As an adoptive parent, I'd suggest one of your top priorities would be to make a concerted effort to alter your language here. "Real" is not helpful; it's got judgment loaded in it, since if you're not real you must be fake. And as a commenter on the question points out, by most standards of good parenting the real father is the one who is there for the child. In the adoption community we refer to birth parents. While sperm donor is certainly descriptive, it may not be an image your tween daughter will welcome :)
Similarly, "evil" isn't going to help things any. Your daughter is going to have complicated feelings about this, possibly forever. They won't necessarily be bad feelings, but she has a genetic heritage she can't ever really connect with. This can be tough for adopted kids, just as it would be tough if she had an absent father who didn't want contact. Using a word like evil will just make it harder. She's going to draw her own conclusions about his character based on him taking a powder when she was still in diapers. Any further editorializing might be a basis for her to question her own character.
In your shoes, I'd simply say he was troubled and had a problem with drugs and alcohol. He chose to leave when she was an infant and never showed an interest in being a parent. Presumably he either agreed to the adoption or no-showed and had his parental rights terminated, clearing your husband to adopt.
I think, depending on the kind of relationship you all have, the best thing would be to have a sit-down and say you wanted to let her know something about her past. I'd refer to your husband as "your father" just to be clear that that is who he is, genetics be damned. You might just present this as something she should know about her heritage for the sake of her health; people with parents who have addiction problems are more likely to have those problems themselves, and there might be other issues in his medical history worth knowing. If you describe it as something that now you are old enough to understand the genetics of things, then she may be more likely to see it as about bodies rather than families.
For our part we are simply always open with our child about his adopted status, though we didn't have the complicating factors you did. He's not yet as old as your daughter but we think being matter-of-fact about it is the simplest thing. You don't need to keep the way he treated you from her forever, though I think letting them come out over time will make it a less overwhelming thing for her to come to terms with. But you know her and we don't - perhaps she'll do better knowing it all up-front. But I think the more dispassionate you can manage to be the better; his actions speak for themselves.
