A composition and method particularly designed to treat blackwater deposit. In at least one example, a composition for use in removing and preventing buildup of blackwater deposits in blackwater collection/treatment systems. The composition includes in the range of about 2 to about 15 wt. % of acidic solubilizing agent; in the range of about 0.2 to about 8 wt. % of wetting agent; in the range of about 0 to about 1 wt. % corrosion inhibitor; and a solvent/carrier medium. Another aspect is a concentrated composition to be diluted before or during use, the concentrated composition comprising in the range of about 10 to about 70 wt. % of acidic solubilizing agent; in the range of about 1 to about 40 wt. % of wetting agent; in the range of about 0 to about 5 wt. % corrosion inhibitor; and a solvent. In another example, a method for removing and preventing buildup of blackwater deposit in a blackwater collection system. In at least one example, the method includes: contacting at least a portion of the blackwater collection system with the blackwater deposit treatment composition above; and removing at least a portion of the treatment composition from the portion of the blackwater collection system.