Degassing drinking water to remove THMs and Radon gas
Dryden Aqua Air diffusers
Air diffusers for the aeration and degassing of drinking water to gas strip VOC’s such as THMs from water supplies. The diffusers may also be used for gas stripping radioactive gas from drinking water.
For gas stripping chlorine disinfection by-products such as THM’s the diffusers are located in the buffer tanks after the addition of chlorine. For stripping out radio active gas they may be located in the same position, however in Norway the preferred location is usually prior to the sand filters
Diffusers details and installation
Dryden Aqua manufactures a fine bubble air diffuser manufactured from plastic and stainless steel. Our diffusers are a semi flexible tubular construction, 32mm in diameter and typically 3000mm long. A ½” hose tale is screwed onto a ½” male BSP threaded fitting at one end for the air supply. The diffusers have their own internal ballast so they do not need to be anchored down to the base of the tank. Installation can be very simple, ½” flexible hose connected to a diffusers and dropped into the tank. If more than one diffuser is required, a manifold may be assembled to sit on the base of the tank or above water levels. To recover the diffuser, simply pull on the ½” hose.
Sizing a system
The systems are sized on the basis of the water flow rate as a starting point. If the maximum water flow through the treatment works is 100m3/hr, the airflow through the diffusers should be the same. You cannot over aerate so if the collection tank is very large, or if less than 2m deep, additional aeration may be required.
Typically we can achieve a 50% to 90% reduction in THM concentrations and radioactive gas.
Maintenance and cleaning
Dryden Aqua air diffusers are among the most efficient and robust air diffusers available, typically they will last for more than 10 years in clean water applications. All diffusers in contact with water require some attention. Dryden Aqua air diffusers should be cleaned every 6 to 12 months. Cleaning is very simple, just pull them out of the tank using the ½” hose, given them a shake and a brush, rinse with clean water and put back in place. If alkalinity is very high, they may need an acid soak in 5% phosphoric acid for 10 minutes once a year to dissolve out carbonate scale.
Materials of construction
The male threaded fittings in the diffusers are manufactured from 316 stainless steel. The end cap and the female ring and tail ½” hose fittings are manufactured from POM plastic and are supplied with the diffusers as standard. The diffusers can also be supplied with hose fittings in brass, or 316 stainless steel as an optional extra.
The diffusers are manufactured from a very heavy-duty polyester fabric tube; a nylon distributor hose runs down the centre of the tube. Between the nylon hose and polyester tube there is a ballast comprising of spherical glass beads.
The diffuser is banded using 316 stainless steel compressed on to the nylon inner tube with a nitride rubber bush and covered in blue compression plastic.
The diffuser is semi flexible, 32mm in diameter, 3000mm long and negatively buoyant.
|Air flow per diffusers||10 m3/hr|
|Typical bubble size||0.5 to 2mm|
|Length of diffuser||3000mm (different lengths and flow rates available)|
Dryden Aqua diffusers are also used for the thermal and chemical destratification of reservoirs as well the treatment of wastewater by aeration of activated sludge. Energy demand is approx. 25% lower than other diffusers and 50% lower than surface aerators.
The diffusers may also be used to aerate the collected sludge on treatment plants and can metabolise up to 80% of the waste in 24 hours. In some cases this is a better option than a tanker