The Problem
A hazardous waste landfill in Belleville, MI, owned by the Environmental Quality Company had a problem. They needed to develop a treatment process to remove COD, high TDS, heavy metals, phenol, PCB’s, Ammonia, and Molybdenum from the landfill leachate. Current treatment comprised of chlorination and activated carbon treatment was very costly.
Evaluation
The treatment process was challenging. The chemical treatment supplied was based upon the experience batch treating the wastewater and numerous bench scale treatability studies. An MBR process was selected for piloting because it was the best option to nitrify, reduce the high COD and phenol and overcome the potentially toxic conditions. Dynatec was engaged to supply a pilot treatment plant to be used as an investigative tool for the design of the full scale treatment process. The pilot operation phase of the project lasted almost 3 years, where problems were identified and solutions found.
Some unique challenges offered by this application were:
Foaming - Toxicity from the metals, phenol , and other unidentified substances
Mixed Liquor conditioning
Biological temperature sensitivity
Sensitive nitrification process
Difficult chemical precipitation of metals
Small footprint required
Dynatec was engaged to supply and install the full scale system because of Dynatec’s experience with the treatment technologies employed, their familiarity with the project, and the requirement for a high rate MBR process operating at high MLSS.
The Solution
Dynatec provided and installed a system that included a stainless steel insulated covered bioreactor with both heating and cooling capabilities to control temperature within a range suitable for achieving the treatment goals. To solve the foaming problem, a combination of jet aeration, defoamer, DO control, and concentrate return splash plates were employed along with an emergency potable water spray to prevent foam-over.
The membrane filtration equipment was designed to make efficient use of a small existing building that houses the membranes, controls, dewatering and other equipment.
The process includes chemical / physical treatment of the leachate both before and after the MBR. The post MBR chemical precipitation is for Molybdenum. The MBR removes compounds that were found to interfere with the precipitation process. The treated water is discharged to sanitary sewer.
A sludge tank receives the solids from both clarifiers of the pre and post chemical treatment systems as well as the WAS. Additional iron and lime is added and mixed in the sludge tank prior to feed to the filter press for dewatering. The solids are discharged within the landfill.
The Process
The process design consists of the following:
The hazardous wastewater is pretreated for removal of CN, Cr, Cu, Pb, Ni and Zn.The hazardous wastewater is mixed with non hazardous wastewater in a 500,000 gallon EQ tank to help make nitrification work. Approximately 65% of the wastewater discharged to the EQ tank is hazardous WW and 35% is non haz.The WW in the EQ tank is sent to the MBR for treatment for reduction in phenol ammonia nitrogen and COD.The MBR permeate is post treated for removal of molybdenum. The moly is apparently organically bound and does not precipitate adequately in the pretreatment.Sludge from the metals precipitation is mixed with WAS and dewatered in a filter press.Operation
The system started up in March of 2010. As expected, the activated sludge took less than two months of conditioning before effective treatment was achieved due to the information and knowledge that was gained during piloting. A special bacterial culture was added to promote nitrification, which improved performance.
The COD of the hazardous wastewater varies significantly, typical values observed have been between 5,000 mg/L and 12,000 mg/L. After blending with non hazardous leachate the COD is typically in the range between 3,000 mg/l and 6,000 mg/l.
The system operator is able to adjust conditions as needed. The system is currently operating at high mixed liquor concentration, an average of 24,000 mg/l. The jet aeration system makes operation at this level possible. Temperature ranges from a low of 25’C in the winter to 36’C in the summer. A natural gas fired heater heats the leachate in the winter in the recirculating loop between the bioreactor and the UF. The heater runs very little as the tank is covered and insulated. The system also has the ability to cool the mixed liquor as the temperature approaches 38’C to prevent thermophilic conditions from developing.
The continuous addition of defoamer is necessary. The concentrate return hits splash plates in the reactor to create a spray of sorts to help depress foam. There is also a fresh water spray available for use that rings the top inside of the reactor.
After startup, the system is operating as designed. The operators have used the emergency potable water spray to prevent foam-over of the bioreactor a couple times, with no other major issues. The system is exceeding expectations. Phenol in the effluent is typically below 0. 1 mg/L and metals removal is consistently below discharge requirements and below toxicity levels required to protect the biological process.
Conclusion
This is a very tough job. The complete and comprehensive system that Dynatec provided made this a success, and many lessons were learned for future projects. Dynatec was the right choice for this difficult MBR application. The many years of experience Dynatec has applying membranes to wastewater has enabled it to design and provide systems that perform in even the most difficult applications.
The system payback is expected to be very short. The system is meeting all its treatment objectives.
