In the second quarter, we achieved an operating EBITDA of $1.31 billion, which we converted into strong cash from operations of more than $1 billion.
With all of this powerful momentum, we now expect to generate 2021 adjusted operating EBITDA of at least $5 billion with free cash flow of at least $2.5 billion, all while continuing to make growth investments in our sustainable solutions and technology platforms.
At our automated facilities, labor costs were 35% lower in the second quarter compared to our other single-stream MRFs.
Next month, we're hosting a supplier diversity initiative called Share the Green, which will give women-owned businesses the opportunity to become a supplier for one or more of the 45 companies participating in the event.
We are now connecting our advanced technologies to automatically insert 90% of our new commercial customers into existing routes, reducing our cost to serve and improving our speed to service.
We produced exceptional EBITDA growth of almost 24% in the collection and disposal business as the economy continues to recover from the pandemic's steepest impacts in the second quarter of 2020.
Collection and disposal volume climbed 9.6% in the quarter, which exceeded our expectations.
And our focus on disciplined pricing programs produced a substantive second-quarter collection and disposal yield of 3.7%.
For the full year, we now expect organic volume in the collection and disposal business to grow 2.5% or more.
This focus is particularly evident in our residential core price of 5.4%, landfill core price of 4.7% and transfer core price of 3.4%.
Our new full-year outlook for collection and disposal yield is 3.7% or greater.
Churn was 8.8% in the quarter, and service increases outpaced service decreases by more than twofold.
Second-quarter operating expenses as a percentage of revenue improved 10 basis points to 61.1%, demonstrating that we are continuing to manage our cost as volumes recover even in the face of inflationary cost pressures.
To date, we've combined around 45% of the ADS operations into our billing and operational systems, which has allowed us to capture synergies and provide additional services to those customers.
Year to date, we have achieved more than $30 million of annual run-rate synergies, and we expect cost synergies of between $80 million and $85 million in 2021.
This will bring the annual run-rate synergies to around $100 million at the end of 2021, and we continue to forecast another $50 million to be captured in 2022 and 2023 from a combination of cost and capital savings.
Robust volume growth since last year's peak pandemic impact, dynamic pricing efforts, record recycling results, disciplined integration of the ADS business, and our continued focus on cost management combined to deliver 28% operating EBITDA growth and 50 basis points of operating EBITDA margin expansion.
Full-year revenue growth is now expected to be 15.5% to 16%, with organic growth in the collection and disposal business of 5.5% or greater.
For adjusted operating EBITDA, we expect to generate between $5 billion and $5.1 billion, an increase of $225 million at the midpoint from the original guidance we provided in February.
While the bridge from our initial guidance to the current guidance has a number of puts and takes, the most significant drivers have accelerated price and volume recoveries in the collection and disposal business of about $135 million; improved recycling profitability of another $135 million; renewable energy increases of about $55 million; and additional ADS synergies of around $25 million.
These increases are partially offset by elevated cost inflation and incentive compensation costs that we currently estimate to be about $125 million.
The increase in adjusted operating EBITDA guidance is expected to translate directly into incremental free cash flow, and we now expect that we will generate between $2.5 billion and $2.6 billion of free cash flow for the year.
SG&A was 9.6% of revenue in the second quarter, a 30-basis-point improvement over 2020.
Second-quarter net cash provided by operating activities grew more than 20%.
In the second quarter, capital spending was $396 million, bringing capital expenditures in the first half of 2021 to just over $665 million.
We continue to target full-year capital spending within our $1.78 billion to $1.88 billion guidance range.
In the first half of 2021, our business generated free cash flow of $1.5 billion, a conversion from operating EBITDA of 61%.
In the second quarter, we paid $242 million in dividends and allocated $250 million to share repurchases.
Our leverage ratio of 2.84 times has improved even more quickly than expected due to our strong operating EBITDA growth, and it's tracking well toward our target leverage of 2.75 times by the end of the year.
At the same time, our robust cash generation in the first half of the year positions us to increase our full year share repurchase expectation up to our full $1.35 billion authorization.
With this increase, we expect our weighted average share count for the full year to be approximately 422 million shares.

Summary:
Full-year revenue growth is now expected to be 15.5% to 16%, with organic growth in the collection and disposal business of 5.5% or greater.
For adjusted operating EBITDA, we expect to generate between $5 billion and $5.1 billion, an increase of $225 million at the midpoint from the original guidance we provided in February.
The increase in adjusted operating EBITDA guidance is expected to translate directly into incremental free cash flow, and we now expect that we will generate between $2.5 billion and $2.6 billion of free cash flow for the year.