Over the trailing 12 months, Darling's Ingredients business has generated in excess of $4 billion in sales and now more than $1 billion of combined adjusted EBITDA.
Darling opportunistically repurchased approximately $76 million of common stock during the second quarter because we believe that our Diverse Green Global business will continue to appreciate in value in the near future.
In total, our Global Ingredients business generated approximately $222 million of EBITDA and DGD produced $132 million, which is our half, making our combined adjusted EBITDA just shy of $354 million for the second quarter.
We are very excited about the anticipated start-up of the new 400 million gallon renewable diesel expansion in Norco.
We are approximately 60 days from the largest project of its kind to begin producing, one of the greenest hydrocarbons on the planet.
Also, we are pleased that the start-up of the 470 million gallon renewable diesel plant located in Port Arthur, Texas has now moved through the first half of 2023 for start-up.
Once Port Arthur is online, the DGD platform will have 1.2 billion gallons of renewable diesel production capacity and 50 million gallons of Green gasoline capability.
Net income for the second quarter of 2021 total a $196.6 million or $1.17 per diluted share compared to net income of $65.4 million or $0.39 per diluted share for the 2020 second quarter.
Net sales increased 41.2% to $1.2 billion for the second quarter of 2021 as compared to $848.7 million for the second quarter of 2020.
Operating income increased 152.4% to $268.3 million for the second quarter of 2021 compared to $106.3 million for the second quarter of 2020.
The increase in operating income was primarily due to the $104.3 million increase in gross margin, which was a 48.2% increase in gross margin over the same quarter in 2020.
Adding to our operating income improvement was our 50% share of Diamond Green Diesel's net income, which was $125.8 million as compared to $63.5 million for the second quarter of 2020.
For the first six months of this year, our gross margin percentage was 26.5% compared to 24.8% for the same period a year ago, which comes out to a 6.8% improvement year-over-year.
Depreciation and amortization declined $4.1 million in the second quarter of 2021 compared to the second quarter of 2020.
SG&A increased $8.9 million in the quarter as compared to the prior year.
Interest expense declined $2.7 million for the second quarter 2021 as compared to the 2020 second quarter.
Now turning to income taxes, the Company recorded income tax expense of $55 million for the three months ended July 3, 2021.
The effective tax rate is 21.7% which differs from the federal statutory rate of 21% due primarily to biofuel tax incentives, the relative mix of earnings among jurisdictions with different tax rates, and certain taxable income inclusion items in the U.S. base on foreign tax -- foreign earnings.
For the six months ended July 3 2021, the Company recorded income tax expense of $83.7 million and an effective tax rate of 19.2%.
The Company has also paid $25.3 million of income taxes as of the end of the second quarter.
For 2021, we are projecting an effective tax rate of 22% and cash taxes of approximately $20 million for the remainder of this year.
Our balance sheet remains strong with our total debt outstanding as of July 3 at approximately $1.44 billion and the bank covenant leverage ratio ended the second quarter at 1.71 times.
Capital expenditures were $65.3 million for Q2 2021 and totaled $126.1 million for the first six months of 2021, which is in line with our planned spend of approximately $312 million on capital expenditures for fiscal 2021.
Through the first half of 2021, we have produced $638.5 million of combined adjusted EBITDA and we believe based on what we see in our markets at the present time, the second half performance of 2021 will be as strong as the first.
DGD has sold 162 million gallons of renewable diesel in the first half of 2021 and with DGD II starting up in Q4, we should see over 200 million gallons sold in the back half of 2021.
I do want to point out that we would expect the EBITDA margin per gallon for DGD to normalize back into the original guidance range that we gave you of $2.25 to $2.40 per gallon over the next six months.
Earning $2.97 EBITDA per gallon in the first half was well above our expectations.
And with margins normalizing in the second half, DGD can still put up EBITDA per gallon north of $2.50 per gallon during all of 2021.
With our current Global Ingredients business approaching $800 million of EBITDA for 2021, we believe that our base business could grow in the range of 5% to 10% for 2022.
We anticipate that DGD will earn $2.25 per gallon in 2022 and at a 700 million gallon sold rate that puts Darling's half of DGD EBITDA at approximately $800 million.
Adding it all up, Darling Ingredients combined adjusted EBITDA for 2022 should be in the range of approximately $1.6 billion to $1.7 billion.
For a quick comparison, last year we reported $841.5 million of combined adjusted EBITDA.
And I am very confident that they will, because for the last half-year and -- year-and-a-half, our 10,000 employees have delivered stellar results in what has been one of the most challenging environments a business or a community or our people and people around the world have ever faced with the ongoing pandemic.

Summary:
Net income for the second quarter of 2021 total a $196.6 million or $1.17 per diluted share compared to net income of $65.4 million or $0.39 per diluted share for the 2020 second quarter.
Net sales increased 41.2% to $1.2 billion for the second quarter of 2021 as compared to $848.7 million for the second quarter of 2020.