Digestate Fertilizer Research Articles

Effect of Digestate and Straw Combined Application on Maintaining Rice Production and Paddy Environment.

Few studies have focused on the combined application of digestate and straw and its feasibility in rice production. Therefore, we conducted a two-year field experiment, including six treatments: without nutrients and straw (Control), digestate (D), digestate + fertilizer (DF), digestate + straw (DS), digestate + fertilizer + straw (DFS) and conventional fertilizer + straw (CS), to clarify the responses of rice growth and paddy soil nutrients to different straw and fertilizer combinations. Our results showed that digestate and straw combined application (i.e., treatment DFS) increased rice yield by 2.71 t ha−1 compared with the Control, and digestate combined with straw addition could distribute more nitrogen (N) to rice grains. Our results also showed that the straw decomposition rate at 0 cm depth under DS was 5% to 102% higher than that under CS. Activities of catalase, urease, sucrase and phosphatase at maturity under DS were all higher than that under both Control and CS. In addition, soil organic matter (SOM) and total nitrogen (TN) under DS and DFS were 20~26% and 11~12% higher than that under B and DF respectively, suggesting straw addition could benefit paddy soil quality. Moreover, coupling straw and digestate would contribute to decrease the N content in soil surface water. Overall, our results demonstrated that digestate and straw combined application could maintain rice production and have potential positive paddy environmental effects.

Effect of Fertilization on the Energy Profit of Tall Wheatgrass and Reed Canary Grass

Cultivation of energy crops is a part of modern agriculture. In particular, maize (Zea mays L.) is widely grown in central Europe. However, in terms of erosion risk and high demands on fertilization and protection against diseases and pests, its growing is not environmentally friendly. Therefore, possibilities of utilization of other more environmentally friendly energy crops have been examined at present. The aim of the study was to evaluate the effects of various fertilization (mineral, digestate, control) on the yields of tall wheatgrass (TWG) (Elymus elongatus subsp. ponticus) and reed canary grass (RCG) (Phalaris arundinacea L.) cultivated in a long-term field experiment on the experimental site in Czech Republic. The energy profit from cultivation of these crops and its protective anti-erosion effect were evaluated. The average yields ranged from 4.6 (RCG, mineral fertilization) to 7.4 t/ha (TWG, digestate fertilization). The more profitable species was tall wheatgrass, the biomass of which also had the higher heating value. The energy profit ranged from 80 GJ/ha (RCG, control variant and mineral fertilization) to 133 GJ/ha (TWG, digestate and mineral fertilization). It has been found that the tested plants excel in anti-erosion effect and could therefore be a suitable alternative to maize, especially in less-favored areas.

Thermochemical digestate fertilizer from solid waste: Characterization, labile carbon dynamics, dehydrogenase activity, water holding capacity and biomass allocation in banana

Thermochemical digestion is a rapid technology of biowaste management resulting in the instant production of organic fertilizer. Characterization and assessment of its suitability as an organic fertilizer is essential for recommendation for crop application. Biowaste and the thermochemical digestate were subjected to physicochemical and biochemical characterization and the compost maturity parameters assessed. The product integrated with inorganic fertilizers was tested in an Ultisol grown with banana in comparison with farmyard manure based fertilizers. Temporal variation in soil reaction, water holding capacity, carbon dynamics, dehydrogenase activity and plant biomass were determined. The thermochemical digestate fertilizer had a bulk density (0.76 Mg m−3), pH (neutral), C:N ratio (16.26), CEC (85.70 cmol(+) kg−1), CEC/ TOC ratio (3.99), Fertilizing index (4.7) and a Clean index (5.0). Field evaluation revealed enhanced water holding capacity (38.75–83.17%). Total carbon increased with consistently high labile (R2 = 0.9551) and non labile carbon fractions and the lowest average lability index (0.78). Dehydrogenase activity at harvest enhanced by 72.81%. An even biomass allocation resulted in 38.84% more biomass production in the fruit over farmyard manure based treatments. In addition to ensuring the safety of the environmental ecosystem, the thermochemical digestate conformed to be a quality resource favoring microbial proliferation and carbon sequestration, thereby restraining carbon dioxide emission. The thermochemical digestate fertilizer based nutrition serves the key deliverables of natural resource management, ecofriendly rapid disposal of biowaste and quality organic fertilizer for banana in Ultisols.

The Effect of Digestate Fertilization on Grass Biogas Yield and Soil Properties in Field-Biomass-Biogas-Field Renewable Energy Production Approach in Lithuania

The shift from fossil economy to bio-economy will stimulate the demand for bio-based energy generation. The promising strategy to meet the growing demand of biomass for energy production is to re-cultivate set-aside arable land. The digestate fertilization approach for the sake of increased biomass yields is the key strategy towards sustainable biogas generation in many regions. In order to minimise digestate utilization costs, biogas plant operators seek to spread the liquid digestate as close as possible to its storage location. The present work is focused on the evaluation of the digestate impact for the eroded agricultural soil, the improved biomass yield of semi-natural grassland biomass and its biogas potential. Three-year field experiments results indicate the positive effect of solid and liquid digestate on soil fertility and quality. The amount of dissolved organic carbon in eroded loamy Retisol increased 3.7% and 15% in soil 0–10 cm layer with fertilization rate of 170 kg ha -1 N of liquid and solid digestate, respectively. In terms of total nitrogen 11.6% and 20% increase was achieved using 170 kg ha -1 N of liquid and solid digestate compared to the untreated. Furthermore, the grass fresh biomass yield was up to 3 times higher compared to untreated. The biomethane yield of biomass from digestate fertilized fields was higher for every fertilization rate applied. The highest biomethane yield was for 170 kg N ha-1 liquid digestate applied yielding 19% more biogas compared to untreated field biomass both due to increased biogas yield and increased methane content.

Study of Occurrence Characteristics of Antibiotic Resistance Genes in Pig manure during Anaerobic Digestion and Digestate Fertilization

Antibiotic resistance genes (ARGs) existing in livestock and poultry manure have the risk to spread and proliferate. This might endanger people’s health. The common treatment of livestock and poultry manure is anaerobic digestion. But the change of ARGs during anaerobic digestion require further study, and the effect of digestate fertilization to the antibiotic resistance of cropland soil is still unclear. This study investigated the pig manure, biogas liquid, biogas residue, and cropland soils fertilized with and without digestate. The results showed that, the relative abundance of ARGs in biogas residue was much higher than other samples. The average relative abundance was 1.46×10-1 copy ratio (copy of ARG/copy of 16S rRNA gene), and the total relative abundance was 3.07 copy ratio. There were 21 ARGs detected in the 5 samples. 11 of them were shared by the 5 samples. The main ARGs were aminoglycoside, chloramphenicol, sulfonamide, tetracycline, and multidrug. Aminoglycoside had the highest relative abundance, and the total relative abundance in all samples was 1.18 copy ratio. Anaerobic digestion increased the total relative abundance of ARGs in pig manure from 1.14×10-1 to 1.70×10-1 copy ratio. Fertilization of digestate increased the total relative abundance of AGRs in soil from 3.27×10-1 to 7.29×10-1 copy ratio.

Greenhouse gas emissions in agricultural cultivated soils using animal waste-based digestates for crop fertilization

AbstractAgricultural waste contributes significantly to greenhouse gas (GHG) emissions if not adequately recycled and sustainably managed. A recurring agricultural waste is livestock waste that has consistently served as feedstock for biogas systems. The objective of this study was to assess the use of animal waste digestate to mitigate GHG emissions in agricultural fields. Wheat (Triticumspp. L.) was fertilized with different types of animal waste digestate (organic fertilizers) and synthetic nitrogen fertilizer (inorganic fertilizer). The 170 kg N/ha presented in digestates were split fertilized at an application rate of 90 and 80 kg N/ha. Emissions of GHGs (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)) were monitored directly by a static chamber system. The soil and environmental variables were measured to determine their influence on GHG emissions. Emission peaks in N2O and CO2after the first application of fertilizers with the emissions flattening out over the cultivating season while CH4emission was negligible with no apparent patterns observed. Results showed individual and cumulative emissions of CO2, CH4and N2O from the digestates were relatively low and digestate fertilization could be an efficient method for reducing GHGs from agricultural sources in temperate climate conditions.

Towards a bio-based circular economy in organic waste management and wastewater treatment – The Polish perspective

Bio-based solutions are expected to ensure technological circularity in priority areas such as agriculture, biotechnology, ecology, green industry or energy. Although Poland, unlike the other EU member states, has not yet adopted a precise political strategy to promote bioeconomy, it has taken several actions to enable smart, sustainable and inclusive growth. This goal can be achieved by developing selected bioeconomy-related areas such as the biogas industry together with novel technologies implemented to optimize treatment of municipal sewage and management of organic solid waste. Here, the relatively strong status of the Polish biogas sector is presented. The widely used practice of sewage sludge biomethanation has led to construction of numerous complex installations combining biological wastewater treatment plants with anaerobic digesters. Based on physico-chemical processing of biostabilized sludges, a novel method for efficient granulated soil fertilizer production is elaborated, in line with the concept of circular economy and the notion of “waste-to-product”. It is also shown that anaerobic fermentation of sewage sludges can be optimized by co-digestion with properly selected co-substrates to increase bioprocess yield and improve the resultant digestate fertilizer quality. The problem of post-fermentation eutrophic sludge liquors, environmentally hazardous waste effluents requiring proper treatment prior to discharge or field application, is addressed. Attempts to optimize biological treatment of digestate liquors with complex microbial consortia are presented. The Polish innovations described show that the “zero waste” path in circular bioeconomy may bring advantageous results in terms of transformation of waste materials into commercial, added-value products together with recovery of water resources.

Biogas digestate as a renewable fertilizer: effects of digestate application on crop growth and nutrient composition

AbstractBiogas digesters convert waste matter into a natural gas-like fuel and a nutrient-rich digestate by-product. This digestate has the potential to be used as a soil amendment to benefit crop production with or without biochar, a purported nutrient sponge. In a greenhouse study of several crop species, the effects of digestate fertilization on crop growth, photosynthetic efficiency, vegetable production and chemical nutrient levels were tested. Results indicate that increasing potency of the applied digestate fosters higher growth and fruit production rates of several studied plants but to a lesser degree than a conventional fertilizer. More potent digestate application increases antioxidant capacity, total phenolics content and ascorbic acid levels in kale compared to the control chemical fertilizer test groups but has confounding results on legume nutrient levels. Additionally, the combined application of biochar and biogas digestate added to compost and used as potting media positively impacts crop germination. This work has relevance to agrarian communities that could benefit from recycling livestock and food waste into fuel and a renewable fertilizer.

Life Cycle Assessment of Giant Miscanthus: Production on Marginal Soil with Various Fertilisation Treatments

In Poland, unutilised land occupies approximately two million hectares, and it could be partly dedicated to the production of perennial crops. This study aimed to determine the environmental impact of the production of giant miscanthus (Miscanthus x giganteus J.M. Greef & M. Deuter). The experiment was set up on a low-fertility site. The crop was cultivated on sandy soil, fertilised with digestate, and mineral fertilisers (in the dose of 85 and 170 kg ha−1 N), and was compared with giant miscanthus cultivated with no fertilisation (control). The cradle-to-farm gate system boundary was applied. Fertilisers were more detrimental to the environment than the control in all analysed categories. The weakest environmental links in the production of miscanthus in the non-fertilised treatment were fuel consumption and the application of pre-emergent herbicide. In fertilised treatments, fertilisers exerted the greatest environmental impact in all the stages of crop production. The production and use of fertilisers contributed to fossil depletion, human toxicity, and freshwater and terrestrial ecotoxicity. Digestate fertilisers did not lower the impact of biomass production. The current results indicate that the analysed fertiliser rates are not justified in the production of giant miscanthus on nutrient-deficient soils.

The effect of digestate and mineral fertilisation of cocksfoot grass on greenhouse gas emissions in a cocksfoot-based biogas production system

BackgroundClimate mitigation is a major consideration when choosing bioenergy systems. Anaerobic digestion of biomass is a bioenergy system, which is normally used for the treatment of manure or other residues, but cultivated energy crops may also provide a potential feedstock. One of the main crops for biogas production is still maize, but it may be desirable to replace it by perennial grasses, which also have high yields, but do not require as much management. The aim of this study was to analyse greenhouse gas (GHG) emissions in a biogas production system based on a perennial grass, cocksfoot, grown under different fertiliser application systems.MethodsField and laboratory experiments were carried out over a 7-year period to evaluate the influence of mineral nitrogen and digestate fertiliser application on cocksfoot biomass and biogas productivity. The obtained data were used to calculate GHG emissions and emission savings for the whole biogas production cycle, by use of the SimaPro v.8 software with the IMPACT 2002+ model, based on the climate change environmental impact category.ResultsProductivity of cocksfoot (Dactylis glomerata L.) was influenced by the annual rate of nitrogen applied as fertiliser, the fertiliser type and year, as influenced by the weather conditions. The biomass yield of cocksfoot fertilised with 180 kg nitrogen ha−1 year−1 was similar regardless if the nitrogen was applied as digestate or mineral fertiliser. At higher rates of nitrogen application (360–450 kg ha−1 year−1), higher yields and lower net GHG emissions could be obtained from the biogas production cycle when the nitrogen was applied as digestate compared to mineral fertiliser, especially in dry years. Energy input over the whole cycle was mainly influenced by the type of fertiliser and the biomass yield. Mineral fertiliser generally caused higher levels of GHG emissions than organic digestate fertiliser, when the same amount of energy is produced.ConclusionsThe cocksfoot grass-based biogas production system showed that a significant GHG emission saving potential exists, if nitrogen is added as digestate instead of mineral fertiliser, for similar yields of biomass and energy from biogas. Cocksfoot grass fertilised with digestate is thus a promising feedstock for biogas production.

Biogas Digestate in Vegetable Hydroponic Production: pH Dynamics and pH Management by Controlled Nitrification

Soilless cultivation of vegetables with digestate fertilizer from biogas production as a nutrient source is a promising method for integrating food production and organic waste management. In this study, bok choy (Brassica rapa var. chinensis) was cultivated in a hydroponic nutrient film technique system with biogas digestate as the only fertilizer source. Nitrification in moving bed biofilm reactors (external and/or integrated into the hydroponic cultivation system) was employed to lower the high ammonium concentration in the digestate prior to use. Treatments with differing nitrification and digestate input strategies were compared with respect to pH dynamics, crop growth, shoot water content, and shoot mineral content. The results showed that < 20% longer cultivation time (< 1 week) gave similar yield in biogas digestate-based hydroponics as in conventional hydroponics based on synthetic fertilizers. Automatic pH control through addition of digestate resulted in similar shoot dry weight as in the mineral fertilizer reference system. It can be concluded that biogas digestate is a suitable plant nutrient source for hydroponic production of bok choy, considering productivity and circularity aspects. The combined impact of digestate ammonium content, digestate pH, and the nitrification step needs to be considered when designing a hydroponic system with biogas digestate as the fertilizer source.Graphic

Soil incubation study showed biogas digestate to cause higher and more variable short‐term N2O and N2 fluxes than mineral‐N

AbstractToday, a large share of mineral fertilizer is substituted by biogas digestates. Biogas digestates are known to promote N2O production, compared to mineral fertilizer. In particular, the initial phase following fertilizer application is crucial for the N gas release as N2O and also N2. However, this period impact has been rarely investigated, especially not across various field sites. Thus, undisturbed soil cores from two fertilizer types (biogas digestate vs. mineral fertilizer) at five sites with different site characteristics were investigated in a short‐term laboratory experiment under N2‐free helium–oxygen incubation atmosphere. Across sites, biogas digestate soil cores showed significantly higher absolute N2O fluxes compared to mineral fertilizer soil cores, even though this effect was dominated by samples from one site (Dornburg with the highest biogas digestate fertilization rate). Also relative N2O fluxes showed a similar tendency. On average, absolute and relative N2 fluxes differed between the two fertilizer types, while N2 fluxes were highest at the Dornburg site. A N2O/(N2O+N2) ratio of denitrification below or equal to 0.5 clearly highlighted the importance of N2O reduction to N2 for three of five the biogas digestate soil cores. Soil characteristics like bulk density and water‐filled pore space as proxies for gas diffusivity in soil, as well as N availability ( , ), significantly affected the N2O and N2 fluxes from the biogas digestate soil cores. While this study presents data on short‐term N2O and N2 fluxes, there is a need for further studies in order to investigate the dynamics, the duration of the observed effects and their significance at the field scale.

Effect of solid-liquid separation on anaerobic digestion of dairy manure in semi-continuous stirred tank reactors: Process performance and digestate characteristics.

The objective of this study was to investigate the effect of solid-liquid separation on anaerobic digestion of dairy manure in semi-continuous stirred tank reactors. Reactors fed with liquid fraction of dairy manure (screened liquid manure) were kept in water baths at mesophilic (Run 1) and thermophilic (Run 3) temperatures, respectively, while reactors fed with water diluted manure and kept at mesophilic (Run 2) and thermophilic (Run 4) temperatures as control reactors. The performances of reactors were compared in terms of biogas and methane production, and digestate characteristics. The methane yields obtained from screened manure were higher than those from diluted manure at both mesophilic and thermophilic temperatures, while the highest methane yield was 185L/kg VSadded under thermophilic temperature. Solid-liquid separation also had improved the effect on digestate fertilizer characteristics. Among four digestates from reactors, the highest contents of nutrients, N (4.12g/kg) and P (2.36g/kg) were found in Run 3, while the highest content of K (3.42g/kg) was found in Run 1. These results showed the benefits of solid-liquid separation of dairy manure on process performance and digestate characteristics.

The potential of digestate as a biofertilizer in eroded soils of Lithuania

The objective of this work was to determine the potential of using of solid and liquid digestate, as biofertilizer and soil amendment, and to address adverse unfertile soil erosion problems after analysing areas of potential use. We found a high concentration of organic carbon in a solid fraction of the digestate, which indicates a significant potential for returning carbon to the soil. The influence of digestate fertilization on soil fertility as a function of the amount of available phosphorus (P2O5) and potassium (K2O) in the 0–40 cm layer was found to be very important. The soil fertility category was changed from “high” (200–300 mg kg−1) to “very high” (>300 mg kg−1) according P2O5, using only 170 kg ha−1 of nitrogen in solid and liquid digestate rate. Fertilization with all phases and rates of digestate tend to increase the amount of K2O. The solid digestate fertilization using the 170 kg ha−1 N rate showed a significant increase (5 times) of mineral nitrogen content in the 0–40 cm soil layer. The advantage of solid digestate as a soil improver has been highlighted because it has a positive effect on soil fertility, quality, sustainability and durability. The amount of mobile humic acids (MHA) in eroded loamy Retisol increased 1.6 times in soil 0–40 cm layer with a fertilization rate of 170 kg ha−1 and 1.5 times – of 85 kg ha−1 of solid digestate compared to the untreated. Similar trends of MHA but in lower amount were identified when liquid digestate was applied.

Yield, content and nutrient uptake by winter wheat and spring barley in response to applications of digestate, cattle slurry and NPK mineral fertilizers

ABSTRACT Digestate represents an alternative source of nutrients for crops in sustainable agriculture. We aimed to evaluate the effects of digestate fertilization on grain (GY) and straw yield (SY) and nutrient content and uptake in winter wheat (WW) and spring barley (SB). The study duration was from 2012 to 2016, with the following crop rotation: WW/WW/SB/WW. Every year, the same fertilizers were applied to each respective plot: control, digestate, digestate + straw, cattle slurry and mineral NPK fertilizer. Significantly higher GY and SY were noted after fertilizer application each year compared to the non-fertilized control. The average effect of the fertilizers on GY of WW was control < NPK ≤ digestate + straw ≤ cattle slurry ≤ digestate. Fertilizer application also increased N, S, Na, Zn and Fe content in the grains, especially when digestate was used as fertilizer. However, in non-fertilized plants (control), only the K content increased in the grains, although the uptake of K is positively correlated with GY. Our results show that digestate can be used not only as a replacement for cattle slurry but also as an alternative fertilizer, which, under certain soil conditions, is more effective than NPK fertilizer.

Steel slag as accelerant in anaerobic digestion for nonhazardous treatment and digestate fertilizer utilization

Accelerants can effectively enhance the performance of anaerobic digestion (AD) system. The effects of optimized steel slag as accelerant in the AD of cow manure and the fertility utilization of the digestate were investigated. Results show that all steel slags collected from different iron and steel companies (slag-1, slag-2, and slag-3) positively affect AD performance in terms of enhancing the biogas yield, methane yield, and chemical oxygen demand (COD) degradation rate. The cumulative biogas yield, methane yield, and COD degradation rate of slag-2 are 507.29 mL/g VS, 274.70 mL/g VS, and 58.62%, respectively. Thermal analysis reveals that the digestate with steel slag has excellent thermal stability and potential application as a component of nitrogen, phosphorus, and potassium organic compound fertilizers. The use of different steel slags as accelerants in the AD system provides a safe and economical avenue to realize the resource utilization and harmless treatment of waste resource.

Coming Late for Dinner: Localized Digestate Depot Fertilization for Extensive Cultivation of Marginal Soil With Sida hermaphrodita.

Improving fertility of marginal soils for the sustainable production of biomass is a strategy for reducing land use conflicts between food and energy crops. Digestates can be used as fertilizer and for soil amelioration. In order to promote plant growth and reduce potential adverse effects on roots because of broadcast digestate fertilization, we propose to apply local digestate depots placed into the rhizosphere. We grew Sida hermaphrodita in large mesocosms outdoors for three growing seasons and in rhizotrons in the greenhouse for 3 months both filled with marginal substrate, including multiple sampling dates. We compared digestate broadcast application with digestate depot fertilization and a mineral fertilizer control. We show that depot fertilization promotes a deep reaching root system of S. hermaphrodita seedlings followed by the formation of a dense root cluster around the depot-fertilized zone, resulting in a fivefold increased biomass yield. Temporal adverse effects on root growth were linked to high initial concentrations of ammonium and nitrite in the rhizosphere in either fertilizer application, followed by a high biomass increase after its microbial conversion to nitrate. We conclude that digestate depot fertilization can contribute to an improved cultivation of perennial energy-crops on marginal soils.

Semi-continuous anaerobic co-digestion of dairy manure, meat and bone meal and crude glycerol: Process performance and digestate valorization

Abstract The objective of this study was to investigate the effects of the addition of meat and bone meal (MBM) and crude glycerol (CG) on the anaerobic digestion of dairy manure (DM) with respect to digestion performance and digestate fertilizer value. The anaerobic co-digestion of DM, MBM and CG was conducted in semi-continuous stirred tank reactors at 37 °C with organic loadings between 2.63 and 2.86 g volatile solids (gVS)/L·d. Run 1 was a control reactor, while in Runs 2 and 3, DM was co-digested with MBM at ratios of 3.0:1.0 and 1.0:1.0 (gVSDM:gVSMBM), respectively. In Run 4, DM and MBM were co-digested with CG at a ratio of 1.0:0.7:0.3 (gVSDM:gVSMBM:gVSCG). The results showed that methane yields were increased by 9.1% and 30.2% in Runs 2 and 3, respectively, compared to Run 1, while the highest methane yield (0.39 L/gVSadded·d) was obtained in Run 4. The co-digestion of DM with MBM increased the ammoniacal nitrogen in the digestate by 2.1- to 2.3-fold, while no significant difference was observed for phosphorus. Due to the overabundance of nutrients in soil, the recovery of phosphorus and nitrogen and the recycling of water are the best strategies to sustain anaerobic digestion via an environmentally friendly approach.

Assessment of agro-ecological service crop managements combined with organic fertilisation strategies in organic melon crop

In organic horticultural systems, cover crops could provide several ecological services, therefore, they can be defined agroecological service crops (ASCs). The objective of this two-year research was to study the suitability on melon production of different ASC termination strategies, in combination with organic fertilisers application. In a split-block design, the main-plot was the ASC management, comparing: i) green manure, in which the vetch was chopped and plowed into the soil; and ii) roller-crimper (RC), in which the vetch was flattened by a roller-crimper; with iii) fallow control, without vetch. The subplot consisted of offfarm organic inputs: i) commercial humified fertiliser; ii) anaerobic digestate fertiliser; iii) composted municipal solid wastes; which were compared to iv) unfertilised control (N0). At vetch termination, above soil biomass and nitrogen (N) content were determined. At harvesting, crop yield performance and quality, N status and N efficiency were investigated. Also, main soil characteristics were assessed at the end of the trial. Among the ASC managements, the slightly reduced yield in the RC plots particularly in combination with N0 might have been the result of less N supplied by the vetch during the melon cycle. Anyway, no negative effects were observed for yield quality. The use of the RC showed a great potential in enhancing soil fertility. Our study suggests the suitability in organic farming of properly matching management of ASC and fertilisation strategies on melon crop.

A potential phosphorous fertilizer for organic farming: recovery of phosphorous resources in the course of bioenergy production through anaerobic digestion of aquatic macrophytes

BackgroundA major problem with farming systems is the deficiencies in phosphorus (P) due to fixation in soils, erosion and run-off, and exports of herbal and animal products. P resources for the compensation of these losses will sooner or later be depleted. For this reason, innovative ideas for phosphorus recycling are highly relevant.The P excess from farming systems mostly ends up in surface waters, leads to eutrophication, and promotes the growth of aquatic plants. Particularly invasive neophytes such as western waterweed (Elodea nuttallii) can rapidly generate high levels of biomass in waters with good nutrient supply and bind relevant amounts of phosphorus.MethodsIn the renatured open-pit mine Goitzsche (Saxony-Anhalt, Germany), biomass from E. nuttallii was harvested (2005–2008) and the biomass dry matter and the P concentration were determined. The phosphorus recovery potential from this plant biomass was calculated by extrapolation based on the phosphorus analyses and the area potentially populated by E. nuttallii. One analysis of E. nuttallii was conducted to evaluate the content of potentially toxic elements (PTEs).ResultsThe results showed that with 0.5 to 6.3 kg P/Mg of total solid (dry matter), E. nuttallii could have a high potential to recycle phosphorus, e.g., by anaerobic digestion and digestate fertilization. Lake Goitzsche offered an annual recovery potential from 0.5 to 1.7 Mg phosphorus in the investigation period. This could meet the needs of 114-ha organic farming land based on a 7 kg/(ha*year) regional phosphorus deficit.The digestate of E. nuttallii is very well suited as a fertilizer due to its high phosphorus concentration. The concentrations of PTEs in the current digestate (related to an individual case) are sufficient for legal admission in Germany. In this study, nickel was above the threshold values for Germany. The elevated nickel levels in the Elodea biomass correspond to the geogenic high nickel concentrations in the sediment of this lake.ConclusionsAquatic macrophytes have a significant potential for recovering phosphorus from waters and sediments of relevant phosphorus concentrations. Further studies of surface water zones, particularly with regard to the aquatic plant biomass and phosphorus concentration of sediments, are needed to assess future exploration.