Municipal solid waste incineration fly ash can be harmful, but using it in cement kilns is a good way to get rid of it. A study looked at how this process affects the environment. They found that how you handle the by-products during the pretreatment process can change the results. Using water-washing to treat the fly ash can have an impact, especially from making electricity. When looking at the final cement product, the way you allocate the by-products can change the results for acidification potential.