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Abstract:The present study aimed at investigating perceptions and preferences about the use and the chemical characteristics of pellets made from composted animal manure in a sample of Italian farmers and agricultural advisors (Piedmont region, Northwestern Italy). The study encompassed two different steps: At first, the participants were administered a questionnaire about their actual use of pellets and preferences about their chemical characteristics. Then, a subgroup participated into a hands-on experience with different pelletized animal manures and some final questions. Concerning the use of pellets made from composted animal manure, even if the participants affirmed to be interested in using organic pellets and declared to own the appropriate equipment needed for their application, the results indicated that pelletized compost utilization had not yet become a common practice for agricultural crops. The obtained results highlighted a lack of knowledge, especially among farmers, about the importance of some chemical properties of this pelletized organic material. The participants, both farmers and advisors, were particularly attracted by the total nitrogen content of organic pelletized fertilizers, probably because the supplying of nutrients, nitrogen particularly, is the function of fertilizers they were interested in the most due to its direct connection with crop production. The hands-on session allowed the participants to better understand the benefits of the principal chemical properties-organic matter and carbon to nitrogen ratio-of pelletized animal manure compost. On the other hand, organic matter content and carbon to nitrogen ratio, more related with biological fertility and biodiversity of soils, are immediately less interesting and, as the hands-on experience pointed out, require more effort to be appreciated by agricultural operators. Targeted information campaigns and training activities may be developed among the agricultural community to make them aware of the importance of increasing soil organic matter content, and the possible use of pelletized composted animal manure. Further studies should be addressed toward gaining more insights into the beneficial effects of the information and training activities for pelletized compost adoption.

Compost derived from swine solid fraction is a low density material (bulk density less than 500 kg m-3). This makes it costly to transport from production sites to areas where it could be effectively utilized for value-added applications such as in soil fertilization. Densification is one possible way to enhance the storage and transportation of the compost. This study therefore investigates the effect of pressure (20-110 MPa) and pressure application time (5-120 s) on the compaction characteristics of compost derived from swine solid fraction. Two different types of material have been used: composted swine solid fraction derived from mechanical separation and compost obtained by mixing the first material with wood chips. Results obtained showed that both the pressure applied and the pressure application time significantly affect the density of the compacted samples; while the specific compression energy is significantly affected only by the pressure. Best predictor equations were developed to predict compact density and the specific compression energy required by the densification process. The specific compression energy values based on the results from this study (6-32 kJ kg-1) were significantly lower than the specific energy required to manufacture pellets from biomass feedstock (typically 19-90 kJ kg-1).

Abstract:The phytotoxicity of four different composts obtained from pig slurry solid fraction composted by itself (SSFC) and mixed with sawdust (SC), woodchips (WCC) and wheat straw (WSC) was tested with bioassay methods. For each compost type, the effect of water extracts of compost on seed germination and primary root growth of cress (Lepidium Sativum L.) was investigated. Composts were also chemically analysed for total nitrogen, ammonium, electrical conductivity and heavy metal (Cu and Zn). The chemicals were correlated to phytotoxicity indices. The mean values of the germination index (GI) obtained were 160.7, 187.9, 200.9 and 264.4 for WSC, WCC, SC and SSFC, respectively. Growth index (GrI) ranged from the 229.4%, the highest value, for SSFC, followed by 201.9% for SC, and 193.1% for WCC, to the lowest value, 121.4%, for WSC. Electrical conductivity showed a significant and negative correlation with relative seed germination at the 50% and 75% concentrations. A strong positive correlation was found for water-extractable Cu with relative root growth and germination index at the 10% concentration. Water-extractable Zn showed a significant positive correlation with relative root growth and GI at the 10% concentration. These results highlighted that the four composts could be used for organic pellet production and subsequently distributed as a soil amendment with positive effects on seed germination and plant growth (GI > 80%).

19Conversion of pig slurry to pellets is a desirable fertilizer option for farmers who want to 20 mitigate environmental pollution from slurry accumulation. The goals of the current 21 investigation were to determine the fertilizer properties of pig slurry solid fraction (SF) pellets 22 and to assess its potential to enhance soil properties in order to reduce ammonia (NH3) 23 volatilization and greenhouse gas (GHG) emissions. Various parameters influence SF-24 based pellet fertilizer effectiveness: bulking agent use during composting, pellet diameter 25 sizing and soil application type (superficially or incorporated into the soil). Two composts 26 from the same pig slurry SF obtained from a screw press separator were prepared: pig SF 27 compost without a bulking agent (SSFC) and pig SF compost with wood chips as the bulking 28 agent (wood chip compost (WCC)). For each compost type, pellets of two different diameters 29 (6 and 8 mm) were produced. A mesocosm experiment, conducted with maize plants, was 30 used to test the fertilizer value of the considered pellets. In total, three compost fertilizers -31 SSFC, WCC and nitrogen: phosphorus: potassium mineral fertilizer 15 : 15 : 15, plus one 32 unfertilized control treatment -were applied at the same N rate (equivalent to 200 kg/ha) 33 using two different methods (surface and soil incorporation). After 65 days, above-ground 34 biomass, roots and soil samples were collected and analysed. Subsequently, a second 35 mesocosm study was undertaken to measure NH3 and GHG emissions released from pellet 36 fertilization. Ammonia volatilization was determined immediately after pellet application, 37 while carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions were 38 monitored for 57 days. Study results indicated that both pellet types were effective slow-39 release fertilizers for maize. Additionally, three actions seemed to make the nutrients 40 contained in pig SF compost pellets more available to plants: addition of a bulking agent 41 before com-posting, use of small diameter pellets and soil incorporation of the fertilizer. 42 43

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The brewing industry is characterized by the large production of by-products. Following the fundamentals of a circular economy, several attempts to recycle brewers’ spent grain (BSG) have been investigated. However, little information is available on its use for composting. Considering the main parameters required for optimal development of composting, the objective of the present review was to analyze the literature to determine whether the microbial and physicochemical characteristics of BSG make it suitable for direct composting. As the main factors in the composting process, we considered the BSG moisture content, total carbon, total nitrogen, C/N ratio, and pH. As described in the literature, the BSG moisture content, C/N ratio, and pH range from 70.6% to 81.3%, 7.1 to 26.5, and 3.8 to 6.9, respectively. This C/N ratio range is lower than the composting target range (20–30). Instead, the mean moisture content in the literature is higher than the 60% to 65% recommended for composting. Optimum pH for aerobic stabilization of compost ranges from 5.5 to 7.5, while the BSG pH in the literature is typically more acidic. Therefore, BSG is not suitable for direct composting. Addition of lignocellulosic bulking agents improves the reduction of moisture content during composting, while also optimizing the substrate properties, such as C/N ratio, air spaces, and pH, to positively affect the composting process. Moreover, livestock manure should be included as a starting material to promote the composting process. In this context, two hypothetical initial mixtures of BSG plus a lignocellulosic bulking agent and livestock manure are presented.