BioCycle October 2011, Vol. 52, No. 10, p. 54
Research evaluates options to more efficiently utilize nitrogen and other nutrients contained in manure in highly concentrated farming regions of the European Union.
F. Adani, G. D’Imporzano, A. Schievano, G. Boccasile, F. Sommariva and A. Deias

BioCycle Web Extra
Additional Figures
Biological stabilization (measured as anaerobic biogasification potential, ABP) of the organic matter during AD (Schievano et al., 2008, 2009).
Typical trend of pathogen indicators during anaerobic digestion of manure, under thermophilic conditions (> 40 °C) (data by Gruppo Ricicla, 2011)
Increased fertilizing properties of anaerobically digested materials, as compared to other types of mixed organic-mineral materials applied to agricultural land (Tambone et al. 2010).
Increased biological stability and amendment properties of anaerobically digested materials, as compared to other types of mixed organic-mineral materials applied to agricultural land (Tambone et al., 2009, personal communication).
N-Free® System. Mass flow scheme
(a) (per 100 kg wet weight) and total nitrogen balance
(b) (per 100 kg of total N)
THE economical and environmental sustainability of farming must deal with sustainable management of manure. In highly-concentrated farming regions in the European Union, such as Lombardy (Italy), Catalunya (Spain), Flanders (Belgium), Bavaria (Germany), Jutland (Denmark), The Netherlands, etc., primary concerns linked to actual manure management practices revolve around environmental, economic, social and public health factors. These include the following:
Large volumes of manure concentrated in very restricted agricultural areas cause high management costs, affecting the whole sector; Excess nitrogen and other nutrients applied to soil cause risk of leaching into groundwater and the sea; Inefficient use of N and other nutrients contained in manures when they could replace petroleum-derived mineral fertilizers; Direct emissions of methane and other greenhouse gases from manure storage tanks; Emissions of ammonia, volatile organic compounds (VOCs) and particulates from manure storage tanks and direct spreading on agricultural land severely affect air quality and public health; and Odor emissions cause low social acceptability of the entire agricultural and farming sectors.
In Lombardy Region, a protocol developed over the last several years has helped the agricultural sector address these problems. This protocol involves three steps that create a pathway to environmental, economic and social sustainability of agriculture and farming. First, anaerobic digestion (AD) has been proposed as a key biotechnology to reduce environmental impacts, improve manure’s organic and mineral matter quality and provide additional revenues to the sector. Table 1 highlights these benefits. Table 2 provides methane emissions reductions obtainable by digestion of manure.
Second, a path has been identified for how agronomic utilization of digested manures and digestates from AD plants should be directed to ensure high nutrient distribution and utilization efficiencies, minimize leaching and ammonia volatilization in the atmosphere, the possible substitution of mineral fertilizers, etc. As a third step, new technologies have been observed and analyzed as potential responses to feasibly solve the nitrogen and nutrients surplus typical of highly concentrated farming areas.

Agronomic Utilization Of Digestate
Use of digestate in agriculture is linked both to its fertilizer properties that suggest its use as a substitute to chemical fertilizers, and with the possibility of carbon cycling, the base of sustainable agriculture, i.e. organic matter as the key factor to support agricultural production and soil quality. For digestate to have the status of fertilizer, the chemical and biological features must be carefully analyzed, along with any agronomic and environmental consequence of its utilization. A good characterization of digestate should consider its fertilizing properties, odor impact, sanitary and public health features, and impacts on soil, air and water.
To consider digestate as a nitrogenous fertilizer in place of chemical fertilizer, we believe the NH4+ nitrogen content should not be below 70 to 80 percent of total N content. If the organic N content is higher than 30 percent, the digestate tends more similar to a slow-release N-fertilizer. In this case, ammonia could be released when the plant does not require it. On the contrary, digestate with high ammonia-N content (>75% of total N) must be considered very close to a chemical N-fertilizer (similar efficiency of the N-uptake in plants).
Therefore, the mineral-N quota of digestate should be dosed to agricultural soil according to a crop’s “nitrogen budget” and “nitrogen requirement,” instead of undergoing nitrogen restriction of the EU Nitrate Directive (170 kg/ha for vulnerable areas). It is not logical to limit mineral-N coming from manure, when petroleum-derived mineral-N is normally used to meet crop needs. The impacts of mineral fertilizer production on the environment must be taken into account as well in the comparison (Table 3).
High ammonia/N ratios in the liquid phase of digestate are achieved through AD followed by solid-liquid separation and subsequent settling in covered stock pools. A manure or digestate can achieve the status of fertilizer/amendment and can be used on agricultural land in equivalence/substitution of mineral fertilizers (thereby completely covering crop needs, in substitution of mineral fertilizers, even in “vulnerable zones”) only after efficient digestion and efficient solid-liquid separation by centrifugation and/or decantation (Figure 1).
To ensure satisfactory soil conditioning properties, low gaseous emissions and odor impacts, and high hygiene levels (with no public health impacts), the liquid and solid fractions must strictly meet the criteria outlined in Tables 4 and 5 (similar to a product quality control form).

Nitrogen and Nutrient Surplus
When nitrogen and other nutrients contained in manure are produced in excess for the agronomic needs of local agriculture, the surplus must be reduced (by concentrating N and other nutrients) or exported to other land. Determining how to manage excess N and other nutrients has been the focus of collaborative research and development of sustainable and feasible systems between the Lombardy Agriculture Department, the Ricicla Group of University of Milan, the A.r.a.l. (Sata) and a number of small-medium enterprises in the last few years.
Two examples of innovative technologies that have been coupled to AD systems and appear to be feasible solutions for agricultural operations are the N-Free® system and ammonia stripping using thermal heat recovered from a biogas cogeneration engine. The N-Free technology reduces manure volumes by concentrating organic/mineral matter. The second technology focuses exclusively on N-reduction.
The N-Free system integrates solid-liquid separation, ultrafiltration (UF), reverse osmosis (RO) and low-temperature ammonia stripping (Figure 2). These sequential technologies allow the accumulation of organic and mineral fractions in a series of concentrated streams. After RO, the permeate is refined through zeolites and stored in tanks, continuously analyzed and finally discharged. Characteristics and advantages observed after two years of full-scale operation include: Complete purification of up to 60 percent of the liquid fraction; accumulation of up to 70 percent of N-NH4+ (i.e. up to 50% of total N) in concentrated ammonium sulphate solution (to be sold as a fertilizer); digestate mass reduction of up to 60 percent (reducing transportation costs to half); diversification into four different concentrated solid-liquid fractions; electric power consumption of 1 €/m3 of digestate; management costs 1-2 €/m3 of digestate; overall costs (treatment+investment) of 3.5 to 4.5 €/m3 of digestate. The concentrated streams can be used directly on agricultural land by the farm or exported.
The second technology, based on a heat ammonia stripping process, relies on around 130 kW of thermal heat power produced by cogeneration in a biogas plant. As such, this technology must be strictly correlated to anaerobic digestion. Figure 3 provides a mass flow diagram of the thermal treatment system. Figure 4 draws mass and nitrogen balances resulting from a year-long observation performed by Regione Lombardia. The technology demonstrated the potential of converting around 75 percent of the N-NH4+ contained in digested manures to ammonium sulphate. Depending on the type of manure, this corresponds to a removal of the 50 to 60 percent of the total-N.

References
Börjesson, P., Berglund, M., 2006. Environmental systems analysis of biogas systems-Part I: Fuel-cycle emissions. Biomass Bioen., 30 (5), 469-485 et al., 2009.
D’Imporzano G., Crivelli F., Adani F. (2008). Biological Compost Stability Influences Odor Molecules Production Measured by Electronic Nose During Food-Waste High-Rate Composting. Sci Total Environm., 402, 278-284.
Schievano A., Scaglia B., D’Imporzano G., Malagutti L., Gozzi A.,Adani F., 2009. Prediction of biogas potentials using quick laboratory analyses: upgrading previous models for application to heterogeneous organic matrices. Bioresource Technology, 100, 5777—5782.

Fabrizio Adani, Giuliana, D’Imporzano and Andrea Schievano are with GRUPPO RICICLA, DiProVe—Università degli Studi di Milano. Gabriele Boccasile, D.G. is with Agricoltura, Regione Lombardia, Flavio Sommariva is with Sata—A.r.a.l and Aldo Deias is with Distretto Agroenergetico Lombardo, Parco Tecnologico di Lodi.