Minimization of the concentration and mobility of trace metals is a primary concern when considering the land application of wastewater sludges. The effects of pelletization/drying, composting, incineration, and N-Viro chemical stabilization on composition and mobility of trace metals and P were compared. One day's production of dewatered digested sludge (Syracuse, NY) was used as the sole feedstock so that observed differences would solely be a result of the process used. Mobility was determined using the toxic characteristic leaching procedure (TCLP). Analyte concentrations were essentially constant during dewatered sludge production with mean values (mg kg TS) of 5.6 Cd, 10.7 Co, 130 Cr, 587 Cu, 49.7 Mo, 35.8 Ni, 26 880 P, 132 Pb, and 545 Zn. Concentrations in pellets were similar to dewatered sludge, but were reduced in composted sludge and N-Viro product by the addition of amendments. Incineration concentrated all analytes except Cd and Pb, which experienced volatilization losses. The mode of processing had widely ranging effects on mobilities. The TCLP-mobile fraction (percent of total) of analytes in dewatered sludge was <3% except Ni (7.1%), P (6.0%), and Zn (11.2%). Composting slightly increased Cd mobility, but reduced that of Ni and P. Pelletization increased the mobility of Cd (7.9%), Cu (3.8%), Ni (15.4%), and Zn (15%). The N-Viro process substantially increased mobilities of Cu (43%), Mo (50%), and Ni (24%) at elevated pH. Incineration increased mobilities of Cd and Mo, but reduced Ni, P, and Zn mobility. These results, with those of longer term in situ studies, can be used to guide the selection of sludge processes that minimize potential metal and P mobility.

http://soilandwater.bee.cornell.edu/publications/RichardsJEQ97.pdf

Effect of Processing Mode on Trace Elements in Dewatered Sludge Products

.......................................................................................................................................... ii Acknowledgements .........................................................................................................................ix List of Tables ............................................................................................................................... xiii List of Figures .................................................................................................................................ix Chapter 1. General Introduction.......................................................................................................1 1.1 Arsenic source.....................................................................................................................1 1.2 Arsenic chemistry ...............................................................................................................2 1.3 Arsenic treatment technologies ...........................................................................................6 1.4 Objectives............................................................................................................................8 CHAPTER 2. Synthesis and Characterization of a New Class of Polymeric Ligand Exchangers for Selective Removal of Arsenate from Drinking Water ......................................................10 2.

Removal and Immobilization of Arsenic in Water, Ion Exchange Brine, and Soil Using a New Class of Ion Exchangers and Nanoparticles

Los Angeles processes sewage sludge by dehydration and combustion at its Hyperion Treatment Plant. The ash product is usually classified as hazardous because of its heavy metal content, and four readily‐available fixing agents have been evaluated for possible use as stabilizers. The ash leachability was assessed before and after fixation using the California Waste Extraction Test. The leaching characteristics of dewatered wet‐cake sludge were also measured. While the fixing agents were found to decrease the leachability of ash considerably, ash and dewatered wet‐cake mixtures also immobilize metals to some extent. Chemical binding with fixing agents (i.e., wet‐cake, Portland cement alone, cement/silicate and cement/citrate mixtures) stabilizes the ash.

Ruey S. Huang

Papers

Chemical fixation of sewage sludge derived ash