A method for removing contaminants from a liquid includes filtering objects of a relatively large dimension. The liquid is then mixed with additives to adjust the chemistry of the liquid. The liquid is pressurized and directed through a gasification device to dissolve gas into the liquid. This is accomplished by directing the liquid into an inlet of a hydrocyclone of the gasification device, directing the liquid exiting the hydrocyclone upwards to remove large bubbles, and removing liquid containing dissolved gas from a bottom portion of a vessel of the gasification device. The pressure of the liquid is then reduced and the liquid is introduced into a separation tank, and the contaminants are removed from the liquid by stratification. The treated water is removed from the separation tank, and sludge formed by skimming flocs from a liquid surface of the tank is subjected to a dewatering process.