Expanded
Summary
Assessment of biomass in drinking water biofilters
by adenosine triphosphate
L I ZANNE PHARAND, M IC H E L E I. VA N D YKE , W I L L I AM B. AN D ER S O N , AN D P ET ER M. H U C K
http://dx.doi.org/10.5942/jawwa.2014.106.0107
Biofilters have gained in popularity for drinking water
treatment for reasons that include reducing disinfectant
demand, disinfection by-product formation, and
regrowth in distribution systems. Adenosine tri­
phosphate (ATP) detection is being used more frequently
as an easy and rapid method to quantify viable biomass
in biofilters; however, there is little information on the
relationship of ATP levels to biofiltration parameters
and performance. In this study, a comprehensive
comparison of published ATP data found that
concentrations at the top of active, ac­­climated biofilters
typically were in the range of 102 to 103 ng ATP/cm3
media. The effect of various biofilter parameters (source
water characteristics and quality, pretreatment, hy­­
draulic loading rate, temperature, and sampling depth)
on ATP levels is discussed and evaluated using published
ATP data. The authors also assess the relationship
between ATP and biofilter performance in terms of
carbon removal and identify a need for further research
in this area.
Biological filtration (biofiltration) is gaining wider
acceptance for drinking water treatment, as evidenced by
the fact that in 2013 AWWA hosted its first Biological
Treatment Symposium. To better understand the ability
of biofilters to degrade biodegradable organic matter
(BOM), many studies have included methods to measure
the quantity and activity of the biomass present within
biofilters. Numerous methods have been developed or
adapted for this purpose, including those that determine
the concentration of ATP present in the filters.
ATP is the primary energy carrier in all living cells and
is used for cell synthesis and maintenance. It is rapidly
used by cells and has been used as an indicator of viable
biomass in drinking water treatment biofilters in published studies. Because little information is available to
provide guidance on the levels of ATP that would normally be expected in active biofilters, this study included
a survey and comparison of published data available on
ATP in biofilters used for drinking water treatment. In
addition, published studies were evaluated to determine
whether biofilter design and operating parameters can
affect ATP concentration and if there is a relationship
between biofilter performance and ATP concentration.
developed to provide the reagents and instructions for
ATP determination. These methods often consist of an
initial physical, chemical, or enzymatic cell lysis step that
releases ATP from cells. A luciferase–luciferin complex is
then added, which reacts with the ATP to emit light, and
the intensity is quantified using a luminometer. The ATP
method typically is used to measure the quantity of viable
biomass attached to the surface of biofilter media because
it is this attached biomass that most contributes to the
measurable removal of BOM in biofilters.
METHODS TO MEASURE BIOMASS QUANTITY
AND ACTIVITY IN BIOFILTERS
In recent years, the use of ATP analysis to quantify
viable biomass in drinking water treatment biofilters has
increased, in part because of the ease of analysis, limited
laboratory equipment needed, and the fact that it is a
culture-free method. ATP quantification is most often
performed using a luminescence-based method for which
many commercial products on the market have been
FACTORS AFFECTING ATP IN BIOFILTERS
In the current research, the authors surveyed 16 published studies that used ATP to measure the biomass in
drinking water biofilters, including both pilot- and fullscale biofilters. Only ATP data from acclimated biofilters
sampled from the top 15 cm of the filter bed were compared. (This depth range was defined here as representing
the surface of the biofilter.) Of the studies reviewed, the
typical ATP concentration was approximately 600 ng
ATP/cm3 media; although substantial variations were
observed, concentrations typically were in the range of
102 to 103 ng ATP/cm3 media. These benchmark ATP
concentrations are beneficial, particularly for water treatment plants that do not have historical data. For biofilters
with ATP concentrations less than this benchmark, further investigation is recommended.
The effect of biofilter design and operating parameters
on ATP levels was assessed. Factors included temperature,
water source, pretreatment, hydraulic loading and contact
time, media type, and biofilter sampling. Of the studies
evaluated, the ATP level at the surface of biofilters
remained essentially constant at varying temperatures.
P H A R A ND ET A L | 106: 10 • JO U R NA L AWWA | O C TO B ER 2014
2014 © American Water Works Association
63
The microbial and nutrient content of water used to feed
biofilters can be expected to have an effect on ATP concentration. However, there appeared to be no difference
in ATP concentration in media at the surface of biofilters
fed with river or lake water. It may be that the BOM was
similar in biofilters fed from rivers and lakes, either at the
source or following pretreatment steps.
Certain biofilter pretreatment processes, such as ozonation, can increase the BOM in water, which may lead
to increased bacterial regrowth in distribution systems
and thus affect chlorine demand. For this reason, utilities often use biofiltration after ozonation to reduce
BOM concentrations. A comparison of ATP levels in
published studies demonstrated that the addition of
ozone before granular activated carbon (GAC) biofilters,
operated at various temperatures, led to ATP concentrations two to three times higher than biofilters operated
without ozone pretreatment. Further analysis showed
an increasing trend in ATP concentration with increasing
influent dissolved organic carbon (DOC) for biofilters
without ozone pretreatment, although only limited data
were available. No relationship was found between
ATP concentration at biofilter surface versus
DOC removal through biofilters
FIGURE 1
CONCLUSION
Pretreatment without ozone
Pretreatment with ozone
ATP can be used to measure the amount of viable biomass within drinking water treatment biofilters, and newer
ATP methods are simple and less time-consuming than
other biomass quantification methods. In a review of published studies available to date, only increased nutrient
concentrations in the feedwater were found to affect ATP
concentrations at the surface of acclimated biofilters. However, ATP levels were not necessarily related to biofilter
performance in terms of DOC removal. Because only
limited results comparing organic carbon removal with
ATP are available, it is recommended that additional
research be performed and that future studies incorporate
methods that specifically measure BOM as opposed to
total carbon. The results will ultimately help determine
whether ATP analyses can provide a good measure of
viable biomass present within biofilters and if that amount
can be related to overall biofilter performance.
100,000
‡
ATP Concentration—ng ATP/cm3
§ §
§
10,000
†
**
1,000
*
†
†
*† *
100
10
1
0
20
40
DOC Removal—%
60
80
ATP—adenosine triphosphate, DOC—dissolved organic carbon,
TOC—total organic carbon
Values shown are mean values except where indicated.
*When mean ATP concentration or DOC removal data were not
available, the median of the range was used.
†TOC removal was used instead of DOC removal.
‡Data include both pretreatment with and without ozone because
data separated based on pretreatment were not available.
The inclusion of this data point does not appear to affect the
relationship observed within the figure.
§Naidu et al, 2013
64
influent DOC and ATP concentration in biofilters with
ozone pretreatment. This suggests that DOC composition, particularly the biodegradable fraction, is important for microbial growth and activity, as would be
expected. In some studies, a higher hydraulic loading
rate was found to increase the ATP concentration at the
surface of acclimated biofilters. However, the empty bed
contact time and anthracite versus GAC media typically
did not affect the ATP concentration at the surface of
acclimated biofilters. Most studies found that the concentration of ATP decreased through biofilter bed depth,
but more research is needed to gain a better understanding of this relationship.
Published studies were also used to investigate the
relationship between ATP and biofilter performance in
terms of DOC removal. In this research, DOC removal
was used as the main biofilter performance indicator
despite its limitations; the decision to use DOC was made
because of its common use in water treatment studies as
well as its ability to describe overall filter performance
with respect to organics removal. The comparative evaluation demonstrated that there was essentially no relationship between DOC removal and ATP concentration
(Figure 1). However, further studies should be conducted
that incorporate ATP quantification and methods that
specifically measure BOM as opposed to total carbon.
REFERENCE
Naidu, G.; Jeong, S.; Vigneswaran, S.; & Rice, S.A., 2013. Microbial
Activity in Biofilter Used as a Pretreatment for Seawater
Desalination. Desalination, 309:15:254. http://dx.doi.org/10.1016/j.
desal.2012.10.016.
Corresponding author: Michele I. Van Dyke is a
research associate in the Department of Civil and
Environmental Engineering, University of Waterloo,
200 University Ave. West, Waterloo, ON N2L 3G1;
[email protected].
OCT OBE R 2 0 1 4 | J O U R N A L AW WA • 1 0 6 :1 0 | P H A R A N D ET A L
2014 © American Water Works Association