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Fate of pathogens in thermophilic aerobic sludge digestion
Water Re,~. Vol 16. pp. 1051 to IObO. 1982 Printed in Great Britain ,All rights reser',ed
0043-t354 82 061051-10S0300 0 Copyright C 1~82 Pergamon Press Lid
FATE OF PATHOGENS IN THERMOPHILIC AEROBIC SLUDGE DIGESTION RANDOLPH M. KABRICK and WILLIAM J. JEWELL Department of Agricultural Engineering Cornell University, Ithaca. NY. U.S.A. (Received November 1981)
Abstract--The effect of autoheated aerobic thermophilic digestion on the pathogen content of sewage sludges was studied and compared to that of conventional mesophilic anaerobic digestion. Both systems were full scale, continuously-fed facilities operated in parallel and utilized a feed sludge of thickened primary and waste-activated sludge. The relative populations of viruses, Salmonella sp.. total and fecal coliforms, fecal streptococci and parasites found before and after digestion were compared. The full scale mesophilic anaerobic digesters were operated at relatively constant conditions, i.e. digester temperature constant at 35'C, and loading rates constant, etc., while the full scale autoheated aerobic digester was operated under a wide range of loading conditions. At all of the conditions studied, the autoheated digester temperature exceeded 45 C. Virus and Salmonella sp. concentrations in the effluent from the aerobic unit were below detectable limits in 10 of II samples and 6 of 6 samples, respectively, whereas the anaerobic digester effluent contained detectable numbers of viruses and Salmonella sp. Bacterial indicator counts and parasite concentrations were less in the autoheated digester effluent than in the effluent from the anaerobic digester. It was concluded that the simple autoheated aerobic digestion process could be used to produce a virtually pathogen-free sludge at a cost comparable to that of conventional, mesophilic anaerobic digestion.
INTRODUCTION
tern (Jewell & Kabrick, 1980). It was shown to be
The relatively low incidence of water-borne disease outbreaks in the United States and other highly developed nations reflects the ability to satisfactorily
capable of achieving a stabilized pasteurized sewage sludge at costs comparable to present sludge processing systems. The results presented here summarize the fate of the background levels of various pathogens in sewage sludge produced in a large urban community
treat wastewater by biological, chemical, and physical processes and subsequently disinfect the liquid portion. e.g. with halogen compounds, prior to returning the liquid portion to the environment. Accepted treatment processes for wastewater generate a large amount of sludge that contains the pathogens separated in the water treatment processes. At present, the sludge production rate in the U.S. is estimated to be 4.5 billion dry kg year-*. Traditionally, little emphasis has been placed on the ultimate disposal of these wastewater sludges with the majority of sludge buried, burned or dumped at sea. The United States Environmental Protection Agency has put forth guidelines which suggest that sewage sludges and other waste organics be used for beneficial purposes when such practices are safe and cost-effective. At this time. land application of sludges appears to be the most cost-effective alternative since sludges could provide the required plant nutrients for millions of acres of cropland. Approximately 20°o of these sewage sludges are now used in agriculture (Bastian, 1977). However. sludge management technology often cannot guarantee public health protection or cost-effective solutions. This paper details the pasteurization ability of the autothermal aerobic digestion process in contrast to that achieved in conventional anaerobic digestion systems. An earlier paper discussed the details of the air-aerated autoheated sys-
when treated by an aerobic thermophilic system and a conventional mesophilic anaerobic digestion system. BACKGROUND Autoheated aerobic digestion
The autoheating phenomenon commonly observed in composting of solids has not been applied to liquid organic slurries until recently. Because of the small amount of energy contained in waste organics such as ,sewagesludge and the large amount of water that would need to be heated, it was thought that autoheating might not be leasible with existing approaches to this topic. The details of most of the previous experiences with autoheated aerobic digestion are summarized elsewhere (Smith et al.. 1975: Jewell et al.. 1980L Increases in temperature resulting from the exothermic heat of substrate oxidation ranged from 0 up to 40 C with air and oxygen aeration of sewage sludge. Most of these studies were short-term, batch-like tests. Maximum autoheated temperature achieved with continuous full scale systems with pure oxygen or air prior to the Cornell University study was 3g C. Matsch & Drnevich (1977} reported autoheated reactor temperatures of up to 58 C for pilot scale systems utilizing pure oxygen: however. maximum temperature achieved in the full scale systerns was 33 C. Initial investigations of the autoheated aerobic thermophilic digestion process utilizing agricultural wastes were performed at Cornell University by Koenig (19741 and Wright 119751 with bench scale and pilot scale reactors.
1051
1052
RANDOLPH M
K.ABRICK and WILLI.*~( J JEt, ELL
Subsequently. a commercially available full scale system was installed at Corne[I University to study dairy waste substrate treatment over a 2-year period (Cummings & Jewell, 1977). Because of this successful demonstration of the autoheating concept, a single stage digestion facility was designed and constructed at the Binghamton-Johnson City Sewage Treatment Plant in Binghamton, NY. where this study took place over a 2-year period. The Binghamton sewage treatment facility is a modern 0.15 million m 3 day-z (40 million ga[ day-~) activated sludge plant that was constructed in 1960. A complete description of the theoretical potential of autoheating, the process design, and process performance of the autoheated aerobic digestion system was reported previously by Jewell & Kabrick (1980) and Jewellet al. (1980).
The study of ~irus occurrence m sludges and their mactz',ation in sludge treatment is currently a topic of much research. Ward & Ashley(1976. 1977. 1978) have pubhshed numerous papers of late concerning the mechanisms of virus inactivation. From their studies, it may be generalized that at temperatures of 50:C or greater and a high pH, i.e. pH 1> 7. virus inactivation within several hours v,ill be assured. Another study performed in Europe, on the fate of ',irus in the aerobic thermophilic digestion of animal manures, also demonstrated the concept of heat and pH synergism for virus inacti',ation (Nage[ et at., 1977). Berg & Berman (1980) showed significant virus inactivation in anaerobic thermophilic digestion. One of the most environmentally resistive pathogemc organisms is the egg of the roundworm, Ascaris sp. Several studies have demonstrated the tenacity of these organisms (Hayes, 1977- Theis & Storm, 1978). It is generally conceded that temperatures of 60'C, for exposure times of at least 30 rain. are needed for inactivation of Ascaris. Inactiration temperatures are somewhat lower for the environmentally more sensitive parasitic cysts, e.g, Entamoeba. European researchers have long been concerned with the presence of pathogens in human and animal manures. Much research has been performed on the survival of virus and pathogenic bacteria in the liquid composting process (autothermal aerobic digestion) in Europe (Strauch et al.. 1970: Nagel et al., 1977). The process was shown to eliminate virus and Salmonella sp. from the manures. Another study (Drnevich & Smith. 1975) on aerobic thermophilic digestion of sewage sludges found that the thermophilic digestion process successfully brought enteric pathogenic bacteria, i.e. Salmonella, below detectable limits with ternperatures of 50:C and hydraulic retention periods of one day. In summary, zt ~s clear that the achievement of high temperatures in liquid and dry sludge can be used to effectively control most. if not all. human and animal pathogens and parasites found n sewage sludge,
Pathogenic organisms in sludge Municipal wastewater, typically speaking, has been shown to contain a wide variety, as well as a large number, of enteric microorganisms (Rudolfs et al., 1950; Foster & Engetbrecht, 1973). Many of these organisms are pathogenie for man and animal. Several studies have demonstrafed that conventional wastewater treatment processes will remove many of these enteric microorganisms from the liquid fraction, especially if the final effluent is disinfected, e.g., with chlorine, bromine, ozone, etc., prior to discharge (Kabler, 1959; Kelly & Sanderson, 1959). However, many organisms become associated with the separated solids, i.e. sludge, resulting in high concentrations of these organisms in sludges from both raw and secondary wastewater treatmerit sludges (Wellings et al., 1976: Smith. 1976). Traditional biological stabilization processes for sludge, such as aerobic or anaerobic digestion, have been shown to lower the number of pathogenic organisms in the sludge, but these processes do not achieve complete removal (disinfection or pasteurization) of the pathogens (McKinhey et al., 1952; Ward & Ashley, 1976; Farrah et al., 1978), The literature also describes other methods of sludge treatment that act to reduce the levels of pathogens in sludge (Farrel et al., 1974: Ward & Ashley, 1978). These techniques include drying or dessication, heat treatment (pasteurizaMATERIALS AND METHODS tion, etc.), irradiation, long-term storage, chemical treatment, and thermoradiation. Many of these methods are Full scale digestion systems limited due to economics, energy or secondary impact conA combination of primary and waste-activated sludge straints, was used as substrate for both the thermophilic aerobic Three major groups of organisms are of primary concern digester and the mesophilic anaerobic digesters. The sludge in assessing the health risk(s) associated with handling and was gravity-thickened to an average concentration of 4.5"0 disposing of sludge. Some of the important members o f total solids with an average volatility of 65°~o by the existeach group are presented in Table 1. ing gravity thickeners at the Binghamton-Johnson City The enteric bacteria, e.g. Salmonella, for the most part Sewage Treatment Plant I STP). Other conditions under are known to be heat sensitive (thermolabile). Although the which the sludge was generated are given m Table 2. optimum growth temperature for many of the pathogenic The existing anaerobic digesters had a total volume of (Enterobacteriaceae) organisms ranges from 35 to 42~C, 6524m J and were operated as high rate digesters at an long exposure to temperatures above 45=C is lethal for approximate hydraulic retention time of 15-20 days and a these microbes, in fact, a study by Drnevich & Smith temperature of 35:C. They utilized external gas heat and (1975) showed that at a temperature of 45"C, Salmonella sp. gas mixing. Loadings to the digester averaged 1.17 kg vola(seeded into sewage sludge) were below detectable limits tile solids m - J day- 1 with a volatile solids destruction effiwithin 24 h, while at 60~C, die-off of the microbes was quite ciency of approx. 367g. The average gas production was rapid, with Salmonella sp. below detectable limits within approx. 1.37m 3 kg-~ volatile solids destroyed with an several hours, average methane content of 625o. Table 1. Pathogenic organisms associated with wastewater sludges Bacteria I. Emerobacteriaceae (a) Salmonella (b) Shigella (c) KlebsieUa 2. Pseudomonads 3. Clostridium 4. M ycobacterium
Virus 1. Enterovirus 2. Adenovirus 3. Agent causing infectious hepatitis
Parasites 1. Protozoa (a) Entamoeba histolytica 2. Helminths (a) Schistosoma mansoni 3. Nematodes (a) Ascaris sp.
8115177 8/29/77 9/26/77 3/I 5/78 3/27/78 4/04/78 4/25/78 5/08/78 5/I 5/78 5/22/78 6/26/78 8/07/78 8/14/78 I I/I 3/78
I 2 3 4 5 6 7 8 9 I0 II 12 13 14
8.02* 7.20 4.88 4.39 5.51 ~ 5.0** 3.03 3.51 3.64 3.30 3.60 -~4 i! ~-4 il I 1.0
HRT (days)
2.96 2.92 4.41 6.98 5.71 -~ 6.0 13.5 9.76 9.22 10.4 ~ -~ 8.0 -~ 8.0 2.60
*Calculations from Binghamton-Johnson City STP records. t N o anaerobic .sample. ~:Fecd p u m p problems. ~System marginally operational. ~Aerator problems.
Dale of sample collection
Sample no. 42.1 38.0 19.5 28.7 37.8 ~ 30 28.7 15.5 22.6 18.9 ~ ~- 35 -~ 35 33.2
Thermophilic aerobic digester Volatile Volatile solids solids loading treatment rate efficiency (kg m - J d a y - 1 ) (,,.) 48.5 45.2 47. I 48.0 49.7 55.0 54.9 42.0 52.9 45.8 40.0 50.0 55.0 65.0
Reactor temp. (C) 7.7 7.8 7.9 7.2 7.2 -7.3 7.0 7.2 7. I ~ --8.3
pH reactor 22.4 21.4 20.0 6.5 5.5 5.0 9. I 10.8 12. I 13.2 20.0 20.0 21.0 I 1.0
Feed temp. (C) 5.4 -6.0 5.8 5.7 -5.6 5.9 5.6 5.6 ~ -~ -5.6
pH feed
Table 2. Operational data for dates of pathogen sampling
19.9 -. 19.2 30.6 24.7 37.6 18.9 20.2 19.7 23.0 30.6 30.6 24.3
HRT (days)
.
0.48 --t. . 0.65 0.72 0.52 0.45 0.48 0.48 0.45 0.34 0.28 0.28 0.45 .
. 6.8 6.9 6.9 7.2 7.0 7. I 6.9 7. I 7. I 7. I 6.9
6.4 --
Mesophitic anaerobic digester Gas production [ Vol.~as ~ pH ~ ~ V reactor o l . reactor
35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0
35.0 -
Reactor temp. (C)
~-
~.
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2' ~.
o
"n
1054
RANDOLPH M. KABRICK and V~'[LLIA~,I J JE~,VELL
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REACTOR VI[S~EL EFFLUENT PUMP
"~r:-:._::_~..r...~, ~ I / I J
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EFFLUENT TANK
Fig. I. Binghamton full scale thermophilic digestion facility. The thermophilic aerobic (experimental) digestion systern was designed to enable measurement of mass balances for flow and energy by providing large completely mixed and insulated feed and effluent tanks, each one capable of storing a volume approximately equal to one hydraulic retention period. The reactor was a cylindrical 3.7 m d i a tank with a depth of 4.3 m. A schematic diagram of the experimental test facility ts given in Fig. 1. The full scale thermophilic aerobic digestion system was operated under conditions which would result in significant biodegradation. but would reflect the advantages of high temperature stabilization. All conditions tested were at relatively high loading rates [ > 2.6 kg VS m - ~ day- t ( > 1621bs 10 -~ ft -3 d a y - t ) ] with the majority of operation at less than a 5-day hydraulic retention time. Several conditions were maintained constant for periods up to 60 days in order to provide time to evaluate practical operation and maintenance problems, as well as to measure the irapact of sludge composition variations on the process, Pathogen isolation and detection The fate of three groups of pathogens, bacteria, viruses and parasites in the full scale thermophilic aerobic digester and full scale mesophilic anaerobic digesters was invest]gated during this study. Laboratories were contracted to perform the analyses for the various pathogens. These angencies are listed below along with the kind(s) of organism(s) they were to identify and/or quantify. Contracted agency I. U.S. Environmental Protection Agency Environemntal Monitoring and Support Laboratory. Cincinnati. OH 2. Dr. M. Dale Little School of Public Health and Tropical Medicine, Tulane Universffy, New Orleans, LA
Pathogenic organism bacteria, viruses
parasites,
Pathogen .sample collection and shipment were always conducted on a Monday to ensure that the contract laboratories were able to analyze the samples, especially the bacteria samples, the same week of collection. Typically, sludge samples, approximate volume of 10 1. (2.6 gal), were collected from the three sources: raw sludge from the thickener pumps, aerobic sludge from the experimental thermophilic reactor, and anaerobic sludge from the existing STP digester (specifically, samples were obtained from the draw-offvalveused to fill tanker-spreaders used in land
application of the sludge from the anaerobic digester). Samples from the aerobic digester (samples were taken from the bottom drain valve and/or taken from the top of the reactor through the sample ports) were collected under batch-mode conditions, i.e. the feed pump was disconnected for 12-24 h prior to sample collection to mimic a system that was being operated to ensure optimum pathogen kills, i.e. to ensure no hydraulic short-circuiting. After the collection of the gross samples. 250ml (0.066gat) subsamples were extracted and placed in sterllized (autoclaved at 151C and t5 p.s.i, for 15 min) nalgene bottles and sealed. Typically, each of three sets of three subsamples, consisting of one set for viral analysis, one set for parasite analysis, and one set for bacterial analysis. were placed in insulated shipping containers (Trans, Temp. System 509) with cold packs Inote that the virus samples were rrozen with dry ice at - 7 0 : C in the shipping containers) and sealed. The shipping containers were appropriately labeled and addressed, then dispatched via air freight (Airborne Freight Corp.) to the various laboratories. All of the analyses for virus in the sludge samples were performed by the Environmental Monitoring and Support Laboratory of the U.S. EPA. Methods similar to {hose developed by Berg (1972) were employed: however, the exact methodology is still under development and refinement. and has not been published to date (Safferman & Berman, 1979I. The analyses for parasites were performed by Tulane University, School of Public Health and Tropical Medicine. employing techniques developed for a separate study under EPA contract ILittle et al., 1979). This technique utilized a modification of the zinc sulfate flotation method with viability of the parasite eggs determined by morphological observations by the Tulane researchers. The U.S. EPA Environmental Monitoring and Support Laboratory performed analyses for fecal coliform, total coliform, and fecal streptococci in accordance with Standard Methods IAPHA. 1975) and Microbiological Methods for Monitoring the Encironment tU.S. EPA. 19791. Analysis was also made for enteric pathogens, specifically Salmonella sp.. by use of the modified Kenner-Clark procedure for enumerating Salmonella sp. (U.S. EPA. 1974). This procedure was also used to enumerate Pseudomonas aerug~nosa. an opportunistic pathogen. RESULTS Fifteen sets of p a t h o g e n s a m p l e s were collected and sent to two l a b o r a t o r i e s for the various p a t h o g e n
Fate of pathogens in thermophilic aerobic sludge digestio n
1055
Table 3. Summary of the fate of fecal coliforms and fecal streptococci during mesophilic anaerobic digestion and thermophilic aerobic digestion of primary and waste-activated sludge mixtures
Sludge type
Counts of organisms per 100 ml wet sludge Fecal coliforms Fecal streptococci Range Mean Range
Mean
Feed sludge Anaerobic sludge Aerobic sludge
3.7 x l0 r 8.4 x l0 s 1.8 x 10`*
1.1-9.6 x l0 T 1.1 x 10"*-2.0 x 1 0 6 1.0 x 105-7.0 x 10`*
analyses. The conditions of operation of the digesters on the given pathogen sample dates are given in Table 2. Samples were collected under a wide range of operating conditions for the thermophilic aerobic digester with all reactor samples at or above 40-'C and pH of 7.0. Loading rates for the thermophilic digester ranged from 2.6 to 13 kg TVS m - s day- t (162-809 lbs 10-3 ft-s day-1), with treatment efflciencies varying between 20 and 42?/0 TVS destruction, respectively. Sample Nos 6, 11, 12 and 13 from the thermophilic aerobic digester were collected under marginally operational conditions. That is, the ternperature was lower than steady state operations, or the reactor was DO limited. However, as will be shown later, this did not significantly affect the pathogen inactivation ability of the system, The mesophilic anaerobic digester was operated under fairly constant conditions with reactor ternperature stable at around 35"C and reactor pH varying between 6.4 and 7.1. Pathogenic bacteria A summary of the results of the analyses for fecal coliforms and fecal streptococci is shown in Table 3. Historically. fecal coliforms and fecal streptococci
2.7 x 10T 9.3 x l0 s 8.2 x 10`*
3.3 × 105-5.0 x l0 T 1.1 x 10'*-2.2 x 106 1.0 x 105-3.0 x 106
have been used as indicator organisms for water quality. However, in this study the fate of these organisms was of secondary interest with the primary focus on the fate of Salmonella sp. and Pseudomonas aeruginosa. For all dates of analysis, the number of fecal coliforms and fecal streptococci were reduced at least an order of magnitude more than the levels in the raw sludge for both the anaerobic and aerobic digesters. The thermophilic aerobic digester demonstrated even larger reductions, one to three orders of magnitude, of these organisms" destructions over the anaerobic digester. The number of Salmonella sp. found in all samples analyzed is graphically shown in Fig. 2. On all of the sample dates, with the exception of 8/15/77, the aerobic digester effluent had far greater reductions in Salmonella sp. than the anaerobic digester effluent. The results of the analyses for pseudomonads are graphically depicted in Fig. 3. in most cases the thermophilic aerobic digester exhibited larger reductions in pseudomonads than the conventional mesophilic anaerobic digester.
Viruses--total plaque-forming units A histogram representing total
plaque-forming
?.0
w ¢o
I~5.0 E
0 0
4.0
3.0
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I
.
O
II/ISs~
~
Isliln7 tsliln'r ~wlwTII Islilsve OATtS OF SAU~.[ COU.[CTION
./13/7e
Fig. 2. Salmo,ella sp. as found in raw. anaerobic, and aerobic sludges (~<3 organisms per lOOml considered below limits of detection).
1056
Ra?,,E~)LPH M. K , , s r i c g and %ILLIAM J, JEWELL _
7.0 ×
o s.0
'
I
o
8/19177
i '~
Q/'~9177 S ~ 4 / T 7 DATES OF
5/Z 7/78
G ~
llJq~V T 8
COLLECTION
Fig. 3. Results of analyses for P.~eudomonas aeruginosa m raw. anaerobic, and aerobic sludges.
units ( P F U ) in all samples for all dates of collection is shown in Fig. 4. In all cases, the aerobic digester exhibited higher levels of viral reactivation than did the anaerobic digester with undetectable levels of viruses in all but one sample of the aerobic unit effluent. The anaerobic digester exhibited levels of virus inactivation equal to or less than 98.6°0. No effort was made to distinguish between the various kinds of enteroviruses or other viruses. Nor was any effort made to distinguish the distribution of the viruses between the sludge solids and the liquid,
Parasites
A summary of the parasite analyses as performed by Tulane University for all dates of collection is given in Table 4. In all samples, with the exception of 5/8/78. the aerobic digester exhibited higher reduction of total viable ova over the anaerobic digester. It should be noted that the distinction between viable and nonviable ova was made solely rrom morphological observations, e.g. disrupted membranes, without subseq,,ent culturing of the suspect ova for confirmation of the morphological diagnoses.
~7.0 Q .d IQ.O
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Fig. 4. Results of virus analyses (total PFU per 100 ml wet sludge) On raw. anaerobically (mesophilic)
and aerobically (thermophilic} digested sludge.
Raw Aerobic Anaerobic
Raw Aerobic* Anaerobic'l"
Raw Aerobic Anaerobic
Raw~ Aerobic Anaerobic
Raw Aerobic Anaerobic
Raw Aerobic Anaerobic
Raw Aerobic Anaerobic
4/04/78
4/24/78
5/08/78
5/22/78
6/26/78
8/07/78
8/14/78
3 2 0
0 0 0
0 0 0
2 0 3
0 1 I
4 0 .
I 0 3
V
*Only 80 ml sludge analyzed. 'tContainer broken in transit. :[:Only 90 ml sludge analyzed. V = Viable. NV = Non-viable.
Sludge type
Date of couection
.
.
0 3 2
0 0 0
0 4 0
0 3 0
1 2 I
2 2
0 4 0
Am'clri.~ NV
.
I 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0
0 0 2
.
.
0 0 0
0 4 0
0 0 0
0 I 0
0 1 0
I 0
0 I 0
T. trichiura v NV
.
2 0 2
2 0 2
2 I 3
3 0 I
I 1 I
5 0 .
I 0 5
.
0 4 0
0 4 0
0 0 0
0 0 0
0 0 I
1 1
0 2 0
.
.
8 0 2
3 0 5
3 0 2
10 I 5
0 2 1
5 0
3 1 8
.
.
0 3 4
I I 0
1 I 2
I I 1
7 8 3
2 6
2 8 2
.
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0
0 0 0
Parasite counts per 100 ml of sludge H. 7: rulpis Toxocara dimim~ta V NV V NV V NV
0 0 0
0 0 0
1 0 0
I 0 0
0 0 0
0 0 0
0 0 0
0 0 0
Toxascaris leonia V NV
I 0 0
0 0 0
0 0 0
0 0 0
0 0 1
0 1 0
0 0 0
0 1 0
Capillaria sp. V NV
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 Few 0
Few 0 0
Few 0 0
21 55 35
20 50 35
20 40 35
13 46 35
II 42 35
9. I 55 35
50 55 35
Temp. of l:.ntameba coci sample when (like cysts) collected V NV (' C)
Table 4. Results of parasitologic examinations of all samples with primary and waste-activated sludge combinations. All analyses conducted by Tulane University
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complete inactivation, i.e. beiov, limits of dete,~tion, of viruses at temperatures of greater than or equal to The fate of three groups of pathogenic organisms in 40:C and pH of greater than or equal to 7.0 was the thermophitic aerobic digestion process and in the expected based on information in the literature {Ward mesophilic anaerobic digestion process (both were full & Ashley, 1976, 1978: Nagel et al.. 1977: Berg & scale systems) was studied utilizing only the back- Berman, 1980}. This synergistic action of temperature ground levels of these.organisms in the raw sludge, and pH worked effectively in reducing viruses in the It was realized that fluctuations in the background anaerobic digester, also. Although viruses were not levels of pathogens could have been due to nonrepre- reduced below detectable limits in the anaerobic sentative samples or inadequacies in screening high digester effluent, they were significantly reduced from solids sludge samples for pathogens, the numbers in the raw sludge with destruction effiThe performance of the autoheated aerobic thermo- ciencies as high as 98.6°o. philic digester in the inactivation of pathogenic bacThe low number of parasites found in the raw teria, viruses and parasites was examplary of the effect sludge was a function of the climate and population of a high temperature treatment process on patho- of Binghamton. NY. Studies have shown high gens, On the other hand. the conventional mesophilic numbers of various parasites present in raw sludges, anaerobic digester performance, with regard to patho- e.g. greater than 50,000 Ascaris eggs per kg dry sludge gen inactivation, was typical of performance data (Leftwich et al., 1979). with organism concentration reported in the literature, dependent upon climate as well as on the socioeconThe reduction of Salmonella sp. from feed concen- omic structure of the community (Hays, 1977: trations as high as 2200 organisms per 100ml wet Leftwich et al., 19791. When the data from Tulane sludge to below the limits of detection in all of the University's parasite analyses were reviewed as total aerobic thermophilic samples was a function of reac- viable and nonviable parasitic ova, the aerobic thertor temperature as well as the chemical nature (e.g. mophilic digester was shown to be superior to the pHI of the sludge environment. In all but one sample, anaerobic mesophilic digester in the reduction of the reactor temperatures were greater than or equal viable parasitic ova (Table 4). The high reactor ternto 45 C. This temperature, combined with an ex- peratures in the aerobic digester were responsible for posure time of approx. 24 h, was shown to effectively the observed decrease in viable ova over the anaeroreduce Salmonella sp. to below detectable limits bic unit. Since a small number of viable ova were (Drnevich & Smith, 1975). The reactor temperature isolated from the aerobic digester on 5 sample dates, for the other sample date (26 June, 1978) was 40:C. it must be concluded from the {limited) available data, Strauch (1970) showed that an exposure time of 24h the number of parasitic ova are reduced by the at a temperature of 40:C and pH of 7.8 was sufficient aerobic thermophilic digestion process: however, to reduce Salmonella d,blin below detectable limits in complete inactivation of parasitic ova and cysts aerated liquid swine manure. Strauch (1970) also would require temperatures of greater than or equal reported that inactivation of S. enteritidis in swine to 6 0 C with corresponding exposure times of greater manure required 40h of exposure time at 42:C and than or equal to one hour. This could be acpH 8.0. Therefore, it can be concluded that inactiva- compiished in a multi-stage digestion system in conlion of Salmonella sp. in aerating sewage sludge junction with heat exchangers for boosting the reacrequires temperatures above 40:C with the pH of the tor(s) temperature to around 70C. slurry and the species of Salmonella playing important Several practical concerns should be noted if the roles, thermophilic aerobic process is applied for disease Reductions of Salmonella sp. in the anaerobic digesorganism destruction. In all continuous flow and ters operated at 35-C were comparable to those mixed processes, a certain amount of the influent reported in the literature (Bertucci et al., 1977). rangliquid passes rapidly through the system, i.e. shorting from 44 to 99°g. The inability of the anaerobic circuiting occurs. This can be avoided by the use of digesters to completely inactivate Salmonella sp. was several series-fed reactors, or by using sequencing probably a function of the low operating temperature batch units. During start-up and shut-down, the autoof 35:C. heated temperatures may not be high enough to The fates of the other indicator organisms, Pseudoachieve pasteurization. Instead. under non-optimum monas aeruginosa, fecal coliforms and fecal streptoconditions the presence of oxygen and higher terncocci, followed the same trends as Salmonella sp. in peratures may promote the viability of the organisms. both the anaerobic and aerobic digesters. The larger Proper design of feedback should minimize this percentages of organism reduction in the thermophilic potential disadvantage. Finally, the aeration energy aerobic digester was most likely due to the higher (costing approx. $10 per dry ton of sludge) needs to be temperatures of operation, evaluated in relation to the risks presented by the Virus inactivation, as measured by total PFU, for specific sludge handling and disposal operations. the thermophilic aerobic digester was complete on all In summary, it can be stated that the aerobic therbut one occasion. On that sample date. 14 August mophilic digester exhibited superior performance over 1978, the digester was marginally operational. The a mesophilic anaerobic digester with respect to the
Fate of pathogens in thermophilic aerobic sludge digestion inactivation of pathogenic bacteria, visuses, and parasites. The thermophilic aerobic digester yielded cornplete inactivation of Salmonella sp. and total plaqueforming units, i.e. below the limits of detection, on all but one occasion, thereby demonstrating the system's ability to control these pathogens. Parasite numbers were reduced by the aerobic thermophilic system, but not completely. The inability of the system to deliver parasite-free sludge may be indicative of the need for a multi-stage system with heat exchangers to prevent possible short-circuiting {hydraulic) and increase reactor temperatures for control of the environmentally resistant parasites, e.g. Ascaris sp.
Acknowledgements--Partial financial support was provided by the U.S. Environmental Protection Agency (U.S. EPA) under Research Grant R 804636-01, J. A. Spada served as Research Technician and Draftsman. Dr Dale M. Little, Tulane University, performed parasite analyses. A. Venosa and H. Clark, U.S. EPA, performed bacterial analyses, D. Berman, U.S. EPA, was responsible for the viral analyses. J. P. Greene served as Service Technician on the full scale experimental facility. DeLaval Separator Company provided the centri-rator aerator, and LFE Corp. provided the Midland-Frings aerator. Mr B.V. Salotto was the U.S. EPA Project Manager.
REFERENCES APHA (1972) Viruses in Water (Edited by Berg et al.). American Public Health Association, New York. APHA (1976) b'tandard Methods Jot the Examination of Water and Wastewater. 14th Edition. American Public Health Association, New York. Bastian R. K. (1977) Municipal Sludge Management. In Land as a Waste Management Alternative (Edited by Loehr R. C.), p.' 677. Ann Arbor Science Press, Ann Arbor, MI. Berg G. & Berman D. (1980) Destruction by anaerobic mcsophilic and thermophilic digestion of viruses and indicator bacteria indigenous to domestic sludges. J. a p p l . Envir. Microbial. 39, 361. Bertueci J. J., Lue-Hing C., Zenz D. & Sedita S. J. (1977) Inactivation of viruses during anaerobic sludge digestion. J. Wat. Pollut. Control Fed. 49, 1642. Cummings R. J. & Jewell W. J. (1977) Thermophilic aerobic digestion of dairy waste. In Food, Fertilizer and Agricultural Residues (Edited by Loehr R. C.), p. 6 3 7 . Ann Arbor Science Press, Ann Arbor, MI. Drnevich R. F. & Smith J. E. Jr (1975) Pathogen reduction in the thermophilic aerobic digestion process. Presented at the 48th Water Pollution Control Fed. Conf., Miami Beach, FL. Farrah S. R., Pancorbo O. E. & Bitton G. (1978) Inactivation of enteric viruses and bacteria during aerobic digestion of wastewater sludge. Department of Microbiology, Cell Science, and Environmental Engineering Science. University of Florida, Gainesville, FL. Farrell J. B., Smith J. E. Jr, Hathaway S. W. & Dean R.B. (1974) Lime stabilization of primary sludges. J. Wat. Pollut. Control Fed. 46, 113. Foster D. H. & Englebreeht R. S. (1973) Microbial hazards of disposing wastewater on soil. In Recycling Treated Municipal Wastewater and Sludge Through Forest and Cropland (Edited by Sopper W. E. & Kardos L.T.), p. 247. Pennsylvannia State Press, University Park, PA. W.R. 16 ' 6 ~ T
1059
Hays B. D. (1977) Potential for parasitic disease transmission with land application of sewage plant efltuents and sludges. Water Res. 11, 583. Jewell W. J. & Kabrick R. M. (1978) Autoheated aerobic thermophilic digestion with aeration. J. War. Pollur. Control Fed. 52, 113, part 1, 513. Jewell W. J., Kabrick R. M. & Spada J. A. (1979) Autoheated aerobic thermophilic digestion with air aeration. U.S. Environmental Protection Agency Report. Kabter P. (1959) Removal of pathogenic microorganisms by sewage treatment processes. Sewage ind. Wastes 31, 1373. Kelly S. & Sanderson W. W. (1959) The effect of sewage treatment on viruses. Sewage ind. Wastes 31,683. Kenner B. A. & Clark H. P. (1974) Detection and enumeration of Salmonella and Pseudomonas aeruginosa. J. Wat. Pollut Control Fed. 46, 2163. Koenig A. {1974) Heat generation during aerobic oxidation of concentrated organic wastes. M.S. Thesis. Cornell University, Ithaca, NY. Leftwich D. B., Reimers R. S. & England A. J. Jr (1979) Investigation of parasites in southern domestic waste sludges--a possible industrial waste point source. Presented at the 34th Purdue Industrial Waste Conference. Purdue University. West Lafayette, IN. LittleM. D. etal.(1979) Survey of wastes sludges for parasitic contamination in the U.S.A. and investigation of possible waste treatment alternatives to inhibit contamination. U.S. EPA study under development. School of Public Health and Tropical Medicine, Tulane University, New Orleans, LA. Matsch L. C. & Drnevich R. F. (1977) Autothermal aerobic digestion. J, War. Pollut. Control Fed. 49, 2. McKinney R. E., Langely H. E. & Tomlinson H. D. (1958) Survival of Salmonella typhosa during anaerobic digestion. Sewage ind. Wastes 30, 1469. Nagel R., Straub O. C. & Strauch D. (1977) The recirculating aeration method (Fuchs System) for the treatment of liquid animal and communal sewage. Department of Animal Hygiene, University of Hohenheim and Federal Research Institutes for Research on Animal Virus Diseases. Popel F. & Ohnmacht Ch. (1972) Thermophilic bacterial oxidation of highly concentrated substrates. Water Res. 6, 107. Rudolfs W., Frank L. L. & Ragotzkie R. A. (t950) Literature review on the occurrence and survival of enteric, pathogenic and relative organisms in soil, water, sewage, sludges and vegetation. Sewage ind. Wastes 22, 1261. Safferman R. & Berman D. (1979) Personal communication. U.S. EPA, Environmental Monitoring and Support Laboratory, Virology Section. Smith J. E, (1976) Mammalian viruses in raw sewage and sludge digests, Onandaga County, NY. Department of Biology, Syracuse University. Smith J. E. Jr, Young K. W. & Dean R. B. (1975) Biologieal oxidation and disinfection of sludge. Water Res. 9, 17. Strauch D., Miiller W. & Best E. (1970) Partial results of the hygienic-bacteriological investigation of the aerationagitation system. Landtechn. Forschung. 18, 147. Theis J. H. & Storm D. R. (1978) Helminth ova in soil and sludge from twelve U.S. urban areas. J. War. Pollut. Control Fed. 50, 2485. U.S. EPA (1979) Microbiological Methods for Monitoring the Environment (Edited by Winter J.). Environmental monitoring and support laboratory, U.S. EPA, Cincinnati, OH. Ward R. L. & Ashley C. S. (1976) Inactivation of poliovirus in digested sludge. J. appl. Envir. Microbiol. 31, 921. Ward R. L., Ashley C. S. & Moseley R. H. (1976) Heat inactivation of poliovirus in wastewater sludge. J. appl. Envir. Microbiol. 32, 339.
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RANDOLPH M. KABRICK and WILLIAM J. JEWELL
Ward R. L. & Ashley C. S. (1977) Inactivation of enteric viruses in wastewater sludge through dewatering by evaporation. J. appl. Envir. Microbiol. 34, 564. Ward R. L. & Ashley C. S. (1977) Discovery of an agent in wastewater sludge that reduces the heat required to inactivate reovirus. J. appl. Envir. Microbiol. 34, 681. Ward R. L. & Ashley C. S. (1977) Identification of the virucidal agent in wastewater sludge, J. appl. Envir. Microbiol. 34, 860.
Ward R. L. & Ashley C. S. (1978) Methods to inactivate enteric viruses in wastewater sludge. Sandia Laboratories. Albuquerque. NM. Sand 77-1498. Wellings F. M. et al. (I976} Demonstration of solids-associated virus in wastewater sludge. J. appt. Ent:ir~ Microbiol. 31,354. Wright P. J. (1975) Thermophilic aerobic digestion of a concentrated organic slurry; M.S. Thesis. Cornell University, Ithaca, NY.
0043-t354 82 061051-10S0300 0 Copyright C 1~82 Pergamon Press Lid
FATE OF PATHOGENS IN THERMOPHILIC AEROBIC SLUDGE DIGESTION RANDOLPH M. KABRICK and WILLIAM J. JEWELL Department of Agricultural Engineering Cornell University, Ithaca. NY. U.S.A. (Received November 1981)
Abstract--The effect of autoheated aerobic thermophilic digestion on the pathogen content of sewage sludges was studied and compared to that of conventional mesophilic anaerobic digestion. Both systems were full scale, continuously-fed facilities operated in parallel and utilized a feed sludge of thickened primary and waste-activated sludge. The relative populations of viruses, Salmonella sp.. total and fecal coliforms, fecal streptococci and parasites found before and after digestion were compared. The full scale mesophilic anaerobic digesters were operated at relatively constant conditions, i.e. digester temperature constant at 35'C, and loading rates constant, etc., while the full scale autoheated aerobic digester was operated under a wide range of loading conditions. At all of the conditions studied, the autoheated digester temperature exceeded 45 C. Virus and Salmonella sp. concentrations in the effluent from the aerobic unit were below detectable limits in 10 of II samples and 6 of 6 samples, respectively, whereas the anaerobic digester effluent contained detectable numbers of viruses and Salmonella sp. Bacterial indicator counts and parasite concentrations were less in the autoheated digester effluent than in the effluent from the anaerobic digester. It was concluded that the simple autoheated aerobic digestion process could be used to produce a virtually pathogen-free sludge at a cost comparable to that of conventional, mesophilic anaerobic digestion.
INTRODUCTION
tern (Jewell & Kabrick, 1980). It was shown to be
The relatively low incidence of water-borne disease outbreaks in the United States and other highly developed nations reflects the ability to satisfactorily
capable of achieving a stabilized pasteurized sewage sludge at costs comparable to present sludge processing systems. The results presented here summarize the fate of the background levels of various pathogens in sewage sludge produced in a large urban community
treat wastewater by biological, chemical, and physical processes and subsequently disinfect the liquid portion. e.g. with halogen compounds, prior to returning the liquid portion to the environment. Accepted treatment processes for wastewater generate a large amount of sludge that contains the pathogens separated in the water treatment processes. At present, the sludge production rate in the U.S. is estimated to be 4.5 billion dry kg year-*. Traditionally, little emphasis has been placed on the ultimate disposal of these wastewater sludges with the majority of sludge buried, burned or dumped at sea. The United States Environmental Protection Agency has put forth guidelines which suggest that sewage sludges and other waste organics be used for beneficial purposes when such practices are safe and cost-effective. At this time. land application of sludges appears to be the most cost-effective alternative since sludges could provide the required plant nutrients for millions of acres of cropland. Approximately 20°o of these sewage sludges are now used in agriculture (Bastian, 1977). However. sludge management technology often cannot guarantee public health protection or cost-effective solutions. This paper details the pasteurization ability of the autothermal aerobic digestion process in contrast to that achieved in conventional anaerobic digestion systems. An earlier paper discussed the details of the air-aerated autoheated sys-
when treated by an aerobic thermophilic system and a conventional mesophilic anaerobic digestion system. BACKGROUND Autoheated aerobic digestion
The autoheating phenomenon commonly observed in composting of solids has not been applied to liquid organic slurries until recently. Because of the small amount of energy contained in waste organics such as ,sewagesludge and the large amount of water that would need to be heated, it was thought that autoheating might not be leasible with existing approaches to this topic. The details of most of the previous experiences with autoheated aerobic digestion are summarized elsewhere (Smith et al.. 1975: Jewell et al.. 1980L Increases in temperature resulting from the exothermic heat of substrate oxidation ranged from 0 up to 40 C with air and oxygen aeration of sewage sludge. Most of these studies were short-term, batch-like tests. Maximum autoheated temperature achieved with continuous full scale systems with pure oxygen or air prior to the Cornell University study was 3g C. Matsch & Drnevich (1977} reported autoheated reactor temperatures of up to 58 C for pilot scale systems utilizing pure oxygen: however. maximum temperature achieved in the full scale systerns was 33 C. Initial investigations of the autoheated aerobic thermophilic digestion process utilizing agricultural wastes were performed at Cornell University by Koenig (19741 and Wright 119751 with bench scale and pilot scale reactors.
1051
1052
RANDOLPH M
K.ABRICK and WILLI.*~( J JEt, ELL
Subsequently. a commercially available full scale system was installed at Corne[I University to study dairy waste substrate treatment over a 2-year period (Cummings & Jewell, 1977). Because of this successful demonstration of the autoheating concept, a single stage digestion facility was designed and constructed at the Binghamton-Johnson City Sewage Treatment Plant in Binghamton, NY. where this study took place over a 2-year period. The Binghamton sewage treatment facility is a modern 0.15 million m 3 day-z (40 million ga[ day-~) activated sludge plant that was constructed in 1960. A complete description of the theoretical potential of autoheating, the process design, and process performance of the autoheated aerobic digestion system was reported previously by Jewell & Kabrick (1980) and Jewellet al. (1980).
The study of ~irus occurrence m sludges and their mactz',ation in sludge treatment is currently a topic of much research. Ward & Ashley(1976. 1977. 1978) have pubhshed numerous papers of late concerning the mechanisms of virus inactivation. From their studies, it may be generalized that at temperatures of 50:C or greater and a high pH, i.e. pH 1> 7. virus inactivation within several hours v,ill be assured. Another study performed in Europe, on the fate of ',irus in the aerobic thermophilic digestion of animal manures, also demonstrated the concept of heat and pH synergism for virus inacti',ation (Nage[ et at., 1977). Berg & Berman (1980) showed significant virus inactivation in anaerobic thermophilic digestion. One of the most environmentally resistive pathogemc organisms is the egg of the roundworm, Ascaris sp. Several studies have demonstrated the tenacity of these organisms (Hayes, 1977- Theis & Storm, 1978). It is generally conceded that temperatures of 60'C, for exposure times of at least 30 rain. are needed for inactivation of Ascaris. Inactiration temperatures are somewhat lower for the environmentally more sensitive parasitic cysts, e.g, Entamoeba. European researchers have long been concerned with the presence of pathogens in human and animal manures. Much research has been performed on the survival of virus and pathogenic bacteria in the liquid composting process (autothermal aerobic digestion) in Europe (Strauch et al.. 1970: Nagel et al., 1977). The process was shown to eliminate virus and Salmonella sp. from the manures. Another study (Drnevich & Smith. 1975) on aerobic thermophilic digestion of sewage sludges found that the thermophilic digestion process successfully brought enteric pathogenic bacteria, i.e. Salmonella, below detectable limits with ternperatures of 50:C and hydraulic retention periods of one day. In summary, zt ~s clear that the achievement of high temperatures in liquid and dry sludge can be used to effectively control most. if not all. human and animal pathogens and parasites found n sewage sludge,
Pathogenic organisms in sludge Municipal wastewater, typically speaking, has been shown to contain a wide variety, as well as a large number, of enteric microorganisms (Rudolfs et al., 1950; Foster & Engetbrecht, 1973). Many of these organisms are pathogenie for man and animal. Several studies have demonstrafed that conventional wastewater treatment processes will remove many of these enteric microorganisms from the liquid fraction, especially if the final effluent is disinfected, e.g., with chlorine, bromine, ozone, etc., prior to discharge (Kabler, 1959; Kelly & Sanderson, 1959). However, many organisms become associated with the separated solids, i.e. sludge, resulting in high concentrations of these organisms in sludges from both raw and secondary wastewater treatmerit sludges (Wellings et al., 1976: Smith. 1976). Traditional biological stabilization processes for sludge, such as aerobic or anaerobic digestion, have been shown to lower the number of pathogenic organisms in the sludge, but these processes do not achieve complete removal (disinfection or pasteurization) of the pathogens (McKinhey et al., 1952; Ward & Ashley, 1976; Farrah et al., 1978), The literature also describes other methods of sludge treatment that act to reduce the levels of pathogens in sludge (Farrel et al., 1974: Ward & Ashley, 1978). These techniques include drying or dessication, heat treatment (pasteurizaMATERIALS AND METHODS tion, etc.), irradiation, long-term storage, chemical treatment, and thermoradiation. Many of these methods are Full scale digestion systems limited due to economics, energy or secondary impact conA combination of primary and waste-activated sludge straints, was used as substrate for both the thermophilic aerobic Three major groups of organisms are of primary concern digester and the mesophilic anaerobic digesters. The sludge in assessing the health risk(s) associated with handling and was gravity-thickened to an average concentration of 4.5"0 disposing of sludge. Some of the important members o f total solids with an average volatility of 65°~o by the existeach group are presented in Table 1. ing gravity thickeners at the Binghamton-Johnson City The enteric bacteria, e.g. Salmonella, for the most part Sewage Treatment Plant I STP). Other conditions under are known to be heat sensitive (thermolabile). Although the which the sludge was generated are given m Table 2. optimum growth temperature for many of the pathogenic The existing anaerobic digesters had a total volume of (Enterobacteriaceae) organisms ranges from 35 to 42~C, 6524m J and were operated as high rate digesters at an long exposure to temperatures above 45=C is lethal for approximate hydraulic retention time of 15-20 days and a these microbes, in fact, a study by Drnevich & Smith temperature of 35:C. They utilized external gas heat and (1975) showed that at a temperature of 45"C, Salmonella sp. gas mixing. Loadings to the digester averaged 1.17 kg vola(seeded into sewage sludge) were below detectable limits tile solids m - J day- 1 with a volatile solids destruction effiwithin 24 h, while at 60~C, die-off of the microbes was quite ciency of approx. 367g. The average gas production was rapid, with Salmonella sp. below detectable limits within approx. 1.37m 3 kg-~ volatile solids destroyed with an several hours, average methane content of 625o. Table 1. Pathogenic organisms associated with wastewater sludges Bacteria I. Emerobacteriaceae (a) Salmonella (b) Shigella (c) KlebsieUa 2. Pseudomonads 3. Clostridium 4. M ycobacterium
Virus 1. Enterovirus 2. Adenovirus 3. Agent causing infectious hepatitis
Parasites 1. Protozoa (a) Entamoeba histolytica 2. Helminths (a) Schistosoma mansoni 3. Nematodes (a) Ascaris sp.
8115177 8/29/77 9/26/77 3/I 5/78 3/27/78 4/04/78 4/25/78 5/08/78 5/I 5/78 5/22/78 6/26/78 8/07/78 8/14/78 I I/I 3/78
I 2 3 4 5 6 7 8 9 I0 II 12 13 14
8.02* 7.20 4.88 4.39 5.51 ~ 5.0** 3.03 3.51 3.64 3.30 3.60 -~4 i! ~-4 il I 1.0
HRT (days)
2.96 2.92 4.41 6.98 5.71 -~ 6.0 13.5 9.76 9.22 10.4 ~ -~ 8.0 -~ 8.0 2.60
*Calculations from Binghamton-Johnson City STP records. t N o anaerobic .sample. ~:Fecd p u m p problems. ~System marginally operational. ~Aerator problems.
Dale of sample collection
Sample no. 42.1 38.0 19.5 28.7 37.8 ~ 30 28.7 15.5 22.6 18.9 ~ ~- 35 -~ 35 33.2
Thermophilic aerobic digester Volatile Volatile solids solids loading treatment rate efficiency (kg m - J d a y - 1 ) (,,.) 48.5 45.2 47. I 48.0 49.7 55.0 54.9 42.0 52.9 45.8 40.0 50.0 55.0 65.0
Reactor temp. (C) 7.7 7.8 7.9 7.2 7.2 -7.3 7.0 7.2 7. I ~ --8.3
pH reactor 22.4 21.4 20.0 6.5 5.5 5.0 9. I 10.8 12. I 13.2 20.0 20.0 21.0 I 1.0
Feed temp. (C) 5.4 -6.0 5.8 5.7 -5.6 5.9 5.6 5.6 ~ -~ -5.6
pH feed
Table 2. Operational data for dates of pathogen sampling
19.9 -. 19.2 30.6 24.7 37.6 18.9 20.2 19.7 23.0 30.6 30.6 24.3
HRT (days)
.
0.48 --t. . 0.65 0.72 0.52 0.45 0.48 0.48 0.45 0.34 0.28 0.28 0.45 .
. 6.8 6.9 6.9 7.2 7.0 7. I 6.9 7. I 7. I 7. I 6.9
6.4 --
Mesophitic anaerobic digester Gas production [ Vol.~as ~ pH ~ ~ V reactor o l . reactor
35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0
35.0 -
Reactor temp. (C)
~-
~.
~--....: ~. ,~
2' ~.
o
"n
1054
RANDOLPH M. KABRICK and V~'[LLIA~,I J JE~,VELL
THICKENER
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REACTOR VI[S~EL EFFLUENT PUMP
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EFFLUENT TANK
Fig. I. Binghamton full scale thermophilic digestion facility. The thermophilic aerobic (experimental) digestion systern was designed to enable measurement of mass balances for flow and energy by providing large completely mixed and insulated feed and effluent tanks, each one capable of storing a volume approximately equal to one hydraulic retention period. The reactor was a cylindrical 3.7 m d i a tank with a depth of 4.3 m. A schematic diagram of the experimental test facility ts given in Fig. 1. The full scale thermophilic aerobic digestion system was operated under conditions which would result in significant biodegradation. but would reflect the advantages of high temperature stabilization. All conditions tested were at relatively high loading rates [ > 2.6 kg VS m - ~ day- t ( > 1621bs 10 -~ ft -3 d a y - t ) ] with the majority of operation at less than a 5-day hydraulic retention time. Several conditions were maintained constant for periods up to 60 days in order to provide time to evaluate practical operation and maintenance problems, as well as to measure the irapact of sludge composition variations on the process, Pathogen isolation and detection The fate of three groups of pathogens, bacteria, viruses and parasites in the full scale thermophilic aerobic digester and full scale mesophilic anaerobic digesters was invest]gated during this study. Laboratories were contracted to perform the analyses for the various pathogens. These angencies are listed below along with the kind(s) of organism(s) they were to identify and/or quantify. Contracted agency I. U.S. Environmental Protection Agency Environemntal Monitoring and Support Laboratory. Cincinnati. OH 2. Dr. M. Dale Little School of Public Health and Tropical Medicine, Tulane Universffy, New Orleans, LA
Pathogenic organism bacteria, viruses
parasites,
Pathogen .sample collection and shipment were always conducted on a Monday to ensure that the contract laboratories were able to analyze the samples, especially the bacteria samples, the same week of collection. Typically, sludge samples, approximate volume of 10 1. (2.6 gal), were collected from the three sources: raw sludge from the thickener pumps, aerobic sludge from the experimental thermophilic reactor, and anaerobic sludge from the existing STP digester (specifically, samples were obtained from the draw-offvalveused to fill tanker-spreaders used in land
application of the sludge from the anaerobic digester). Samples from the aerobic digester (samples were taken from the bottom drain valve and/or taken from the top of the reactor through the sample ports) were collected under batch-mode conditions, i.e. the feed pump was disconnected for 12-24 h prior to sample collection to mimic a system that was being operated to ensure optimum pathogen kills, i.e. to ensure no hydraulic short-circuiting. After the collection of the gross samples. 250ml (0.066gat) subsamples were extracted and placed in sterllized (autoclaved at 151C and t5 p.s.i, for 15 min) nalgene bottles and sealed. Typically, each of three sets of three subsamples, consisting of one set for viral analysis, one set for parasite analysis, and one set for bacterial analysis. were placed in insulated shipping containers (Trans, Temp. System 509) with cold packs Inote that the virus samples were rrozen with dry ice at - 7 0 : C in the shipping containers) and sealed. The shipping containers were appropriately labeled and addressed, then dispatched via air freight (Airborne Freight Corp.) to the various laboratories. All of the analyses for virus in the sludge samples were performed by the Environmental Monitoring and Support Laboratory of the U.S. EPA. Methods similar to {hose developed by Berg (1972) were employed: however, the exact methodology is still under development and refinement. and has not been published to date (Safferman & Berman, 1979I. The analyses for parasites were performed by Tulane University, School of Public Health and Tropical Medicine. employing techniques developed for a separate study under EPA contract ILittle et al., 1979). This technique utilized a modification of the zinc sulfate flotation method with viability of the parasite eggs determined by morphological observations by the Tulane researchers. The U.S. EPA Environmental Monitoring and Support Laboratory performed analyses for fecal coliform, total coliform, and fecal streptococci in accordance with Standard Methods IAPHA. 1975) and Microbiological Methods for Monitoring the Encironment tU.S. EPA. 19791. Analysis was also made for enteric pathogens, specifically Salmonella sp.. by use of the modified Kenner-Clark procedure for enumerating Salmonella sp. (U.S. EPA. 1974). This procedure was also used to enumerate Pseudomonas aerug~nosa. an opportunistic pathogen. RESULTS Fifteen sets of p a t h o g e n s a m p l e s were collected and sent to two l a b o r a t o r i e s for the various p a t h o g e n
Fate of pathogens in thermophilic aerobic sludge digestio n
1055
Table 3. Summary of the fate of fecal coliforms and fecal streptococci during mesophilic anaerobic digestion and thermophilic aerobic digestion of primary and waste-activated sludge mixtures
Sludge type
Counts of organisms per 100 ml wet sludge Fecal coliforms Fecal streptococci Range Mean Range
Mean
Feed sludge Anaerobic sludge Aerobic sludge
3.7 x l0 r 8.4 x l0 s 1.8 x 10`*
1.1-9.6 x l0 T 1.1 x 10"*-2.0 x 1 0 6 1.0 x 105-7.0 x 10`*
analyses. The conditions of operation of the digesters on the given pathogen sample dates are given in Table 2. Samples were collected under a wide range of operating conditions for the thermophilic aerobic digester with all reactor samples at or above 40-'C and pH of 7.0. Loading rates for the thermophilic digester ranged from 2.6 to 13 kg TVS m - s day- t (162-809 lbs 10-3 ft-s day-1), with treatment efflciencies varying between 20 and 42?/0 TVS destruction, respectively. Sample Nos 6, 11, 12 and 13 from the thermophilic aerobic digester were collected under marginally operational conditions. That is, the ternperature was lower than steady state operations, or the reactor was DO limited. However, as will be shown later, this did not significantly affect the pathogen inactivation ability of the system, The mesophilic anaerobic digester was operated under fairly constant conditions with reactor ternperature stable at around 35"C and reactor pH varying between 6.4 and 7.1. Pathogenic bacteria A summary of the results of the analyses for fecal coliforms and fecal streptococci is shown in Table 3. Historically. fecal coliforms and fecal streptococci
2.7 x 10T 9.3 x l0 s 8.2 x 10`*
3.3 × 105-5.0 x l0 T 1.1 x 10'*-2.2 x 106 1.0 x 105-3.0 x 106
have been used as indicator organisms for water quality. However, in this study the fate of these organisms was of secondary interest with the primary focus on the fate of Salmonella sp. and Pseudomonas aeruginosa. For all dates of analysis, the number of fecal coliforms and fecal streptococci were reduced at least an order of magnitude more than the levels in the raw sludge for both the anaerobic and aerobic digesters. The thermophilic aerobic digester demonstrated even larger reductions, one to three orders of magnitude, of these organisms" destructions over the anaerobic digester. The number of Salmonella sp. found in all samples analyzed is graphically shown in Fig. 2. On all of the sample dates, with the exception of 8/15/77, the aerobic digester effluent had far greater reductions in Salmonella sp. than the anaerobic digester effluent. The results of the analyses for pseudomonads are graphically depicted in Fig. 3. in most cases the thermophilic aerobic digester exhibited larger reductions in pseudomonads than the conventional mesophilic anaerobic digester.
Viruses--total plaque-forming units A histogram representing total
plaque-forming
?.0
w ¢o
I~5.0 E
0 0
4.0
3.0
_e 2 . 0
I
.
O
II/ISs~
~
Isliln7 tsliln'r ~wlwTII Islilsve OATtS OF SAU~.[ COU.[CTION
./13/7e
Fig. 2. Salmo,ella sp. as found in raw. anaerobic, and aerobic sludges (~<3 organisms per lOOml considered below limits of detection).
1056
Ra?,,E~)LPH M. K , , s r i c g and %ILLIAM J, JEWELL _
7.0 ×
o s.0
'
I
o
8/19177
i '~
Q/'~9177 S ~ 4 / T 7 DATES OF
5/Z 7/78
G ~
llJq~V T 8
COLLECTION
Fig. 3. Results of analyses for P.~eudomonas aeruginosa m raw. anaerobic, and aerobic sludges.
units ( P F U ) in all samples for all dates of collection is shown in Fig. 4. In all cases, the aerobic digester exhibited higher levels of viral reactivation than did the anaerobic digester with undetectable levels of viruses in all but one sample of the aerobic unit effluent. The anaerobic digester exhibited levels of virus inactivation equal to or less than 98.6°0. No effort was made to distinguish between the various kinds of enteroviruses or other viruses. Nor was any effort made to distinguish the distribution of the viruses between the sludge solids and the liquid,
Parasites
A summary of the parasite analyses as performed by Tulane University for all dates of collection is given in Table 4. In all samples, with the exception of 5/8/78. the aerobic digester exhibited higher reduction of total viable ova over the anaerobic digester. It should be noted that the distinction between viable and nonviable ova was made solely rrom morphological observations, e.g. disrupted membranes, without subseq,,ent culturing of the suspect ova for confirmation of the morphological diagnoses.
~7.0 Q .d IQ.O
5.0
~
4.0
I
~3.0 G.
-*,.o
0
.....
I. L,I! i
~
• OATtS
~ Or
SAMPLE
~
i s,~ e
COLLECTION
Fig. 4. Results of virus analyses (total PFU per 100 ml wet sludge) On raw. anaerobically (mesophilic)
and aerobically (thermophilic} digested sludge.
Raw Aerobic Anaerobic
Raw Aerobic* Anaerobic'l"
Raw Aerobic Anaerobic
Raw~ Aerobic Anaerobic
Raw Aerobic Anaerobic
Raw Aerobic Anaerobic
Raw Aerobic Anaerobic
4/04/78
4/24/78
5/08/78
5/22/78
6/26/78
8/07/78
8/14/78
3 2 0
0 0 0
0 0 0
2 0 3
0 1 I
4 0 .
I 0 3
V
*Only 80 ml sludge analyzed. 'tContainer broken in transit. :[:Only 90 ml sludge analyzed. V = Viable. NV = Non-viable.
Sludge type
Date of couection
.
.
0 3 2
0 0 0
0 4 0
0 3 0
1 2 I
2 2
0 4 0
Am'clri.~ NV
.
I 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0
0 0 2
.
.
0 0 0
0 4 0
0 0 0
0 I 0
0 1 0
I 0
0 I 0
T. trichiura v NV
.
2 0 2
2 0 2
2 I 3
3 0 I
I 1 I
5 0 .
I 0 5
.
0 4 0
0 4 0
0 0 0
0 0 0
0 0 I
1 1
0 2 0
.
.
8 0 2
3 0 5
3 0 2
10 I 5
0 2 1
5 0
3 1 8
.
.
0 3 4
I I 0
1 I 2
I I 1
7 8 3
2 6
2 8 2
.
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0
0 0 0
Parasite counts per 100 ml of sludge H. 7: rulpis Toxocara dimim~ta V NV V NV V NV
0 0 0
0 0 0
1 0 0
I 0 0
0 0 0
0 0 0
0 0 0
0 0 0
Toxascaris leonia V NV
I 0 0
0 0 0
0 0 0
0 0 0
0 0 1
0 1 0
0 0 0
0 1 0
Capillaria sp. V NV
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 Few 0
Few 0 0
Few 0 0
21 55 35
20 50 35
20 40 35
13 46 35
II 42 35
9. I 55 35
50 55 35
Temp. of l:.ntameba coci sample when (like cysts) collected V NV (' C)
Table 4. Results of parasitologic examinations of all samples with primary and waste-activated sludge combinations. All analyses conducted by Tulane University
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o
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RANDOLPH M. KABRICK and V~"ILLI.-~'el J. JEWELL
105,q
DISCUSSIOX
complete inactivation, i.e. beiov, limits of dete,~tion, of viruses at temperatures of greater than or equal to The fate of three groups of pathogenic organisms in 40:C and pH of greater than or equal to 7.0 was the thermophitic aerobic digestion process and in the expected based on information in the literature {Ward mesophilic anaerobic digestion process (both were full & Ashley, 1976, 1978: Nagel et al.. 1977: Berg & scale systems) was studied utilizing only the back- Berman, 1980}. This synergistic action of temperature ground levels of these.organisms in the raw sludge, and pH worked effectively in reducing viruses in the It was realized that fluctuations in the background anaerobic digester, also. Although viruses were not levels of pathogens could have been due to nonrepre- reduced below detectable limits in the anaerobic sentative samples or inadequacies in screening high digester effluent, they were significantly reduced from solids sludge samples for pathogens, the numbers in the raw sludge with destruction effiThe performance of the autoheated aerobic thermo- ciencies as high as 98.6°o. philic digester in the inactivation of pathogenic bacThe low number of parasites found in the raw teria, viruses and parasites was examplary of the effect sludge was a function of the climate and population of a high temperature treatment process on patho- of Binghamton. NY. Studies have shown high gens, On the other hand. the conventional mesophilic numbers of various parasites present in raw sludges, anaerobic digester performance, with regard to patho- e.g. greater than 50,000 Ascaris eggs per kg dry sludge gen inactivation, was typical of performance data (Leftwich et al., 1979). with organism concentration reported in the literature, dependent upon climate as well as on the socioeconThe reduction of Salmonella sp. from feed concen- omic structure of the community (Hays, 1977: trations as high as 2200 organisms per 100ml wet Leftwich et al., 19791. When the data from Tulane sludge to below the limits of detection in all of the University's parasite analyses were reviewed as total aerobic thermophilic samples was a function of reac- viable and nonviable parasitic ova, the aerobic thertor temperature as well as the chemical nature (e.g. mophilic digester was shown to be superior to the pHI of the sludge environment. In all but one sample, anaerobic mesophilic digester in the reduction of the reactor temperatures were greater than or equal viable parasitic ova (Table 4). The high reactor ternto 45 C. This temperature, combined with an ex- peratures in the aerobic digester were responsible for posure time of approx. 24 h, was shown to effectively the observed decrease in viable ova over the anaeroreduce Salmonella sp. to below detectable limits bic unit. Since a small number of viable ova were (Drnevich & Smith, 1975). The reactor temperature isolated from the aerobic digester on 5 sample dates, for the other sample date (26 June, 1978) was 40:C. it must be concluded from the {limited) available data, Strauch (1970) showed that an exposure time of 24h the number of parasitic ova are reduced by the at a temperature of 40:C and pH of 7.8 was sufficient aerobic thermophilic digestion process: however, to reduce Salmonella d,blin below detectable limits in complete inactivation of parasitic ova and cysts aerated liquid swine manure. Strauch (1970) also would require temperatures of greater than or equal reported that inactivation of S. enteritidis in swine to 6 0 C with corresponding exposure times of greater manure required 40h of exposure time at 42:C and than or equal to one hour. This could be acpH 8.0. Therefore, it can be concluded that inactiva- compiished in a multi-stage digestion system in conlion of Salmonella sp. in aerating sewage sludge junction with heat exchangers for boosting the reacrequires temperatures above 40:C with the pH of the tor(s) temperature to around 70C. slurry and the species of Salmonella playing important Several practical concerns should be noted if the roles, thermophilic aerobic process is applied for disease Reductions of Salmonella sp. in the anaerobic digesorganism destruction. In all continuous flow and ters operated at 35-C were comparable to those mixed processes, a certain amount of the influent reported in the literature (Bertucci et al., 1977). rangliquid passes rapidly through the system, i.e. shorting from 44 to 99°g. The inability of the anaerobic circuiting occurs. This can be avoided by the use of digesters to completely inactivate Salmonella sp. was several series-fed reactors, or by using sequencing probably a function of the low operating temperature batch units. During start-up and shut-down, the autoof 35:C. heated temperatures may not be high enough to The fates of the other indicator organisms, Pseudoachieve pasteurization. Instead. under non-optimum monas aeruginosa, fecal coliforms and fecal streptoconditions the presence of oxygen and higher terncocci, followed the same trends as Salmonella sp. in peratures may promote the viability of the organisms. both the anaerobic and aerobic digesters. The larger Proper design of feedback should minimize this percentages of organism reduction in the thermophilic potential disadvantage. Finally, the aeration energy aerobic digester was most likely due to the higher (costing approx. $10 per dry ton of sludge) needs to be temperatures of operation, evaluated in relation to the risks presented by the Virus inactivation, as measured by total PFU, for specific sludge handling and disposal operations. the thermophilic aerobic digester was complete on all In summary, it can be stated that the aerobic therbut one occasion. On that sample date. 14 August mophilic digester exhibited superior performance over 1978, the digester was marginally operational. The a mesophilic anaerobic digester with respect to the
Fate of pathogens in thermophilic aerobic sludge digestion inactivation of pathogenic bacteria, visuses, and parasites. The thermophilic aerobic digester yielded cornplete inactivation of Salmonella sp. and total plaqueforming units, i.e. below the limits of detection, on all but one occasion, thereby demonstrating the system's ability to control these pathogens. Parasite numbers were reduced by the aerobic thermophilic system, but not completely. The inability of the system to deliver parasite-free sludge may be indicative of the need for a multi-stage system with heat exchangers to prevent possible short-circuiting {hydraulic) and increase reactor temperatures for control of the environmentally resistant parasites, e.g. Ascaris sp.
Acknowledgements--Partial financial support was provided by the U.S. Environmental Protection Agency (U.S. EPA) under Research Grant R 804636-01, J. A. Spada served as Research Technician and Draftsman. Dr Dale M. Little, Tulane University, performed parasite analyses. A. Venosa and H. Clark, U.S. EPA, performed bacterial analyses, D. Berman, U.S. EPA, was responsible for the viral analyses. J. P. Greene served as Service Technician on the full scale experimental facility. DeLaval Separator Company provided the centri-rator aerator, and LFE Corp. provided the Midland-Frings aerator. Mr B.V. Salotto was the U.S. EPA Project Manager.
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1059
Hays B. D. (1977) Potential for parasitic disease transmission with land application of sewage plant efltuents and sludges. Water Res. 11, 583. Jewell W. J. & Kabrick R. M. (1978) Autoheated aerobic thermophilic digestion with aeration. J. War. Pollur. Control Fed. 52, 113, part 1, 513. Jewell W. J., Kabrick R. M. & Spada J. A. (1979) Autoheated aerobic thermophilic digestion with air aeration. U.S. Environmental Protection Agency Report. Kabter P. (1959) Removal of pathogenic microorganisms by sewage treatment processes. Sewage ind. Wastes 31, 1373. Kelly S. & Sanderson W. W. (1959) The effect of sewage treatment on viruses. Sewage ind. Wastes 31,683. Kenner B. A. & Clark H. P. (1974) Detection and enumeration of Salmonella and Pseudomonas aeruginosa. J. Wat. Pollut Control Fed. 46, 2163. Koenig A. {1974) Heat generation during aerobic oxidation of concentrated organic wastes. M.S. Thesis. Cornell University, Ithaca, NY. Leftwich D. B., Reimers R. S. & England A. J. Jr (1979) Investigation of parasites in southern domestic waste sludges--a possible industrial waste point source. Presented at the 34th Purdue Industrial Waste Conference. Purdue University. West Lafayette, IN. LittleM. D. etal.(1979) Survey of wastes sludges for parasitic contamination in the U.S.A. and investigation of possible waste treatment alternatives to inhibit contamination. U.S. EPA study under development. School of Public Health and Tropical Medicine, Tulane University, New Orleans, LA. Matsch L. C. & Drnevich R. F. (1977) Autothermal aerobic digestion. J, War. Pollut. Control Fed. 49, 2. McKinney R. E., Langely H. E. & Tomlinson H. D. (1958) Survival of Salmonella typhosa during anaerobic digestion. Sewage ind. Wastes 30, 1469. Nagel R., Straub O. C. & Strauch D. (1977) The recirculating aeration method (Fuchs System) for the treatment of liquid animal and communal sewage. Department of Animal Hygiene, University of Hohenheim and Federal Research Institutes for Research on Animal Virus Diseases. Popel F. & Ohnmacht Ch. (1972) Thermophilic bacterial oxidation of highly concentrated substrates. Water Res. 6, 107. Rudolfs W., Frank L. L. & Ragotzkie R. A. (t950) Literature review on the occurrence and survival of enteric, pathogenic and relative organisms in soil, water, sewage, sludges and vegetation. Sewage ind. Wastes 22, 1261. Safferman R. & Berman D. (1979) Personal communication. U.S. EPA, Environmental Monitoring and Support Laboratory, Virology Section. Smith J. E, (1976) Mammalian viruses in raw sewage and sludge digests, Onandaga County, NY. Department of Biology, Syracuse University. Smith J. E. Jr, Young K. W. & Dean R. B. (1975) Biologieal oxidation and disinfection of sludge. Water Res. 9, 17. Strauch D., Miiller W. & Best E. (1970) Partial results of the hygienic-bacteriological investigation of the aerationagitation system. Landtechn. Forschung. 18, 147. Theis J. H. & Storm D. R. (1978) Helminth ova in soil and sludge from twelve U.S. urban areas. J. War. Pollut. Control Fed. 50, 2485. U.S. EPA (1979) Microbiological Methods for Monitoring the Environment (Edited by Winter J.). Environmental monitoring and support laboratory, U.S. EPA, Cincinnati, OH. Ward R. L. & Ashley C. S. (1976) Inactivation of poliovirus in digested sludge. J. appl. Envir. Microbiol. 31, 921. Ward R. L., Ashley C. S. & Moseley R. H. (1976) Heat inactivation of poliovirus in wastewater sludge. J. appl. Envir. Microbiol. 32, 339.
1060
RANDOLPH M. KABRICK and WILLIAM J. JEWELL
Ward R. L. & Ashley C. S. (1977) Inactivation of enteric viruses in wastewater sludge through dewatering by evaporation. J. appl. Envir. Microbiol. 34, 564. Ward R. L. & Ashley C. S. (1977) Discovery of an agent in wastewater sludge that reduces the heat required to inactivate reovirus. J. appl. Envir. Microbiol. 34, 681. Ward R. L. & Ashley C. S. (1977) Identification of the virucidal agent in wastewater sludge, J. appl. Envir. Microbiol. 34, 860.
Ward R. L. & Ashley C. S. (1978) Methods to inactivate enteric viruses in wastewater sludge. Sandia Laboratories. Albuquerque. NM. Sand 77-1498. Wellings F. M. et al. (I976} Demonstration of solids-associated virus in wastewater sludge. J. appt. Ent:ir~ Microbiol. 31,354. Wright P. J. (1975) Thermophilic aerobic digestion of a concentrated organic slurry; M.S. Thesis. Cornell University, Ithaca, NY.