Comprehensive evaluation of sewage sludge and sewage sludge char soil amendment impact on the industrial hemp growth performance and heavy metal accumulation

https://doi.org/10.1016/j.indcrop.2020.112396Get rights and content

Highlights

  • Hemp biomass production on clay loam soil on average latitudes.

  • Heavy metal, alkaline earth-alkali metals and non metals distribution in hemp parts.

  • Bioconcentration factor impact to soil remediation of heavy metals.

  • Alkaline earth-alkaline metals and non metals impact to slagging process in combustion.

Abstract

Industrial hemp (Cannabis sativa L.) has emerged as a potential multipiurpose crop: fibre crop, energy crop, and phytoextractor of pollutants from the soil. However, the multipurpise grwoth of hemp was restricted as its cultivation in EU was legalized only in the past two decades. Most scientific researches of sewage sludge (SS) describe it at relatively low application levels for cultivation of different crops. Such lack of information requires a wide range of practices for fertilizing hemp with high level of sewage sludge or sewage sludge char (SSCh) doses. At this moment there are no guidelines for sewage sludge char fertilization of energetic plants, depending on soil type. The aim of the study was to analyze and compare SS and SSCh soil application effect on industrial hemp (Cannabis sativa L.) growth performance, and heavy metals accumulation to determine optimum SS or SSCh application rates for the growth of hemp. The experimental design consisted of four treatments: 1–25; 2–50; 3–100; 4–200 of sewage sludge and sewage sludge char Mg ha−1, and control soil (clay loam). It was determined that hemp ability to accumulate heavy metals depending on fertilisation intensity of sewage sludge and sewage sludge char decreased in all parts. Heavy metal distribution of hemp was selective; therefore their contents were decreasing in the following order: roots > stems > leaves. The study has confirmed the nutritional value of SS and SSCh. The potential of using the sewage sludge and its char as a source of organic matter for improvement of clay loam soil and a reasonable production of bioenergy crop like hemp without the use of inorganic fertilizers was shown.

Introduction

Fossil fuel reserves are becoming depleted and the need for increasing the share of renewable energy is increasing. The energy crops have high potential to increase the share of renewable energy. Many crop species are multi-purpose, i.e. they can be used to produce more than one type of bioenergy, for example oil and solid biofuel (Tuck et al., 2006), they can be grown as industrial crop or for seeds. The use of energy crops is highly promoted in EU as it may decrease greenhouse gas emissions and mitigate climate change (Banja et al., 2019).

Industrial hemp (Cannabis sativa L.) has emerged as a potential energy crop having numerous advantages: high land use efficiency and biomass content, other factors such as low feed-stock cost, good weed suppression, low nutrients requirement, no/zero pesticide demand and improvement of soil health (Lehmann et al., 2011; Li et al., 2010; Prade et al., 2011). It can be effectively grown in diverse climates and can be used in organic crop rotation (Barberá et al., 2011; Kreuger et al., 2011). Because of these properties, hemp is valuable crop for the bio-based economy. European Union produces about 29 % hemp of total world production (Barberá et al., 2011). The cultivation of hemp is increasing in EU reaching more than 33,000 ha in 2016 (Carus, 2017). Different climate change models under SRES scenarios have showed that the distribution of hemp in Europe in the 21st century is expected to move northwards, and hemp cultivation would disappear from Southern Europe and shift to Northern Europe by the 2050s and 2080s (Tuck et al., 2006).

It is recommended to use industrial or energy plant species not only for energy purposes but also for the phytoextraction of pollutants (such as heavy metals, organic pollutants) from the soil (Bielińska, 2016). Many authors confirm that it is possible to use energy plants (grasses) for the phytoremediation of soils polluted with heavy metals (Barbosa et al., 2015; Shrestha et al., 2019; Van Ginneken et al., 2007).

Despite the positive properties of industrial hemp, its cultivation was legalized in EU countries only in the 1990s or even later, i.e., in Lithuania the cultivation of hemp (Cannabis sativa L.) was legalized in 2014. Thus, the cultivation of industrial hemp for energy purposes is a relatively new agricultural branch that requires knowledge about the optimal fertilization rates to get as much biomass as possible (Prade, 2011). The energy value of the biomass obtained is the main parameter of energy plants, which depends on plant density, environmental conditions (soil properties), cultivation pattern, etc. The biomass of energy plants could be increased with fertilizers application or sewage sludge/biosolids amendments (Schröder et al., 2018).

Sewage sludge (SS) is a source of many valuable nutrients (especially N and P), trace elements (S, Mg, Ca), but also contains potentially toxic compounds such as heavy metals, persistent organic pollutants posing a risk to humans and environment. The application of SS for energy plants cultivation may be good and cheap alternative to the fertilizer’s application, could help to improve soil quality, reduce sewage sludge disposal in landfills and herewith greenhouse emissions from landfills and contribute to climate change mitigation (Schröder et al., 2018). Hemp is an excellent soil phytoremediation agent because it extracts heavy metals (Mihoc et al., 2012).

At very heavily contaminated and denuded sites, such as former mine areas, particularly where there are surface leachates of heavy metals and unconsolidated soils and wastes, biochar may be useful to restrict the wider impact of contamination beyond site boundaries (Moreno-Jiménez, 2016). However, most crop plants cannot survive on soils heavily contaminated with heavy metals (Mihoc et al., 2012). Therefore, more extensive research is needed to determine the optimum dosage of SS in order to have high energy plants yield and do not pose risk to soil biota.

Most of research has focused only on SS application impact and sewage sludge char (SSCh) application was less studied. Sewage sludge char is the most appropriate pyrolysis product, which was also preferable from point view of energy balance (Wang et al., 2012). The energy implications of biochar production were discussed recently by Callegari and Petr Hlavinek, 2018 and Capodaglio et al., 2016. Sewage sludge char physico-chemical properties and afterwards impact to soil biota is driven by pyrolysis process temperature and feedstock (sewage sludge) properties (Callegari and Capodaglio, 2018; Hossain et al., 2011; Lehmann et al., 2011). Physico-chemical characteristics of SSCh; in addition to microstructures based on their pores (specific areas), heavy metal content and leaching potential, has an important benefits to use it as fertilizer in energy crop production. Heavy metals accumulation, particularly As, Cd, Cr, Cu, Pb, Ni, Se and Zn and, is of specific concern as far as agricultural activities are concerned, and is also one of the principal reasons for the existing limitations on continuing sludge agricultural disposal practices (Callegari and Capodaglio, 2018). More detailed analysis of biochar after microwave pyrolysis of sewage sludge was recently discussed by Racek et al., 2019.

Heavy metal solubility and bioavailability in a Mediterranean agricultural soil after amended with raw SS or its biochar and found that the leaching of Cu, Ni and Zn was lower in the soil treated with biochar than in the soil treated directly with SS, and plant availability of Ni, Zn, Cd and Pb has also been reduced in the biochar-amended soil when compared with the SS-amended soil (Méndez et al., 2012). However no information is available on difference in heavy metal and trace elements bioconcentration when biochar was produced at different temperatures (Praspaliauskas et al., 2018; Song et al., 2014). In some studies of sewage sludge (SS) (Bielińska, 2016) or sewage sludge char (Finnan and Burke, 2013) has been applied at relatively low levels following recommendations for productive arable crops. The studies of fertilization with municipal sewage sludge (Borkowska and Molas, 2013; Kołodziej et al., 2015) provided evidence that the best effects on the growth and development of plants are exerted by nitrogen, phosphorus, and potassium. The sewage sludge used for fertilizing energy crops is a perfect source of these elements, particularly of nitrogen and phosphorus (Kołodziej et al., 2015). However, sewage sludge contains too little potassium to meet the needs of energy crops, therefore it should be applied in mineral form after a prior evaluation of the soil resources of this component. This lack of information has led to a wide range of practices for fertilizing hemp with high level of SS and SSCh char doses.

However, sewage sludge contains too little potassium to meet the needs of energy crops, therefore it should be applied in mineral form after a prior evaluation of the soil resources of this component (Kirchmann et al., 2017). This lack of information has led to a wide range of practices for fertilizing hemp with high level of SS and SSCh doses. The effects of plant fertilization with sewage sludge and sewage sludge char have been extensively studied, there is insufficient information on the amount of heavy metals, alkaline earths and alkali metals being accumulated by the increasingly used energy crops that are increasingly used. There is not enough information on how heavy metals are distributed in different parts of the industrial hemp: roots, stems and, leaves at different fertilization intensities. It is important to take into account these factors, since the further use of biomass of energy plants, due to the increased concentration of elements, causes problems related to ash melting in the boilers.

Taking into account the above considerations, our aim was to analyze and compare SS and SSCh application effect on industrial hemp (Cannabis sativa L.) growth performance, and heavy metals accumulation to determine optimum SS or SSCh application rates for the growth of hemp.

Section snippets

Soil, municipal sewage sludge and sewage sludge char

Clay loam soil was selected due to reason that this type of soil is predominant in Lithuania and covers about 21 % of the total area. The soil pHKCl was of 7.20 ± 0.04, the content of available phosphorus, potassium and magnesium was at a low level.

Sewage sludge was collected from the local municipal wastewater treatment plant. Char was prepared using also this sewage sludge at selected condition. More details are presented in paper of Praspaliauskas, Pedišius and Striūgas, 2018 Table 1.

Sewage

Soil properties after soil treatment with SS and SSCh

Heavy metal content in the soil did not exceed permissible values when SS and SSCh were used for reclamation. Exception was Zn which exceeds the limited value in highest fertilization intensity of SSCh, and chromium which concentrations in all soil types (even in the control) of this experiment were increased (Table 2). Be, Cd and Pb was not found in untreated soil and in soil after treatment with SS and SSCh. The analysis of these elements will not be discussed further in this paper.

It has

Conclusions

The study has highlighted that different rates of sewage sludge char and sewage sludge modified the soil characteristics compared with the unamended soil:

  • Accumulation of Co, Cr, Cu and Zn in all parts of the hemp decreased with amount of both sewage sludge and sewage char added to the soil. Accumulation of Ni was increasing significantly in the roots and stems when sewage sludge was used for fertilization. Accumulation of Ti and Fe in the roots decreased and increased in the stems and leaves

references

Tuck et al. (2011).

CRediT authorship contribution statement

Marius Praspaliauskas: Conceptualization, Investigation, Data curation, Writing - original draft, Visualization. Jūratė Žaltauskaitė: Investigation, Formal analysis, Data curation, Writing - original draft, Visualization. Nerijus Pedišius: Resources, Data curation, Visualization. Nerijus Striūgas: Resources, Data curation, Visualization.

Declaration of Competing Interest

None.

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