Study On The Utilization Of Blue-green Algae From The Taihu Lake As An Resource

Salvaging the blue-green algae from polluted water timely not only can purify water body through taking away lots of nitrogen and phosphorous, but also can avoid the deterioration of water body caused by the rotting of algae in the water. However, secondary pollution can't be expected because of the roting of salvaged algae if they were stacked simply and weren't treated timely and effectively, especial the flowing and leaching of nitrogen, phosphorus and algae toxins. How to deal with the Taihu lake algae effectively and promptly is one of key questions in the course of solving Tailu Lake algae pollution. This study aimed at the energy utilization of blue-green algae through anaerobic fermenting and the resource utilization of blue-green through composting, and focused on the potential of methane production, floating and inflation during the process of blue-green algae fermentation. A series of pilot experiments with ABR craft were adopted to test the practical effect and optimize the craft of algae engineering treatement. At the same time, in order to obtain useful parameters of composting process, the composting process of dehydrated algae was monitored, whereafter, the security and feasibility of the application of algae compost into field was assessed through comparing algae and conventional organic compost with pot experiment, which provide the theoretic basis for promoting the application process of algae composting in China.The result indicated that the theoretical potential of biogas and methane production of blue-green algae were 689ml biogass·g^-1TS and 350ml methane·g^-1TS, separately. However, the practical potential of methane production of blue-green algae from the Taihu lake is 378.61 ml·biogas g^-1 TS, 410.80 ml·biogas g^-1 VS and 278.77 ml·methane g^-1 TS under the temperature 35℃and the fermentation time 60 days. In the first 15 days, the volume of biogas production accounted for more than 60% of total biogas production and the reduction rate of COD reach to 46.68%. The pretreatment on algae with anaerobic digestion indicated that floating overcoming of algae can improve the efficiency of biogas production. The homogeneity of algae can achieved through adjusting the pH less than 3, whereafter neutralizing the pH to 7.0～7.5, and the production volume of algae fermentation increased through homogeneity. The results indicated that the expansion of algae can reach the maximum naturally in 3 days, and it can decrease 17% after pump treatment, and 1/3 volume of the acidification pool can be saved.The results of pilot-scale experiment indicated that the reduction rate of COD is about 65%～70% on average and the value of pH is stable under the organic load between 10000 to 30000mg·L^-1 when the HRT (hydraulic retention time) was 10 days. However, the reduction rate of COD decreased to about 42%～68% when the outside temperature decreased and the HRT doubled. Throughout the course of pilot-scale experiment, the pH value stabilized at 7.5, and it was not affectd by the pH, temperature and loading of the feed-in matter. The content of microcystins (MC-RR, MC-LR) in the fermented liquid dropped from 80～150μg·L^-1 to 0.02～0.5μg·L^-1, which were lower than those values recommended by World Health Organization (WHO), and it was indicated that the anaerobic fermentation can be used for blue-green disposal satisfactorily.The dehydrating algae compost can reach maturity after a month during 40 days experiment with the ratios of algae: cow dung: lees 40%: 40%: 20%. The mature algae compost character were as follows: the pH value 8.05, the content of organic matter 32.62 percent, total nitrogen 1.59 percent, total phosphorus (P2O5) content 0.99 percent, potassium (K₂O) content 1.5 percent, the nutrient content of 4 percent, in line with the request of "the People's Republic of the agricultural industry standards - organic fertilizer ( NY525-2002) ". In addition, the result of potted plants test in 60 days found that, the application of compost algae can increase yield of 25.63 percent compared with no fertilizer application, and increase field of more than 12.2 percent compared to the organic fertilizer. The application of algae compost can increase the Vc conten of greengrocery more than 65.97 percent compared with no fertilizer application, but less than the conventional organic fertilizer (97.22%). Thus, the application of algae compost is higher than that of conventional organic fertilizer in the effect of increase yield, but slightly less than it in the quality.