Research is being conducted to determine to what extent herbicides break down in composted yard and garden wastes. If you are concerned with this issue you may wish to completely avoid herbicide-treated sources. Most kitchen scraps are valuable to composting because of the variety of nutrients they contribute. Coffee grounds contain nitrogen, phosphorus, potassium and trace elements. Tea leaves contribute similarly, and can be easily disposed of by composting the filter bag at the same time.
Crushed eggshells are mostly calcium.
Banana and citrus peels are a source of nitrogen, phosphorus and potassium. Do not use grease, as it will delay degradation of other materials by its coating action. Bones and meat scraps should be avoided because of their slow decomposition and risk of luring animals. Manure can contribute a variety of nutrients and bacteria. If straw or sawdust is used as animal bedding, nearly all of the nutrients are preserved that were not used by the animal.