BioCycle August 2007, Vol. 48, No. 8, p. 60
A 2006 Directive limiting the quantity of manure that can be landspread leads to new examination of anaerobic digestion, composting and thermal-chemical conversion.
R. Chiumenti, A. Chiumenti and L.F. Diaz

THE ITALIAN farming world has recently been influenced by an April 2006 Directive which sets new rules for management of farming residues in compliance with the European Nitrates Directive (91/676/CEE). These new regulations limit the quantity of manure that can be spread on land in relation to the concentration of nitrogen, with a shift from the previous amount of 340 kg N/ hectare to the new maximum of 170 kg N/hectare. This new cap is limited to vulnerable areas, but the European Union stated that the entire Po valley, which crosses northern Italy, must be considered vulnerable This will force farmers to double the amount of land available for manure application, to reduce the number of animals on their farm or to manage manure in order to reduce the concentration of N.
This situation is even more problematic if we consider that in the Po valley, there is a high concentration of farms (most of the Italian poultry farms are located in Veneto and Emilia Romagna Regions), and limited availability of land for agricultural utilization.
This change was sudden because previous laws were less severe; no Agricultural Utilization Plan was required for solid manure but only for the liquid. For this reason, in many cases liquid/solid separation was adopted in order to reduce the amount of nitrogen in the slurry only by diverting part of the nitrogen in the solid fraction. Now the entire amount of nitrogen, contained both in the solid and liquid fractions of the manure, is considered in the Agricultural Utilization Plan.
Poultry livestock farms are one of the types of farms that are mostly affected by these changes, since, in general, they are characterized by having limited or no land property. The land required for the proper management of different poultry wastes is calculated in Table 1 in relation to Italian limits for vulnerable and not vulnerable areas.
In order to face this situation, considering the limited land availability and the difficulty of signing a contract with other farmers for spreading manure on their land, the only solution could be represented by the implementation of technologies that could improve the management of manure.
A few decades ago, several systems were implemented for treatment of poultry wastes: different directions were taken by both industrial and research sectors, always with the primary objective of a valorization of the fertilizing properties of the manure; composting and the production of fertilizer were considered as practical options for many years.
COMPOSTING SYSTEMS
The first generation of composting systems, developed back in the middle of the 1980s, granted income for farmers, but, nonetheless, encountered several problems related to the significant environmental impact, mainly in terms of odors. The composting technology improved, with enhancements that limit and control emissions deriving from the process. In the meantime, the compost market also evolved, albeit in a negative way. The marketing of compost produced from farming wastes, in fact, is heavily affected by the availability of large quantities of relatively low-cost product from the organic fraction of MSW. Only in Italy’s Veneto Region, the production of compost from MSW in 2004 was of 200,000 t/year (data from ARPAV), and the final product is transported, and often also spread on land, at no cost to those farms that receive it.
Private compost producers, like farmers, are heavily affected by this situation since they have to cover production costs, about 30 to 40 euros per ton of compost, but there are limited possibilities of finding a market for the product, even if it is of high quality. This represents a major obstacle for the implementation of the composting technology as a solution for manure management.
Furthermore, restrictive environmental regulations impose expensive air treatment in order to reduce the emission of gases and odors, so that small-scale plants no longer are profitable. Only centralized plants for the production both of compost and organic fertilizer may be cost-effective.
The process of producing fertilizer from manure from laying hens and from poultry litter is technically feasible but affected both by law and commercial limitations. Today, it is not clear if the high temperature determined by the extrusion of pellets is considered sufficient for the disinfection of the material as far as the public administration is concerned. The market for pellets, furthermore, is difficult because extensive farms cannot afford to buy costly fertilizers, and generally a single farmer/producer of fertilizer would not be able to produce quantities required for extensive land application. Tests for production of pellets from poultry manure were performed by the University of Udine, Italy, in cooperation with CRPA with encouraging results.
ENERGY AND THERMO-CHEMICAL CONVERSION
One of the reasons why thermo-chemical management for poultry litter is becoming more common in Europe is the profit related to the so-called Green Certificates, which are EU incentives for the production of energy from renewable sources. In Italy, for example, they grant 0.125 euros per kW of electricity produced over a 12 year period.
Main options are represented by thermo-chemical conversion and anaerobic digestion. Both technologies produce energy, but have a different effect in term of N removal: thermo-chemical treatment, in fact, leads to N2 emissions, leaving only a relatively small amount of ash to be managed, while anaerobic digestion produces a digested liquid effluent with unaltered N concentration (compared to untreated manure). This is a substantial difference in terms of land requirements according to the legislation previously indicated.
The different technologies for thermo-chemical transformation of biomass are represented by direct combustion, gasification and pyrolysis. Gasification (uses sub-stoihiometric air) and pyrolysis (absence of air, at high pressure and temperature) are very interesting and, in theory, more efficient than combustion, but at the present time these technologies are not mature and reliable for treatment of farming wastes. Much research on this field is underway and results are expected to be available in the near future.
ANAEROBIC DIGESTION
The spread of anaerobic digestion for treatment of farming residues began in the 1980s but a substantial boost was evident in the recent past. During the 1980s, more than 50 plants were built in Italy and today about 2,800 biogas plants are present in Germany alone.
The size of the new generation of plants ranges from about 60 kW to more than 2 MW. In many cases, the higher outputs are reached with a mix of manure and other organic products, usually corn silage. The addition of such products, in fact, can increase the biogas yield, but one of the main drawbacks is the higher amount of nitrogen that would have to be managed.
The anaerobic digestion process, in fact, does not reduce the nitrogen content of the feedstock, and the codigestion of manure and other biomass determines an amount of nitrogen higher than that of manure itself: for each hectare of maize, for example, 200 kg of N are added. With the view of nitrogen reduction, this technology is not a valid solution for the management of manure, unless it is used in combination with other processes such as nitrification/denitrification. This technology for N removal is efficient but expensive; other technologies, like reverse osmosis, are costly and simply divert a part of the nitrogen from the liquid to the solid fraction, without solving the problem.
Some advantages achieved from anaerobic digestion include: Digested manure has a lower odor impact, lower phytotoxicity, less pathogens and good fertilizing properties than raw manure; Production of energy results in income generation, granted by the Green Certificates; furthermore the energy surplus could be used internally, also for additional N removal.
Anaerobic digestion is suitable for treatment of liquid manure, like that of bovine and swine farms, rather than poultry manure, which is solid. In modern poultry housing, in fact, the moisture content of manure is lower than in the past; laying hen housing features manure drying systems that reduce the moisture content to an average of 30 percent (two-floor housing, or external drying tunnels), and even values as low as 15 percent could be reached; in the worst conditions a moisture of 50 percent is reached.
Even for broilers, the moisture content of litter is decreasing, with an average of 35 percent as a consequence of the improved design and insulation of housing, prevention of water spilling (as imposed by IPPC directive) and litter turning operations.
Considering that the anaerobic digestion process requires a dry matter content lower than 15-16 percent, treatment of solid feedstocks such as poultry wastes does not make much sense; the addition of water would be necessary to meet the limits required by the technology (3 parts water for each 1 part litter, by weight). Furthermore, dilution would also be necessary to guarantee the appropriate conditions in terms of parameters limiting the process, in particular the volumetric load and NH3 concentration: ammonia concentrations exceeding 3,500 mg/l are toxic and can lead to the inhibition of microbial activity. For this reason, the recirculation of digested manure, which could reduce the need of water to dilute manure, could cause a progressive increase of ammonia concentration.
The dilution of poultry manure (or litter) also creates a higher quantity of final product to be managed, compared to dry materials, with different equipment (since it is liquid instead of solid) and higher costs for transportation and distribution. A possible option could be the codigestion of limited quantities of poultry wastes with other residues, such as liquid manure. For all of these reasons the anaerobic digestion process, particularly suitable for treatment of other farming residues, could not be considered, in general, as a practical solution for the management of poultry wastes.
OBSERVATIONS ON METHODS
From this analysis of the problem of managing poultry manure and litter, mainly considering the need for nitrogen reduction, it appears that the most promising technology is represented by combustion. In the Veneto Region, Northern Italy alone, the nitrogen produced by livestock farms is about 62,000 t, of which 17,500 t are derived from poultry farms, while the total availability of land for agricultural use is about 852,000 hectares. In theory, the possibility of diverting poultry wastes, as a consequence of the implementation of combustion technology, would reduce the regional N load from 73 kg N/hectare to 52 kg N/hectare, with benefits for the comprehensive impact of farming activities.
Additionally, from an economic point of view, combustion plants that use poultry manure as fuel to produce energy could be very interesting, considering that the revenues granted by the Green Certificates determine a payback time of about four years, and even after the end of the incentives (12 years) the plant could be profitable by selling energy; the physical lifetime of a plant is considerable, since the turbines generally are guaranteed for 20 years.
The profit of the plant could be increased by utilization of the thermal energy. The use of thermal and electrical energy could give a contribution to the reduction of emissions of CO2: a facility of the size of 1 MWe, for example, prevents the production of 5000 t of CO2 from fossil fuels, considering only the benefit of electric energy and not of thermal energy.
A comprehensive evaluation of the combustion technology – evaluating regulations that prevent contamination from nitrates of surface water, reduction of CO2 from nonrenewable sources that could be obtained, paying attention to the limits determined by the Kyoto Protocol, and systems implemented to control atmospheric emissions – should lead to a positive consideration.
The Italian Government’s Decree 387/2003 that enforces EU Directive 2001/77/CE relative to the production of electrical energy from renewable sources indicates that the facilities for the production of energy from renewable sources are to be considered “of public utility, urgent and that cannot be deferred.”
Roberto Chiumenti is Professor of Construction and Facilities For Farming at the University of Udine, Italy while Alessandro Chiumenti is a lecturer on farming equipment in Udine, Italy. Luis F. Diaz is President, CalRecovery, Inc, California.