No abstract

Commercial cellulosic biofuel operation requires a reliable, low-cost, and stable feedstock logistic system. One great challenge is its long-term storage at least for one harvest cycle (1 year for agricultural crop residues) with a minimum loss of bulky, geographically dispersed, inflammable, and easily degradable lignocellulosic biomass. This study conducted an investigation of year-round storage of the agricultural crop residue feedstock under the scenario of performing dry acid pretreatment at the distributed regional collection depots, instead of the central biorefinery plant. The dry acid pretreatment method provides a practical basis for the storage operation by its ability for high preservation of polysaccharide solids, highly compacted accumulation density, being free from wastewater generation, low capital investment, and low energy consumption. Three major agricultural crop residues (corn stover, wheat straw, and rice straw) were pretreated by dry acid pretreatment and then stored in their major planting regions under varying natural conditions of temperature, rain and snow fall, humidity, wind, and sunlight. The pretreated corn stover, wheat straw, and rice straw contained approximately 50% (w/w) of moisture, and their high water absorption capacity maintained the crop residues in solid and fine-particle forms without free wastewater generation and flammability. Meanwhile, the pretreated crop residues were of low pH value and contained various inhibitory compounds for microbial growth. The results show that the crop residue feedstocks were well preserved with negligible solid and fermentable sugar loss after year-round storage in different regions. The physical properties, chemical compositions, enzymatic hydrolysis yields, and ethanol fermentability were maintained essentially constant with a few positive exceptions such as the increased hydrolysis yield and reduced inhibitor content. A case study shows that the feedstock transportation cost of the long-term stored feedstocks under the scenario of dry acid pretreatment at collection depots was significantly reduced compared to that of the direct transportation of virgin crop residual feedstocks. This study provided an efficient and practical logistic system for large-scale biorefinery plants.

In order to address the issues regarding the high water content, poor dewatering performance, and occupied space of landfill, the physical property tests and experiments on the lake silt samples were conducted. The effects of cationic polyacrylamide (CPAM), lime dosage, and dehydration time on the dehydration performance indexes such as the concentration ratio, the water content, and the decreasing ratio of water content of the lake silt with the initial water content of 91% were investigated. The results revealed that the concentration ratio reached 3.6 times when the dosage of CPAM was 40mg/L, and the water content decreased to 70% and the decreasing ratio of water content decreased to 29% after dehydration for 10min. The concentration ratio was about 2.6 times when the dosage of lime was 3.8g/L, and the water content decreased to 73% and the decreasing ratio of water content decreased to 24% after dehydration for 10min. The variation laws of water content of the lake silt with initial water content of 91%, 85%, and 80% after flocculation concentration dehydration was studied based on the concept of the decreasing ratio of water content. It was concluded that the decreasing ratio of water content was independent of the initial water content. It was only significantly proportional when the dosage of CPAM was 15∼45mg/L and lime was 1∼7g/L. The linear constant depended on the intrinsic properties of the lake silt. According to the variation laws of the water content and the water-hinge hypothesis, the calculation formula of the water content was proposed and the mechanism of critical addition value breaking the silt hinge in flocculation concentration dehydration was formulated.

The aluminum based compound flocculant was prepared with components such as polyaluminum chloride (PAC), calcium oxide (CaO) and polyaluminosilicate ferric oxide (PSAF) by adopting mixed and compound method. On the basis of single factor experiment, the main factors affecting the preparation of aluminum based compound flocculant were selected, and the preparation conditions were optimized through Box-Behnken design experiment and response surface analysis. The results showed that the quadratic polynomial model had significant regression, but the loss of fit term was not noticeable. The determination coefficient R2 is 0.9603, which indicated that the model had good fit. The optimum preparation condition of the aluminum based compound flocculant was as follows: the mass ratio of PAC:CaO:PSAF was 8:4:5. When the influent initial fluorine content was 4.0∼6.0mg/L, the dosage of the flocculant was 0.85mg/L, and the initial pH value was 7.5, the removal rate of fluoride ion (F−) reached 92.95%, the fluoride ion content in the supernatant was less than 1.0mg/L, and the relative error with the predicted value of the model was 2.31%. The response surface curve optimization model was reliable.