Automated batch system gets nod for treating oily waste
Problem
A U.S. aircraft maintenance-and-service center generates a waste stream (about 15 to 20 GPD) that contains high concentrations of oil, heavy petroleum hydrocarbons, grease, heavy metals, and suspended solids. This waste stream must be segregated and treated separately from the facilities main wastewater stream.
In the past, the oily waste was hauled away as a hazardous waste (sludge). More recently, the treatment of the waste was by a GAC-based adsorption system. However, the nature of the wastewater made the system prone to fouling and in need of continuous monitoring. Further, expired GAC cartridges required vendor removal and replacement. Last, the system failed to meet requirements for the removal of heavy metals. Therefore, the system's replacement was sought.
The replacement technology would be assessed for environmental benefits, labor, and cost and its ability to interface with the various routine operations.
Replacement Technology
One of the potential replacements involved an Aquasil product. A performance study was conducted during the spring of 1999 on a sample of the oily wastewater, which resulted in Aquasil's being chosen as the most cost-effective technology. Subsequently, Aquachem signed a contract to design and install a fully automated batch treatment system.
The Aquasil system employs a proprietary advanced non-hazardous blend of natural and synthetic materials "tuned to" the chemistry of the particular waste stream. Each product is stand-alone and completely hydrophilic and has the capacity to take up various contaminants from the waste stream simultaneously.
Automated Batch System Design
The automated batch system consists of a 500-gal conical-bottom reaction tank equipped with a level control, a dry-powder feeder and an air-operated diaphragm pump, and two bag-filter assemblies—one in use and the other on standby. Also included are a 500-gal treated-water holding tank and a control panel with an audible horn and flashing red beacon alarms. The alarms signal the readiness of the system to treat, as well as bag-filter-full and cycle-complete conditions.
Wastewater collected in drums is brought to the treatment system. Most light fuel—if present in substantial amounts—is removed prior to treatment by siphoning, and the waste is pumped into the treatment tank.
The treatment cycle starts with the mixer's initiation when the water level in the treatment tank reaches a predetermined level. Then the ready-to-treat alarm energizes, the feed pump stops, and the dry-powder feeder starts dispensing a timed dose of Aquasil. The mixer continues operating for a timed period. A timed settling period starts, at the end of which an alarm starts flashing, signaling cycle-complete. The entire cycle takes about one to three hours, depending on the quality of wastewater.
The content of the treatment tank is pumped through a bag filter, which separates the floc from the clean water. The alarms on the control panel indicate when the operating filter bag is full. The operator manually switches to a standby filter bag. Clean treated effluent is collected in the clean water tank equipped with sampling and viewing ports. The effluent is released once its quality has been approved.
System Achievement
The Aquasil treatment delivered high-quality effluent with consistent performance during a period of more than eight months—achieving almost 100% removal of heavy metals and oil and grease and more than 99% of TSS. It was able to take up 140% its weight in oil and yet remain active for heavy metals and suspended solids. The system required no maintenance and only minimal operator attention.
Solids generated by the Aquasil treatment displayed none of the (flammable, corrosive, reactive, toxic) characteristics that would consign it as a hazardous waste under RCRA.
Costs to construct and install the system were about U.S.$33,000. Annual O&M costs are estimated at about $3000 based on worst-case scenarios. Processing cost, based on a 20-yr amortization, is estimated at $0.625/gal ($0.165/L)—representing savings of about 69.5% and 87% compared with GAC adsorption and haul away, respectively.
Contact: Aquachem, Inc., 5820 Canton Center Road, Unit 180, Canton, MI 48187. Tel: 877-278-2745, 734-459-0607; Fax: 734-451-5578
This case study was adapted from an excerpt of an article appearing in Environmental Protection, vol. 11, No. 9, Sept. 2000, pg. 52.