A process has been developed for reducing both the mass and volume of waste activated sludge generated by the biological treatment of a pharmaceutical wastewater. As a result of the mixture rule, the sludge is classified as a hazardous waste. Thus, treatment and disposal have traditionally been very costly. This study focused on optimizing an engineered hydrolysis operation in terms of solids reduction, environmental impact, practicality and cost. Dewaterability screening studies were also conducted in an attempt to transform the residual solids into a readily filterable material.
The resultant hydrolysis/thickening/filtration process begins with room temperature sludge acidification using sulfuric acid. This results in 50 to 60 percent solubilization of suspended solids, thus sharply reducing the mass of solids to be handled. Also, carbon dioxide is liberated during the reaction phase, enabling solids separation and thickening to occur via flotation. Subnatant hydrolysate can then be recycled to enhance solids solubilization. Once properly conditioned with acid and cationic polymer, the residual solids are readily pressure filtered to cake dryness in excess of 50% solids. Results of laboratory studies indicate that the overall process is capable of substantially reducing sludge cake production.
