The present study aimed to investigate the relationship between the desorption and biodegradability of phenanthrene sorbed to biochars by employing two approaches that may change the desorption and biodegradability: the use of powdered biochars and nonionic surfactants. Biochars derived from two feedstocks (rice husk and sewage sludge; pyrolyzed at 500 degrees C but showing different aromaticity) were used. When the biochars were powdered to obtain particles < 250 mu m the mass fractions of the desorbed phenanthrene at similar to 80 days (f(des)) increased from 0.303 to 0.431 for sewage sludge biochars. On the other hand, f(des) for rice husk biochars remained virtually unchanged (from 0.264 to 0.255). The mass fractions of the biodegraded phenanthrene (f(bio)) increased from 0.191 to 0.306 for rice husk biochars and from 0.077 to 0.168 for sewage sludge biochars. When a nonionic surfactant was added at the sub-critical micelle concentration (CMC), f(bio) increased by 4.7 times and 8.3 times for rice husk and sewage sludge biochars. For both types of biochars, f(bio) was larger than f(des) when the surfactant was added. This study suggests that the addition of nonionic surfactants can be considered if the inhibition of microbial activity is of concern in soils and sediments treated by biochar.