating oil. The harvesting is usually conducted in intervals between 3 to 5 years depending on the formation and the tree species. Since water is their main growth limitation factor, on nutrient poor and dry soil yield can be increased significantly by adding nutrient-rich wastewater. The chipped harvested wood is an excellent fuel, which can be used in regional power plants, district heating systems or households. While constructed wetlands focus mainly on wastewater treatment and are sealed at their base for groundwater protection, the advantage of SRCs over constructed wetlands lies in the combined wastewater treatment and the production of wooden biomass, which means an additional income for farmers. A SRC represents an open-bottom fixed-bed reactor of a construction height of between 1.0 and 1.5 m resulting in an effective reduction of pathogens. To avoid a nutrient overload it is important to control and document the amount and quality of the applied wastewater and sewage sludge.

For this treatment system the main requirement is land. In Europe, cost-effectiveness using fully mechanical planting and harvesting systems is reached starting at 5 ha. The plantation of a SRC and its harvest can be also done manually. Cuttings from tree nurseries are required as seedlings. In one hectare up to 12,000 trees like willows, popular or eucalyptus can be grown. For the distribution of the wastewater a drip irrigation system and slurry pump are needed. Before the wastewater enters the system, a mechanical pre-treatment would be needed to filter and avoid clogging. To maintain SRC, typical farmer skills like knowledge about plants, fertilizer, irrigation, and familiarity with agricultural machinery are needed.

The running cost of a SRC are minimal, mainly the rent of the land. After establishment the main cost factor is incurred in the harvesting process, cost largely compensated by the sales profit on the wood chips. As a reference, the total cost for establishing a plantation are around 2,500 €/ha in Germany. The material cost for a simple and cheap drip irrigation system are approximately 300€. External financing is usually not needed and since the most of the work needed is unskilled labour, it can be done by the entrepreneur himself. To avoid losses, it is very important to take care of the sprouts during the first year.

The system SRC as water treatment system requires significant areas of land. The outskirts of urban areas are good locations due to the need of the produced fuel and availability of wastewater. Due to climatic conditions, in Europe the combination of SRC with wastewater treatment is only established in regions with less than 600 mm rainfall and nutrient poor soil. Different examples can be cited. For instance, a 5 ha SRC (willow, poplar, alder and robinia) was established in an old sewage sludge and wastewater dump nearby Berlin (Germany) (HECKER 2012). Other experiences can also be cited in the south of Europe (Granada-Spain, Ferrara-Italy)with poplars(EUBIA 2008), were it was possible to double the biomass production. As for other regions, reference projects in Bangladesh and China (INAWAB 2006; LADAS 2005) can be cited as well. With a pre-treated wastewater, the environmental risk is low, and contributes to the reduction of conventional wastewater treatment. The hygienic risk from SRC biomass is also low due to the fact that the biomass is not for the food sector. The use of wastewater and sludge saved natural drinking water sources for irrigation and fertiliser because it contains valuable plant nutrients (especially Nitrogen and Phosphorus).

The experiences and established tree species in SRC made in Europe are not transferable one to one to India due to different climate conditions. Different climatic regions inside India make it even more difficult to transfer successfully used tree species into other regions. The potential use of timber in India has a broad spectra beginning with fire wood, raw material for industry or as building material (I.e. bamboo). A summary about the experiences made with SRC trees in India is presented: In Jodhpur (North West India) trials with SRC species Acacia nilotica and Eucalyptus camaldulensis irrigated with municipal wastewater where conducted. In this study, Eucalyptus showed the advantage of the highest uptake rate of nutrients, which is an important parameter towards avoiding negative long term effects by accumulation of nutrients (SINGH et al. 2010). In a study conducted in Palwal (70 km from New Delhi), different tree species were irrigated with secondary treated wastewater. The Tereticornis eucalyptus specie showed to have the highest biomass yield per tree. However, due to a higher survival rate the net biomass production per hectare was higher for Melia Azedarach (38 t/ha) followed by Ailanthus excels. The plants were grown for 2.5 years and showed a strong variation in survival rate. In this study different water/wastewater ratios where used with up to 100% wastewater. No effects were found concerning the ratio of wastewater used (TOKY 2011). The first species, which comes in mind for Indian climate, is probably bamboo. However studies on bamboo biomass production are scarce (NATH et al. 2009). A study conducted in subtropical warm and humid conditions in the Barak Valley Region found a biomass production of 37.7 t/ha /year. The productivity of acacia and bamboo was compared in a study in Kallipatty, India (SHANMUGHAVEL & FRANCIS 2001). The biomass production showed a strong increase with age and a high advantage of bamboo compared with acacia. The variation from 2.2 t/ha in year one to 298 t/ha in year 6 and back to 16 t/ha in year 10 after planting makes it clear that it is critical to consider rotation length when comparing studies. However, the biomass uptake was higher for bamboo during all periods. In a study carried out at the Haryana University of Agriculture, Leucaena leucocephala showed the highest net primary production of 33 t/ha /year closely followed by Eucalyptus teriticornis with 29 t/ha /year. Compared with these species, Acacia nilotica trees had just half the primary biomass production (SINGH & TOKY 1995). Altogether it has been seen that eucalyptus is the most experimented specie in India, not just as SRC plantation but also in combination with wastewater irrigation. Bamboo, which has a high potential due to its adaptation to Indian climate conditions as well as its broad spectrum for usage after harvesting, has been lest studied, and in particular not with irrigation of wastewater.

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