A hydrolysis/thickening/filtration process for the treatment of waste activated sludge
Abstract
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. The sludge is classified as a hazardous waste because of the "mixture" and "derived-from" rules. Hence, sludge treatment and disposal are very costly. The current sludge minimization technology involves aerobic digestion and centrifugation. The solids are thickened to approximately 8.5% solids, and transported to an incinerator. The ambient temperature acid hydrolysis/thickening/filtration process begins with acidification. Reclaimed sulfuric acid is added to waste activated sludge and reacted under room temperature, well mixed conditions. 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 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 mathematical modeling indicate that the process is capable of reducing sludge cake production by as much as 92%. Preliminary research demonstrated the feasibility of using acid hydrolysis to solubilize a significant fraction of the waste activated sludge suspended solids, thereby potentially mitigating the sludge disposal problem. Subsequent studies focused on optimizing the hydrolysis operation in terms of solids reduction, environmental impact, practicality and cost. It was also of interest to investigate the impact of the new hydrolysate stream on the activated sludge system. A bioassay screen was conducted on the biotreated hydrolysate to assess the potential for toxicity. Chemical characterization studies were performed on the hydrolysate and residual solids. Filtration screening studies were also conducted, demonstrating the transformation of the unfilterable sludge into a well conditioned, readily filterable material. A mathematical model of the combined activated sludge/hydrolysis treatment system was then constructed to evaluate full scale performance possibilities.
Degree
Ph.D.
Advisors
Wukasch, Purdue University.
Subject Area
Civil engineering|Sanitation
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