Recycling of Biogas Digestates in Crop Production—Soil and Plant Trace Metal Content and Variability

Abstract

Production of biogas and utilization of the resulting digestates as fertilizers has been increasing in Europe in the last few decades. Depending on the feedstock used for the anaerobic digestion process, these organic fertilizers may be a source of different pollutants, such as trace metals. When applied to soils, digestates may influence the natural metal content and enhance the release of metals to the environment since they can be rich in different trace metals and are usually rich in dissolved organic matter. This study focused on investigating metal presence, seasonal variability of their soluble forms and crop uptake in a 2-year field experiment, using two different biogas digestates as fertilizers. The use of digestates as fertilizers was compared to cattle manure, mineral fertilizer and a control without fertilizer addition, with respect to the presence and distribution of the trace metals Cd, Cu, Zn, Ni, Cr, Mn, and Mo, as well as Al in the soil and plant. The results of the study showed that both biogas digestates have caused a 10-20% increase in the total soil concentration of Ni, Cd and Cr compared to control plots without fertilizer addition. Application of biogas digestates had only a minor effect on metal uptake in plants. Overall, the selected application rate of 100 kg/ha of plant available nitrogen has had little effect on plant metal uptake and crop quality and the use of biogas digestates was comparable to the use of animal manure.

Using highly stabilized digestate and digestate-derived ammonium sulphate to replace synthetic fertilizers: The effects on soil, environment, and crop production

“…These data confirmed previous reports in the literature for similar work, namely that after the use of digestate in agriculture, no significant accumulations of heavy metals are found in the soil (Barłóg et al, 2020;Dragicevic et al, 2018).…”

Effects of Organic Fertilizer Mixed with Food Waste Dry Powder on the Growth of Chinese Cabbage Seedlings

“…On the other hand, AD technology allows for the recycling of nutrients when digestates are applied on agricultural lands, either used as food waste powder directly or mixed with other fertilizers [14,16]. For instance, anaerobic digestion for biogas production results in large amounts of liquid digestate, which contains high amounts of nutrients, such as nitrogen, potassium, and phosphorus, as well as micronutrients in plant-available forms [17]. The long-term application of food waste organic fertilizer was shown to improve soil quality, stimulate crop yields, and even have a positive influence on the growth of soil bacteria [17].…”

“…For instance, anaerobic digestion for biogas production results in large amounts of liquid digestate, which contains high amounts of nutrients, such as nitrogen, potassium, and phosphorus, as well as micronutrients in plant-available forms [17]. The long-term application of food waste organic fertilizer was shown to improve soil quality, stimulate crop yields, and even have a positive influence on the growth of soil bacteria [17]. Furthermore, food waste can be used as organic fertilizer by compositing natural biological degradation processes [2,18,19].…”

Assessment of the Quality of Liquid Digestate from Small-scale Anaerobic Biodigesters Used for Crop Irrigation in Urban and Peri-urban Maseru, Lesotho

“…However, there are some problems associated with excessive soil organic matter, which may not be obvious. Dissolved organic matter strongly influences the mobility of metals in soil [41]. High soil organic content greatly increases the activity of soil microbes, thus increasing their requirement for nitrogen and hence compete with crops for the nitrogen resource, the effect of which can be retarded plant growth [35].…”

“…The total nitrogen content of the LD is in the range of 11.4 mg/L to 35.4 mg/L with larger proportion as ammonium nitrogen, (NH 4 -N), which is readily accessible to plants. Though readily available to plants, NH 4 -N can readily be lost as ammonia through volatilisation, denitrification, or leaching through the soil profile, which may result in groundwater pollution [44].The content of NH 4 -N of the LD as a percentage of the total nitrogen content, was within the range of 27% to 67%, which is within the range reported by other authors [37]. All the LD samples had a high content of readily available nitrogen to plants, however, best management practices are required during application to avoid losses due to volatilisation, nitrification, leaching , soil erosion and runoff.…”