Study On The Biogas Production From Blue-Green Algae And Pig Manure By Anaerobic Digestion

Biogas production from blue-green algae and pig manure by anaerobic digestion at 35℃was investigated for the purpose of resource recovery and harmless treatment of the blue-green algae salvaged from Taihu Lake. In the studied laboratory-scale batch fermentation and large-scale fed-batch fermentation, we obtained the optimum conditions and the main parameters in the fermentation process and further carried out the 1000 m3 biogas production demonstration project. In this paper, we found a new effective way to manage the blue-green algae from Taihu Lake . Results were concluded as follows:(1) The inoculum to substrate ratios (ISRs), pH and algae concentration were studied by single-factor experiments and response surface experiments. Results showed that the best conditions of production of biogas from blue-green algae and pig manure by anaerobic digestion were as follows: ISRs 2:1, pH 7.9, and fermentation broth concentration of 2.9%.(2) When ISR was 3.0, 2.0, 1.0, 0.5 and 0.25, methane production content reached 206, 202, 97, 48, 21 mL CH4/gVSadded respectively. ISR had a great effect on methane producing blue-green algae when ISR was lower than 2.0 and methane production increased with inoculation ratio. However, the amount of methane produced was the same when ISR was3.0. Under different conditions of ISRs, the whole methane production abided the Cheynoweth formula (Β=Β0(1 ? e?kt))and the regression analysis was R2>0.97. As ISR decreased, the values of BD (%) of blue-green algae decreased from 46.5 to 4.2. With regard to the pH, polysaccharides, protein, VS, ammonia and VFAs in fermentation broth, the parameters depleted gradually. Especially, VFAs depleted completely when VS degradation rate was at the range of 18-35%. Polysaccharides degradation was fast during the initial stage of fermentation,so was visible protein degradation at a later stage. Protein degradation caused ammonia content to increase at the later stage of the fermentation. The optimum pH range for anaerobic fermentation should be within 7.1-7.7.(3) Finally, we did the demonstration project of production of biogas from blue-green algae and pig manure by anaerobic digestion, and found out that the gas volume increased with the blue-green algae addition level. When the reactor was operated stably, the gas production was between 650 m3 and 700 m3, which included about 60%-65% methane, 20% CO2, 5% N2.However, H2S gas was not detected in the biogas.Biogas residues after fermentation by the algae were also analysed, was found that the main effective nutrient content of the test results were as follows: total nitrogen content was 4.0 g/L to 5.8 g/L, total phosphorus content was 0.41 g/L to 0.50 g/L, total potassium content was 0.21 g/L to 0.33 g/L. Furthermore, the cyanophycean toxins levels of the raw materials was high with MC-RR content of 39.5 mg/L and MC-LR of 10.3 mg/L. MC-RR and MC-LR were not detected after the anaerobic fermentation. Therefore,regardless of nutrient content or the safety , the residues are good organic fertilizers.