BETT Process & Pilot Plant

BETT Process & Pilot Plant

 

Introduction to the Process

Thermophilic aerobic treatment processes have undergone a fair amount of research and development in recent years for treatment of residuals (sludge) from domestic wastewater treatment plants. The process is used fairly extensively in Europe and is gaining acceptance in the United States. Thermophilic treatment processes operate at temperatures between 40°C and 60°C. Because biological oxidation of organic matter is exothermal, the process can be made to be autothermal if precautions are taken to conserve heat, and the concentration of biodegradable organic matter in the feed source is sufficiently high. The benefits of thermophilic treatment processes for treatment of sludge and high strength wastewaters are many.

The first step in biological treatment is hydrolysis of organic matter, which makes the soluble substrate available for biological oxidation. The high operating temparatures of the thermophilic process has been shown to highly accelerate the hydrolysis process, making it posssible to achieve equivalent levels of organic removal at much shorter hydraulic retention times and consequently, much smaller reactor volumes compared to conventional aerobic or anaerobic treatment systems operating in the mesophilic temperature range. Additionally, the organisms that predominate in the thermophilic systems exhibit a very low rate of new cell synthesis (biosolids production). Biosolids production in thermophilic systems is a small fraction of the quantity generated by mesophilic aerobic treatment processes. Since disposal of excess sludge is a major operating cost for any biological treatment system, this characteristic is one of the primary benefits of thermophilic treatment processes.

Description of the Pilot Plant

The BETT™ Process Pilot Scale System is a trailer-mounted unit containing a 900 gallon insulated reactor for thermophilic wastewater or sludge treatment. The oxygen for treatment is supplied by a jet aeration system using a single jet nozzle located 1.5 feet from the bottom of the reactor. The air for aeration can be provided by an aspiration line or by a blower installed on the skid. The recirculation for the aeration system is provided by recirculating the reactor contents using a recirculation/mixing pump. A rotometer on the airline facilitates the measurement of the recirculation flow rate. The airflow rate is measured by a magnetic flow meter provided on the discharge side of the recirculation pump. The liquid flow rate can be controlled using a flow control valve downstream of the flow meter.

The pilot scale unit is designed for either batch (fill and draw) mode operation or continuous flow operation. The batch mode of operations is normally utilized for sludge digestion studies, while the continuous flow mode of operations is normally used for liquid processing activated sludge studies. The fill and draw cycles when operating in batch mode are accomplished by using a diaphragm pump mounted on the trailer for this purpose. The diaphragm pump is operated by a variable speed controller. The pilot unit is also provided with a combined sludge fill tank and foam overflow tank. In the fill tank mode of operation, this tank is used for conditioning waste sludge prior to dewatering on the rotary drum thickener provided with the pilot plant. The conditioned sludge is pumped to the thickener with the sludge diaphragm pump, and the thickened sludge is then transferred by gravity to the thermophilic reactor. There is a foam overflow pipe from the reactor to the fill tank allowing this tank to also serve as a foam collection tank if excess foam is generated in the reactor. Both a foam spray system and a foam cutter are provided inside the reactor tank to dissipate the foam and keep it inside the reactor tank. The unit is provided with various outlets and valves at appropriate locations on the piping arrangement on the trailer to facilitate system operations and monitoring for process control. The reactor’s active volume can be measured on the side of the reactor via a site glass. An on-line temperature, ORP, pH, and conductivity meter is also mounted on the trailer for continuous on-line monitoring of these parameters.

A three-foot diameter clarifier (approximately 200 gallon capacity) is provided on the trailer for liquid process activated sludge studies. During this mode of operation, a continuous feed of wastewater is provided to the pilot plant. The wastewater flow is provided by a variable speed peristaltic pump. The wastewater can be pumped into the fill tank or a portable tank and then pumped into the reactor. Effluent from the reactor flows by gravity into the clarifier where sludge is settled on the bottom and supernatant flows by gravity out the top of the clarifier. The settled sludge from the bottom of the clarifier can be returned back to the thermophilic reactor as return activated sludge or wasted as waste activated sludge.

Photographs of the Pilot Plant

Following are a series of photographs displaying the BETT Process pilot plant. Images open in a new window.

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In addition the following photographs display a typical full-scale BETT Process treatment plant. Images open in a new window.

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Contact Information

The Stover Group
P.O. Box 2056
Stillwater, Oklahoma 74076

Phone: (405) 624-0018
Fax: (405) 624-0019

E-mail: [email protected]