Biosolids CornerSnippets by Diane D. Garvey

The WaterEnvironment Federation 2004 Annual Residuals and Biosolids SpecialtyConference and Exhibition 2004 was held at the Grand America Hotel, Salt LakeCity, Utah February 22-25, 2004. It wasan outstanding opportunity to hob-nob with fellow wizards and immerse yourselfin four days of biosolidology.

Did you ever wonder why do biosolidsstink? But were afraid to ask? A pre-conference workshop that wasespecially appropriate for Pennsylvania attendees was Managing Odors fromBiosolids- New Science and New Solutions. The Session Chair was Rich Gianni, formerly of PADEP now working forWashington DC Water and Sewer Authority (DCWASA). Many readers may also know the co-chair, John Walker, USEPA, who recentlyretired.

A paper titled Impact ofLime Dosage Rates and Lime Incorporation Levels on Biosolids Odor Productionreported on research sponsored by DC WASA and was presented by JasonNorth. The take-away messages were thatlime should be dosed at 20% or greater on a dry weight basis and thoroughblending of lime and biosolids is important to minimize odors. This dosage should be increased to 30% ifthe biosolids will be stored for more than a week before land application. A clever approach was developed to determineif lime was well mixed- take very small samples (~1 gram) of the limestabilized biosolids and analyze for Calcium concentration. Taking 8 or more samples and observing thevariation in Ca is a good indicator of the efficacy of mixing and the potentialfor pH to drop and ultimately, the potential to create odors. The study also found that limecharacteristics were very important in process optimization. Lime purity, dosage rate, and mostimportantly, particle size were found to impact biosolids stability and odorcausing potential.

Mid Atlantic Biosolids Association Research- Another paper worth the price of admission wasState of Knowledge: Odors in Anaerobically Digested Biosolids[1]. The research sought to address thequestions:

• What compounds cause odors?
• How are they produced?
• What factors affect odors?
• What can we do to reduce or control odors?

Some interesting findingsinclude:

The compounds that causeodors are primarily Methyl Mercaptan and Dimethyl Sulfide. Unfortunately, these are produced throughbiodegradation of protein.

Fortunately, Mannichpolymers used during dewatering can sequester proteins in the biosolids cake.

Fortunately, anotherbacterial strain, Methanogens, normally found in anaerobic digesters, will consumethese odor causing sulfur compounds.

Unfortunately, high sheer inhigh speed centrifuges inhibit survival of Methanogens in biosolids cake.

Unfortunately, long termstorage of cake can change the odor causing compounds to volatile aromatics suchas cresol, toluene, styrene, indole and skatole.

Fortunately, adding ferricchloride prior to dewatering could potentially reduce odors during storage. (Otherchemicals are being tested.)

Fortunately, several coalash sources were co-applied with biosolids and one in particular, Gilbertoncoal ash, reduced odors during land application by 80%.

Applying the Research-Another timely paper on odors was presented by Ralph Eschborn of Material Matters,Inc. titled Managing Wastewater Treatment Processes for Odor Characteristics. This presentation offered case studies onodor control strategies that could be readily implemented. Some key take-away points include:

Avoid septic conditionsin the WWTP and the biosolids odors will be minimized.

Go beyond compliance toensure vector attraction reduction and stabilization is achieved.

Use an EnvironmentalManagement System to address critical control points in the process.

Case studies were used toshow how understanding of the causes of odors could be used to implement a morepublicly supportable land application program.

Conclusions- That is only some of the valuable informationpresented in the first session alone! The major complaint was that there were too many good sessions going onat once. Pencil in next yearsResiduals and Biosolids Specialty Conference scheduled for April in Nashville,Tennessee. I hear they have both kinds of music there?Country ANDWestern!