Research On The High-concentration Anaerobic Digestion Of Microalgae Chlorella Producing Biogas Technology

Microalgae bioenergy is an excellent new energy. The research on the technology of fixing carbon dioxide combining with protecting the environment and using the waste to produce energy which unites microalgae cultivation together with anaerobic digestion of microalgae to produce biofuel is of great significance. It will help to solve the energy crisis and environment problems in the future. The widely studied microalgae Chlorella was selected in this study. There were 10 billion algae cells in one milliliter of the high concentration microalgae solution(TS 10%) with dry algae cell carbon content 50%. The biochemical methane potential of the Chlorella reached 0.461m3/kg VS added with the methane percentage in the biogas about 70%. The basic properties of Chlorella were fully studied. The BMP(biochemical methane potential) experimental analysis showed that microalgae biomass can be easily degraded by anaerobic microorganisms with the organic(including microalgae oils, proteins, carbohydrates, other cellular components) completely converted into methane, BMP of microalgae is relatively high among published literature reports. Thermal hydrolysis treatment experiments on microalgae and anaerobic methane potential experiments showed that: thermal hydrolysis can improve the dissolution rate of the algae organics, destructing microalgae solid phase material into the liquid. After the hydrothermal treatment Chlorella chloroplasts was destroyed with the algae color and flavor changed greatly; hydrothermal treatment had no significant impact on the potential of algae methane production but benefited for the whole algae fixing carbon dioxide producing methane bioenergy system. In the anaerobic digestion, carbon, nitrogen and other nutrients were transferred into the liquid phase in the thermal hydrolysis, so as to be used for the growth and reproduction of algae. Moreover carbon dioxide in the biogas can also be reused during microalgae cultivation process, so the system is a good self-sustaining one. Finally, the CSTR reactor(5L) was operated to run under different loading rates for Chlorella anaerobic digestion. The CSTR reactor load rate was 1.8, 2.0, 3.0, 3.6kg VS/m3 d in semi-continuous experiments respectively. In conditions of different loading rates methanogenic performance, organic matter degradation percentage and the stability of the reactor were analyzed. Under the 50 d, 45 d, 30 d, 25 d HRT, the CSTR got volum biogas production of 0.928, 1.149, 1.637 and 2.0m3/m3 d, respectively, with the production of methane reaching 0.584, 0.632, 0.948, 1.118m3/m3 d. The reactor was stable, with relatively high methane content in the biogas(around 60%), producing available high-quality fuel. The VS degradation rate reached 60% with methane yield 0.30 ~ 0.33 m3CH4/kg VSadded. With the improvement of the organic load, VS degradation rate declined, which was 61.83%, 60.21%, 60.17% and 59.14%, respectively. This study constructed a microalgae anaerobic digestion system, in which algae liquid was directly digested without dewatering. Microalgae liquid anaerobic digestion omitted collection step, which is consuming a lot of money and energy, the use of anaerobic digestion and methane production technology is energy saving, economical and feasible.