Chitosan-containing blends and methods of dissolving and using chitosan are disclosed. A blend includes a solid acid or a solid agent that generates a proton in situ in the presence of water mixed together with a dry solid chitosan, and may optionally contain other components. The blends are in a dry, free-flowing, particulate form. Methods of dissolving a blend typically comprise adding a quantity of the blend to a low volume of water and mixing until the chitosan and solid acid or solid agent are dissolved and then further diluting this mixture by the addition of water, or used as-is. Devices containing the blends are also described along with methods of using the devices, such as for controlled release of solubilized chitosan in a body of water, such as a stream, containing impurities (e.g., particles, sediment, or suspended matter or dissolved substances) to cause flocculation or precipitation of such impurities.