Two-Stage Conversion of Land and Marine Biomass for Biogas and Biohydrogen Production
Author
Summary, in English
Two-stage, dry anaerobic digestion of mussels, reeds, seaweed, solid cow manure, and a mixture of seaweed and manure was studied. The system consisted of a leach bed reactor for hydrolysis and an upflow anaerobic sludge blanket (UASB) reactor for methane production. The results showed that mussels with shells, seaweed, and the seaweed and manure mixture were efficiently digested in the two-stage system; 68 to 83% of the methane being produced in the UASB reactor. The manure by itself, and reeds, which are slowly degradable, were efficiently digested in the one-stage dry leach bed process, in which most of the biogas was produced. Seaweed and manure can also be co-digested in the one-stage dry digestion process, since methano¬genic conditions prevailed in the leach bed reactor, thus reducing the cost of operating two biogas reactors. Technically, both the new feedstocks and the one- and two-stage dry anaerobic systems have great potential for biogas production. However, economic evaluations are needed to validate practical applicability.
The removal of heavy metals from seaweed hydrolysate was studied in the two-stage system. The heavy metals Cd, Cu, Ni and Zn were adsorbed using iminodiacetic acid Cryogel® carriers. However, removal of the heavy metals resulted in low methane yields, possibly due to the removal of micro¬nutrients needed for anaerobic digestion. It is therefore suggested that the metals be removed after methane production in a UASB reactor. Alkaline and autoclave post-treatment of the seaweed digestate resulted in 86% organic matter solubilisation and the leachate may be treated in a UASB reactor, providing a means of handling digestate with high heavy metal content. Co-digestion of leachates from the leach bed reactor and the post-treatment resulted in a high methane yield, 0.34 l/gVSadded in a batch test. Subsequent treatment of the leachate from the leach bed reactor resulted in a high methane productivity at a loading rate of 20.6 g COD/l.day in a UASB reactor. Treatment of the seaweed leachate in the UASB reactor resulted in a stable process without the need for additional nutrients or buffer. As the seaweed leachate was rich in nutrients and buffer capacity, its co-digestion with wheat straw hydrolysate in the UASB reactor resulted in a stable process.
Biohydrogen and biogas were co-produced from wheat straw hydrolysate in a two-stage system consisting of a CSTR and a UASB reactor, employing the thermophile, Caldicellulosiruptor saccharolyticus in the first H2 reactor. Straw hydrolysate was efficiently produced by acid-catalysed steam and enzyme pretreatment, giving a 95% sugar yield of the theoretical yield. High biofuel production rates of 1.8 to 3.5 l H2/l.day and 2.6 to 4.0 l CH4/l.day were obtained under stable operational conditions and treatment efficiencies. However, the cost of nutrient supplementation was high, and cheaper nutrient sources will be required to make the production cost economically competitive.
This research has demonstrated the versatility of a two-stage system that allowed the digestion of new kinds of biomass such as seaweed with sand, mussels with shells, reeds, manure and wheat straw. It has also been shown to be possible to remove heavy metal from seaweed to improve fertiliser quality. High hydrogen and methane production rates were also demonstrated, and the two-stage anaerobic system is thus, technically, a promising reactor configuration for the production of biofuels.
Department/s
Publishing year
2012
Language
English
Full text
Document type
Dissertation
Publisher
Printed in Sweden by Media-Tryck, Lund University
Topic
- Industrial Biotechnology
Keywords
- steam pretreatment
- dry digestion
- biogas
- biohydrogen
- Caldicellulosiruptor saccharolyticus
- cadmium
- anaerobic digestion
Status
Published
Research group
- Environmental and Energy Systems Studies
Supervisor
- Marika Murto
ISBN/ISSN/Other
- ISBN: 978-91-89627-87-1
Defence date
29 November 2012
Defence time
13:15
Defence place
Lecture Hall B, Sölvegatan 39, Center for Chemistry and Chemical Engineering, Faculty of Engineering, Lund University
Opponent
- Åke Nordberg (Dr.)