Study On Hydrothermal Pretreatment For Methane Production From Anaerobic Digestion Of Antibiotic Mycelial Residue

Antibiotic Mycelial residue is a kind of biowastes produced from production of antibiotic, which organic mainly consists of mycelia and fermentative substrates. Because of being rich in nutrition ingredients including proteins, carbohydrates and the like., they were ever used as animal feed additives and soil conditioner after drying, but since 2008, they have been put in "the national hazardous waste list" because of residual antibiotics in them, which are considered to easily form resistance in plants and animals and thus cause serious safety hazard. They are rigidly prohibited to be use as animal feed and fertilizer and require to be subjected to innocent treatment before discharged. Up to this day, there is not any effective technology to treat and utilize the antibiotic mycelial residues, since they are usually rich in water and are difficult to be mechanically dewatered in addition to the block of residual antibiotics on employing conventional solid biowaste treatment measures. Research and development methods enabled to safely and effectively manage various antibiotic mycelial residues are in urgent need.With cephalosporin C residue(CPCAR) as the representative material, hydrothermal pretreatment coupled with anaerobic digestion for methane production is involved in this thesis. The main research contents and results are as follows:First, the effects of different thermal pretreatment conditions on anaerobic digestion of the CPCAR were studied and the potential for biogas production tested. The thermal pretreatment conditions included: treatment temperatures: 80 oC, 120 oC, 160 oC, 180 oC, treatment times: 0 min, 30 min, 60 min. After thermal pretreatment the dewatering and drying properties of the solid matters in the CPCAR were improved to certain degrees, above all the SCOD representing biodegradability was visibly increased. This result meant higher biogas yields after thermal pretreatment. The thermal pretreatment at the optimized condition of 120 oC, 60 min gave the best methane yield 290 mlCH4 / g VS, which was three times as the raw material was.Secondly, the researches on low temperature thermal pretreatment were conducted to lower pretreatment strength and addition of alkali was performed in view of the problem of lower methane yields obtained after hydorthermal pretreatment at lower temperatures, The hydorthermal pretreatment conditions invloved were as follows: treatment temperatures: 60 oC, 80 oC and 100 oC, treatment time: 0min, 60 min, 120 min. 0.04gCaO/g TS was added at the hydrothermal pretreatment condition of 80 oC, 60 min and 100 oC, 60 min. The results showed that prolonging pretreatment time did not significant improve the methane yield at low hydorthermal pretreatment temperatures and the presence of alkali generated certain positive effect. When performing hydrothermal pretreatment at 100 oC, 60 min, addition of alkali led to a 213 mlCH4/g VS yield, 20 ml CH4/g VS higher than the case without adding alkali.Finally, anaerobic digestion for the hydrothermally pretreated CPCAR with different concentrations and inoculum ratios of anaerobic fermentation were conducted for biogas production, to explore and find out inhibitive factors and their removal methods, respectively. Hydrothermally pretreated CPCAR(pretreated at 120 oC 30 min) was respectively inoculated with seed sludge at volume ratios of 1:5, 2:4, 3:3 for conducting anaerobic fermentation. It was found that due to the inhibition of ammonia nitrogen generated from protein in the CPCAR during hydorthermal pretreatment and especially anaerobic digestion, the methane yield reduced with the the increase in the concentration of digestion substrate; and the digestion failed for the inoculation ratios of 3:3, when the ammonia nitrogen concentration was over2800mg/L. Against the inhibition caused by high ammonia nitrogen concentration, various methods to remove ammonia nitrogen including zeolite adsorption, physical ammonia-stripping method and a chemical method(adding CaO during thermal pretreatment and then stripping the ammonia nitrogen from the residue) were used. The results showed that the methane yields could be recovered to big extents.