Reed canary grass (Phalaris arundinacea L.) is a perennial fast-growing C 3 plant belongs to family Poaceae with an early season growth, a wide physiological tolerance and with large possibilities of utilization. Recently, the use for bioenergy has become very perspective mainly because its high yield (5-10 t dry matter ha/year) and very good properties for combustion. The mean calorific value is about 16-18 MJ/kg dry matter. It can be usually harvested twice a year at lower cultivation inputs and shows the ability to grow in wide range of soil conditions including on land, which is not appropriate for other agricultural purposes. It has also the potential for different industrial applications, for example for biogas, ethanol, pulp and paper production, or for the production of chemical raw materials, too. The cultivation area rapidly increases, mainly in North Europe, where it is cultivated on thousands of hectares. The cultivation for energy or other industrial purposes has also benefits to the environment because of low intensity on agricultural management, supporting biodiversity and soil preservation against erosion.
Hybrid sorrel is a perennial crop whose benefits include good wintering, early ripening, and relatively high biomass and energy yields. The average yields are usually in the range from 4 to 10 t ha−1 dry matter (DM) per year. Based on a long‐term study, a significant fertilization effect on hybrid sorrel yield was found. The crop establishment in spring is preceded by plowing in autumn. Hybrid sorrel can be harvested in the year following the establishment. As a perennial crop, hybrid sorrel provides ecosystem services to a greater extent than first‐generation annual crops. They are, for example, habitat functioning, air regulation, biodiversity conservation, anti‐erosion effect, and groundwater protection. After cultivation, it can leave up to 60 t ha−1 of slightly mineralizable organic matter in the soil. Hybrid sorrel's drawbacks include low resistance against weeds and sensitivity to drought damage. According to the available data, this hybrid sorrel is one of the most promising energy crops in the temperate zone. It is suitable for both combustion and biogas production. In biogas production, sorrel produces a total methane yield of about 2500 to 3500 mN3 ha−1, and as a biofuel for combustion it shows a relatively high DM calorific value, of about 18 MJ kg−1. Alongside its use for energy and fodder purposes, it can be cultivated to produce medicines and unique building materials. It can also be used for the phytoremediation of contaminated soils. © 2020 Society of Industrial Chemistry and John Wiley & Sons Ltd
Biogas plants receive inputs of different sources of carbon, nutrients, metals and other pollutants from large areas that result in a digestate that is a very complex and concentrated matrix. How to redistribute all these components without causing imbalances in the receiving environments is one of the main questions that arises regarding the reuse of digestate. The main end destinations of digestate within the EU are agriculture, landfill and incineration, in addition to open-mine land reclamation. There are European and country specific end destinations of digestate that have been recently reviewed and made publicly available in an EU commission report. In terms of agricultural application, digestate is seen as a valuable source of carbon and nutrients, but its application is conditioned by disposal limits for nitrogen, phosphorous and metals. Here, we discuss the need for redesign of the process of digestate manipulation in order to increase its value as fertiliser, through addition of compounds, different solid/liquid phases separation or additional treatments. Potential recovery techniques are also discussed. Phytoremediation, the use of plants to uptake metals from different substrates, can be used not only to remove trace metals from the digestate but also for the recovery of metals from plant biomass or their reintroduction into the biodigester. In addition, a combination of landfill with phytoremediation can be a good alternative for the recovery of degraded soils, or for the reclamation of polluted soil for landscape recovery. Another option can be the use of digestate to produce biochar to be applied in agriculture, a technique that increases carbon content in soils while decreasing trace metal bioavailability. Finally, we discuss the new opportunities that are arising for the use of digestate, including microalgae biomass production and bioenergy.
The removal of heavy metals from sewage sludge using the combined influence of hydrothermal pretreatment and chelate extraction was tested. The classical method of batch extraction with chelates and the advanced hydrothermal pretreatment (HTP) extraction process with chelates were compared. Both experiments with removal of selected HMs were performed with 0.1 M solutions of 5 different chelating agents: citric acid (CA), S-carboxymethyl-L-cysteine (SCLC), ethylenediamine disuccinic acid (EDDS), methylglycine diacetic acid (MGDA) and ethylenediaminetetraacetic acid (EDTA). The sequential order of potential extraction efficiency at chelates was found as EDDS> EDTA> MGDA >>> SCLC> KC. The mixture of sewage sludge with high sand content soil (A) had in all cases the higher removal efficiency in comparison to the sewage sludge mixture with clay soil (B). The removal of the tested HMs from mixture A and B was better than from the sewage sludge alone. HTP extraction method showed better removal efficiency and significantly shorter time of the process. Also, this extraction method had the higher potential of efficiency in the mixture of soils and sewage sludge. More detailed research on this topic is desirable.
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