| Eutrophicated algae were generated by algal blooms from eutrophic water, which could bring about serious problems. Dianchi Lake, a typical eutrupic lake in China, has been invoved in the big problematic algal blooms for years. This study tried to treat this huge and troublesome algae produced from Dianchi Lake (named as Dianchi algae) using hydrothermal liquefaction (HTL). HTL advantageously allows a direct conversion of wet and low-lipid algae into biocrude oil due to it is relative low enengy input and whole algae conversion. Especially pointed that these Dianchi algae were high ash (36.6%-45.2%) low lipid (0.7%-2.1%, dry ash free basis, daf) which were harvested after a large-scal separation procedure (flocculation and centrifugation). The further investigation of biochemical compositions and biodiversities indicated that they were different from the algae growth in the lake. The feedstocks were obtained in four typical moths during algal blooms happened, i.e., April, June, August, and October. Among four monthly algae, June alga had highest HTL biocrude oil yield (23.8%, daf) thogether with lowest content of ash and Microcystis (dominant specie), highest protein and biodiversity, and highest weight loss rate of thermogravimetric analysis (TGA). October alga had cell damage due to the separation procedure and may caused organic matter loses, followed decrease the biocrude yield. These four monthly algae HTL indicated that higher protein, lower ash would be helpful for biocrude oil production.The HTL of four monthly algae and intensification process were both studied under the optimized parameters. A highest biocrude oil yield (18.4%, daf) was achieved at 300℃ of holding temperature (HT), 60 min of retention time (RT), and 20% of total solid (TS). This result was obtained during study the operational parameters (HT, RT and TS) influence on HTL products distribution. This study also indicated that total carbohydrates had highest contribution to biocrude oil due to its high content. However, the conversion efficiency of total carbohydrates was too low, together with high ash content, leading the low biocrude oil yield. From a perspective of element migration, the Dianchi algae HTL was a deoxygenation and denitrogenation; hydrogen migration was not significant. This feature of element migration made higher heating value (HHV) of oil could reach to about 36MJ/kg. For more effective utilization Dianchi algae, both high ash characterization and low HTL conversion issue must be considered. This study have provided a process intensification plan that recovery inorganics and reduce ash in Dianchi algae via deashing and promotion composition of organic compounds for higher HTL conversion via co-liquefaction. The following study showed that they were all feasible.According to the study of acid treatment influence on deashing efficiency and HTL conversion, the acid deashing treatments were suggested to make in the room temperature (25-30℃) and should consider the TS of algae in treating system to make choice for right acid and its concentration. The increased oil yield could reach 4.0%-4.6% when using deashed algae HTL. When TS is relative low (≤2%), higher concentration (e.g.,>0.4M) of organic weak acid (e.g., acetic acid) would be better; while inorganic strong acid (e.g., sulphuric acid) could treat higher TS of algae (2% ～ 4%) in the system, in addition, its concentration must be right (e.g.,0.7N). For a perspective of element migration, deashing could significantly decrease N/C, HTL of deashed algae would followed make deoxygenation.The study for respectively co-liquefaction with Dianchi algae using high lipid alga (Chlorella sp.) and high protein alga (Spirulina sp.) showed that, higher synergistic effect of biocrude oil yield (11.3%～37.0%) would be generated when using high lipid alga; while using high protein alga would get high synergistic effect of liquefaction (2.7%～3.5%). In the aspect of mixed ratio, i.e., the treating mass ratio of Danchi algae, when using high lipid alga obtain high synergistic effect of biocrude oil yield (11.3%), the mixed ratio of Dianchi algae is just 25%; while using high protein alga obtain high synergistic effect, especially for liquefaction (2.7%), the mixed ratio of Dianchi algae is high to 75%, but relative low synergistic effect of biocrude oil yield (6.3%). For a perspective of element migration, obvious deoxygenation happed when using high lipid alga to co-liquefaction, in addition, also higher hydrogen kept; while both deoxygenation and denitrogenation were happed when using high protein alga to co-liquefaction. |
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