Recovery of nutrients from the liquid fraction of digestate: Use of enriched zeolite and biochar as nitrogen fertilizers

Abstract

The liquid fraction after liquid/solid separation of biogas digestate has a high potential as a fertilizer due to its high nutrient concentration. However, the direct application of digestate in agricultural fields results in practical problems due to its voluminous nature. One solution to this could be to concentrate nutrients onto sorbents such as biochar or zeolites, which can subsequently be used as a fertilizer. This study investigated the ability of biochar and zeolite ‘clinoptilolite' enriched with digestate nutrients to supply nitrogen (N) when used as a fertilizer. A pot experiment with ryegrass was conducted to test the effect of a nutrient‐enriched biochar and clinoptilolite by determining plant biomass growth and N uptake. This included untreated biochar and clinoptilolite as controls and two levels of N application (15 and 45 mg N per pot) each at two initial loading ratios (low and high). Nutrient‐enriched biochar and clinoptilolite increased plant biomass yield (up to 1.02 and 2.39 g per pot) and N uptake (up to 11.23 and 39.94 mg N per pot) compared to the untreated sorbents treatments. Initial loading ratio had a significant effect on plant biomass response and apparent N recovery (ANR) for enriched clinoptilolite, and lower initial loading ratio improved plant growth. In contrast to clinoptilolite, higher initial loading ratio resulted in higher ANR. In conclusion, our results reveal that N released from enriched clinoptilolite and biochar could be taken up by the plants, clinoptilolite performed more effectively than biochar, and initial loading ratio affected the performance of the sorbents when used as a fertilizer.

Feasibility of Nitrogen-Enriched Chars as Circular Fertilizers

“…5%) of the retained N was released but high releasing ratios of 40-70% have also been observed [30,50]. Kocatürk-Schumacher et al [31] conducted a pot experiment with ryegrass to examine the plant availability of N enriched in wood-based biochar and recorded an apparent N recovery of merely roughly 10%, which was attributed to high N retention. Clearly major differences in the strength of N retention occur between chars and both the sorption and release capacities need to be assessed while estimating the feasibility of different chars as N carriers.…”

“…Even though some chars seem to be able to carry agronomically meaningful amounts of N, the approach may be challenged by strong retention. Limited release of the added N to salt extracts (0.001-1 M KCl or CaCl 2 ) [22,26,30] and by plant uptake [31] has been reported. However, more results on the plant availability of N loaded in chars are needed from pot and field tests involving plants to assess the usability and value of various N enriched chars in agriculture.…”

A critical review: emerging bioeconomy and waste-to-energy technologies for sustainable municipal solid waste management

“…Based on the water content in the slurry of the organic wastes, AD systems can be primarily classified into two types: (1) wet (< 5% of total solids) and (2) dry (> 20% of total solids) processes [84]. The volume of liquid digestate from dry AD is much lower than from the wet one, while the nutrients (mainly nitrogen and phosphorus) in the liquid digestate can be further recovered by various biorefinery technologies [85][86][87][88][89][90]. Solid digestate can be used as compost which provides the same value as organic conditioners in land amendment application [91][92][93], lessening the dependence on chemical fertilizers, enhancing soil moisture retention and reducing irrigation requirements [94][95][96][97][98].…”

A time‐ and cost‐saving method to check the point‐to‐point distribution of soil improvers

“…Addition of ZT to soil, in time, have met various target such as, for example and recently reviewed, organic waste composting ( Soudejani et al., 2019), trapping of heavy metals ( Koshy and Singh , 2016), and radionuclide ( Parajuli et al., 2016) at water/soil interface. Nevertheless, the most common application is related to the ability of zeolites in uptake ammonium from circulating aqueous solutions and release it gradually to plant roots, limiting nitrogen leaching into groundwater and, therefore, mitigating its dispersion in the environment ( e.g ., Eslami et al., 2018; Faccini et al., 2018; Kocatürk‐Schumacher et al., 2019; Sun et al., 2019; Bortolini et al., 2020). A prerequisite for the application of this technology is that the amount and composition of ZT spread on soil is controlled to match the features of soil and of crop production.…”