Alessandro Chiumenti

Treatment of digestate from a co-digestion biogas plant by means of vacuum evaporation: tests for process optimization and environmental sustainability.

Vacuum evaporation consists in the boiling of a liquid substrate at negative pressure, at a temperature lower than typical boiling temperature at atmospheric conditions. Condensed vapor represents the so called condensate, while the remaining substrate represents the concentrate. This technology is derived from other sectors and is mainly dedicated to the recovery of chemicals from industrial by-products, while it has not been widely implemented yet in the field of agricultural digestate treatment. The present paper relates on experimental tests performed in pilot-scale vacuum evaporation plants (0.100 and 0.025 m(3)), treating filtered digestate (liquid fraction of digestate filtered by a screw-press separator). Digestate was produced by a 1 MWe anaerobic digestion plant fed with swine manure, corn silage and other biomasses. Different system and process configurations were tested (single-stage and two-stage, with and without acidification) with the main objectives of assessing the technical feasibility and of optimizing process parameters for an eventual technology transfer to full scale systems. The inputs and outputs of the process were subject to characterization and mass and nutrients balances were determined. The vacuum evaporation process determined a relevant mass reduction of digestate. The single stage configuration determined the production of a concentrate, still in liquid phase, with a total solid (TS) mean concentration of 15.0%, representing, in terms of mass, 20.2% of the input; the remaining 79.8% was represented by condensate. The introduction of the second stage allowed to obtain a solid concentrate, characterized by a content of TS of 59.0% and representing 5.6% of initial mass. Nitrogen balance was influenced by digestate pH: in order to limit the stripping of ammonia and its transfer to condensate it was necessary to reduce the pH. At pH 5, 97.5% of total nitrogen remained in the concentrate. This product was characterized by very high concentrations of total Kjeldhal nitrogen (TKN), 55,000 mg/kg as average. Condensate, instead, represented 94.4% of input mass, containing 2.5% of TKN. This fraction could be discharged into surface water, after purification to meet the criteria imposed by Italian regulation. Most likely, condensate could be used as dilution water for digestion input, for cleaning floor and surfaces of animal housings or for crop irrigation. The research showed the great effectiveness of the vacuum evaporation process, especially in the two stage configuration with acidification. In fact, the concentration of nutrients in a small volume determines easier transportation and reduction of related management costs. In full scale plants energy consumption is estimated to be 5-8 kWh e/m(3) of digestate and 350 kWh t/m(3) of evaporated water.

Complete nitrification–denitrification of swine manure in a full-scale, non-conventional composting system

A full-scale composting plant (track type, aerated by screws), treating liquid swine manure (94.8% on mass basis) with straw (<0.8%) and sawdust (4.4%), was monitored. The main objectives were testing the performance of the process and assessing its environmental sustainability. Particular attention was dedicated to verify the possibility that this process could determine significant mass reduction, along with Nitrogen reduction, mainly by denitrification. Emissions were evaluated by measuring NH3, N2O and CH4 (by static chamber), H2S and odor emissions (by dynamic olfactometry). Quality and quantity of inputs and outputs and process parameters (redox, oxygen, and temperature) were monitored. The process produced a mature, highly humified (Humification Index=0.27), solid product with 92.8% mass reduction (mainly evaporation), and nitrogen reduction (85.8% referred to input TN). The process was revealed to be environmentally sustainable: emissions of odors and H2S resulted negligible; emissions of N-N2O represented 0.18% of TN input, while emissions of N-NH3 represented 0.87% of input TN. Microbiological analyses determined the presence of 10(7) CFU/g of bacteria related to N cycle and real time PCR demonstrated the presence in the final product of 4.77 ⋅ 10(7) couples of genes of Bacterial amoA/gTS and 2.46 ⋅ 10(7) couples NosZ/gTS, indicating nitrification and complete denitrification. These results exhibit that nitrification and complete denitrification can efficiently occur in a composting process effectively transforming N2O into N2 as consequence of the optimized alternation of aerated and anoxic phases in the feedstock.

Dry anaerobic digestion of cow manure and agricultural products in a full-scale plant: efficiency and comparison with wet fermentation.

For years, anaerobic digestion processes have been implemented for the management of organic wastes, agricultural residues, and animal manure. Wet anaerobic digestion still represents the most common technology, while dry fermentation, dedicated to the treatment of solid inputs (TS>20%) can be considered as an emerging technology, not in terms of technological maturity, but of diffusion. The first agricultural dry anaerobic digestion plant constructed in Italy was monitored from the start-up, for over a year. The plant was fed with manure and agricultural products, such as corn silage, triticale, ryegrass, alfalfa, and straw. Three Combined Heat and Power units, for a total installed power of 910kWe, converted biogas into thermal and electric energy. The monitoring included the determination of quality and quantity of input feedstocks, of digestate (including recirculation rate), of leachate, biogas quality (CH4, CO2, H2S), biogas yield, energy production, labor requirement for loading, and unloading operations. The results of the monitoring were compared to performance data obtained in several full scale wet digestion plants. The dry fermentation plant revealed a start-up phase that lasted several months, during which the average power resulted in 641kWe (70.4% of nominal power), and the last period the power resulted in 788kWe (86.6% of installed power). Improving the balance of the input, the dry fermentation process demonstrated biogas yields similar to wet anaerobic digestion, congruent to the energy potential of the biomasses used in the process. Furthermore, the operation of the plant required significant man labor, mainly related to loading and unloading of the anaerobic cells.

Traffic effects on soil compaction and sugar beet (Beta vulgaris L.) taproot quality parameters

Soil compaction is a critical issue in agriculture having a significant influence on crop growth. Sugar beet ( Beta vulgaris L.) is accounted as a crop susceptible to compaction. Reduction of leaf area, final yield, and root quality parameters are reported in compacted soils. The most obvious visual indicator of topsoil compaction is root depth affected by agricultural tractor and machinery traffic up on the soil. Such indicators are mainly correlated to initial soil condition, tyre features, and number of passages. Monitoring and controlling frequency and position of machine traffic across the field, in such a way that passages are completed on specific, well-defined tracks, can assist with minimization of compaction effects on soil. The objective of the present work was to analyze the subsoil compaction during the growing period of sugar beet with different farming approaches including controlled traffic passages and random traffic. To this end, tests were carried out following each agro technical operation using penetrometer readings in order to monitor the state of cone-index after each step. In addition, at the harvesting time, root quality parameters were analyzed with particular attention to length and regularity of the taproot, total length, circumference, mass, and above-ground biomass. Such parameters were usefully implemented in order to evaluate the effects of controlled traffic passages compared to the random traffic in a cultivation of sugar beet. Results highlight how an increase in crop yield, derived from samples monitored, higher than 10% can be expected with implementation of a careful traffic management.

THE EFFECTIVENESS OF THE VACUUM SYSTEM AS A SLURRY MANAGEMENT FOR PIG HOUSES IN ITALY

Experiments were conducted in finishing pig houses located in the Veneto Region (Po Valley, Northern Italy). The pig houses, which have fully slatted floor with slurry channels, are cleaned by means of a “vacuum system.” On the bottom of the channels, pipe outlets are placed every 10 m2 and connected to a sewerage system. Slurry is discharged by opening a valve in the main slurry pipe, without any mechanical pump; a slight vacuum develops and allows the slurry to flow. Tests were carried out in order to assess the effectiveness of the vacuum system with different slurry levels in the channels (0.15 – 0.40 m) and different channel lengths (40 – 60 m). Discharge times, cleaning efficiency, and sludge settling were studied. Moreover, gaseous emissions (i.e., carbon dioxide, ammonia, methane, nitrous oxide) and odors were monitored before, during, and after the cleaning operations, in order to assess the environmental effects of the technique. Preliminary results show that the vacuum system with slurry levels higher than 0.30 m and once a week slurry removal was effective.

Comparison Between Dry and Wet Fermentation of Biomasses as Result of the Monitoring of Full Scale Plants

The first agricultural dry anaerobic digestion plant realized in Italy was monitored from the start-up, for over a year. The plant is fuelled by manure and other biomasses, corn silage in particular. The installed power is of about 910kWe. Biogas quality, biogas yield, energy production, labor requirement for loading and unloading operations were monitored. The results of the monitoring were compared to performance data obtained in several full scale wet digestion plants. The dry fermentation plant showed a set up phase that lasted several months during which the average power resulted of 641 kWe ( 70,4 % of nominal power), in the following period the power resulted of 788 kWe ( 86,6 % of installed power). With a correct feeding of digesters, the dry fermentation process showed biogas yields similar to wet anaerobic digestion, congruent to the energy potential of the biomasses used in the process. The operation of the plant furthermore, required relevant man labor, mainly related to loading and unloading of the anaerobic cells.

Anaerobic Digestion of Swine Manure in Conventional and Hybrid Pilot Scale Plants: Performance and Gaseous Emissions Reduction

This study aims to present the results of a series of experimental tests performed with pilot scale digesters operating with swine manure: two digesters were conventional high load, completely mixed type, while the third digester was a hybrid type, with a fixed bed up-flow section.