Exploitation of Mowed Grass from Green Areas by Means of Anaerobic Digestion: Effects of Grass Conservation Methods (Drying and Ensiling) on Biogas and Biomethane Yield

Abstract

Grass from landscape management or from agricultural practices is currently destined mainly for composting, with the production of a valuable product; however, this process demands energy. Anaerobic digestion, instead, represents an energy-positive process that results in the production of fuel, biogas, and a fertilizer, namely digestate. Previous tests for the evaluation of biogas yield from freshly harvested grass gave promising results. However, for a practical exploitation of this resource, appropriate conservation is necessary in order to enable the daily load of digesters while reducing the loss of organic matter. The present work is focused on the evaluation of biogas and methane yield from dried and ensiled grass (without conditioning) in order to assess eventual biogas potential losses in comparison to digested fresh grass. Tests were performed with grass collected from riverbanks (Veneto, Northern Italy) in batch, lab scale digesters. Dry and ensiled grass showed a good potential for exploitation in the anaerobic digestion process, reaching biogas yields of 565.9 and 573.4 NL∙kgVS−1, respectively. Compared to the biogas yield of 639.7 NL∙kgVS−1 of the fresh grass, the conservation treatment determined yield reductions of 11.5% and 10.4% for dried and ensiled grass, respectively. However, considering the methane yields, conservation treatments showed lower reductions, amounting to 4.8% for dry grass and 0.5% for ensiled grass; presumably the higher concentration of organic acids in ensiled grass determined a higher methane content in biogas and the consequently lower reduction of methane yield.

A Comparative Study of Biogas Production from Cattle Slaughterhouse Wastewater Using Conventional and Modified Upflow Anaerobic Sludge Blanket (UASB) Reactors

“…Anaerobic digestion technology has appeared to be a promising technique due to its efficiency in waste volume reduction while producing energy in the form of biogas and digestate as biofertilizer [23]. The anaerobic digestion process involves four groups of bacteria responsible for degrading the complex organic matter, however, the conversion process of the complex substrate to biogas is a function of the mutually inclusive symbiotic relationship among the microorganism.…”

Energy Efficiency of Comminution and Extrusion of Maize Substrates Subjected to Methane Fermentation

“…The concentration of methane, carbon dioxide, hydrogen sulfide, ammonia, and oxygen in the biogas was measured with a certified Geotech GA5000 gas analyzer. The cumulated biogas and methane yields were calculated in an Excel spreadsheet, and converted from dm 3 •g −1 into m 3 •Mg −1 and then expressed as m 3 •Mg −1 in relation to the fresh weight, dry matter, and dry organic matter. The test of the biogas efficiency of substrates was carried out in three replicates.…”

“…Anaerobic digestion (AD) is a proven technology of handling organic waste, which yields high-energy products such as methane and digestate [2]. Apart from that, the use of biodegradable waste significantly reduces the emissions of greenhouse gases and odors resulting from uncontrolled fermentation [3].…”

“…Its main components are methane-CH 4 (50%-75%), carbon dioxide-CO 2 (25%-50%), and the following volatile compounds in trace amounts: water vapor (H 2 O), hydrogen sulfide (H 2 S), ammonia (NH 3 ), hydrogen (H 2 ), and oxygen (O 2 ). Another product of anaerobic digestion is digestate pulp, which is a valuable fertilizer [3].…”

Economic and Environmental Analysis of Small-Scale Anaerobic Digestion Plants on Irish Dairy Farms

“…They can also reduce pathogenic loads, odours and greenhouse gas emissions emanating from the agricultural processes [5][6][7][8]. Furthermore, the technology has received considerable research attention, advancing its potential capability through optimisation strategies [9][10][11][12][13][14]. Despite the apparent benefits, Ireland has been slow to adopt the technology, ranking 20th in AD penetration among the EU-28 countries [15][16][17].…”