Photo:, Flickr.

Certainty is nice to have, but it's hard to come by in the stock market. Still, you can always choose to focus on relatively reliable industries and companies. Smartphones, social media, and cloud computing are exciting and have great potential. But it's hard to know what those universes will look like in five or 10 years, and what the best stocks will be.

On the other hand, it's fairly certain that we will always have garbage, and that it will always need to be managed. Thus, let's look at some of the best stocks in waste management to add a little certainty to our portfolios. 

Waste Management (NYSE:WM)
Waste Management is a biggie, with a market capitalization of nearly $23 billion and a dividend yield of 3.1%. It's North America's largest waste-management company, providing collection, transfer, recycling, and resource recovery, and disposal services to residential, commercial, industrial, and municipal customers. It's not just an old-fashioned garbage collector, though -- it also owns and operates landfill gas-to-energy facilities.

It's hard for such a big company to grow briskly, but Waste Management has been working on keeping costs down, in part by converting its fleet to run on liquefied natural gas, while raising some prices. The company generates more than $1 billion in free cash flow annually, and its net margin was recently near 7%, a respectable number and greater than that of its closest competitor.

Photo: atramos, Flickr.

U.S. Ecology Inc. (NASDAQ:ECOL)
U.S. Ecology Inc serves the commercial and government worlds, treating, disposing of, and recycling hazardous, non-hazardous, and radioactive waste, among other services. It recently acquired The Environmental Quality Company, greatly expanding its capacity, but also delivering a large debt burden, which the company is working on paying down.

One intriguing catalyst for the company is Tesla Motors (NASDAQ:TSLA), which is building a "Gigafactory" to produce lithium-ion batteries in large quantities. The process will inevitably produce hazardous waste, which U.S. Ecology, via its location some 440 miles away, might be able to handle. The company's dividend recently yielded 1.6%.

Photo: Mr.TinDC, Flickr.

Clean Harbors Inc. (NYSE:CLH)
Clean Harbors Inc also serves industry and governments, offering end-to-end hazardous-waste management, emergency spill response, industrial cleaning and maintenance, and recycling services. Having acquired Safety Kleen in 2012, it's now "North America's largest re-refiner and recycler of used oil and a leading provider of parts washers and environmental services to commercial, industrial, and automotive customers."

The company's first-quarter results were disappointing, in part because falling oil prices slowed down business; but management noted: "Looking ahead, Clean Harbors is entering its seasonally strongest quarters, and the trends in our core environmental and industrial businesses are promising. We expect a number of our key vertical markets to drive large-volume project activity and additional opportunities."

Waste Connections (NYSE:WCN)
Waste Connections is another integrated waste-management company, collecting, disposing, recycling, and composting various waste from residences, businesses, and oilfields. It even offers intermodal services, moving containers of cargo and solid waste. It, too, is turning methane from landfills into electricity. Its recycling efforts are impressive; as the company notes, "[W]e recycle over 50% of our collected waste volumes on the West Coast, in some cases over 70%."

Revenue, net income, and earnings per share have all been growing by double digits, on average, over the past 10 years. Waste Connections also has some of the highest margins in the industry, with net margins expanding in recent years to approximately 11% today.

Photo: Kevin Gessner, Flickr.

Also interesting ...
You might also keep an eye on Covanta Holding Corp. (NYSE:CVA) and Republic Services (NYSE:RSG). Covanta Holding Corp. specializes in turning trash into energy at some 46 plants. Its bottom line has turned red in the past few years while revenue growth has stalled, in part because energy and metals prices have put pressure on its business. That's a temporary problem, though, and Covanta does offer patient believers a 4.7% dividend yield.

Republic Services is America's second-largest trash hauler. As Waste Management has also done, it has bought up some oilfield waste operations, which may seem inopportune at the moment, with oil prices sagging and weakening interest in drilling. However, it could pay off over the long haul. Interestingly, Bill Gates' Cascade Investments owns nearly a third of Republic Services. The company is free cash flow-positive and offers a 2.8% dividend yield.