Research On NaOH Pretreatment Parameters Of Asparagus Stalk For Biogas Production

China is a big agricultural country and produces huge number offarming waste annually. These farming wastes will result in resourceswaste and environmental pollution if not properly dealt with and reused.The total planting area of asparagus in Chongming Island of Shanghai in2008reached267hectares, and asparagus annual output was3,000tonswhile1,000tons of asparagus waste straw was abandoned. A largenumber of asparagus stalks piled up by the road and fermented naturally,harming living environment and health of residents. Therefore, resourcetreatment of farming waste like asparagus stalks is a serious problem. Asa kind of eco-energy use pattern, anaerobic methane fermentation systemwhich can solve pollution problem as well as turning waste into energy isa ideal choice without doubt. The combustion products of biogas arecarbon dioxide and water, which is a kind of broad-spectrum and nopolluted energy. The residual products of fermentation can be used tofertilize and produce biological pesticide. Zero emission of environmentwill come true. At present, the anaerobic fermentation with plant waste,livestock manure and food industry wastewater is becoming mature. Because the main organic composition of plant waste such as straw arecellulose, hemicellulose and lignin, and its structure is complex, so it ishard to utilize by anaerobic microorganisms and the fermentationefficiency is limited. In order to solve the problem, many pretreatmentmethods are used to pretreat the straw and break the structure of structureand improve the decomposition efficiency.In this paper, NaOH chemical pretreatment technology was applied toslove the obstacle of plant stalk anaerobic digestion and to optimizebiogas production. It is expected that these tests will supply practicalreference for biogas commercial production from agricultural wates.The process parameters such as NaOH pretreatment time, NaOHconcentration, NaOH solution dosage and the particle size of rawmaterials were applied as the independent variables, while the cellulose,hemicellulose and lignin content changes after pretreatment and biogasfermentation, biogas production, pH value and the methane contentchanges in the fermentation process were used as observables. Therefore,the optimum conditions of asparagus stalks NaOH pretreatment can bedetermined. All the results demenstratied that:(1) Under NaOH pretreatment conditions, the lignocellulosesdegradation ratio was hemicellulose>lignin>cellulose, compared to thestraw which dried naturally. When NaOH pretreatment concentration isbetween0%and10%, lignin degradation grows with NaOH concentration increases, while hemicellulose degradation increases fristbut then decreases. The NaOH concentration of2.5%is the best conditionfor cellulose to degrade. But in biogas fermentation, a majority ofcellulose and hemicellulose were degraded therefore the content of ligninrose up150%-200%relatively.(2) The NaOH reagent used in pretreatment will effect biogasdigestion in some degree. But after pretreatment, the impact oflignocellulose degradation will mild the negative impact brought about byNa+. In observation of measuring indicators of biogas fermentation, theoptimized parameters of NaOH pretreatment for asparagus stalk were asfollows: NaOH concentration was3.6%-5%and pretreatment time was15-20d.(3) The particle size of straw which was cut up below2.5cm wasbetter to NaOH pretreatment and biogas fermentation than the sievinggroups. Therefore, it is not necessary to sieve during the NaOHpretreatment and biogas fermentation processes.(4) According to the results of multifactorial experiment, theoptimized parameters of NaOH pretreatment for asparagus stalk were asfollows: the pretreatment time was18d, the dosage of NaOH solution was74ml, and the concentration of NaOH was4.2%(wt). The total biogasproduction rate in the optimized conditions was13893ml while thepredicted value was13352.9ml. The relative error between true value and predicted value was4.04%. The methane content of biogas was morethan60%in fastigium stage. The fermentation system fuction was sound.