A highly sensitive colorimetric sensing platform for the selective trace analysis for Co(2+) ions is reported, based on glutathione (GSH)-modified silver nanoparticles (AgNP). The shape of metallic nanoparticles used in colorimetric detection, using the unique optical properties of plasmonic nanoparticles, is almost spherical. Therefore, in this work we attempted to investigate the selective detection of heavy metal ion (Co(2+)), with the shape of AgNPs (nanosphere, nanoplate, and nanorod). GSH-AgNP with spherical shape shows a high sensitivity for all of the metal ions (Ni(2+), Co(2+), Cd(2+), Pb(2+), and As(3+)) but poor selective recognition for target metal ions. Whereas, AgNPs solution containing rod-type GSH-AgNP has a special response to Co(2+), and its selective detection might be based on the cooperative effect of CTAB and GSH. Therefore, Co(2+) ion could be selectively recognized using rod-type GSH-AgNPs.

The highest quality of biosolids is called exceptional quality. To qualify for this classification, biosolids must comply with three criteria: (1) metal concentrations, (2) vector‐attraction reduction, and (3) the Class A pathogen‐density requirements. The City of Los Angeles Bureau of Sanitation Hyperion Treatment Plant (HTP) (Playa del Rey, California) meets the first two requirements. Thus, the objective of this study was to ensure that HTP's biosolids production would meet the Class A pathogen‐reduction requirements following the time–temperature regimen for batch processing (U.S. EPA, 1993; Subsection 32, Alternative 1). Because regulations require the pathogen limits to be met at the last point of plant control, biosolids sampling was not limited to immediately after the digesters, i.e., the digester outflows. The sampling extended to several locations in HTP's postdigestion train, in particular, the last points of plant control, i.e., the truck loading facility and the farm for land application. 
 
 A two‐stage, thermophilic‐continuous‐batch process, consisting of a battery of six egg‐shaped digesters, was established in late 2001 for phase I of this study and modified in early 2002 for phase II. As the biosolids were discharged from the second‐stage digesters, the Salmonella sp. (pathogen) and fecal‐coliform (indicator) densities were well below the limits for Class A biosolids, even though the second‐stage‐digester temperatures were a few degrees below the temperature required by Alternative 1. Salmonella sp. densities remained below the Class A limit at all postdigestion sampling locations. Fecal‐coliform densities were also below the Class A limit at postdigestion‐sampling locations, except the truck‐loading facility (phases I and II) and the farm for final use of the biosolids (phase II). Although federal regulations require one of the limits for either fecal coliforms or Salmonella sp. to be met, local regulations in Kern County, California, where the biosolids are land‐applied, require compliance with both bacterial limits. Additional work identified dewatering, cooling of biosolids after the dewatering centrifuges, and contamination as possible factors in the rise in density of fecal coliforms. These results provided the basis for the full conversion of HTP to the Los Angeles continuous‐batch, thermophilic‐anaerobic‐digestion process. During later phases of testing, this process was demonstrated to produce fully disinfected biosolids at the farm for land application.

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The City of Los Angeles Hyperion Treatment Plant (HTP) has conducted a multiphase study of thermophilic digestion to meet a newly stringent pathogen standard in the counties where it sends its biosolids for land application. The original plan was that Phase III of the studies would be a test of a batch process that was guaranteed to meet the time/temperature requirement of Alternative 1 of 40 CFR 503, the Federal sludge regulation. However, operational problems delayed the startup of this process. Consequently, Phase III became a full-scale test of a continuous two-stage thermophilic anaerobic digestion process. These tests were conducted in August and September, 2002. Thermophilic digestion was at average digester temperatures in the first and second stage of 128.1 -131.7 0 F (53.4 -55.4 0 C) and 122.0 -127.8 0 F (50 -53.2 0 C), respectively, and at an overall mean HRT of about 12 days. Almost full compliance with the Class A pathogen requirements was demonstrated in biosolids at the Truck Loading Facility and the farm for biosolids land application. Salmonella sp. in raw sludge were completely removed and these pathogens were non-detect in all samples taken at the farm. Kern County requires testing for both Salmonella sp. and fecal coliforms. Reactivation and/or growth of fecal coliforms in biosolids after the digesters, as was previously observed during Phase I (late 2001) and Phase II (early 2002) tests, did not occur during Phase III. This can possibly be attributed to two modifications implemented in the Phase III process. First, insulation of the post-digestion train prevented cooling of biosolids during post-digestion processing, i.e., biosolids temperatures from the digester outflow to the Truck Loading Facility decreased only by approximately 1 0 F. Second, the full conversion of HTP to thermophilic treatment prevented the risk of contamination by mesophilic plant operations. Further studies in the laboratory with biosolids from the Truck Loading Facility and the farm demonstrated that no reactivation and/or growth of fecal coliform occurred when the biosolids were stored for up to six days at 75 0 F. The Phase IV Class A Biosolids program at HTP (October 2002) will test the timetemperature relationship for batch treatment (Alternative 1 of 40 CFR 503). Experiments were conducted during this write-up and the results will also be presented at the conference.