3.1. Preliminary Survey Results and Operative Choices
According to the data collected by means of the preliminary survey, the private farm “Iasi Agrizoo” has a total agricultural surface of 400 hectares; 330 hectares of these are arable soil cultivated with wheat, barley, fodder, hay, and stable meadows (Figure 3
). The farm center is composed by large sheds occupying about 20,000 m². They are used as a shelter for 650 dairy cattle divided into 100 heifers, 50 cows in dry, 400 lactating cows, and 100 weaning calves. The breeding produces 3200 tons of milk and 40 tons of meat yearly. Manure is firstly separated into a thin and thick fraction. The separate liquid fraction feeds a biogas plant producing electricity sold entirely to the electricity manager. The separate solid is equal to 2555 m3
per year and is partly used as litter in the bunks and partly in the field. Taking into account the re-employment within the farm, “Iasi Agrizoo” can allocate about 7 m3
of separated solid to composting daily. Other organic matrices available within the farm itself—such as straw, unifeed waste, deteriorated forage—and indicatively quantifiable in not more than 10% the total annual separated solid, can be beneficially used for composting.
Considering the preliminary analysis on the type and extent of the farm waste to be managed, the static windrow with active aeration was suggested as composting method. This is a low-cost composting technology, which allowed the total recovery of the pre-existing structures within “Iasi Agrizoo” (waterproofed area covered by a roof and served by a point of distribution of electricity). This strategy had the following functions: a) To sanitize and further dry the separated solid to be put as bedding in the bunks; b) to compost part of the separated solid in the presence of litter straw and other farm waste such as deteriorated fodder, moldy straw, etc. The composting mixture was placed on ventilation pipes, suitably drilled and positioned, and fed by a fan (Figure 4
). A digital timer allowed air injection (0.43 m3
) for 5 min every hour during the first 20 days of the process. Air insufflation for aerobic composting systems is essential for providing metabolic oxygen, controlling temperature variations inside the heap, minimizing odors, and removing water. The use of forced aeration systems for composting facilitates and improves the controlled and uniform distribution of air in the heap, significantly improving the quality of the final compost.
Technical features of the composting module were the following: Power supply and control panel certified in accordance with the law, equipped with a magnetothermal switch, timer, and 220V/380V socket (220V service socket; 380V fan supply); 2.5 kW high-pressure power (0.43 m3
) and ventilation cable; main duct (Ø 110 mm PVC pipes) for air insufflation system with two secondary ducts in polyethylene (Ø 66 mm), length 8 m with end cap. The temperature was monitored daily by means of a digital probe with a 1.5 m-foot stem (Figure 5
). An operator recorded the temperature values from six different point samples within the pile, at two depths (40 cm; 90 cm). The composting process was stopped when the pile temperature remained more or less constant, after the turning and wetting of some sample parts of the pile. In any case, the time for obtaining mature compost was about three months. In this study, temperature was taken as guide parameter to control composting process evolution and to evaluate compost maturity. Other simple and empirical parameters, based on own senses (touch, smell, sight), can be used to assess the quality of the composting process. Samples should be taken from different pile locations, at 30–40 cm depth in the compost pile, and mixed together to make a representative sample. Observations have to be carried out on fresh samples or samples stored at 4 °C for a couple of days. Compost changes color during the process passing from a variegated color, due to the different starting matrices, to a more homogeneous tint, until a brown or black color of the mature compost. Disagreeable odors indicate an incorrect process management, while a mature compost smells of woodland. Again, a crumbly structure with some wooden pieces is indicative of a mature compost. In any case, it is strongly advisable to make a complete physico-chemical analysis of the final compost in order to standardize the product and to guarantee its quality. The analysis should be performed at least twice a year on compost obtained from similar raw materials.
This demonstration composting plant was able to transform approximately 100 m3 per year of separated solid into mixed compost (v/v: 60% separated solid + 40% bulking agent). This compost was distributed within “Iasi Agrizoo” farm—on fodder and cereals—at doses ranging from 10 to 12 tons per hectare, during the seedbed preparation operations.
The type of waste produced within the cooperative “Coop. Agrocarne Sud” is slurry (135 m3 per week) that ends up in collection tanks in which the first separation occurs by flotation and rolling of the solid material—called “cruschello”; the latter is collected in heaps as a palatable material. The liquid fraction is directed to the company biogas plant through pipes; the digestate leaving the digester is then separated into a solid fraction and a liquid one. The solid digestate is placed in the pit where it undergoes maturation before its use. The liquid fraction undergoes a treatment in the company purification plant before to be placed in the municipal sewer system. Annual average livestock number is 2000. The cooperative characteristics can be summarized as follows:
Training system: Intensive;
Average productions of dejections—as it is—per week: 7020 m3;
Average production of “cruschello” per week: 130 m3 (40 tons);
Average production of solid separated per week: 364 m3 (234 tons);
Surface of the ex-drying beds: 1200 m2;
Availability of mechanical means (third, shovel, manure spreader, etc.): Tractor with loader.
At “Coop. Agrocarne Sud”, composting in static windrow with active aeration was proposed, similarly to what indicated for “Iasi Agrizoo” farm. Particularly, this low-cost composting plant was made in one ex-drying tank within the cooperative, according to the drawing reported in Figure 6
The plant consisted of a 2.2 kW power fan with a flow rate of 0.43 m3
per second applied for 5 min every hour during the first 20 days of the process, an electrical panel equipped with a timer, and a 90 PE pipe for a length of 13 m. The working capacity was about 18 m3
allowing the farm to produce about 10 tons of finished product per composting cycle. Considering an average duration of the bio-oxidative phase of 60 days, the demonstration plant allowed to obtain about 60 tons of mature compost per year. The separated solid from pig slurry was mixed with about 8 m3
of bio-triturate with a structuring function and corresponding to about 40% (v
) of the mixture (Figure 7
). Once prepared, the composting pile was covered by a non-woven sheet to protect the materials from rain and solar radiation, without compromising the gas exchanges (Figure 8
). Pile temperature was measured daily as described for “Iasi Agrizoo” farm. The time for obtaining mature compost was three months. In agricultural lands nearby the cooperative “Coop. Agrocarne Sud”, in addition to forage and cereal crops, several hectares of vineyards are cultivated. In the case of the vine, the post-harvest phase, especially when harvest occurs precociously, appears to be the optimal moment for compost distribution at the recommended quantities of around 10 tons per hectare. In any case, soil characteristics have to be taken into account in the compost distribution plan.
“Nardozza and Rosa” farm has about 250 hectares of agricultural land planted with fodder, grain cereals, and pastures. A sheepfold of about 850 m² is located in the farm center. The livestock consistency is of about 600 heads of Italian Merino-derived breed (350 sheep and the remaining part composed by rams, lambs for meat, and breeding animals). The breeding system is semi-extensive. The animals are raised in stalls on straw litter, which is removed when reaching the level of the front of the manger. The declared annual quantities of material able to be shoveled are 440 m3. The removal of the litter is performed about four times a year with the mechanical shovel available in the farm. The farm has a manure spreader with side discharge, and it can easily access the use of rear discharge manure spreader.
A composting technology in static heaps, with passive aeration, was realized in an area adjacent to the sheepfold. The linear pile was made with the help of the rear discharge manure spreader (Figure 9
The pile was built on a bed of straw placed directly on the ground, as allowed by the Italian law (Decree 7 April 2006, implemented in Basilicata with the D.G.R. n. 413, 19 April 2016) in the presence of not very permeable soil. The straw bed represented an initial layer of cellulosic material with a structuring function for the air passive inlet, and an "insulator" and "buffer" function against any excess leachate leaking from the organic matrices. Then, the mixture composed by sheep manure and additional “structuring” material (straw, about 30% by volume) was prepared. Particularly, sheep manure was very rich in straw and stabilized for 90 days in the housing stables of the existing sheepfold; this assured the correct performance of the composting process. The starting matrices, about 30 m3, were mixed with the aid of a side discharge manure spreader, which was also used to create a single windrow of about 15 m in length, a width of 2 m, and an average height of 1.5 m. The heap dimensions resulted from the material amount deriving from a cycle of straw litter removal. During the bio-oxidative phase of the composting process, a non-woven cover was used to insulate the windrow without compromising gas exchange and avoid water losses (essential steps for the quality of the final compost). The pile temperature was daily measured in six different point samples at two depths (40 cm; 90 cm), using a portable digital device 1.5 m long. Also in this case, the temperature was used as a guiding parameter of the composting process. The composting cycle lasted six months. Within “Nardozza and Rosa” farm, compost was distributed to the fodder at doses of around 10–15 tons per hectare per year, coinciding with seedbed preparation (autumn). Compost could have fruitful application in numerous vineyards spread in the rural areas close to the farm.
“Santoro” farm has a total agricultural surface of 24.3 hectares seven of which are covered by woods. The breeding is of Friesian dairy cattle for a total of 49 heads including 31 cows, 13 heifers, and 5 calves. Housing is fixed. Livestock waste is removed twice a day with a scraper and the use of straw is limited to the beds of lactating cows. Waste production is approximately 708 m3 year−1 of material able to be shoveled and 423 m3 year−1 of slurry. The latter is introduced into a 16m × 4m × 4m collection tank, which does not fully respond to the current farm needs and leads to management problems, especially in the winter period. Livestock waste is distributed in the field by tank-wagon after homogenization.
Aerated static pile was the most appropriate composting option. The farm improvement intervention has been realized recovering the pre-existing manure storage facilities/spaces. Particularly, the plant consists of a storage concrete platform and a composting cell of 50 m2
with retaining walls high 2 m, built ex novo, and it is free of cover (Figure 10
). Such a small number of modifications can allow the farmer to eventually return to the pre-intervention situation without additional costs. The composting plant, whose total size is about 210 m2
, can annually process 1800 m3
of starting matrices and produce around 600 tons of compost from manure. With respect to the management of the stall, only two new actions were introduced: Direct addition of shredded wood/sawdust as bedding for the animals and its cleaning with mechanical shovel. The materials composted in the plant were the cattle manure from the farm, bedding from the stable, and biomass resulting from cleaning and maintenance of Basilicata woods. The temperature of the pile was measured as described for the other demonstration cases. The duration of the composting cycle was one month.
A summary of the characteristics of the farms involved in the study and of the solutions adopted for composting are reported in Table 4
3.2. Composting Versus Conventional Manure Treatment Methods: A Further Study on “Santoro” Farm
The results of the energy, environmental, and economic analysis performed within “Santoro” farm are reported in Table 5
. Against a slight increase in energy consumption (+10%), the manure composting solution impacted less (−6%) and showed lower costs (−37%) than the conventional management with scraper. The higher energy consumption, measured in the post-intervention situation, was due to the energy incorporated in concrete used for the construction of the composting plant (Figure 10
). In the composting solution, pile management (26%) and chips transport to the farm (26%) were the most impactful actions. Wood chips acquisition/transport to the farm was also the most expensive phase (59%) within the compost alternative being chips price equal to 9.50 € ton−1
(on dry matter basis), excluding the loading phase and the transport to the field. In the conventional management, the most impactful (87%) and expensive (81%) operations were the stall cleaning, the transport of manure, and its distribution in the field.
The comparison of the pre-intervention situation (conventional) and the post-intervention with compost production—by means of LCA, EA, and LCC methodologies—clearly gave indications on which are the strengths and weaknesses of the different manure managements. This can allow one to identify where it is possible to intervene in order to contain impacts or enhance positive effect, guiding farmers choices. In this case, it would be desirable to find the bulking agent within “Santoro” farm (i.e., residues from woods) or from other nearby farms to break down impacts due to wood chips acquisition/transport (Table 5
). In addition to the lower environmental impact found (656 kg CO2
eq versus 695 kg CO2
eq of the manure conventional management), on-farm composting should be recommended thanks to the several agronomical benefits and defense capacity from pests testified by many studies [14
]. However, the most noticeable result coming from this experience was the economic savings of the alternative manure management (Table 5
) and the compost added value. According to Italian law [35
], compost coming from a mixture of manure and other organic material can be classified as mixed composted soil conditioner and counted among the types of fertilizers allowed in agriculture. Therefore, farms producing compost could join the list of fertilizer manufacturers and place the product on the market at very attractive prices (25 € m−3
), able to cover waste management costs, and in some cases, assure an interesting farm profit.