Study On Enhancing Biodiesel Yield From Sludge Of Municipal Wastewater Plant

The treatment and disposal of sludge from waste water treatment plant(WWTP) is a thorny problem in the field of environmental engineering. At the same time the global energy shortage and environmental deterioration require an alternative renewable energy source. Biodiesel is a kind of green renewable energy, whereas, its raw material has been the bottleneck of its development. The sludge of WWTP contains a certain amount of lipid that can be converted into biodiesel oil. Thus sludge may be the potential raw materials for biodiesel production. However, at present the cost of biodiesel production from sludge is higher, because the oil content in the sludge is low.The purpose of this paper is to raise the oil content of the sludge for biodiesel production.The biological sludge of the No.4 WWTP in Xi'an was selected to study the effect of initial ratio of carbon to nitrogen(C: N=70, 140, 210) on the lipid accumulation and the subsequent biodiesel yield of sludge under continuous cultivation, Then the oil composition and content of the primary sludge was analysed and the primary sludge was activated by acid for biodiesel production. The main conclusions were as the followings:(1) The yield of the fatty acid methyl esters(biodiesel) was enhanced via cultivating the activated sludge at different high C:N ratios and a higher biodiesel yield happened under the cultivation of higher C: N ratio. The maximum biodiesel yield of all the cultivated sludge was achieved on the 5th day, which were 4.65%, 5.53% and 6.59% respectively when the ratio of C: N was 70, 140 and 210.The above values were 3.58, 4.25 and 5.07 times of biodiesel yield of the raw biological sludge.(2) The content of the fatty acids in the cultivated sludge under different ratio of carbon to nitrogen were changed. The content of oleic acid was remarkably increased, consistently accounting for 40% of the total fatty acids when compared with the raw biological sludge.(3) The capillary suction time of the sludge began to increase rapidly from 5th day during the cultivation, the best cultivation time was five days from the dehydration of the cultivated sludge.(4) At the same time, the dominant microbes in the sludge cultivated under high C:N ratio were apt to yeast, which accumulated mostly of the lipid.(5) After the sludge was acid activated, the yield of biodiesel productionwas 12.03%, which was 2 times of the original primary sludge.