Element concentrations in urban grass cuttings from roadside verges in the face of energy recovery

Analysis of the Possibility of Energetic Utilization of Biomass Obtained from Grass Mowing of a Large-Area Golf Course—A Case Study of Tuscany

The mowing of sports fields generates a significant amount of waste biomass which requires appropriate management. On the largest scale, this problem affects golf courses with a grass surface area of up to 100 ha. Currently, the main directions for grass clippings management include composting, grass cycling, and waste. A certain alternative may be the energetic utilization of grass clippings, which not only solves the problem of organic waste management, but also brings measurable economic profits in the form of generated electricity and heat. This paper presents a techno-economic analysis of the application of a micro biogas plant, fed with grass clippings from a golf course project in Tuscany, with a grass surface of 111.21 ha. It has been shown that the annual biomass potential is 526.65 tDM∙year−1 (±45.64 tDM∙year−1), which makes it possible to build a micro biogas plant with an electric power of ca. 46 kW. The potential amount of electricity produced during the year is able to cover 16.95–37.35% (depending on the season) of electricity demand in the hotel resort, which includes two golf courses and practice facilities. The produced heat in the amount of 1388.41 GJ, in turn, is able to cover the annual heat demand in the range of 7.95–17.24% (depending on the season). In addition, the electricity and heat produced exceeds the energy expenditures for mowing, making the energy balance positive. Unfortunately, the analysis showed that the construction of a micro scale biogas plant is economically unprofitable and is characterized (in the period of 10 years) by negative IRR and ROI (−17.74% and −34.98%, respectively). However, it should be emphasized that with the additional income resulting from the avoidance of fees for the export and management of organic waste and the reduction of fertilization costs (fertilization of part of the golf course with digestate), the application of a micro biogas plant may turn out to be economically feasible (NPV > 0).

Mild hydrothermal conditioning prior to torrefaction and slow pyrolysis of low-value biomass

The aim of this research was to establish whether hydrothermal conditioning and subsequent thermochemical processing via batch torrefaction or slow pyrolysis may improve the fuel quality of grass residues. A comparison in terms of fuel quality was made of the direct thermochemical processing of the feedstock versus hydrothermal conditioning as a pretreatment prior to thermochemical processing. Hydrothermal conditioning reduced ash content, and particularly nitrogen, potassium and chlorine contents in the biomass. The removal of volatile organic matter associated with thermochemical processes can increase the HHV to levels of volatile bituminous coal. However, slow pyrolysis only increased the HHV of biomass provided a low ash content (<6%) feedstock was used. In conclusion, hydrothermal conditioning can have a highly positive influence on the efficiency of thermochemical processes for upgrading low-value (high-ash) biomass to a higher quality fuel.