Enhancement of methane production from barley waste

doi:10.1016/j.biombioe.2005.12.003

Biomass and Bioenergy

Volume 30, Issue 6, June 2006, Pages 599-603

https://doi.org/10.1016/j.biombioe.2005.12.003 Get rights and content

Abstract

Two different approaches were attempted to try and enhance methane production from an industrial waste composed of 100% barley, which results from production of instant coffee substitutes. In previous work, this waste was co-digested with an excess of activated sludge produced in the wastewater treatment plant located in same industrial unit, resulting in a very poor methane yield (25 LCH_4(STP)/kgVS_initial), and low reductions in total solids (31%) and in volatile solids (40%).

When the barley waste (BW) was subjected to alkaline hydrolysis pre-treatment before co-digestion with activated sludge, the methane production increased to 222 LCH_4(STP)/kgVS_initial and the total and volatile solids reductions increased to 67% and 84%, respectively.

The second approach, followed in the present work, consisted of co-digestion with kitchen waste (40% BW, 60% kitchen waste). The methane production was 363 LCH_4(STP)/kgVS_initial and the total and volatile solids reductions were 61% and 67%, respectively.

Introduction

EU legislation, through the Council Directive 1999/31/EC [1], states that the amount of biodegradable organic waste that is disposed in landfills should be decreased by 65%, relatively to the total amount of organic fraction of municipal solid waste (OFMSW) produced in 1995, by July 2016. In this framework, anaerobic digestion (biomethanation) can be an alternative potential treatment for biodegradable solid waste.

The anaerobic digestion (AD) process was first employed in the treatment of wastewater. However, in the last two decades, this technology has been started to be used in the management of solid waste. This differs from wastewaters due to its high insoluble organic matter content and chemical oxygen demand (COD). This process is considered as organic recycling as it provides renewable energy (biogas) and organic compost after aerobic stabilisation of the digestate. Nevertheless, some organic solid wastes present a low biodegradability in spite of the high COD content and, therefore, studies to enhance the biomethanation process of such wastes are still required.

Coffee waste is a typical example of such a waste. In previous work on the co-digestion of five different wastes from an instant coffee substitutes production industry with sewage sludge, the authors verified that four of the tested wastes gave a methane yield of 240–280 LCH_4(STP)/kgVS_initial, corresponding to 76–89% of the theoretical methane production. However, a waste composed of 100% barley, attained only 11% of the theoretical methane production, which corresponds to a methane yield of 25 LCH_4(STP)/kgVS_initial [2]. This poor methane yield was likely due to the presence of products from the hydrolysis of complex heterocyclic compounds rather than to the levels of volatile fatty acids (VFA), that were lower than in the other tested assays. Moreover, in a study relating the influence of the chemical structure of instant coffee wastes with the anaerobic catabolism, it was found that the individual chemical structure of compounds greatly influences and determines the rate and mechanisms of methanogenic degradation [3].

Acid or alkaline hydrolysis can be applied as a pre-treatment to enhance the anaerobic biodegradability of a recalcitrant waste. Alkaline hydrolysis at ambient temperatures has been proposed as a chemical pre-treatment more compatible with the AD process, since the bioconversion generally requires an adjustment of pH by increasing alkalinity [4]. On the other hand, co-digestion with biodegradable wastes has also been successfully and increasingly applied to several agricultural and industrial organic wastes [5].

The aim of this work was to attempt to enhance methane production from a waste composed of 100% barley by using two different approaches: first, an alkaline pre-treatment before co-digestion with sewage sludge, and second co-digestion with kitchen waste, which is the greatest fraction of the OFMSW and is a typical biodegradable waste.

Section snippets

Analytical methods

The COD, total solids (TS), volatile solids (VS) and total Kjeldhal nitrogen (TKN) were determined according to standard methods [6]. The methane content of the biogas was measured by gas chromatography using a Porapack Q (180–100 Mesh) column, with He as the carrier gas at 30 mL/min and a thermal conductivity detector. Temperatures of the detector, injector and oven were 110, 110 and 35 °C, respectively. VFA (acetate, propionate, iso-butyrate and n-butyrate) were determined by high-performance

Alkaline hydrolysis pre-treatment

Fig. 1 presents the cumulative methane production obtained in the co-digestion of the pre-treated BW with sewage sludge.

The comparison of the methane production, % methanation as well as the TS and VS reduction obtained in this assay, with the previously reported assay where the BW was not pre-treated is given in Table 2.

The alkaline hydrolysis pre-treatment increased the methane production up to 222 LCH_4(STP)/kgVS_initial, achieving 100% of the theoretical methanation. Furthermore, this

Conclusions

An alkaline hydrolysis pre-treatment and co-digestion with kitchen waste were beneficial to enhance the methane production of a BW.

Although the best outcome in TS and VS reduction was in the assay with the alkaline hydrolysis, the pH correction in industrial applications can be a costly process when treating large amounts of waste. The co-digestion of the BW with the OFMSW seems to be attractive from an integrated solid waste management point of view because it only decreases the methane

Acknowledgements

The authors thank to FCT for the financial support given to Lúcia Neves through the project POCTI/1999/CTA/36524.

References (8)

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Alkaline treatment of wheat straw for increasing anaerobic digestion
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Enhancement of methane production from barley waste

Abstract

Introduction

Section snippets

Analytical methods

Alkaline hydrolysis pre-treatment

Conclusions

Acknowledgements

Waste Management

The influence of chemical structure on anaerobic catabolism of refractory compound: a case study of instant coffee wastes

Water Science and Technology

Alkaline treatment of wheat straw for increasing anaerobic digestion

Biotechnology and Bioengineering