Timo Kikas

Basis of energy crop selection for biofuel production: Cellulose vs. lignin

ABSTRACT This paper investigates the suitability of Jerusalem artichoke (Helianthus tuberosus L.), fiber hemp (Cannabis sativa L.), energy sunflower (Helianthus annuus L.), Amur silver-grass (Miscanthus sacchariflorus), and energy grass cultivar (cv) Szarvasi-1 for biofuel production in Northern climatic conditions. Above ground biomass, bioethanol production yield, and methane production yield are used as indicators to assess the bio-energy potential of the culture. Results presented show that energy crops of Southern origin produce 30–70% less biomass than in the origin region. Nonetheless, both perennial and annual energy crops produce high above ground biomass yields (660–1280 g m–2) for Northern climatic conditions. Experimental results show that bioethanol yield is dependent on cellulose content of the biomass. The higher the cellulose content, the higher the bioethanol yield. The biogas production on the other hand, depends on lignin content. The lower the lignin content the higher the biogas yield. Therefore, the selection of the energy crop for bioethanol production should be based on high cellulose content, while for biogas production it should rather be based on the low lignin content.

Bioelectronic tongue and multivariate analysis: a next step in BOD measurements.

Seven biosensors based on different semi-specific and universal microorganisms were constructed for biochemical oxygen demand (BOD) measurements in various synthetic industrial wastewaters. All biosensors were calibrated using OECD synthetic wastewater and the resulting calibration curves were used in the calculations of the sensor-BOD values for all biosensors. In addition, the output signals of all biosensors were analyzed as a bioelectronic tongue and comprehensive multivariate data analysis was applied to extract qualitative and quantitative information from the samples. In the case of individual biosensor measurements, most accurate result was gained when semi-specific biosensor was applied to analyze sample specific to that biosensor. Universal biosensors or biosensors semi-specific to other samples underestimated the BOD7 of the sample 10-25%. PLS regression method was used for the multivariate calibration of the biosensor array. The calculated sensor-BOD values differed from BOD7 less than 5.6% in all types of samples. By applying PCA and using three first principal components, giving 99.66% of variation, it was possible to differentiate samples by their compositions.

Nitrosomonas sp. Based biosensor for ammonium nitrogen measurement in wastewater

A bacterial culture of Nitrosomonas sp. was isolated from a nitrifying biofilm to construct a biosensor for ammonium nitrogen (NH4+−N) measurements in high ammonia wastewaters. The pure culture of microorganisms was immobilized into agarose gel matrix to attain a stable biosensor with a long service life. Biosensors were calibrated using (NH4)2SO4 solution and a steady-state method. Subsequently, several experiments with synthetic and industrial wastewaters were conducted. A linear range up to 20 mg/L of NH4+−N, and sensitivities between 0.030 and 0.036 were gained with biosensors. During 14 days of stable service life of the Nitrosomonas sp. biosensors, variation of the signal was less than 7%. Response times of biosensors were 15 ∼ 25 min, while recovery times were up to 25 min. Measurements with high ammonia content synthetic and industrial wastewaters were conducted, and 8.3 and 5.6% over estimation of NH4+−N was gained, respectively, compared with results of Nessler method. In spite of the small overestimation, the biosensor based on a pure culture of Nitrosomonas sp. and calibrated with (NH4)2SO4 is suitable for the analysis of NH4+−N in high ammonia content wastewaters.

Nitrogen explosion pretreatment of lignocellulosic material for bioethanol production

ABSTRACT A novel method for the pretreatment of lignocellulosic material is investigated in this work, using floodplain meadow hay as a feedstock for bioethanol production. Pressurized nitrogen (N2) pretreatment is combined with explosive decompression to achieve high glucose yields with simple technology and low energy input. Results show that N2 explosion yields hydrolysis efficiencies up to 71.8%. The highest hydrolysis efficiency was achieved at a temperature of 210°C with a cellulose to glucose conversion rate of 195.1 g kg−1 of biomass.

Growth of Scenedesmus obliquus under artificial flue gas with a high sulphur concentration neutralized with oil shale ash

Oil shale is the main energy resource in Estonia, which generates large amounts of CO2 and waste oil shale ash. Flue gas from oil shale combustion can also contain large amounts of SO2. Microalgae can be used for biological sequestration of carbon from flue gas. In this research, green algae Scenedesmus obliquus were grown with 14% CO2 in 1 L bioreactors. Sulphuric acid was added with a concentration of 500 ppm and 1000 ppm in order to imitate the dissolution of sulphur dioxide from flue gas into the growth medium. Oil shale ash was used to neutralize SO2. Biomass measurements of S. obliquus, carried out every 24 hours for 7 days, were used as a proxy for carbon fixation. The biomass yields of the untreated control and of the treatments were similar (maximum yield 2.9, 3.1, and 3.9 g L for the control, 500 ppm, and 1000 ppm treatment, respectively), suggesting that neither the sulphur nor the ash had an inhibitory effect on algal growth. In fact, the biomass yield was slightly higher in the treatments, which implies that minerals contained in waste ash could be utilized by algae. The calculated CO2 fixation rate was 0.45 g L d for the control, and 0.62 and 0.83 g L d for 500 ppm and 1000 ppm treatment, respectively. Therefore, microalgae can be used for carbon sequestration from flue gas. Further research should be done in order to optimize the growth conditions and maximize carbon fixation.

Comparative Study of Steam- and Nitrogen Explosion Pretreatment Methods

The aim of this paper was to investigate chemical and physical changes in biomass during N2 explosive decompression pretreatment and compare it with steam explosion pretreatment. The methods are economically and environmentally attractive since only pressure and water/steam are used to break down the biomass structure. Two pretreatment methods were used at different temperatures and samples from all process steps were analysed. The results were used to assess the pretreatment effect and the chemical changes in biomass and, finally, the mass balances of the bioethanol process at different process steps. Results show that the highest glucose and ethanol yields were obtained with the steam explosion pretreatment method at 200 °C (24.29 g and 12.72 g per 100 g biomass, respectively). At lower temperatures, the nitrogen explosion treatment produced better yields.