F. Gioelli

Evaluation of the biogas productivity potential of some Italian agro-industrial biomasses.

Batch trials were carried out to asses the biogas productivity potential of rice and barley straw, grape stalks, grape marcs, maize drying up residues, tomato skins and seeds, and whey. Trials were carried out in 2l glass digesters kept in a thermostate controlled room at 40 degrees C for 40days. The most productive biomasses, in terms of specific methane yield, were the whey and the maize drying up residues. Their specific methane yields were 501 and 317l(N) CH(4) *kgSV(-1), respectively. Barley and rice straw gave a specific methane yield of 229 and 195l(N) *kgVS(-1). Similar result was also obtained from tomato skins and seeds. Grape stalks and grape marcs produced lowest amounts of specific methane, respectively, 98 and 116l(N) CH(4) *kgSV(-1). According to trial results and considering the availability of examined biomasses in Italy, it is possible to estimate their total energetic potential close to a value of 21,900TJ *year(-1). This energetic potential value is equal to that obtainable from the anaerobic digestion of about 6.5 million tons of maize silage.

The methane yield of digestate: Effect of organic loading rate, hydraulic retention time, and plant feeding

In biogas plants, huge volumes of digestate are produced daily and stored in uncovered tanks, which leak methane into the atmosphere and cause negative environmental impacts. To better understand the effect that different operating parameters of anaerobic digestion plants have on digestate residual methane yield, four digestate samples collected from plants with very different operations were analysed in batch reactors. Their methane yields were very heterogeneous and varied between 2.88 and 37.63 NL/kgVS. The methane yield was shown to be highly influenced by the A.D. plant Organic Loading Rate and by feedstock quality; hydraulic retention time had only limited effects.

Acidification of animal slurry– a review

Ammonia emissions are a major problem associated with animal slurry management, and solutions to overcome this problem are required worldwide by farmers and stakeholders. An obvious way to minimize ammonia emissions from slurry is to decrease slurry pH by addition of acids or other substances. This solution has been used commonly since 2010 in countries such as Denmark, and its efficiency with regard to the minimization of NH3 emissions has been documented in many studies. Nevertheless, the impact of such treatment on other gaseous emissions during storage is not clear, since the studies performed so far have provided different scenarios. Similarly, the impact of the soil application of acidified slurry on plant production and diffuse pollution has been considered in several studies. Also, the impact of acidification upon combination with other slurry treatment technologies (e.g. mechanical separation, anaerobic digestion …) is important to consider. Here, a compilation and critical review of all these studies has been performed in order to fully understand the global impact of slurry acidification and assess the applicability of this treatment for slurry management.

Thermal pre-treatment of solid fraction from mechanically-separated raw and digested slurry to increase methane yield

Anaerobic digestion plants rely on large-capacity storage tanks to manage the agronomic utilisation of the digestate. As a consequence, many Italian A.D. plants have introduced mechanical separation of the digested slurry to simplify process requirements. This study evaluated the possibility of reusing mechanically-separated solid fraction as a further biomass input anaerobic digestion plants. The effects of storage and thermal pre-treatment on digested solid fraction were assessed through biogas and methane yield measures, and then compared to the yields associated with undigested solid fraction of raw pig slurry. The specific CH4 yields of digested solid fractions ranged between 71.4 and 156.9 lN/kg VS, whereas the biogas yield from undigested solid fractions was 78.7 lN/kg VS. Solid fraction storage showed no significant effect on specific CH4 yields in any of the examined samples. However, in the case of the undigested solid fraction, thermal pre-treatment proved to be an effective method to increase CH4.

Residual biogas potential from the storage tanks of non-separated digestate and digested liquid fraction

Biogas plants daily produce enormous volumes of digestate that can be handled in its raw form or after mechanical separation. In Italy, effluents are usually stored within aboveground, uncovered tanks, which make them potential emitters of biogas into the atmosphere. The purpose of this study was to estimate the amount of biogas emitted to the atmosphere during the storage phase of non-separated digestate and digested liquid fraction. The trials were performed at two northwest Italy 1 MWel. biogas plants. A floating system for the residual biogas recovery, and a set of three wind tunnels for NH3 emission measurement were used. The experiment demonstrated significant loss to the atmosphere for each of the gases; specifically, on average, 19.5 and 7.90 N m3 biogas MWhel.(-1) were emitted daily from the storage tanks of non-separated digestate and digested liquid fraction, respectively.

Ammonia emissions from rough cattle slurry and from derived solid and liquid fractions applied to alfalfa pasture

A field trial was conducted to assess the emission of ammonia from rough cattle slurry and solid and liquid fractions (generated from its mechanical separation) applied to alfalfa pasture. Three materials (rough slurry, liquid fraction and solid fraction) were applied on alfalfa over two seasons (summer and autumn), with two application rates (40 and 70 kg N/ha) and with two air velocities (0-0.6 m/s) at the soil surface. Ammonia losses were measured either by a set of wind tunnels (adjusting the air velocity at 0.6 m/s) or by a funnel system, allowing measurements to be recorded at an air speed close to 0 m/s. Each trial lasted 5 days with daily sampling of the gaseous emissions. Trial results showed that the rough slurry substrate had the highest level of ammonia emissions, followed by the liquid and solid fractions. Up to 35% of the applied total Kjeldahl nitrogen was lost as ammonia from the rough slurry in 5 days in summer conditions and with an air velocity of 0.6 m/s. No effect due to the application rate was observed, however, a significant effect of the temperature and air velocity on ammonia emissions was measured. Ammonia emissions after the spreading of the rough slurry were up to 26% higher when compared with those generated after application of the two fractions (solid + liquid).

A floating coverage system for digestate liquid fraction storage.

Anaerobic digestion is booming in the nations of Europe. In fact, Italy alone has approximately 500 plants in operation or in some phase of start-up. Previous studies have made evident the potential that lies in digested manure residual biogas. Nevertheless, much of the potential goes unrealized when enormous amounts of digestate are produced, but are then stored in uncovered tanks. This research work designed, constructed, and tested a low-cost digestate storage tank cover system capable of abating CO2eq atmospheric emissions and then recovering the biogas. The experiment, carried out at a 1 MW electric anaerobic digestion plant, demonstrated that collecting the residual biogas from the digested liquid fraction storage tank made it possible to avoid atmospheric emissions of up to 1260t CO2eq annually and to increase the methane yield of the installation by 3%.

Methane and carbon dioxide emissions from simulated anaerobic swine manure treatment lagoons under summer conditions

Most estimates of carbonaceous gas emissions from manure treatment lagoons are based on biogas production from anaerobic digesters, gases collected over covered lagoons, or the CH4 production potential of animal waste. More data from direct measurements are necessary for evaluating mitigation strategies. Researchers at Oklahoma State University have successfully operated a pilot-scale bioreactor consisting of four 270 L columns that recreate environmental conditions found in anaerobic lagoons as indicated by color, temperature, pH, and electrical conductivity (EC). The columns were loaded at a surface organic loading rate similar to lagoons treating manure from commercial swine farms in the state of Oklahoma (935 kg VS/ha-day). The simulated mid-to-late summer CH4 emission rate was determined to range between 200 and 300 kg/ha-day, and the CO2 emission rate ranged between 380 and 580 kg/ha-day. Approximately 65% of the total carbon applied to the surface of the lagoon simulator was recovered as CH4 and CO2 gases; however, lagoon methane production was greater than expected using chemical oxygen demand (COD) as a predictive standard. The daily patterns of gaseous emissions and volatile organic acid concentrations in the liquid suggest that CH4 production takes place across the entire depth of the reactor. Easily digestible organic matter is converted in the upper layers; more slowly digested material settles and is converted at the sludge layer. Data on day versus night emissions show that biogas had a higher proportion of CO2 during the day than during the night.

Acidification with sulfur of the separated solid fraction of raw and co-digested pig slurry: effect on greenhouse gas and ammonia emissions during storage

A study was performed to assess: (1) the feasibility to acidify the separated solid fraction of raw and co-digested pig slurry by using a powdery sulfur-based product; and (2) the effect of this acidification method on greenhouse gases and ammonia emissions during manure storage. Samples of raw and co-digested pig slurry were collected at two commercial farms and mechanically separated by a laboratory-scale screw press device. The sulfur powder (80% concentration) was added to the obtained separated solid fractions at three application rates: 0.5%, 1% and 2% (w/w). Carbon dioxide, methane, nitrous oxide and ammonia emissions were afterwards measured during storage of the acidified samples and compared with those measured from untreated samples (Control). Gaseous emissions were determined with dynamic chamber method by Infrared Photoacoustic Detection. Gaseous losses were monitored along 30 and 60 days of storage time for raw solid fraction and digested solid fraction, respectively. The addition of the tested sulfur powder to solid fractions showed to be a reliable and effective method to acidify raw and co-digested solid fractions. Results showed a significant reduction of both greenhouse gases and ammonia emission regardless of the separated solid fraction type. The highest sulfur application rate (2% w/w) led to a reduction of up to 78% of greenhouse gas emission and 65% of ammonia losses from raw separated solid fraction when compared with the Control. Similar results were achieved from the co-digested solid fraction, with emission reduction of up to 67% for ammonia and 61% for greenhouse gas.

Simulation of Anaerobic/Facultative Lagoon Performance Using a 1,000 Liter Pilot Facility

For the last five years, researchers at Oklahoma State University (OSU) have successfully operated a pilot bioreactor consisting of 4, 270 liter columns that recreate the exact environmental conditions experienced by anaerobic/facultative lagoons. Design and construction of the pilot facility was reported in ASAE Paper 98-4112. In August 1998, the pilot facility was inoculated with effluent and sludge from the OSU Swine Center lagoon, and programmed to repeat heating and lighting patterns experienced by a lagoon under late-summer conditions at 35o N latitude in Oklahoma. An air-conditioning/wind-tunnel system was added to simulate lagoon atmospheric interactions. The atmospheric interaction sub-system became fully functional in 2001. The bioreactors have responded to environmental conditions similar full-sized lagoons as measured by pH and electric conductivity. Methane and Carbon dioxide emissions were measured at 190-280 kg/ha-day and 350-530 kg/haday, respectively. Measured carbon emissions account for 82% of the applied chemical oxygen demand, and respond in a predictable pattern to liquid VFA concentrations.