Abstract

A time–temperature plot presenting the inactivation of Ascaris eggs is expanded with additional literature data. The information is of value to designers and operators of sanitation equipment who have Ascaris inactivation as an objective.

INTRODUCTION

Lack of improved water, sanitation and hygiene (WASH) is associated with the infectious diseases that burden approximately one-third of the world's population (Bardosh 2015). Access to WASH results in diarrhoeal disease prevalence, which manifests as a symptom of bacterial, viral and helminth infections – for the latter, the most common being Ascaris sp. (Fewtrell et al. 2005; Brownell & Nelson 2006).

Temperature is the most effective treatment option for sanitising human excreta and waste streams containing faeces (faecal sludge). Previous studies indicate that above 60°C Ascaris eggs are inactivated within a few minutes, but may survive more than a year at 40°C (Brownell & Nelson 2006). Viscous heating (VH) technology achieves high temperature quickly when a thick fluid passes through a narrow gap between a double cylinder with a stationary outer shell and a rotating inner cylinder (Belcher et al. 2015). The resulting shear field generates heat by molecular friction and inactivates Ascaris sp. eggs in faecal sludge (Podichetty et al. 2014). A key design variable of VH is the faecal sludge residence time at a specific operating temperature. Defining an effluent target temperature is an outcome of this communication. Previous studies, using both simulated and screened (sieved to remove debris) VIP (ventilated improved pit) latrine sludge, indicate that elevated temperatures (up to 95°C at atmospheric pressure) are achieved at low VH residence time (seconds) while deactivating helminth eggs (Belcher et al. 2015). Ensuring Ascaris is deactivated within this brief time is essential, and recent work (Naidoo 2017) defines high-temperature, low-exposure-time inactivation of Ascaris.

SUMMARY OF THE EXISTING STUDY

Details of the experimental procedure and presentation of results can be found elsewhere (Naidoo 2017). Methodology is summarized briefly here. Ascaris suum eggs were procured and exposed to 60°C, 65°C, 70°C, 75°C and 80°C for 5, 10, 15, 30 and 45 seconds, and 1, 2, 3 and 4 minutes, respective to each temperature. Eggs were pipetted into plastic test tubes containing water, which had been preheated to the test temperature. Two samples (triplicated) were treated at each temperature/time combination and processed by either i) washing directly onto a 20 μm sieve (placed in a bowl containing tap water to allow for rapid cooling to room temperature), or ii) transferred into a beaker containing iced water (to allow for rapid cooling) and then washed onto the sieve. Eggs were immediately analysed via light microscopy, washed back into the test tube, and incubated for 28 days to determine whether further development occurred.

At 4-second exposure time, treatment at 80°C was sufficient, with <11% viable eggs recovered pre-incubation and <1% viable eggs recovered post-incubation. Eggs that appeared undeveloped but globular (indicating some form of morphological damage) did not develop further during incubation, indicating successful inactivation. Lower temperatures required longer exposure times (for example, treatment at 60°C required 3 or more minutes for visible damage), and from a visual examination of egg morphology the die-off mechanism appeared different.

COMPARISON WITH LITERATURE DATA

The time versus temperature plot of Thomas et al. (2015) presents comparative Ascaris inactivation data. An updated literature review found additional data for the Thomas et al. figure, as discussed below. The revised Figure 1 also includes data from Naidoo (2017) that extends the time–temperature range. References that cite inactivation as 99 + % are included. Experimental methods vary among the cited papers; a detailed comparative review is not presented.

Figure 1

Comparison of time versus temperature inactivation data for Ascaris sp.

Figure 1

Comparison of time versus temperature inactivation data for Ascaris sp.

Temperature is the focus of this data analysis, whether or not VH is used to generate the heat. Cited studies may include factors such as moisture content, alkaline concentration, pH and anaerobic operating conditions, but these are considered secondary influences and are not differentiated within the plot. The line in Figure 1 is that of Vinnerås et al. (2003) based on the data of Feachem et al. (1983). Their correlation begins at 45°C and does not extrapolate lower.

Data included are briefly discussed. Maya et al. (2012) concluded that times for both A. lumbricoides and A. suum showed negligible differences; as a result, Figure 1 includes both. Low temperature data of Kim et al. (2012), Berggren et al. (2004), Trimmer et al. (2016), Katakam et al. (2014) and Seamster (1950) are included in the plot. The latter considers the effects of chemical agents, and relative humidity (RH). Other researchers considered variables in addition to temperature: Hawksworth et al. (2010) included RH. Pecson et al. (2007) included pH. Capizzi-Banas et al. (2004) looked at lime and quick lime concentrations. Pecson & Nelson (2003) included pH and ammonia concentrations. Brannen et al. (1975) presented higher temperature data that included compost, water and faecal sludge with heat and/or radiation.

In examining the plot, the trend appears consistent with the Vinnerås et al. (2003) equation. A factor contributing to variability is that time scales may be overstated. For example, at high temperatures the Vinnerås et al. equation predicts inactivation of 0.1 sec at 80°C, while controlling exposure time in the laboratory is challenging at 1.0 sec. Below 45°C a new relationship may be appropriate.

Several studies are informative for practitioners but not presented in Figure 1 because complete inactivation was not reported. Vu-Van et al. (2016) monitored A. lumbricoides egg die-off over 181 days with average temperatures from 19 to 32°C and variables such as lime, rice husks and aeration. Berendes et al. (2015) studied inactivation at locations within pits with wide temperature and moisture content ranges. Fidjeland et al. (2015) developed an inactivation expression as a function of temperature and ammonia concentration up to 33°C. Yaya-Beas et al. (2016) presented inactivation percentages for an upflow anaerobic sludge blanket reactor operating at low temperatures. Manser et al. (2015) discussed inactivation near 35°C during anaerobic digestion and presented an inactivation model subsequently (Manser et al. 2016). Some data were omitted because the authors mentioned uncertainty or variability within the data (Brandon 1978; Steer & Windt 1978; Aitken et al. 2005; Popat et al. 2010).

CONCLUSION

Based on data from the current study, 4–5 seconds of exposure at 80°C appears sufficient to inactivate Ascaris eggs. At 75°C and 70°C treatment may also be effective, but exposure time should be increased to achieve the same level of inactivation.

REFERENCES

Aitken
M. D.
,
Sobsey
M. D.
,
Blauth
K. E.
,
Shehee
M.
,
Crunk
P. L.
&
Walters
G. W.
2005
Inactivation of Ascaris suum and poliovirus in biosolids under thermophilic anaerobic digestion conditions
.
Environmental Science & Technology
39
(
15
),
5804
5809
.
Belcher
D.
,
Foutch
G. L.
,
Smay
J.
,
Archer
C.
&
Buckley
C. A.
2015
Viscous heating effect on deactivation of helminth eggs in ventilated improved pit sludge
.
Water, Science & Technology
72
(
7
),
1119
1126
.
Berendes
D.
,
Levy
K.
,
Knee
J.
,
Handzel
T.
&
Hill
V. R.
2015
Ascaris and Escherichia coli inactivation in an ecological sanitation system in Port-au-Prince, Haiti
.
PLoS One
10
(
5
),
e0125336
.
Berggren
I.
,
Albihn
A.
&
Johansson
M.
2004
The effect of temperature on the survival of pathogenic bacteria and Ascaris suum in stored sewage sludge
.
Proc. Ramiran
53
56
.
Brandon
J. R.
1978
Parasites in Soil/Sludge Systems
.
Department of Energy, Sandia Laboratories, National Technical Information Service
,
Springfield, VA
.
Brannen
J. P.
,
Garst
D. M.
&
Langley
S.
1975
Inactivation of Ascaris lumbricoides Eggs by Heat, Radiation, and Thermoradiation. No. SAND--75-0163
.
Sandia Labs
,
Albuquerque, NM
and Livermore, CA
.
Brownell
S. A.
&
Nelson
K.
2006
Inactivation of single-celled Ascaris suum eggs by low-pressure UV radiation
.
Applied Environmental Microbiology
72
(
3
),
2178
2184
.
Capizzi-Banas
S.
,
Deloge
M.
,
Remy
M.
&
Schwartzbrod
J.
2004
Liming as an advanced treatment for sludge sanitisation: helminth eggs elimination – Ascaris eggs as model
.
Water Research
38
(
14
),
3251
3258
.
Feachem
R. G.
,
Guy
M. W.
,
Harrison
S.
,
Iwugo
K. O.
,
Marshall
T.
,
Mbere
N.
,
Muller
R.
&
Wright
A. M.
1983
Excreta disposal facilities and intestinal parasitism in urban Africa: preliminary studies in Botswana, Ghana and Zambia
.
Transactions of the Royal Society of Tropical Medicine & Hygiene
77
(
4
),
515
521
.
Fewtrell
L.
,
Kaufmann
R. B.
,
Kay
D.
,
Enanoria
W.
,
Haller
L.
&
Colford
J. M.
2005
Water, sanitation, and hygiene interventions to reduce diarrhoea in less developed countries: a systematic review and meta-analysis
.
Lancet Infectious Diseases
5
(
1
),
42
52
.
Fidjeland
J.
,
Nordin
A.
,
Pecson
B. M.
,
Nelson
K. L.
&
Vinnerås
B.
2015
Modeling the inactivation of Ascaris eggs as a function of ammonia concentration and temperature
.
Water Research
83
,
153
160
.
Gotaas
H. B.
1956
Composting. Sanitary Disposal and Reclamation of Organic Wastes
.
World Health Organization
,
Geneva
,
Switzerland
.
Hawksworth
D.
,
Archer
C.
,
Rajcoomar
K.
,
Buckley
C.
&
Stenström
T. A.
2010
The effect of temperature and relative humidity on the viability of Ascaris ova in urine diversion waste
.
Katakam
K. K.
,
Mejer
H.
,
Dalsgaard
A.
,
Kyvsgaard
N. C.
&
Thamsborg
S. M.
2014
Survival of Ascaris suum and Ascaridia galli eggs in liquid manure at different ammonia concentrations and temperatures
.
Veterinary Parasitology
204
(
3
),
249
257
.
Kim
M.-K.
,
Kyoung
H. P.
,
Hwang
Y.-S.
,
Park
K.-H.
,
Hwang
I. G.
,
Chai
J.-Y.
&
Shin
E.-H.
2012
Effect of temperature on embryonation of Ascaris suum eggs in an environmental chamber
.
Kor. J. Parasitology
50
(
3
),
239
242
.
Mahmud
Z. H.
,
Das
P. K.
,
Khanum
H.
,
Hossainey
M. R. H.
,
Islam
E.
,
Mahmud
H. A.
,
Islam
M. S.
,
Imran
K. M.
,
Dey
D.
&
Islam
M. S.
2016
Time-temperature model for bacterial and parasitic annihilation from cow dung and human faecal sludge: a forthcoming bio-fertilizer
.
Journal of Bacteriology Parasitology
7
(
284
).
doi:10.4172/2155-9597.1000284
..
Manser
N. D.
,
Wald
I.
,
Ergas
S. J.
,
Izurieta
R.
&
Mihelcic
J. R.
2015
Assessing the fate of Ascaris suum ova during mesophilic anaerobic digestion
.
Environmental Science & Technology
49
(
5
),
3128
3135
.
Manser
N. D.
,
Cunningham
J. A.
,
Ergas
S. J.
&
Mihelcic
J. R.
2016
Modeling inactivation of highly persistent pathogens in household-scale semi-continuous anaerobic digesters
.
Environmental Engineering Science
33
(
11
),
851
860
.
Maya
C.
,
Torner-Morales
F. J.
,
Lucario
E. S.
,
Hernández
E.
&
Jiménez
B.
2012
Viability of six species of larval and non-larval helminth eggs for different conditions of temperature, pH and dryness
.
Water Research
46
(
15
),
4770
4782
.
Naidoo
D.
2017
Inactivation of Ascaris Eggs by Exposure to High Temperature for the Purpose of Sanitizing Sludge by Viscous Heating
.
Masters thesis
,
School of Life Sciences, University of KwaZulu-Natal, Westville Campus
,
Durban
,
South Africa
.
Pecson
B. M.
&
Nelson
K. L.
2003
The effects of exposure time, temperature, pH, and ammonia concentration on the inactivation rate of Ascaris eggs
.
Proceedings of the Water Environment Federation
10
,
534
539
.
Pecson
B. M.
,
Barrios
J. A.
,
Jiménez
B. E.
&
Nelson
K. L.
2007
The effects of temperature, pH, and ammonia concentration on the inactivation of Ascaris eggs in sewage sludge
.
Water Research
41
(
13
),
2893
2902
.
Podichetty
J. T.
,
Islam
M. W.
,
Van
D.
,
Foutch
G. L.
&
Johannes
A. H.
2014
Viscous heating analysis of simulant feces by computational fluid dynamics and experimentation
.
Journal of Water Sanitation & Hygiene for Development
4
(
1
),
62
71
.
Popat
S. C.
,
Yates
M. V.
&
Deshusses
M. A.
2010
Kinetics of inactivation of indicator pathogens during thermophilic anaerobic digestion
.
Water Research
44
(
20
),
5965
5972
.
Seamster
A. P.
1950
Developmental studies concerning the eggs of Ascaris lumbricoides var. suum
.
The American Midland Naturalist Journal
43
(
2
),
450
470
.
Steer
A. G.
&
Windt
C. N.
1978
Composting and fate of Ascaris lumbricoides ova
.
Water SA
4
(
3
),
129
132
.
Thomas
J. E.
,
Podichetty
J. T.
,
Shi
Y.
,
Belcher
D.
,
Dunlap
R.
,
McNamara
K.
,
Reichard
M. V.
,
Smay
J.
,
Johannes
A. J.
&
Foutch
G. L.
2015
Effect of temperature and shear stress on the viability of Ascaris suum
.
Journal of Water Sanitation and Hygiene for Development
5
(
3
),
402
411
.
Trimmer
J. T.
,
Nakyanjo
N.
,
Ssekubugu
R.
,
Sklar
M.
,
Mihelcic
J. R.
&
Ergas
S. J.
2016
Estimation of Ascaris lumbricoides egg inactivation by free ammonia treatment of ash-amended UDDT vault products using stored urine in Uganda
.
Journal of Water Sanitation and Hygiene for Development
6
(
2
),
259
268
.
Vu-Van
T.
,
Pham-Duc
P.
,
Winkler
M. S.
,
Zurbrügg
C.
,
Zinsstag
J.
,
Thanh
H. L. T.
,
Bich
T. H.
&
Nguyen-Viet
H.
2016
Ascaris lumbricoides egg die-off in an experimental excreta storage system and public health implication in Vietnam
.
International Journal of Public Health
62
(
102
),
1
9
.
Wichuk
K. M.
&
McCartney
D.
2007
A review of the effectiveness of current time–temperature regulations on pathogen inactivation during composting
.
Journal of Environmental Engineering and Science
6
(
5
),
573
586
.
Yaya-Beas
R. E.
,
Cadillo-La-Torre
E. A.
,
Kujawa-Roeleveld
K.
,
van Lier
J. B.
&
Zeeman
G.
2016
Presence of helminth eggs in domestic wastewater and its removal at low temperature UASB reactors in Peruvian highlands
.
Water Research
90
,
286
293
.
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