Patented Process Reduces Drying Time, Facility Footprint

Biosolids, also known as sewage sludge, are the residual solids left over after the treatment of municipal wastewater. These include organic matter and inorganic compounds from the sewage itself, as well as those produced in the treatment process. Biosolids can be in either liquid or solid form, depending on the treatment process, and they contain valuable organic matter, plant nutrients and biological activity.

In raw form, biosolids have been used to supplement commercial fertilizers by the farming industry for decades. Today, we treat biosolids further to remove harmful pathogens. By safely returning the nutrients that were taken up by plants to the land, biosolids complete the organic recycling circle. Agriculture benefits from the return of these valuable nutrients and organics to the soil.

N-Viro International of Toledo, Ohio, has developed and patented a processing tool designed to decrease the time needed to dry the product as well as decreasing the footprint of the drying facility.

BioDry accomplishes both of these goals by reducing drying time to 30 minutes and eliminating the need for windows. The footprint of a facility can be cut by more than 50 percent in some cases by installing a BioDry rotary drum dryer. The biosolids are mixed with the alkaline admixtures (AA) and then fed directly into the dryer. Varying amounts of product can be handled by different size dryers based on feed speed and percent solids coming out of the mixer.

The technology can be implemented by a variety of different makes and models. Through controlled particle drying, indigenous microflora are maintained in the N-Viro Soil™ providing additional long term stability. Once out of the dryer the product is stored in the heat pulse bunker for 12 hours and then put directly into storage piles. The dryer also is effective in controlling volatized ammonia while drying the product through its own odor control system.

A recent application of this process was at a municipal biosolids management facility in Sarnia, Ontario, that treats 120 wet tons per day.

In March of 2001, the town of Sarnia began operation of the latest N-Viro Soil processing facility that incorporates the patented BioDry™ biosolids treatment process. Webster Environmental designed the processing facility to use a Duske rotary drum dryer, similar to one used by Leamington, Ontario. This equipment is part of the N-Viro process used to dry alkaline treated biosolids for disinfection and stabilization.

By installing the N-Viro BioDry system, the city was able to eliminate the the use of their digesters thus foregoing the extensive maintenance and updating required of their anaerobic digesters as well as deal with new restrictive air emissions. The former digesters are now used for liquid storage which feeds the new Andritz centrifuges before going through N-Viro processing.

Formerly, treatment at the facility consisted of settled solids in conventional anaerobic digesters. The sludge was then discharged to a remote location and stored in lagoons, which were periodically excavated with the solids going to a landfill.

The 4500 ft2 N-Viro processing facility is located right at the city’s Wastewater Treatment Plant (WWTP). It also includes a 9000-ft2 product curing and storage area. The CemenTech CSP-15 mixer and proportioning unit, the Duske CSD 6000 dryer and the emissions control equipment are located in the N-Viro processing building. The centrifuge discharges an average 28 percent cake into the CSP-15 where it is blended thoroughly with lime kiln dust after which the mixed product is conveyed to the CSD single pass, rotary-drum, low temperature dryer. The rotating and tumbling action of the dryer breaks up the large clumps into progressively smaller particles that can be moved through by the air current; all particles pass through the dryer, completing the process, in an average of 15 minutes. A Venturi scrubber, packed bed acid scrubber and a biofilter provides fine particle and odor control.

The mixed and dried material is then dropped into the “heat pulse” cell where it will reach final desired temperature and pH levels. The product storage building is covered and enclosed on three sides. It provides four to five months of storage, which is ample capacity to cover those times of the year when product cannot be applied to agricultural land.

The town of Sarnia has signed into an agreement with Lakeshore Soils to purchase all the N-Viro Soil™ made at the Sarnia facility for $7.50 CDN ($5 USD) per ton FOB the processing plant. Lakeshore Soils has acknowledged the value of the N-Viro Soil to the farmers near Sarnia. One benefit is that NVS has been proven to reduce the populations of the parasitic soybean cyst nematode (SCN), increasing its value to the end user.

Lakeshore Soils is pleased with the uniformity and consistency of the product and its ability to blend easily with other agricultural products. Area farmers are reportedly excited about the start-up of this facility. Demand for the product has already exceeded the projected production from this facility. Sarnia produces 14,500 tons of N-Viro Soil per year.