Abstract
In many Baltic regions, short-rotation willow (Salix spp.) is used as a vegetation filter for wastewater treatment and recycling of valuable nutrients to upsurge bioeconomy development. In this context, a four-year field trial (2016–2019) was carried out near a wastewater treatment plant in eastern Finland (Outokumpu) to investigate the effect of the processed wastewater (WW) on biomass production as well as the nutrients uptake capability (mainly N and P) by a willow variety (Salix schwerinii). Results indicated that WW irrigation expressively increased the willow diameter growth and biomass yield around 256% and 6510%, respectively, compared to the control treatment site (without WW). The willow was also able to accumulate approximately 41–60% of the N and 32–50% of the P in two years (2018–2019). Overall, willow showed a total 20% mortality rate under WW irrigation throughout the growing periods (2017–2019) as compared to control (39%). The results demonstrate that willow has the potential to control eutrophication (reducing nutrients load) from the wastewater with the best survival rate and can provide high biomass production for bioenergy generations in cold climatic conditions.
Highlights
Nitrogen (N) and phosphorus (P) are essential nutrients for all living organisms, but higher concentrations can exert a negative impact on the ecosystem
When willows were exposed to WW irrigation, a slight decline of around 11% in the willow diameter growth was noticed in the first year 2017, but in 2018 and 2019, a significant annual increase of 90% and 166% were observed, respectively (Figure 3A)
Results indicate that WW application has shown a positive effect on willow diameter growth
Summary
Nitrogen (N) and phosphorus (P) are essential nutrients for all living organisms, but higher concentrations can exert a negative impact on the ecosystem. Technologies to recover essential nutrients from the processed wastewater have become highly essential due to the increase in fertilizers prices and strict discharge limits on excessive mineral nutrients [1]. The overall sustainability of wastewater treatment plants can be upgraded by reducing the use of non-renewable resources, minimizing waste generation, and implementing resource recycling approaches [2]. Municipal wastewater contains a sufficient amount of P and N and is recognized as a valuable resource. It could be favorable for both agroforestry sectors and achieving food security once it has been properly treated. Wastewater can be a valuable source of organic fertilizer if effective recovery processes are adopted [3]
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