Clean Harbors Inc. posted strong net income gains for its fourth quarter, fueled by acquisitions and organic growth.

The Norwell, Mass.-based waste management company reported that net income for the period ended Dec. 31 rose 63.9 percent to $38.2 million, or 72 cents per diluted share, compared with $23.3 million, or 44 cents per diluted share, in the fourth quarter of 2010. The effective tax rate in the 2011 fourth quarter was 21 percent compared with 37 percent a year earlier, the company said in a news release. The 2011 results include a $6.5 million tax benefit.

Revenue for the 2011 fourth quarter climbed 30.9 percent to $545.9 million from $417.1 million in the same period in 2010.

For the year, 2011 net income fell 2.5 percent to $127.3 million, or $2.39 per diluted share, compared with $130.5 million, or $2.47 per diluted share on a split-adjusted basis, in 2010.  The company had a two-for-one stock split in July 2011. Income from operations increased slightly.

Revenues for 2011 increased 14.5 percent to $1.98 billion from $1.73 billion in 2010.

 “We concluded an outstanding 2011 with a strong fourth-quarter performance,” said Alan S. McKim, chairman and CEO. “All four of our operating segments contributed to our profitable growth in the quarter.”

For 2012 McKim said the company will continue to pursue its strategy of internal investments and select acquisitions. Clean Harbors increased its 2012 guidance for earnings before interest, taxes and amortization (EBITA) in the range of $400 million to $410 million.