The experiment for preparation of biochar by pyrolysis of municipal sludge was carried out in a tube furnace reactor at 300—700℃.The results show that with increasing temperature from 300℃ to 700℃

yield of biochar decreases from 90.14% to 73.36%

yield of fixed-carbon fluctuates slightly between 8.76%—12.01%

and efficiency of energy conversion decreases from 75.9% to 28.5%.The concentration of all heavy metals in municipal sludge feed and biochar obtained could meet the requirement for agricultural use.The pyrolysis temperature has large influence on volatility of Hg and Cr

and little influence on that of other heavy metals;the residual ratio fluctuates widely for Hg and Cr

and is at high level for Cu

Ni

As

Pb

Zn and Cd.There is no enrichment in biochar for nutrient element nitrogen

while both phosphorus and potassium are enriched in biochar.There is need for further investigation on how to prepare biochar and make it suitable for agricultural use.