Spruce bark beetles as a biological waste that can be processed in a biogas plant

Jiří Rusín,Marek Barta,Kateřina Chamrádová,Silvia Mudrončeková

doi:10.3906/tar-1902-13

Abstract

Biogas plays an important role in reducing the amount of biowaste that is converted to methane which is usable by multiple pathways in the energy sector. Bark beetles are among the most important pests of spruce forests in Europe. Principal measures of managing bark beetle populations include trapping them with pheromone traps. Biomass of bark beetles collected by the traps constitutes a waste of forest resources that could potentially be processed in biogas plants. The aim of this study was to provide information about the trapping of bark beetles by pheromone traps in Tatra National Park during 2005-2018 and to verify the energy potential of a combination of liquid digestate and bark beetle biomass collected by pheromone traps. The bark beetle biomass is a seasonal smallvolume nitrogen-rich material which could be processed at agricultural biogas plants. The biochemical methane potential batch test performed at 40 °C showed a high degree of digestion of milled beetles within 40 days, with a methane production of 0.242 Nm3 per kilogram of total solids (TS). The single-stage low-solids mesophilic fed-batch anaerobic digestion of untreated beetles was carried out in a lab-scale rotary drum reactor. Within 52 days, the average organic loading rate was 1.019 kg VS m-3 day-1, where VS stands for volatile solids. The specific biogas and methane production reached 0.218 Nm3 kg-1 TS and 0.140 Nm3 kg-1 TS,respectively. The cuticles of the beetle bodies were not obviously disturbed by the fermentation process. The digestate was quite rich in nitrogen, but the other element contents did not differ too much from fertilizer made from manure or phytomass.

Highlights

Bark beetles are a natural component of forest stands
Spruce forests are linked to about 30 species of insects, of which 3-4 are serious pests (Ips typographus L., I. amitinus Eichhoff., I. duplicatus Sahlberg, and Pityogenes chalcographus L.)
The aims of this paper are (1) to verify the wet anaerobic production of biogas, containing methane and liquid, fertilized from bark beetles collected from pheromone traps; (2) to provide information on potentially processing this seasonal biomass in a biogas plant of the agricultural type; and (3) to summarize catches of bark beetles in forests of Tatra National Park in Slovakia during the period of 2005–2018

Summary

Introduction

Bark beetles are a natural component of forest stands. Bark beetles are among the most significant pests of spruce forests in Europe. Spruce forests are linked to about 30 species of insects, of which 3-4 are serious pests (Ips typographus L., I. amitinus Eichhoff., I. duplicatus Sahlberg, and Pityogenes chalcographus L.). In Slovakia, the most dangerous bark beetles of spruce forests are I. typographus and P. chalcographus. They are well-defined and distinguishable species, recognized mainly as pests of spruce (Picea spp.) in Eurasia. These insects normally establish on fallen trees but can mass-attack healthy trees, killing millions of spruces (Jeger et al, 2017). The last decade of the 20th century was marked by several disastrous windstorms in Central Europe, which gave rise to an enormous propagation of bark beetles in the affected

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