Stronghold Digital Mining (SDIG), a crypto mining company in Pennsylvania, is turning waste from old power plants into energy to power hundreds of Bitcoin mining rigs.

The company collects coal refuse, a leftover waste material from the process of coal mining, and burns it in what it says is an emissions-controlled environment at its energy generation facilities.

Coal refuse can cause a raft of environmental problems, such as water and air pollution, and acid mine drainage, the acidic water which comes from coal mining operations. Collecting this waste and safely disposing of it while generating power for crypto mining is a productive way of tackling the problem.

The state of Pennsylvania is the third-largest producer of coal in the United States, estimates put the amount of coal wastage at 881 pounds per 2,200 pounds mined, or 400 kilograms per ton. Stronghold estimates that Pennsylvania alone has over 220 million tons of harmful wastage.

Bitcoin and other proof-of-work cryptocurrencies have caught the attention of regulators recently due to their reliance on energy-intensive processes in order to mine and provide validation for the network.

Earlier this month, a New York state proposal to suspend proof-of-work mining that uses fossil fuels was introduced, citing the negative environmental impact of the process, that proposal today was advanced by the New York State Assembly. If passed, it could see proof-of-work mining suspended for up to 3 years in New York.

Related: Bitcoin mining could be good for US energy independence: Research

Other schemes have seen ways to make Bitcoin mining environmentally friendly. Earlier this month, oil drilling company ConocoPhillips started a program in North Dakota where it would sell the