This thesis served to study the influence of the return flow of sludge and the dosage of calcium hydroxide in the neutralization of acidic waters, being the studied levels of (0.5; 1.0; 1.5; 2.0) l / s and (0.4, 0.5, 0.6, 0.7) l / s respectively; At the same time, the economic comparison that is generated between the use of the sludge return process and the conventional process was made, that is, adding only calcium hydroxide as an alkaline agent also at a dosage of (0.4; 0, 5; 0.6; 0.7) l / s, both tests were carried out under the same conditions, that is, at a calcium hydroxide concentration of 0.1428 t / m3 and at the same inlet flow of acidic water ( 20 l / s). After performing the tests, it was found that, using sludge return, the consumption of calcium oxide is reduced from (7.4 to 6.17) t / day, in addition, the percentage of solids is increased from (1.0 - 2.0) to (3.0 - 4.0) and...