Sune Tjalfe Thomsen

Pretreatment of the macroalgae Chaetomorpha linum for the production of bioethanol - Comparison of five pretreatment technologies

A qualified estimate for pretreatment of the macroalgae Chaetomorpha linum for ethanol production was given, based on the experience of pretreatment of land-based biomass. C. linum was subjected to hydrothermal pretreatment (HTT), wet oxidation (WO), steam explosion (STEX), plasma-assisted pretreatment (PAP) and ball milling (BM), to determine effects of the pretreatment methods on the conversion of C. linum into ethanol by simultaneous saccharification and fermentation (SSF). WO and BM showed the highest ethanol yield of 44 g ethanol/100g glucan, which was close to the theoretical ethanol yield of 57 g ethanol/100g glucan. A 64% higher ethanol yield, based on raw material, was reached after pretreatment with WO and BM compared with unpretreated C. linum, however 50% of the biomass was lost during WO. Results indicated that the right combination of pretreatment and marine macroalgae, containing high amounts of glucan and cleaned from salts, enhanced the ethanol yield significantly.

Statistical prediction of biomethane potentials based on the composition of lignocellulosic biomass

Mixture models are introduced as a new and stronger methodology for statistical prediction of biomethane potentials (BPM) from lignocellulosic biomass compared to the linear regression models previously used. A large dataset from literature combined with our own data were analysed using canonical linear and quadratic mixture models. The full model to predict BMP (R(2)>0.96), including the four biomass components cellulose (xC), hemicellulose (xH), lignin (xL) and residuals (xR=1-xC-xH-xL) had highly significant regression coefficients. It was possible to reduce the model without substantially affecting the quality of the prediction, as the regression coefficients for xC, xH and xR were not significantly different based on the dataset. The model was extended with an effect of different methods of analysing the biomass constituents content (DA) which had a significant impact. In conclusion, the best prediction of BMP is pBMP=347xC+H+R-438xL+63DA.

Consequences of field N2O emissions for the environmental sustainability of plant‐based biofuels produced within an organic farming system

One way of reducing the emissions of fossil fuel‐derived carbon dioxide (CO2) is to replace fossil fuels with biofuels produced from agricultural biomasses or residuals. However, cultivation of soils results in emission of other greenhouse gases (GHGs), especially nitrous oxide (N2O). Previous studies on biofuel production systems showed that emissions of N2O may counterbalance a substantial part of the global warming reduction, which is achieved by fossil fuel displacement. In this study, we related measured field emissions of N2O to the reduction in fossil fuel‐derived CO2, which was obtained when agricultural biomasses were used for biofuel production. The analysis included five organically managed feedstocks (viz. dried straw of sole cropped rye, sole cropped vetch and intercropped rye–vetch, as well as fresh grass–clover and whole crop maize) and three scenarios for conversion of biomass into biofuel. The scenarios were (i) bioethanol, (ii) biogas and (iii) coproduction of bioethanol and biogas. In the last scenario, the biomass was first used for bioethanol fermentation and subsequently the effluent from this process was utilized for biogas production. The net GHG reduction was calculated as the avoided fossil fuel‐derived CO2, where the N2O emission was subtracted. This value did not account for fossil fuel‐derived CO2 emissions from farm machinery and during conversion processes that turn biomass into biofuel. The greatest net GHG reduction, corresponding to 700–800 g CO2 m−2, was obtained by biogas production or coproduction of bioethanol and biogas on either fresh grass–clover or whole crop maize. In contrast, biofuel production based on lignocellulosic crop residues (i.e. rye and vetch straw) provided considerably lower net GHG reductions (≤215 g CO2 m−2), and even negative numbers sometimes. No GHG benefit was achieved by fertilizing the maize crop because the extra crop yield, and thereby increased biofuel production, was offset by enhanced N2O emissions.

Comparison of different pretreatment strategies for ethanol production of West African biomass.

Pretreating lignocellulosic biomass for cellulosic ethanol production in a West African setting requires smaller scale and less capital expenditure compared to current state of the art. In the present study, three low-tech methods applicable for West African conditions, namely Boiling Pretreatment (BP), Soaking in Aqueous Ammonia (SAA) and White Rot Fungi pretreatment (WRF), were compared to the high-tech solution of hydrothermal pretreatment (HTT). The pretreatment methods were tested on 11 West African biomasses, i.e. cassava stalks, plantain peelings, plantain trunks, plantain leaves, cocoa husks, cocoa pods, maize cobs, maize stalks, rice straw, groundnut straw and oil palm empty fruit bunches. It was found that four biomass’ (plantain peelings, plantain trunks, maize cobs and maize stalks) were most promising for production of cellulosic ethanol with profitable enzymatic conversion of glucan (>30 g glucan per 100 g total solids (TS)). HTT did show better results in both enzymatic convertibility and fermentation, but evaluated on the overall ethanol yield the low-tech pretreatment methods are viable alternatives with similar levels to the HTT (13.4–15.2 g ethanol per 100 g TS raw material).