Frankly, I havent personally come across khat abuse in SA mong patients seeking help from me, A local version is known as Bushman's Tea. . Its much better known in East Africa, But maybe that's where you are. It is also known in SA and many other places, especially on the dance club scene, in the form of a synthetic chemical version  of methcathinone, the acive ingredient in the herb. Its similar to amphetamine and to ephedrine. Street names here include Cat, Stroof, Katestroof, Jeff, Bathtub Speed, Wannabe-Speed, Kitty, Meth's Cat, Meth's Kitten or Marzipan
It is a really addictive stimulant, and is not good for one, physically or mentally.
The fact that your husband hides it from you and denies it, suggests he considers it a wrong thing to do. He can hardly persist in denying or explaining why there's such a lare amount of it and related paraphenalia in his home.  Talk calmly to him, directly, and via friends and his family, mking it clear this is damaging to him and hence a risk to the family, and that he needs to accept that he needs help with this from a psychiatrist experienced at dealing with such drug addiction.