Nutrient recovery from digestates : techniques and end-products

In nitrate vulnerable zones application of animal manure to land is limited. Digestate from anaerobic digestion plants competes with manure for nutrient disposal on arable land, which forms a serious hinder for the biogas sector to develop in these regions. Hence, one of its biggest challenges is to find cost-effective and sustainable ways for digestate processing or disposal. Furthermore, primary phosphorus resources are becoming scarce and expensive and will be depleted within a certain time. This urges the need to recycle P from secondary sources, like digestate or manure. From a sustainability point of view, it seems therefore no more than logical that digestate processing techniques switched their focus to nutrient recovery rather than nutrient removal. This paper gives an overview of digestate processing techniques, with a special focus on nutrient recovery techniques. In this paper nutrient recovery techniques are delineated as techniques that (1) create an end-product with higher nutrient concentrations than the raw digestate or (2) separate the envisaged nutrients from organic compounds that are undesirable in the end-product, with the aim to produce an end-product that is fit for use in chemical or fertiliser industry or as a mineral fertiliser replacement. Various nutrient recovery techniques are described, with attention for some technical bottlenecks and the current state of development. Where possible, physicochemical characteristics of the endproducts are given

Nutrient recycling from bio-digestion waste as synthetic fertilizer substitutes: a field experiment

In the transition from a fossil to a bio-based economy, it has become an important challenge to maximally recycle valuable nutrients that currently end up in waste streams. Nutrient resources are rapidly depleting. Significant amounts of fossil energy are used for the production of synthetic fertilizers, whereas costs for energy and fertilizers are increasing. In the meantime, biogas production through anaerobic digestion produces nutrient-rich digestates as a waste stream. In high-nutrient regions this product cannot or only sparingly be returned to agricultural land in its crude unprocessed form. The consequential processing of digestate requires a variety of technologies producing several different derivatives, which could potentially be re-used as green fertilizers in agriculture. As such, a sustainable alternative for fossil-based mineral fertilizers could be provided. The aim of this study was to evaluate the impact of using bio-digestion waste instead of synthetic fertilizers and/or animal manure on soil and crop production. In a field trial, nutrient balances were assessed and the physico-chemical soil quality, including the nitrate residue, leaching, the salt content, pH, sodium adsorption ratio, as well as phosphorus and heavy metal accumulation, were evaluated. The biogas yield of the harvested energy crops was determined by means of an anaerobic digestion batch test. As such, the nutrients coming from the digestate are again recycled to the anaerobic digestion plant and nutrient cycles are maximally closed. Finally, an economic and ecological evaluation was conducted. In the current field-trial, application of waste water from acidic air scrubbers for ammonia removal, digestates and their liquid fraction caused small, yet insignificant, improvement in crop yield, physico-chemical soil fertility and soil quality compared to current common practices involving the use of animal manure and synthetic fertilizers. Moreover, it is observed that the use of bio-digestion waste can stimulate phosphate and potassium mobilization from the soil, thereby increasing the use efficiency of soil nutrients. For all re-use scenarios the energetic potential per hectare of harvested energy maize was slightly higher than in the reference scenario. Finally, the substitution of synthetic fertilizers by these bio-based alternatives resulted in significant economic and ecological benefits. Re-use of bio-digestion waste can so improve the economic viability of anaerobic digestion plants, especially in high-nutrient regions, which in turn can serve as a catalyst to meet the 2020 directives. It is clear that the re-use of bio-based products as nutrient supply in agriculture should be stimulated in European legislation. The results obtained in this research can help to better classify these products and serve as a support to stimulate their use. Further field research is on-going in order to validate the results and evaluate the impact on soil quality in the longer term. The presentation will first give a brief description of the nutrient problem, followed by a detailed description of the aims and set-up of the field experiment, as well as the results of the first fertilization year

Nutrient recovery from digestate: techniques & end-products

In nitrate vulnerable zones application of animal manure to land is limited. Digestate from anaerobic digestion plants competes with manure for nutrient disposal on arable land, which forms a serious hinder for the biogas sector to develop in these regions. Hence, one of its biggest challenges is to find cost-effective and sustainable ways for digestate processing or disposal. Furthermore, primary phosphorus resources are becoming scarce and expensive and will be depleted within a certain time. This urges the need to recycle P from secondary sources, like digestate or manure. From a sustainability point of view, it seems therefore no more than logical that digestate processing techniques switched their focus to nutrient recovery rather than nutrient removal. This paper gives an overview of digestate processing techniques, with a special focus on nutrient recovery techniques. In this paper nutrient recovery techniques are delineated as techniques that (1) create an end-product with higher nutrient concentrations than the raw digestate or (2) separate the envisaged nutrients from organic compounds that are undesirable in the end-product, with the aim to produce an end-product that is fit for use in chemical or fertiliser industry or as a mineral fertiliser replacement. Various nutrient recovery techniques are described, with attention for some technical bottlenecks and the current state of development. Where possible, physicochemical characteristics of the endproducts are given

Source Apportionment of Nitrate Pollution in Surface Water Using Stable Isotopes of N and O in Nitrate and B: A Case Study in Flanders (Belgium)

Excess application to fields of animal manure or mineral fertilizers is generally assumed to be the major source of nitrate pollution in surface and groundwater in agricultural areas in Flanders (Belgium). The Flemish Environment Agency (VMM) suspects, but could not prove, that discharges of untreated domestic sewage or discharges containing mineral fertilizers from hydroculture in greenhouses are also contributing to the nitrate pollution observed in some of the agricultural areas. The objective of this study was to investigate, using stable isotope data of dissolved nitrate and boron, if these suspected sources significantly contribute to the nitrate pollution observed in selected surface water monitoring points in Flanders.JRC.D.4-Isotope measurement

Groene kunstmeststoffen

In Vlaanderen wordt er jaarlijks 66 miljoen kg N en 4,5 miljoen kg P2O5 als kunstmest gebruikt in de landbouw. Nochtans vergt de aanmaak van kunstmest-N m.b.v. fossiele grondstoffen zeer veel energie (37 GJ/ton NH4 of 2 L olie per ton N). Daarnaast heerst wereldwijd de discussie over een dreigend fosfaattekort. Fosfaat is immers een eindige grondstof, in die zin dat rijke fosfaatertsen opraken en de stof na gebruik in de landbouw uiteindelijk met de huidige technologie niet meer beschikbaar is. Tegen het einde van deze eeuw zullen de beschikbare natuurlijke bronnen dan ook grotendeels zijn opgebruikt. Een gelijkaardig probleem stelt zich voor essentiële micronutriënten. Het wordt dan ook meer en meer duidelijk dat we in de overgang van fossiele naar hernieuwbare economie ook meer aandacht zullen moeten besteden aan recuperatie en hergebruik van macro- en micronutriënten, bv. uit mest- en digestaatverwerking