In a recent blog, I told you about a trip to Walmart and how they have slashed waste in all of their stores, saving money and the environment at the same time. The more I talk about this, the more I realize how many companies are starting to look for “gold” and “green” in the dumpster.

Back in the 1990s, California passed a law to divert half its waste from landfills by 2005. As Secretary of the California EPA when the mandate came due, I was pleased to report that we had met the target right on schedule. Now California dares to talk about “zero waste” in the near future and cities like San Francisco have set their own target of being “landfill-free” by 2020. I was in New Zealand recently and heard that their biggest cities are doing the same thing.

Now GM is getting on the bandwagon. It recently announced that by 2010, at least half of its 181 facilities world-wide will be waste free, meaning not a single thing will leave those sites as waste.

So how is it happening and what could this mean for companies? One example is electronic waste and another is cooking oil. Old computers, TVs and adding machines have one thing in common with the used grease from fast food restaurants — until a few years ago, it cost businesses money to have this stuff hauled away. Now companies are paying to get their hands on it and convert it to useful products. I recently toured a company in California, called ECS, that strips down “e-waste” to components and commodities, including precious metals and recyclable plastics. All of that gets put back into the making of new electronics and, the process, reduces waste going to landfills.

The grease is being refined into vehicle fuel and, with oil over $100 per barrel, gets more valuable every day. E-waste and old cooking oil are just two examples of businesses looking at their waste stream and converting liabilities to profits.

So what’s in your dumpster?