There has been a few privately funded efforts to find a way of gasifying land fill waste, this involves feeding the waste into an oxygen free chamber which is heated, the waste is converted to gas and inert ash, the gas is run through an engine turbine to produce electricity, the heat from the engine is re-directed to the initial process. Sounds great but needs a lot more development with the clean up of the gas.
Gas cleanup isnt the problem, the Air Products plant on teesside has all sorts of fancy kit to scrub the gas before it goes into the GT’s. The problem is the gassification. To ensure that anything really toxic is broken down you have to go really REALLY hot (they inject oxygen plasma). And unfortunately the refractory lining just isn’t upto it, which is why it’s not currently working.
The older generation used fluidised beds of rubbish and cleaned up the exhaust gas. It’s much less efficient but it does work.