Depending on the quality of the input substrates, process parameters, and postfermentation treatments, digestates may contain a broad spectrum of potentially toxic elements. We suspected that these ...contents may vary on a broad scale even under seemingly stable process conditions at the biogas plant. Digestates from four biogas plants were therefore continuously analyzed for their contents of phosphorus, nitrogen, cadmium, copper, lead, and zinc over a period of six years. The input substrates varied between the plants (e.g., cattle and pig slurry and rye and maize silage), but were the same for each plant over the whole period. The N : P ratio of the digestates ranged from 2 to 24, with the digestate coming from cofermentation of pig slurry and energy crops (“DG Pig”) having the widest range of N : P ratio over the years. Heavy metal loads of all digestates and during all evaluations did not exceed the limits set by European or German legislation, but as previously expected, showed a large variability especially if cattle or pig manure were used as substrates. Copper content of Cattle slurry before digestion was 897.7 mg kg−1 DM in one case, and zinc content of DG Pig reached 590.2 mg kg−1 DM also once during the investigation. As a result, we strongly recommend to monitor especially phosphorus, copper, and zinc contents in digestates very closely and in short intervals.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Purpose
Fermentation and composting of biowaste has become a preferred method for municipalities to recycle organic byproducts and their valuable nutrient content. Pelletization or agglomeration of ...the resulting digestates may improve their transportability and storability. The aim of this study was to determine the nutrient content and nutrient release from processed biowaste digestates and the immediate as well as the longer-term effect of their application on the early root and shoot development of oat (
Avena sativa
L.).
Methods
Rhizoboxes were used in which rooting compartment and soil are separated by nylon gauze, which allows nutrients and water to pass through, but denies direct contact between roots and soil or digestate products. The obtained root images were analyzed with the WinRhizo Software and chemical properties of the soil were determined at three dates over a period of 28 weeks.
Results
Pelletization and agglomeration of digestates led to an increased immobilization of nutrients and organic matter contained in the digestate. The treated products remained in the soil rather unchanged over many months. A significant influence of the biowaste digestates on plant development was observed only during the first weeks after the application. The application of the digestate products did lead to an increase of total carbon and especially hot water-soluble carbon content in the soil.
Conclusions
The application of biowaste digestates seems therefore well suited for the improvement of humus content in soils. The fertilizing value of processed digestates, however, must be considered as very limited, regardless of their actual nutrient content.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Fermentation in combination with subsequent composting of biowaste is a preferred method for municipalities to recycle organic byproducts and transform them into useful end products for soil ...amelioration or plant fertilization. These compost products, especially if obtained from household wastes, can be a source of hazardous components, e.g. heavy metals, pathogens, synthetic chemicals or toxic organic compounds. An avoidance test with two earthworm species (Eisenia fetida and Aporrectodea caliginosa) was conducted to assess the impact of differently processed biowaste based digestate products on soil invertebrates. Body weight changes were recorded, as well as differences in effects on adult versus juvenile earthworms.
While E. fetida showed no avoidance towards the digestate products (negative avoidance, meaning that the tested products were preferred, of 80 to 100 %), A. caliginosa rejected the crude biowaste digestate compost in higher concentrations (avoidance of 45 %), but not the agglomerated or pelletized variants. A clear weight gain of up to 25 % was observed only for individuals of E. fetida. The developmental stages of the worms were not crucial for the outcome of the avoidance test.
Based on the results of this study the application of biowaste products on arable land cannot be recommended without constraints.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
In einem dreijährigen Feldversuch wurden kompostierte Gärreste aus Bioabfällen hinsichtlich ihrer pflanzenbaulichen Einsatzmöglichkeiten und ihrer Wirkung auf bodenchemische Parameter geprüft. ...Zudem wurden die Aufbereitungsverfahren Pelletierung und Agglomeratbildung und deren Auswirkung auf die Gärprodukteigenschaften untersucht. Es wurde festgestellt, dass die unmittelbare Düngewirkung der Produkte aufgrund der niedrigen Stickstoffverfügbarkeit gering ist. Allerdings zeigte sich nach der Anwendung eine deutliche Erhöhung der Kohlenstoffgehalte im Boden, was auf ein relevantes Humusreproduktionspotential durch derartige Gärprodukte schließen lässt. Agglomeratbildung und Pelletierung scheinen die Mineralisierung der Produkte weiter zu verlangsamen, was sich auf die Nährstofffreisetzung negativ, auf eventuelle Kohlenstoffsequenzierung jedoch positiv auswirkt. Problematisch sind speziell bei Bioabfällen hohe Gehalte an Schwermetallen und anderen Störstoffen. Die gesetzlich vorgegebenen Grenzwerte wurden in 50% der untersuchten Chargen überschritten, wobei jedoch nur max. 7% der ausgebrachten Schwermetalle im oberirdischen Pflanzenmaterial wiedergefunden wurden.
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