A multi-criteria decision analysis of management alternatives for anaerobically digested kraft pulp mill sludge
January
A multi-criteria decision analysis of management alternatives for anaerobically digested kraft pulp mill sludge
Martijn Eikelboom 2 3
Alice do Carmo Precci Lopes 1 3
Claudio Mudadu Silva 2 3
Fa bio de A vila Rodrigues 0 3
Antoà nio Jose Vinha Zanuncio 3 5
Jose Cola Zanuncio 3 4
0 Departamento de QuÂõmica, Universidade Federal de VicËosa, VicËosa , Minas Gerais , Brasil
1 Departmento de Engenharia Civil, Universidade Federal de VicËosa, VicËosa , Minas Gerais , Brasil
2 Departamento de Engenharia Florestal, Universidade Federal de VicËosa, VicËosa , Minas Gerais , Brasil
3 Editor: Vijai Gupta, Tallinn University of Technology , ESTONIA
4 Departamento de Entomologia, Universidade Federal de VicËosa, VicËosa , Minas Gerais , Brasil
5 Departamento de Engenharia Florestal, Universidade Estadual do Centro-oeste , Irati, Parana , Brasil
The Multi-Criteria Decision Analysis (MCDA) procedure was used to compare waste management options for kraft pulp mill sludge following its anaerobic digestion. Anaerobic digestion of sludge is advantageous because it produces biogas that may be used to generate electricity, heat and biofuels. However, adequate management of the digested sludge is essential. Landfill disposal is a non-sustainable waste management alternative. Kraft pulp mill digested sludge applied to land may pose risks to the environment and public health if the sludge has not been properly treated. This study is aimed to compare several recycling alternatives for anaerobically digested sludge from kraft pulp mills: land application, landfill disposal, composting, incineration, pyrolysis/gasification, and biofuel production by algae. The MCDA procedure considered nine criteria into three domains to compare digested sludge recycling alternatives in a kraft pulp mill: environmental (CO2 emission, exposure to pathogens, risk of pollution, material and energy recovery), economic (overall costs, value of products) and technical (maintenance and operation, feasibility of implementation). The most suitable management options for digested sludge from kraft pulp mills were found to be composting and incineration (when the latter was coupled with recycling ash to the cement industry). Landfill disposal was the worst option, presenting low performance in feasibility of implementation, risk of pollution, material and energy recovery.
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Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: The work was supported by the
following: Conselho Nacional de Desenvolvimento
CientÂõfico e TecnoloÂgico (CNPq); CoordenacËão de
AperfeicËoamento de Pessoal de NÂõvel Superior
(CAPES); and FundacËão de Amparo à Pesquisa do
Estado de Minas Gerais (FAPEMIG).
Competing interests: The authors have declared
that no competing interests exist.
Introduction
Brazil holds one of the world's major shares in the pulp and paper export market with 17.2
million tons of pulp produced annually [
1
]. Kraft pulping, the most common pulp producing
process in Brazil, demands approximately 30 m3 of water per ton of pulp produced. This process
generates effluent with high organic content that cannot be discharged without treatment [2;
3]. A typical kraft pulp mill effluent treatment plant produces about 40 kg of primary sludge
and 15 kg of secondary sludge per ton of dry pulp. In countries like Brazil, China and USA,
both sludges are normally disposed into landfills, but could be used to produce biogas [
2,3
].
The waste stream that is digested to produce biogas produces a waste stream that is
dewatered, resulting in a liquid and a solid fraction (biosolids). The liquid fraction is typically used
to product biofuel and fertilizer, while the solid fraction is typically disposed of by land
application, incineration or landfilling (S1 Fig) [3±5].
The objective of this study was to investigate, compare and select, the most suitable options
for managing anaerobically digested primary and secondary sludges from kraft pulp mills,
using the Multi-Criteria Decision Analyzing (MCDA) procedure.
Material and methods
Six alternatives for recycling pulp mill digested sludge were examined, based on the most
common management alternatives adopted in the USA, China and Brazil: land application, landfill
disposal, composting, incineration, pyrolysis/gasification, and biofuel production by algae
[
2,6,7,8
]. The study data were obtained from published literature, and the recycling alternatives
were compared using MCDA, a procedure widely accepted in solid waste management studies
[
9,10
]. The method compares various alternatives and considers the opinion of stakeholders.
To evaluate the recycling alternatives, were considered environmental, economic and
technical aspects, in order to find the best alternatives for sludge treatment. The environmental
criteria considered possible environmental damage from sludge treatment, including the
following decision criteria: CO2 emission (...truncated)