A Class-A Solution

Feb. 27, 2020
Edmonds, Wash., facility installs dryer to produce Class-A biosolid

The 4-mgd Picnic Point Wastewater Treatment Facility (WWTF)—located in Edmonds, Wash., and operated by the Alderwood Water and Wastewater District out of Lynnwood, Wash.—was faced with reaching its plant processing capacity. The plant was sending its biosolids to be incinerated, and part of its challenge was to find a way to manage its biosolids. Hauling and disposing of this sludge was difficult and becoming expensive. It was desirable to produce a Class-A biosolid to alleviate this concern and be more environmentally conscious.


Upgrading the facility with Veolia’s BioCon biosolids dryer has reduced the amount of biosolids to be disposed of, as well as producing a Class-A biosolid. Having Class-A biosolid allows the Alderwood Water and Wastewater District to explore other sludge disposal options. In this case, a third party uses dried biosolids from the BioCon to fertilize nearby agriculture. With the help of the dryer, the plant doubled its sewage treatment capacity, ensuring the site will be able to handle increased biosolids loads for the foreseeable future

BioCon operation is safe, simple and efficient. Dewatered sludge cake is pumped into the drying system through oscillating sludge depositors on top of the dryer cabinet. These depositors are used to distribute the biosolids onto a slow-moving belt for drying. BioCon is a dual-belt dryer; biosolids are deposited onto the first dryer belt and fall to a second belt where the desired dryness is reached before being removed from the dryer by a screw conveyor. BioCon uses hot-air circulation to evaporate water from biosolids, in much the same way a convection oven speeds up the baking process in the kitchen. The air-drying temperatures in the dryer range from 350°F to 175°F as the drying process is completed. BioCon indirectly heats the biosolids with drying air that is recycled in a closed circuit, and the entire dryer is operated under negative pressure to prevent any odor from escaping the dryer.


The effectiveness of Veolia’s BioCon dryer allows the Alderwood Water and Wastewater District to reduce the amount of biosolids that are safely and easily disposed. This solution was executed in a small footprint and allows the municipality to produce a valuable end product, meeting Class-A requirements. The newly constructed BioCon building includes an odor control system, which has earned the plant the support of the surrounding community.