Wastewater-fertigated Short Rotation Coppice (wfSRC) systems are an innovate agroforestry land-use approach, which aims to combine biomass production with wastewater treatment and reuse. In the system, fast growing tree or plant species are managed in short coppicing cycles. The high demand for nutrients and water of these non-food/non-fodder crops is supplied by using pre-treated wastewater and sewage sludge, thus, enabling nutrient recycling and a more sustainable water treatment while enhancing plant growth. The produced biomass can be used as renewable fuel, can be further processed to construction materials, bio crude, or hydro char, among others (SUSANA 2012).
wfSRCs are considered one of the most suitable ecological systems to treat nutrient-rich wastewater due to their natural capacity to translocate minerals and metals contained in the wastewater. wfSRCs are mostly designed to treat all the influent water through evapotranspiration. However, there are also willow systems intended to produce some outflow, so nutrients in the reclaimed water can be used for non-food crops irrigation (LANGERGRABER ET AL. 2019).
|Raw domestic wastewater (Blackwater)|
|Degreased, screened sewage|
|Primary sludge (from e.g. septic tanks or cesspits)|
|Tertiary treated and/or disinfected effluent|
|Total suspended solids (TSS)|
|Total dissolved solids (TDS)|
|Organic compounds / COD / BOD5 / TOC|
The initial step for the design of a wfSRC system is to determine and quantify the total volume of wastewater to be treated and the climatic and soil conditions of the location. Including, for instance, parameters such as the average annual precipitation, potential evotranspiration, infiltration rates and granulometry. Generally, the system is constructed with a width of 8 metres (m,) minimum depth of 1.5 m, leaving 60 centimetres (cm) between the plants, 75 cm between the rows and with slopes on the sides. However, the required dimensions are to be defined according to the identified parameters (LANGERGRABER et al. 2019).
The wastewater (WW) must be pre-treated by means of a sedimentation tank and a grit removal, before being collected in an equalization tank from which the wfSRC bed is loaded. The pre-treated wastewater is distributed within the system by a level-controlled pump, the distribution pipes can be located under or above the ground. A drainage pipe is placed in the bottom of the bed and is used to empty water from the bed, if there is salt accumulation after some years of operation. Additionally, the field needs to be enclosed using a small dam levee to retain the WW on the respective area that is used as wfSRC and for the WW to flow into the low- lying land.
Fig. 1 depicts a typical wfSRC system with underground pipelines:
Fig. 1: Schematic of a zero-discharge willow system. Source: LANGERGRABER et al. (2019)
Among the most suitable species for a wfSRC systems, are Eucalyptus citriodora, Alix tetraspermo, Bambusa bulgaris and several willow and poplar species. The harvesting periods for this species are usually once every 2 - 3 years, where between one half and one third of the crops should be harvested to keep the plants in a young and healthy state with high transpiration rates.
The following aspects need to be considered when deciding if this technology is approporiate for a particular site location or fits the existing context in general:
- The location of the field requires large surface and intermediary zones that protect the system against flooding in case of heavy rainfall. Hence, the system is genereally suitable for rural areas. wfSRC systems are not appropriate for large cities with space limitations.
- In general, wfSRC systems are not appropriate for applying highly polluted industrial WW that varies in composition and characteristics.
- The existing soil, climate conditions and water parameters have a direct impact on the productivity of the system. The plant species used usually do not demand very high quality agricultural soils. Soils with pH 5 - 7.5 will produce satisfactory growth, although research suggest that there is plant material that is tolerant to pH outside this range (CASLIN et al. 2015). In dry areas, light sandy soils will probably have a problem in terms of water availability and therefore may be avoided. The same is valid for shallows soils which will provide low yields. The cultivation on flood lands or sensitive wetland areas needs to be carefully assessed since the cultivation with heavy machinery can be challenging and can have a negative impact on wet soils, such as soil compaction (DIMITRIOU and RUTZ 2015).
- The layout of the wfSRC must be designed to optimise crop densities and yield, to fit into the surrounding landscape and to allow easier operation and access of the machinery involved in the setting up and harvesting processes. Also, in order to keep the system economically, the distance of the wfSRC and WW source should be short (energy for pumping). Further information regarding the layout of wfSRCs can be found in chapter two of the Sustainable Short Rotation Coppice Handbook (DIMITRIOU and RUTZ 2015).
The establishment of the system requires low energy and earth work. However, preparation of the soil, such as leveling, installation of pumps and pipes, among others, are necessary. Since only basic construction materials are needed they can in most locations be easily sourced locally. The plant species are easily accessible, as the species used grow in many parts of South and Southeastern Asia.
Operation and Maintenance
In general, the operation and maintenance of the system do not require complex, high demanding processes, nor intense labour. However, on a regular basis, the operation of the system includes daily standard activities such as opening and closing the valves, running the pumps, besides crop harvesting that is to be executed every 1 - 3 years. These activities can be carried out by a local operator that received basic training on-site. Additionally, qualified personnel is required for the maintenance of the equipment which is executed every year (or on-demand), and the standard agricultural practices, such as planting, conservation, plantation monitoring and weed control which needs to be performed twice per month during the first year and at least once per month after the second year.
The monitoring campaigns as well as their frequency, are subjected to the legislation requirements stated in each country. Ideally, for general performance monitoring, operational parameters such as Chemical Oxygen Demand (COD), Phosphorus (P), Potassium (K), Total Organic Carbon (TOC), the the Biochemical Oxygen Demand (BOD5) and pathogens along with groundwater quality should be monitored regularly, varying from a weekly to a bi-monthly basis, depending on the location and the complexity of the system.
Experiences in India
The experiences in India with natural based systems, and wfSRC specifically, are limited. However, wfSRC systems are expected to be key to improve the situation of water resources and forest ecosystems in India. They have the potential to offer local communities the opportunity to produce their own clean, renewable resources to cover their energy needs, while contributing to reduce pollution and increase the positive environmental impacts and lower negative health impacts of formerly untreated wastewater streams.
An example for the few experiences made in India, is the NAWATECH project, which among other activities, piloted a wfSRC at the Ordenance Factory Ambajhari (OFAJ) in Nagpur. The pilot line consisted of a French reed bed followed by a wfSRC. The local species selected for this pilot treatment line were Melia Dubia and Bambusa bambos (ECOSAN CLUB 2016). However, there is no information on the actual performance of this pilot available.
As described by SINGH et al. (2011), another wfSRC was implemented in Jodhpur (North West India), where the species Acacia nilotica and Eucalyptus camaldulensis were irrigated with municipal wastewater. A second study was conducted in Palwal, a district located 70 kilometres from New Delhi, in which the performance of the species Tereticornis eucalyptus, Melia Azedarach, Ailanthus excels were evaluated after being planted and irrigated with secondary treated wastewater (TOKY et al. 2011). Relevant results were obtained from the projects and valuable data regarding a.o. biomass yield per specie or the nutrient uptake rate.
wfSRCs are known and used in many parts of the world. Especially in Northern Europe and the US commercial systems are in place as described by Haenel et al. (2022). Taking into account the general potential and the wastewater situation, a large-scale implementation in rural areas in South-East Asia but also in Latin America are expected to have very promising potential.
As the wfSRC systems have their origin northern European countries, most of the successful case studies are found for this region. One successful example is the “Enköping model” (BÖRJESSON and BERNDES 2006), where the establishment of a wfSRC in a city located in central Sweden was considered as necessary to complement the regional biomass demand.
Worldwide, for instance in Denmark, Poland, Estonia, Germany, Canada, Australia, Brazil, aspects around wfSRC’s soil and water purification, biomass and bioenergy production, environmental purposes, economic analyses, as well as nutrients dynamics, were studied (GUIDI et al. 2015, DE OLIVEIRA et al. 2014, HOLM and HEINSOO 2013, LIESEBACH et al. 1999, MORTENSEN et al. 1998, HAENEL et.al. 2022).
wfSRC systems have the potential to address in a cost efficient way, two of the most concerning environmental problems nowadays, water pollution and climate change by treating the WW in a sustainable way while producing renewable energy sources. Consequently, the investigation and experience obtained from the different areas will allow practitioners, academics and researchers to gain a better understanding of the systems, and to identify potential challenges and how to successfully overcome them. Besides, boosting the implementation of more technologies in many countries, which benefit both, the communities and the environment.
Evaluation of the Productivity of Irrigated Eucalyptus grandis with Reclaimed Wastewater and Effects on Soil
Wastewater-Fertigated Short-Rotation Coppice, a Combined Scheme of Wastewater Treatment and Biomass Production: A State-of-the-Art Review
Municipal wastewater application to Short Rotation Coppice of willows – Treatment efficiency and clone response in Estonian case study
Aspen for short-rotation coppice plantations on agricultural sites in Germany: Effects of spacing and rotation time on growth and biomass production of aspen progenies
Nitrate leaching during establishment of willow (Salix viminalis) on two soil types and at two fertilization levels
Use of tree seedlings for the phytoremediation of a municipal effluent used in dry areas of north-western India: Plant growth and nutrient uptake
This Scientific and Technical Report (STR) targets engineers on wetland design, academics as well as decision makers and audience from a non-water technical background who have an interest in wetland technology and its potential.
The (STR) outlines the new approach to water management and the roles of wetlands in this new approach, the treatment wetland design and provides practical information in design specific wetland types and typically pitfalls and present relevant case studies.
In chapter 4- Designing wetlands for specific application, subsection 4.7 – Biomass production, the student will find specific information regarding WFSRC including: perspectives, sources, design, among others.ISTENIC, D., BULC, T., CIRELLI, G., MARZO, A. and MILANI, M. (2019): 4.7 Biomass production. In: LANGERGRABER, G., DOTRO, G., NIVALA, J., RIZZO, A. and STEIN, O. (Eds.) ; (2019): Wetland Technology. Practical Information on the Design and Application of Treatment Wetlands. Scientific and Technical Report Nº 27. London: International Water Association (IWA), p.38-41. URL [Accessed: 17.05.2023] PDF
The Handbook, elaborated in the Framework of the SCRPlus Project, provides information for farmers, public landowners, small utilities of heat, woodchip traders and any interested persons and presents the different agricultural practices in Europe, whereas the different framework conditions, such as climate, are considered. The added value of the handbook is the focus on sustainable supply chains and SRC benefits.DIMITRIOU, I. and RUTZ, D. (2015): Sustainable Short Rotation Coppice. A Handbook. Munich, Germany: WIP Renewable Energies URL [Accessed: 17.05.2023] PDF