Compositions containing kiln dust and/or biowaste ash and methods of use

A method comprising:

• identifying a first yield point of a first fluid in a wellbore;
• providing a spacer fluid comprising biowaste ash and water;
• adjusting a yield point of the spacer fluid to be greater than the first yield point, wherein adjusting comprises adjusting an amount of kiln dust, biowaste ash, or both included in the spacer fluid;
• wherein the biowaste ash comprises plant- or animal-derived waste products, wherein the plant-derived waste products are selected from the group consisting of sugar cane ash, wood ash, tree leave ash, corn cob ash, rice hull ash, grain ash, grain husk ash, grain hull ash, orchard ash, vine trimming ash, grass ash, straw ash, ground nut shell ash, legume ash, and combinations thereof and wherein the biowaste ash is present in an amount of about 20% to about 65% by weight of the spacer fluid;
• introducing the spacer fluid into a well bore to displace at least a portion of the first fluid from the well bore;
• wherein the spacer fluid has a transition time to progress from a static gel strength of about 100 lbf/10 ft2 to about 500 lbf/100 ft2 at well bore conditions of about 45 minutes or less;
• and
• introducing a cement composition into the well bore, wherein the spacer fluid separates the cement composition and the first fluid.