Water Treatment for Lasting Relief Continued...

Sewer plants are expensive. But plastic pipes are now used in water treatment plants to make them not only reliable but also economical

Plastic pipe aerators are increasingly used to upgrade water treatment plants. A recent retrofit project in Tauranga, New Zealand, relies on these systems to achieve significant improvements in quality processing and quantity processed.

Overloaded

Population growth can exert critical demands on municipal services. Like many cities, Tauranga had become a victim of its own success. At its Te Maunga wastewater treatment plant, demand inevitably exceeded supply… and vice versa! 

The situation dictated a twofold increase in plant capacity from 8,000 m3/d to 16,000 m3/d. Furthermore, effluent quality requirements were not being met and the need for a sound economical basis for the complete plant was evident. Given its size, only a few cost options were left open to local engineers. 

No downtime

One option that certainly fitted both the bill and the plant equipment was an upgrade scheme that incorporated plastic pipe aerators. These polypropylene pipes are sheathed by a finely perforated silicon membrane that delivers the right quantity of air. 

Replacement of old aerators is usually a simple enough operation. But in this case, the plant had to run continuously without any downtime. A 20 ton crane was therefore used to remove existing diffusers after which divers were employed to mount brackets for the lightweight aerators. 

More for less

After a very short installation time, the new equipment was capable of processing twice the plant's original capacity. Even the quality of effluent was enhanced with full nitrification and ammonia below benchmark levels. 

The pipe aerators together with an improvement in the dissolved oxygen control system led to a significant reduction in airflow and use of blowers. Site power savings are 20 percent and this works out to at least 30 percent given the increase in the aeration system. Capital cost savings were also considerable especially when compared to the price tag for building a second facility from scratch.

Aggressive

Alexander Bassewitz, member of the TEPPFA Civils application group emphasizes the enormous advantages of these plastic pipe systems for water treatment facilities. "These aerators have all the inherent benefits and properties that we expect from plastics in the sewer sector." 

"Heavy metal is no longer what it used to be. Aggressive environments call out for resistance. These aerators are wastewater resistant, they have high impact strength and they can deal with tough temperatures. There will be no hardening or shrinking and their elasticity is most definitely long term. Furthermore, their design ensures low buoyancy and constant mechanical properties. They will therefore perform for a very long time."