EFFECTS OF DEWATERING ON BACTERIA INACTIVATION: Centrifuge Simulation And Field Tests at The Hyperion Treatment Plant

Self Cite

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.

Section: Temperature Profilescontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Occurrence of Fecal Coliform and Salmonella Sp. Following Thermophilic Digestion and Post-Digestion Processing at the Hyperion Treatment Plant

Iranpour¹,

Cox²,

Oh³

et al. 2003

Self Cite

“…Experimental details of these tests have been described by Iranpour et al (2002). In summary, samples were collected from several locations in the post-digestion train and incubated in closed bottles at various temperatures.…”

Section: Laboratory Regrowth Testsmentioning

confidence: 99%

“…Pilot-scale testing at the City of Los Angeles Hyperion Treatment Plant (HTP) demonstrated the recurrence of fecal coliforms in biosolids after thermophilic anaerobic digestion (Iranpour et al, 2002;2003a;2005a). Fecal coliform densities strongly increased in biosolids after the dewatering centrifuges, causing exceedance of the Class A limit in biosolids at the silos and at the farm for land application.…”

Section: Introductionmentioning

confidence: 99%

Lab and Pilot-Scale Tests with Post-Digestion Biosolids to Prevent Indicator and Pathogen Regrowth

Palacios¹,

Cox²,

Fan³

et al. 2005

Self Cite

Several experiments were conducted to investigate the cause of fecal coliform recurrence in biosolids after thermophilic anaerobic digestion. Fecal coliform recurrence has been observed at the City of Los Angeles Hyperion Treatment Plant (HTP) during pilot-scale experiments with a designated thermophilic battery of six digesters, while other digesters were still at a mesophilic temperature. The main results of the present investigation were:-QA/QC plant inspections indicated that the designated thermophilic battery and its post-digestion train likely were isolated from mesophilic operations, but contamination by mesophilically digested biosolids could not entirely be excluded. -High-pressure effluent and Mannich polymer did not contain fecal coliforms, hence, their additions to the post-digestion train could be ruled out as contamination sources. -Laboratory simulations could not confirm the suspected role of dewatering centrifuges in the recurrence of fecal coliforms observed at HTP. -Regrowth tests in the laboratory and the field demonstrated that the minimum temperature for preventing fecal coliform recurrence was about 50 0 C.Based on these results, it was postulated the fecal coliform recurrence observed during the pilot-scale tests could probably be attributed to a combination of contamination by mesophilically digested biosolids and a large drop of the biosolids temperature during post-digestion processing.

“…In response to local bans and ordinances on biosolids land application and growing public concern on the safety of biosolids, an increasing number of plants are implementing thermophilic anaerobic digestion to produce a higher quality of biosolids with indicator/pathogen densities below the limits for Class A qualification (Drury et al, 2002;Iranpour et al, 2002bIranpour et al, , 2004Mittsdörffer et al, 1990;Wilson and Dichtl, 1998). Recent investigations have indicated the recurrence of fecal coliforms in post-digestion biosolids at some wastewater treatment plants that produce Class A biosolids by thermophilic anaerobic digestion (Iranpour et al, 2002a). Such increases are undesirable and could result in noncompliance.…”

Section: Introductionmentioning

confidence: 99%

DISINFECTION OF FECAL COLIFORMS AND SALMONELLA IN THERMOPHILICALLY DIGESTED BIOSOLIDS

Iranpour¹,

Cox²,

Starr³

et al. 2004

Self Cite

Several wastewater treatment plants that were investigated in this study produce biosolids that meet the Class A pathogen reduction requirements for both fecal coliforms (indicator) and Salmonella sp. (pathogen). The U.S. EPA Part 503 Biosolids Rule specifies that the Class A limits for these bacteria shall be met at the last point of plant control, which is usually interpreted as the truck loading facility when the biosolids are prepared for transport or at the farm for land application. However, a recurrence of fecal coliforms was observed in post-digestion biosolids from the City of Los Angeles Hyperion and Terminal Island Treatment Plants and in the biosolids at the farm for land application. Biosolids sampled from dewatering centrifuges, silos and the farm sometimes contained fecal densities in densities up to 10 7 MPN/g dry wt, causing exceedance of the Class A limit for fecal coliforms. In contrast, recurrence of Salmonella sp. was never observed, which indicates that fecal coliforms are a poor indicator of the pathogen content in biosolids after digestion. Regrowth tests with fecal coliforms in biosolids from several locations in the post-digestion train indicated the presence of a self-disinfecting effect that caused killing of fecal coliforms spiked to biosolids from the digester. Such an effect was not present in centrifuge and silo biosolids. Hence, the dewatering centrifuge was identified as the most likely location where the recurrence of fecal coliforms originated. Laboratory simulations of centrifuge dewatering achieving only 10% total solids could not confirm the field observations and the possible role of centrifuge dewatering in the recurrence of fecal coliforms remained unknown. Comparison of observations at three wastewater treatment plants indicated that the recurrence of fecal coliforms can possibly be related to the following combination of factors: i) contamination of Class A biosolids with fecal coliforms from external sources; ii) a large drop of the post-digestion biosolids temperature to below the maximum for fecal coliform growth; iii) the loss of a self-disinfecting effect that causes killing of fecal coliforms in digested sludge. Recurrence of fecal coliforms in biosolids during postdigestion and at the farm was prevented by insulation of the post-digestion train of the Hyperion Treatment Plant, which maintained a biosolids temperature above the maximum for growth of fecal coliforms. When silo and farm biosolids were subsequently stored at 21 0 C, no recurrence of fecal coliforms was observed for at least 6 days. KEYWORDSBiosolids regulations, Class A, last point of plant control, indicator and pathogenic bacteria, anaerobic digestion, regrowth and inactivation, laboratory simulations, selfdisinfecting