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toxins
Article
The Efficiency of Microstrainers Filtration in the
Process of Removing Phytoplankton with
Special Consideration of Cyanobacteria
Wanda Czy˙zewska 1and Marlena Piontek 2, *
1Water and Sewage Laboratory, Water and Wastewater Treatment Plant in Zielona Góra, Poland,
Zjednoczenia 110A, 65-120 Zielona Góra, Poland; wanda.czyzewska@zwik.zgora.pl
2
Institute of Environmental Engineering, University of Zielona G
ó
ra, Licealna 9, 65-417 Zielona G
ó
ra, Poland
*Correspondence: m.piontek@iis.uz.zgora.pl; Tel.: +48-514-111-068
Received: 14 April 2019; Accepted: 17 May 2019; Published: 21 May 2019
Abstract:
The research presented in this manuscript concerns the evaluation of the effectiveness
of microstrainers, which are designed to reduce the amount of plankton in treated surface water.
The efficiency of microstrainer filtration analysis is very important for the proper course of the
water-treatment process not only in the Water-Treatment Plant (WTP) in Zielona G
ó
ra (central western
Poland) but also in other WTPs around the world. The qualitative and quantitative monitoring
of the abundance of plankton including cyanobacteria during the particle-filtration process allows
not only for the assessment of the potential cyanotoxic risk in surface water providing a source of
drinking water, but also allows the evaluation of the action and the prevention of adverse impacts of
microstrainers. Over four years of research, it was observed that the largest amount of cyanobacteria
before microstrainer filtration took place in May. The dominant species was Limnothrix redeckei.
The microstrainer removal of plankton and cyanobacteria was statistically significant. The quantity of
removed plankton increased with its increasing content in raw water. The particle-filtration process,
by reducing the amount of cyanobacteria, contributes to a decrease in intracellular microcystins.
Keywords: cyanobacteria removal; microcystins; microstrainers; particle filtration; water treatment
1. Introduction
1.1. The Significance of the Presence of Phytoplankton Including Cyanobacteria in the Process of Water Treatment
Pollution and eutrophication lead to the presence of high concentrations of organic and inorganic
compounds which enhance phytoplankton (including cyanobacteria) blooms and concomitantly
decrease water quality. The occurrence of these blooms in the source water for drinking-water
production is of critical importance to drinking-water providers. Phytoplankton can have both
a physical impact (e.g., clogging of filters) and chemical impact (e.g., production of cyanotoxins,
disinfection by-products, and taste and odor compounds) on the treatment process [1–3].
Strong growth of undesirable cyanobacteria and algae species is a serious problem in reservoirs
intended as drinking-water intakes for large urban agglomerations in Poland. This is the kind of
problem that is faced by the Warsaw water-supply company, which delivers water from the Vistula
River via the Czerniakowski Settling Pond, the dam reservoir in Przeczyce and the Zegrzy´nski and
Dobromierz Reservoir [
4
]. Toxic cyanobacterial blooms occurred in the following reservoirs: Kozłowa
G
ó
ra [
5
] Goczałkowice, Turawa, Otmuch
ó
w, and Nysa, which supply the inhabitants of Silesia with
water [
6
] in the Dobczyce Reservoir, supplying the city of Cracow with drinking water [
7
] and the
Sulejów Reservoir, which is the source of drinking water for the inhabitants of Łód´z [4].
Toxins 2019,11, 285; doi:10.3390/toxins11050285 www.mdpi.com/journal/toxins
Toxins 2019,11, 285 2 of 13
One of the sources of raw water for the Zielona G
ó
ra water-supply company is the water from
the Obrzyca River, in whose catchment area massive blooms of cyanobacteria occur [
8
]. In the area
under study species of toxic cyanobacteria were identified, including those which synthesize the most
dangerous hepatotoxin, microcystin MC-LR [
9
]. Periodic cyanobacterial blooms in the catchment area
of the Obrzyca River and at its source, Sławskie Lake, initiated research on the possibility of controlling
cyanotoxic risk [
8
]. The research has been conducted with the use of microstrainers in the technological
line for water purification at the Water-Treatment Plant (WTP) in Zielona Góra.
1.2. The Methods of Cyanobacteria and Cyanotoxin Elimination in Treated Water Including Process of Water
Treatment for the Inhabitants of Zielona Góra
The amount of phytoplankton, including cyanobacteria, can be reduced in the processes of
coagulation and flocculation as a result of aggregation of smaller particles into larger ones. However,
studies have shown that the removal rate of cells and cyanotoxins is variable, and influenced by
treatment conditions and by the phytoplankton species present in the water [
10
]. During coagulation,
certain problems may arise such as cell lysis, leading to the release of intracellular toxins [11].
Although chloamountrination and ozonation are effective in removing microcystins, powdered
activated carbon is one if the major treatment barriers for the removal of cyanotoxins in WTPs. Activated
carbons are unique and versatile adsorbents because of their extended surface area, microporous
structure, high adsorption capacity, and economic feasibility. The introduction of powdered activated
carbon during coagulation allows for the removal of cyanobacterial toxins from drinking water [12].
Ozonation in the water-treatment chain may result in algal cells lysis and increase dissolved
microcystins. Effectiveness of ozonation varies depending upon the disinfectant dose and types of
cyanotoxins [11].
Membrane filtration is a physical process that separates contaminants by size and charge depending
on the physical/chemical characteristics of the membrane. An important point when considering
filtration is the lysis of cells. Membrane filtration is a pressure-driven process which uses size
exclusion, charge repulsion, adsorption, and/or diffusion processes for removal mechanisms. Generally,
there are four processes that are considered feasible and more commonly used for membrane treatment
in drinking-water applications: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.
Two types of low-pressure membrane filtration, microfiltration, and ultrafiltration, have been shown to
be effective in the removal of intact cyanobacterial cells. These membranes removed more than 98% of
the cells but are unable to reject dissolved toxins [13].
During low-pressure membrane treatments of cyanobacterial cells, including microfiltration and
ultrafiltration, there have reportedly been releases of intracellular compounds including cyanotoxins
and compounds with an earthy/musty odor into the water, probably owing to products of cyanobacterial
cell breakage being retained on the membrane [14].
Microstrainers consist of a finely woven stainless-steel wire cloth mounted on a revolving drum
that is partially submerged in the water. Water enters through an open end of the drum and flows out
through the screen, leaving suspended solids behind. Captured solids are washed into a hopper when
they are carried up out of the water by the rotating drum. Microstrainers consist of a very fine screen
used primarily to remove algae other aquatic organisms and small debris that can clog treatment plant
filters [
15
]. Application of microstrainers as an improvement to the water purification process is used in
the WTP in Stuttgart (Constance Lake) where 12 microstrainers with a mesh width of 15
µ
m are used.
The Obrzyca River (the right tributary of the Oder River) is the surface water which is purified in
WTP Zawada and supplied as drinking water to the local population (mainly the inhabitants of Zielona
G
ó
ra). Surface water is one of the main sources of raw water used for the purposes of the municipal
water-supply system in Zielona G
ó
ra [
2
,
16
]. The percentage share of particular water sources in the
consumption water supply for the inhabitants of Zielona G
ó
ra in the years 2011–2014 is presented in
Figure 1.
Toxins 2019,11, 285 3 of 13
Toxins 2019, 11, x FOR PEER REVIEW 3 of 15
sources in the consumption water supply for the inhabitants of Zielona Góra in the years 2011–2014
is presented in Figure 1.
Figure 1. The percentage share of particular water sources in the consumption water supply for the
inhabitants of Zielona Góra in the years 2011–2014.
The quality of water taken from the Obrzyca River falls within category 3 (water requiring highly
efficient physical and chemical treatment) [17]. The poor quality of raw water supplied to WTP
Zawada and the need to treat the groundwater and surface water collectively causes numerous
problems in the process of water treatment. Surface water is characterized by pollution typical of
eutrophic waters (high color, oxidizability, periodic blooms, and increased levels of
orthophosphates). The latter are part of household and industrial sewage, but they may also come
from surface runoffs from arable land treated with artificial fertilizers containing phosphorus
compounds. Surface water is strained with grids and sieves. It is then pumped through a pipeline to
the first element of the processing system, where it is strained in three microstrainer drums (Figure
2) fitted with a 10 µm screening mesh. The diagram of the process of surface water treatment at WTP
is presented in [2].
Figure 2. Microstrainers in WTP Zawada. 1 raw water supply; 2 slide flat; 3 mesh baskets; 4
submersible pump; 5 sprinklers; 6 drainage trough; 7 drum drive; 8 clean water outflow.
This study aims to demonstrate that the microstrainers operating at WTP in Zielona Góra are a
useful tool for the water-treatment technology intended to eliminate plankton, including
39% 38.2% 38.8%
43.3%
38% 40.0% 38.7%
33.5%
23% 21.8% 22.5% 23.3%
2011 2012 2013 2014
surface water groundwater - shot siphon groundwater -water wells
Figure 1.
The percentage share of particular water sources in the consumption water supply for the
inhabitants of Zielona Góra in the years 2011–2014.
The quality of water taken from the Obrzyca River falls within category 3 (water requiring highly
efficient physical and chemical treatment) [
17
]. The poor quality of raw water supplied to WTP Zawada
and the need to treat the groundwater and surface water collectively causes numerous problems in the
process of water treatment. Surface water is characterized by pollution typical of eutrophic waters
(high color, oxidizability, periodic blooms, and increased levels of orthophosphates). The latter are
part of household and industrial sewage, but they may also come from surface runoffs from arable
land treated with artificial fertilizers containing phosphorus compounds. Surface water is strained
with grids and sieves. It is then pumped through a pipeline to the first element of the processing
system, where it is strained in three microstrainer drums (Figure 2) fitted with a 10
µ
m screening mesh.
The diagram of the process of surface water treatment at WTP is presented in [2].
Toxins 2019, 11, x FOR PEER REVIEW 3 of 15
sources in the consumption water supply for the inhabitants of Zielona Góra in the years 2011–2014
is presented in Figure 1.
Figure 1. The percentage share of particular water sources in the consumption water supply for the
inhabitants of Zielona Góra in the years 2011–2014.
The quality of water taken from the Obrzyca River falls within category 3 (water requiring highly
efficient physical and chemical treatment) [17]. The poor quality of raw water supplied to WTP
Zawada and the need to treat the groundwater and surface water collectively causes numerous
problems in the process of water treatment. Surface water is characterized by pollution typical of
eutrophic waters (high color, oxidizability, periodic blooms, and increased levels of
orthophosphates). The latter are part of household and industrial sewage, but they may also come
from surface runoffs from arable land treated with artificial fertilizers containing phosphorus
compounds. Surface water is strained with grids and sieves. It is then pumped through a pipeline to
the first element of the processing system, where it is strained in three microstrainer drums (Figure
2) fitted with a 10 µm screening mesh. The diagram of the process of surface water treatment at WTP
is presented in [2].
Figure 2. Microstrainers in WTP Zawada. 1 raw water supply; 2 slide flat; 3 mesh baskets; 4
submersible pump; 5 sprinklers; 6 drainage trough; 7 drum drive; 8 clean water outflow.
This study aims to demonstrate that the microstrainers operating at WTP in Zielona Góra are a
useful tool for the water-treatment technology intended to eliminate plankton, including
39% 38.2% 38.8%
43.3%
38% 40.0% 38.7%
33.5%
23% 21.8% 22.5% 23.3%
2011 2012 2013 2014
surface water groundwater - shot siphon groundwater -water wells
Figure 2.
Microstrainers in WTP Zawada.
1
raw water supply;
2
slide flat;
3
mesh baskets;
4
submersible
pump; 5sprinklers; 6drainage trough; 7drum drive; 8clean water outflow.
Toxins 2019,11, 285 4 of 13
This study aims to demonstrate that the microstrainers operating at WTP in Zielona G
ó
ra are a
useful tool for the water-treatment technology intended to eliminate plankton, including cyanobacteria
and their toxins. The microscopic analysis of the abundance of plankton including cyanobacteria
during the microstrainer process allows not only for the assessment of potential cyanotoxic threat
in supplied drinking water, but also evaluation of the action, and prevention of adverse impacts of
the microstrainers.
2. Results
2.1. The Amount of Plankton Including Cyanobacteria at WTP Zawada Before and After Microstrainers
In the analyzed raw water, the largest share was diatoms, then cyanobacteria. The smallest
participation in phytoplankton was green algae. The microstrainer removal efficiency of plankton and
cyanobacteria, depending on the level, are presented in Table 1.
Table 1.
Microstrainers efficiency in removing plankton and cyanobacteria in WTP Zawada from 2011
to 2014.
Microorganisms Number of
Results
Range of Quantity
[103org. dm−3]
Removal Efficiency
% Average [%]
Plankton
8>100 47.4–83.7 65.1
7 50–100 25.2–85.0 53.7
7 10–50 13.6–76.8 53.7
41 <10 9.1–93.8 50.2
Cyanobacteria
4>100 51.1–81.1 65.9
6 50–100 41.2–85.7 58.6
10 10–50 13.9–93.0 49.7
43 <10 5.00–81.0 48.6
Most samples were with the lowest level of contamination. The widest range and the lowest
average of removal percentage for plankton and cyanobacteria occurred when the amount was the
lowest (<10
·
10
3
org.
·
dm
−3
). Average removal percentage >50% took place throughout the entire
research area for plankton but >50 103org.·dm−3for cyanobacteria.
The largest amount of plankton before microstraining was observed in May 2011 and was
497·103org.·dm-3 (Figure 3) and the dominant group was cyanobacteria.
The smallest amount of plankton before microstraining was observed on July 4, 2012
(0.96
·
10
3
org.
·
dm
−3
). On the same day, the amount of cyanobacteria was 0.12
·
10
3
org.
·
dm
−3
and
the reduction in plankton reached 79.2%. The maximum degree of plankton removal, totaling 93.98%,
took place in June 2011 and the minimum (9.1%) in September 2013. Removal of greater than half
of the total plankton was detected in 42 samples (63.6%) including cyanobacteria (60.6%), diatoms
(51.5%), green algae (63.6%).
The number of removed plankton increased with its increasing content in raw water as presented
in Figure 4. The student’s t-test analysis showed significant differences between the amount of plankton
(tcalc 2.02; tcrit 1,95; p>0.05) before and after microstraining.
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Figure 3. Efficiency of plankton removal after microstraining process in WTP Zawada from 2011 to 2014.
Figure 3. Efficiency of plankton removal after microstraining process in WTP Zawada from 2011 to 2014.
Toxins 2019,11, 285 6 of 13
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The smallest amount of plankton before microstraining was observed on July 4, 2012 (0.96·103
org.·dm−3). On the same day, the amount of cyanobacteria was 0.12·103 org.·dm−3 and the reduction in
plankton reached 79.2%. The maximum degree of plankton removal, totaling 93.98%, took place in
June 2011 and the minimum (9.1%) in September 2013. Removal of greater than half of the total
plankton was detected in 42 samples (63.6%) including cyanobacteria (60.6%), diatoms (51.5%), green
algae (63.6%).
The number of removed plankton increased with its increasing content in raw water as
presented in Figure 4. The student's t-test analysis showed significant differences between the
amount of plankton (tcalc 2.02; tcrit 1,95; p > 0.05) before and after microstraining.
Figure 4. Relationship between amount of plankton in raw water and removed in WTP Zawada.
2.2. The Quantitative and Qualitative Analysis of Cyanobacteria at WTP in Zawada Before and After
Microstrainers
The amount of cyanobacteria in samples before and after microstraining fell into the following
ranges respectively: 0.02–243·103 org.·dm−3; 0.02–118·103 org.·dm−3 (Appendix A, Table A1). The
largest amount of cyanobacteria before microstraining was observed in May 2011 and the dominant
species was Limnothrix redeckei (Meffert).
The most frequent species of cyanobacteria found on microstrainers was Dolichospermum affinis
(Lemmermann) (28% of the analyzed samples) (Appendix A, Table A1). Other species of
cyanobacteria of the same genus that were dominant in the analyses were: Dolichospermum flos-aquae
(Lyngbye), Dolichospermum planctonica (Brunnthaller), Dolichospermum spiroides (Klebahn). The
second in terms of the frequency of dominance was Pseudoanabaena limnetica (Lemmermann) 19
samples and L. redeckei 12 samples (9.09%) of 132 samples, most frequently in May or June. Oscillatoria
granulata (N.L. Gardner) occurred in September in 10 samples. The genus Microcystis was dominant
in 18 samples, of which Microcystis aeruginosa (Kützing) in 15 samples (7.6%) in summer months and
Microcystis flos-aquae (Wittrock) in 3 (1.5%) in August. The Planktothrix agardhii (Anagn. & Komárek)
dominated in 8 samples in September. Other species occurring in the samples included
Aphanizomenon flos-aquae (Ralfs ex Bornet & Flahault), Merismopedia glauca (Kützing), Microcystis
viridis (Lemmermann). M. wesenbergii (Komárek in N.V. Kondrat.), Oscillatoria tenuis (Agardh ex
Gomont), Snowella lacustris (Komárek & Hindák), and Woronichinia naegeliana (Elenkin).
y = 0.724x - 5.369
R² = 0.9479
-50
0
50
100
150
200
250
300
350
400
450
0 100 200 300 400 500 600
Removed plankton
[103org. ·dm-3]
Plankton in raw water [103org.·dm-3]
Figure 4. Relationship between amount of plankton in raw water and removed in WTP Zawada.
2.2. The Quantitative and Qualitative Analysis of Cyanobacteria at WTP in Zawada Before and After Microstrainers
The amount of cyanobacteria in samples before and after microstraining fell into the following
ranges respectively: 0.02–243
·
10
3
org.
·
dm
−3
; 0.02–118
·
10
3
org.
·
dm
−3
(Appendix A, Table A1). The largest
amount of cyanobacteria before microstraining was observed in May 2011 and the dominant species
was Limnothrix redeckei (Meffert).
The most frequent species of cyanobacteria found on microstrainers was Dolichospermum affinis
(Lemmermann) (28% of the analyzed samples) (Appendix A, Table A1). Other species of cyanobacteria
of the same genus that were dominant in the analyses were: Dolichospermum flos-aquae (Lyngbye),
Dolichospermum planctonica (Brunnthaller), Dolichospermum spiroides (Klebahn). The second in terms of
the frequency of dominance was Pseudoanabaena limnetica (Lemmermann) 19 samples and L. redeckei
12 samples (9.09%) of 132 samples, most frequently in May or June. Oscillatoria granulata (N.L. Gardner)
occurred in September in 10 samples. The genus Microcystis was dominant in 18 samples, of which
Microcystis aeruginosa (Kützing) in 15 samples (7.6%) in summer months and Microcystis flos-aquae
(Wittrock) in 3 (1.5%) in August. The Planktothrix agardhii (Anagn. & Kom
á
rek) dominated in 8 samples
in September. Other species occurring in the samples included Aphanizomenon flos-aquae (Ralfs ex
Bornet & Flahault), Merismopedia glauca (Kützing), Microcystis viridis (Lemmermann). M. wesenbergii
(Kom
á
rek in N.V. Kondrat.), Oscillatoria tenuis (Agardh ex Gomont), Snowella lacustris (Kom
á
rek &
Hindák), and Woronichinia naegeliana (Elenkin).
The decrease in the amount of cyanobacteria due to microstraining ranged from 5 to 93%.
The maximum degree of cyanobacteria removal occurred on 27 July 2011 (Figure 5).
The number of removed cyanobacteria increased with its increasing content in raw water.
The student’s t-test analysis showed significant differences between the amount of cyanobacteria
(tcalc 2.05; tcrit 1,95; p>0.05) before and after microstraining.
Toxins 2019,11, 285 7 of 13
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Figure 5. Efficiency of cyanobacteria removal after microstrainers process in WTP Zawada from 2011 to 2014.
Figure 5. Efficiency of cyanobacteria removal after microstrainers process in WTP Zawada from 2011 to 2014.
Toxins 2019,11, 285 8 of 13
On that day, the amount of cyanobacteria fell from 29.5 to 2.06
·
10
3
org.
·
dm
−3
. The amounts of
cyanobacteria and their reduction in particular years are presented in Appendix A, Table A1, and
Figure 5.
The maximum amount of cyanobacteria in 2011, totaling 243
·
10
3
org.
·
dm
−3
, was observed in May
and the dominant species was L. redeckei. In 2007, as a result of the microstraining process, in 10 of the
analyzed samples a decrease in the quantity of cyanobacteria by more than half was observed, which
constitutes 48% of all samples examined in that year (Appendix A, Table A1).
The largest amount of cyanobacteria in 2012, totaling 70.7
·
10
3
org.
·
dm
−3
, was detected in September,
and the dominant species was P. agardhii. In 2012, as a result of the microstraining process, in 9 of the
analyzed samples a decrease in the amount of cyanobacteria by more than half was observed, which
constitutes 75% of all samples examined in that year (Appendix A, Table A1).
The maximum quantity of cyanobacteria in 2013 was in August (86.6
·
10
3
org.
·
dm
−3
) and the
dominant species were D. spiroides, M. aeruginosa. In 2013, as a result of microstrainer filtration, in 6 of
the analyzed samples a decrease in the amount of cyanobacteria by more than half was observed,
which constitutes 40% of all samples examined in that year (Appendix A, Table A1).
The largest quantity of cyanobacteria in 2014 was detected in September (213
·
10
3
szt.
·
dm
−3
) and
the dominant species was P. agardhii. In 2014, as a result of microstrainer work, in 5 of the analyzed
samples, a decrease in the amount of cyanobacteria by more than half was observed, which constitutes
38% of all samples examined in that year (Appendix A, Table A1).
In the years 2011–2014 a decrease in the quantity of cyanobacteria by over 50% was observed in
30 samples (29.2%).
2.3. The Content of Microcystins and the Amount of Cyanobacteria at WTP in Zielona Gora Before and
After Microstrainers
Due to the large amount of cyanobacteria in May 2011 at WTP Zielona G
ó
ra, an additional series
of hydrobiological analyses was performed with a simultaneous microcystin determination using the
HPLC method. In the analyzed samples, neither extracellular nor intracellular MC-YR and MC-RR
microcystins were found. The only intracellular microcystin detected was MC-LR, whose content
is presented in Table 2. The highest concentration of the intracellular MC-LR (0.116
µ
g
·
dm
−3
) was
observed on May 11, 2011, when the amount of cyanobacteria equaled 238
·
10
3
org.
·
dm
−3
and the
dominant species was Limnothrix redeckei (Appendix A, Table A1).
Table 2.
Amount of cyanobacteria and intracellular MC-LR content before and after microstrainers
filtration (WTP Zawada).
Date of Sampling
[D/M/Y]
BEFORE
Microstrainers Process
AFTER
Microstrainers Process
Amount of
Cyanobacteria
Colony
[103org.·dm−3]
Intracellular
MC-LR
[µg·dm−3]
Amount of
Cyanobacteria
Colony
[103org.·dm−3]
Intracellular
MC-LR
[µg·dm−3]
11/05/2011 238 0.116 63.8 0.032
13/05/2011 241 0.098 118 0.040
18/05/2011 60.5 0.056 35.6 0.036
19/05/2011 43.9 0.044 28.2 0.032
25/05/2011 35.0 0.040 15.5 0.029
The MC-LR content in the cells of the cyanobacteria sampled from May 12 to May 25, 2011, before
and after microstraining, fell within the range 0.029–0.116
µ
g
·
dm
−3
. In all 5 samples the MC-LR content
did not exceed 1
µ
g
·
dm
−3
. The student’s t-test analysis showed significant differences between the
amount of intracellular MC-LR (tcalc 2.40; tcrit 2.31 p>0.05) before and after microstrainer filtration.
Toxins 2019,11, 285 9 of 13
3. Discussion
To reduce the number of algae by approximately 80%, including cyanobacteria by 68%,
in September 1994 microstrainers were installed at WTP Zielona G
ó
ra. The WTP is the only plant in
Poland using microstrainers in the water-treatment system [2].
The use of the non-reagent process of particle filtration on microstrainers as a pre-treatment
process for surface water abounding in algae is justified because it reduces the amount of precursors of
oxidation by-products, improving physical and chemical indicators of water quality (e.g., turbidity,
color, and total organic carbon (TOC)). Also, indirectly, reducing the amount of cyanobacteria causes a
decrease in the amount of intracellular toxins [3].
The microstrainer filtration ensures considerable reduction in the content of phytoplankton,
including cyanobacteria. In 2009, the effectiveness of micro-sieving in the removal of cyanobacteria
(35.8–68.8%) increased along with their growing amount. The reduction in the amount of cyanobacteria
was accompanied by decreased contents of the intracellular MC-LR [
2
]. In the last year of this
study, with increased amounts of cyanobacteria, the dominant species was P. agardhii, which has
high capacity for synthesizing hepatotoxins dangerous to humans. To eliminate any toxic threat
from cyanobacteria to Zielona G
ó
ra water-supply system, one should introduce constant MC-LR
monitoring in drinking water. In the last year of this research (2014), the maximum amount of
cyanobacteria equaled 213 10
3
org.
·
dm
−3
(Table 2), which is one of the highest values in the research
period. The dominant group was the P. agardhii species, which is particularly dangerous because it can
produce up to three times as much microcystin as other cyanobacteria e.g., Microcystis sp. In Polish
reservoirs, the most frequently occurring form of microcystin during P. agardhii domination is MC-RR.
This process may have an adverse impact on the quality of treated water in the future. To estimate the
cyanotoxic risk at a drinking-water intake, a systematic (annual) monitoring of cyanobacterial toxins
should be introduced, especially in the summer–autumn season [
18
]. In the studies, cyanobacteria
bloom comprising P. agardhii also occurred in September.
The analysis of microcystin amounts in May 2011 showed low content of intracellular MC-LR
(<1
µ
g
·
dm
−3
), permitted in drinking water [
19
]. However, it must be stressed that in that period of
research, the dominant species was L. redeckei, which is able to produce neurotoxins and not the studied
hepatotoxins [
20
]. In the temperate zone, this species plays an important role in mesotrophic reservoirs,
especially in colder seasons. Little is known about toxicity of this species, despite the urgency of the
problem due to the frequent massive occurrences of this species in drinking-water reservoirs [21].
To eliminate any toxic threat from cyanobacteria to residents of Zielona G
ó
ra in drinking water
supplied by waterworks, constant monitoring not only of hepatotoxins but also neurotoxins should be
introduced. Microscopic analysis should be used as a preliminary test for estimating the potential
cyanobacterial risk in water [22].
4. Materials and Methods
The efficiency of plankton removal on microstrainers at WTP Zawada was estimated by means of
a hydrobiological analysis. 63 samples taken before and after microstraining were analyzed from May
to September 2011–2014. The assumed sampling frequency was once a week on condition that the
microstrainers were in operation. This research is aimed at estimating the levels of plankton removal by
microstrainers at WTP and taking appropriate action (the cleaning of microstrainers, removing leaks).
The samples for hydrobiological analysis were taken using a Sedgewick-Rafter counting chamber
with a volume of 0.001 dm
3
in a given number of fields with the following parameters: height 1 mm,
area 1 mm
2
. A MN 358/A (OPTA-TECH, Warszawa, Poland) microscope was used for observation [
2
].
For cyanobacteria with straight filaments, 100
µ
m was set as one individual (org.). Curved trichomes
of Dolichospermum spp. and one colony of Microcystis spp. were indicated as individuals [
23
]. When
converting the colony count from 0.001 dm
3
into 1 dm
3
sample concentration by the plankton net was
taken into account [
24
]. The results of hydrobiological analysis were expressed as: org.
·
dm
−3
. Species
identification was done with identification keys for algae [25–28].
Toxins 2019,11, 285 10 of 13
To determine the microcystin concentration in water and cyanobacteria cells in May 2011,
an additional series of chromatographic analyses (HPLC) of water samples was performed, which
were then sent to the Department of Applied Ecology, University of Ł
ó
d´z. The chromatographic
analysis was carried out with the use of Agilent 1100 chromatograph with Diode Array Detection
(DAD) (Agilent, Waldbronn, Germany) [29].
A student’s t-test was used to analyze the significance of difference between the amount of
plankton, including cyanobacteria and their toxins before and after microstraining at a significance level
of
α
=0.05. The statistical analysis was performed using the following programs: StatSoft Statistica
version 10.0 and Microsoft Excel 2010.
5. Conclusions
1.
The microstrainer removal of plankton and cyanobacteria from 2011 to 2014 was statistically
significant. The quantity of removed plankton increased with increasing content in raw water.
2.
Cyanobacteria blooms occurred in surface water which is treated in WTP Zielona G
ó
ra.
Cyanobacteria species occurring in WTP are capable of microcystin synthesis (e.g., Planktothrix
agardhii bloom in September 2014). Therefore, cyanotoxin monitoring should be introduced
especially in the summer–autumn season.
3.
The microstrainer process, by reducing the amount of cyanobacteria, contributes to a decrease in
intracellular microcystins. However, after particle-filtration process, cyanotoxic cyanobacteria
may still occur. Therefore, cyanotoxin testing is justified.
4.
The largest amount of cyanobacteria occurred in May and equaled 243
·
10
3
org.
·
dm
−3
(domination
of Limnothrix redeckei) before the microstrainer process. To eliminate any toxic threat from
cyanobacteria to residents of Zielona G
ó
ra in drinking water supplied by waterworks, constant
monitoring of not only hepatotoxins but also neurotoxins should be introduced. It is necessary to
perform microscopic analysis as a preliminary test for estimation of the potential cyanobacterial
risk in surface water for drinking-water supply.
Author Contributions:
Conceptualization, M.P. and W.C.; methodology, W.C.; software, Excell validation, W.C.;
formal analysis, W.C. and M.P. investigation, W.C.; resources, W.C.; data curation, W.C.; writing—original draft
preparation, W.C.; writing—review and editing, X.X.; visualization, W.C.; supervision, M.P.; project administration,
M.P.; funding acquisition.
Funding: This research received no external funding.
Conflicts of Interest: The authors declare no conflict of interest.
Appendix A
Table A1.
The quantitative and qualitative analysis of cyanobacteria in WTP Zawada (before and after
microstraining) sampled in the years 2011–2014.
Sampling Date
[D/M/Y]
Dominant Cyanobacteria
Species
Amount of
Cyanobacteria
(103org.·dm−3)
Dominant Cyanobacteria
Species
Amount of
Cyanobacteria
(103org.·dm−3)
BEFORE Microstrainers AFTER Microstrainers
2011
4/05/2011 Limnothrix. redeckei 243 Limnothrix. redeckei 44.2
11/05/2011 Limnothrix redeckei 238 Limnothrix redeckei 63.8
13/05/2011 Limnothrix redeckei 241 Limnothrix redeckei 118
18/05/2011 Limnothrix redeckei 60.5 Limnothrix redeckei 35.6
19/05/2011 Limnothrix redeckei 43.9 Limnothrix redeckei 28.2
25/05/2011 Dolichospermum affinis 35.0 Dolichospermum afffinis 15.5
1/06/2011 Dolichospermum affinis 0.05 -Not detected
8/06/2011 -Not detected -Not detected
15/06/2011 Dolichospermum affinis 0.16 -Not detected
22/06/2011 Microcystis aeruginosa 0.08 -Not detected
29/06/2011 Microcystis aeruginosa 0.14 Microcystis aeruginosa 0.02
Toxins 2019,11, 285 11 of 13
Table A1. Cont.
Sampling Date
[D/M/Y]
Dominant Cyanobacteria
Species
Amount of
Cyanobacteria
(103org.·dm−3)
Dominant Cyanobacteria
Species
Amount of
Cyanobacteria
(103org.·dm−3)
BEFORE Microstrainers AFTER Microstrainers
2011
06/07/2011 Microcystis aeruginosa 0.37 Microcystis aeruginosa 0.22
14/07/2011 Dolichospermum affinis 0.24 Dolichospermum affinis 0.05
20/07/2011
Dolichospermum affinis
Microcystis aeruginosa
(co-dominance)
0.27 -Not detected
27/07/2011 Microcystis aeruginosa 29.5 Microcystis aeruginosa 2.06
02/08/2011 Microcystis flos-aquae 62.7 Microcystis flos-aquae 15.3
23/08/2011 Dolichospermum affinis 3.50 Dolichospermum affinis 2.13
30/08/2011 Dolichospermum affinis 25.9 Dolichospermum affinis 5.70
14/09/2011 Dolichospermum affinis 2.44 Dolichospermum affinis 0.55
21/09/2011 Dolichospermum affinis 54.6 Dolichospermum affinis 7.80
28/09/2011 Dolichospermum affinis 99.0 Dolichospermum affinis 35.3
2012
9/05/2012 Dolichospermum affinis 0.14 Not detected
16/05/2012 Dolichospermum affinis 0.29 Dolichospermum affinis 0.22
23/05/2012 Dolichospermum affinis 0.56 Dolichospermum affinis 0.12
6/06/2012 -Not detected -Not detected
13/06/2012 Microcystis flos-aquae 0.02 -Not detected
20/06/2012 Dolichospermum flos-aquae 0.04 -Not detected
27/06/2012 Dolichospermum affinis 1.34 Dolichospermum affinis 0.61
04/07/2012
Dolichospermum. flos-aquae
Dolichospermum spiroides
Microcystis aeruginosa
(co-dominance)
0.12 Dolichospermum spiroides 0.03
25/07/2012 Dolichospermum planctonica 1.81 Dolichospermum planctonica 1.01
02/08/2012 Dolichospermum planctonica 0.06 Dolichospermum planctonica 0.05
08/08/2012 Dolichospermum affinis 0.27 Dolichospermum affinis 0.12
28/08/2012 Aphanizomenon flos-aquae 0.07 Aphanizmenon flos-aquae 0.07
05/09/2012 Planktothrix agardhii 0.86 Planktothrix agardhii 0.46
11/09/2012 Planktothrix agardhii 2.22 Planktothrix agardhii 0.40
19/09/2012 Dolichospermum planctonica 2.28 Dolichospermum planctonica 0.64
25/09/2012 Planktothrix agardhii 70.7 Planktothrix agardhii 29.6
2013
15/05/2013
Dolichospermum affinis
Oscillatoria granulata
(co-dominance)
0.68
Dolichospermum. affinis
Oscillatoria granulata
(co-dominance)
0.49
21/05/2013 Pseudoanabaena limnetica 1.92 Pseudoanabaena limnetica 1.27
29/05/2013 Pseudoanabaena limnetica 4.83 Pseudoanabaena limnetica 2.02
4/06/2013 Pseudoanabaena limnetica 1.31 Pseudoanabaena limnetica 0.87
12/06/2013 Pseudoanabaena limnetica 0.26 Oscillatoria granulata 0.19
19/06/2013 Pseudoanabaena limnetica 0.40 Pseudoanabaena limnetica 0.15
25/06/2013 Pseudoanabaena limnetica 0.16 Pseudoanabaena limnetica 0.07
10/07/2013 Dolichospermum planctonica 24.3 Dolichospermum planctonica 19.2
31/07/2013 Dolichospermum affinis 0.96 Dolichospermum affinis 0.33
7/08/2013
Dolichospermum spiroides
Microcystis aeruginosa
(co-dominance)
86.6
Dolichospermum spiroides
Microcystis aeruginosa
(co-dominance)
35.1
13/08/2013 Microcystis aeruginosa 3.16 Microcystis aeruginosa 1.30
3/09/2013 Dolichospermum affinis 2.41 Dolichospermum affinis 2.40
11/09/2013 Dolichospermum affinis 14.7 Dolichospermum affinis 7.90
17/09/2013 Dolichospermum affinis 15.1 Dolichospermum affinis 14.9
24/09/2013 Dolichospermum affinis 16.6 Dolichospermum affinis 14.3
Toxins 2019,11, 285 12 of 13
Table A1. Cont.
Sampling Date
[D/M/Y]
Dominant Cyanobacteria
Species
Amount of
Cyanobacteria
(103org.·dm−3)
Dominant Cyanobacteria
Species
Amount of
Cyanobacteria
(103org.·dm−3)
BEFORE Microstrainers AFTER Microstrainers
2014
7/05/2014 Limnothrix redeckei 0.54 Limnothrix redeckei 0.49
14/05/2014 Pseudoanabaena limnetica 3.02 Pseudoanabaena limnetica 1.75
28/05/2014 Pseudoanabaena limnetica 0.07 -Not detected
4/06/2014 Pseudoanabaena limnetica 0.15 -Not detected
11/06/2014 Pseudoanabaena limnetica 0.22 -Not detected
17/06/2014 Pseudoanabaena limnetica 0.20 Pseudoanabaena limnetica 0.19
24/06/2014 Dolichospermum flos-aquae 3.31 Dolichospermum flos-aquae 0.94
2/07/2014 Dolichospermum planctonica 0.64 Dolichospermum planctonica 0.20
8/07/2014 Pseudoanabaena limnetica 0.14 -Not detected
15/07/2014 Dolichospermum spiroides 0.60 Dolichospermum spiroides 0.31
23/07/2014 Dolichospermum planctonica 14.4 Dolichospermum planctonica 8.30
19/08/2014 Oscillatoria granulata 0.15 Oscillatoria granulata 0.04
26/08/2014 Oscillatoria granulata 0.25 Oscillatoria granulata 0.05
2/09/2014 Oscillatoria granulata 0.32 -Not detected
10/09/2014 Planktothrix agardhii 213 Planktothrix agardhii 91.1
16/09/2014 Oscillatoria granulata 6.80 Oscillatoria granulata 2.28
24/09/2014
Microcystis aeruginosa
Planktothrix agardhii
(co-dominance)
34.4
Microcystis aeruginosa
Planktothrix agardhii
(co-dominance)
13.3
Maximum values of cyanobacteria before micro-sieves in one year were underlined. Maximum values of
cyanobacteria before microstrainers one year were underlined.
References and Notes
1.
Ewerts, H.; Swanepoel, A.; du Preez, H.H. Efficacy of conventional drinking water treatment processes in
removing problem-causing phytoplankton and associated organic compounds. Water SA
2013
,39, 739–750.
[CrossRef]
2.
Piontek, M.; Czy˙zewska, W. Efficiency of drinking water treatment processes. Removal of phytoplankton
with special consideration for cyanobacteria and improving physical and chemical parameters. Pol. J.
Environ. Stud. 2012,21, 273–281.
3.
Grochowiecka (Czy˙zewska), W.; ´
Swiderska-Br
ó
˙z, M.; Wolska, M. Efficiency of the Micro-sieves Process
Towards the Removal of Phytoplankton Organisms and Some Chemical Pollutants from Surface Water.
Ochrona Srodowiska (Environ. Prot.) 2009,2, 25–30.
4.
Häggvist, K.; Akçaalan, R.; Echenique-Subiabre, I.; Fastner, J.; Horeck
á
, M.; Humbert, F.-F.; Izydorczyk, K.;
Jurczak, T.; Kokoci ´nski, M.; Lindholm, T.; et al. Case Studies of Environmental Sampling Detection and
Monitoring of potentially Toxic Cyanobacteria. In Handbook of Cyanobacterial Monitoring and Cyanotoxin
Analysis, 1st ed.; Meriluoto, J., Spoof, L., Codd, G.A., Eds.; John Wiley & Sons: Chichester, UK, 2017; pp. 70–84.
5.
Jachniak, E. The evaluation of eutrophication level of Kozlowa Gora dam reservoir base on assemblages
planktonic algae. Chem. Didact. Ecol. Metrol. 2013,18, 69–76. [CrossRef]
6.
Kabzi´nski, A. State of threat by cyanobacterial blooms in Poland at period 1995–2007. In Ekotoksykologia
w Ochronie ´srodowiska (Ecotoxicology in Environmental protection); Kołwzan, B., Grabas, K., Eds.; Polskie
Zrzeszenie In˙zynierów i Techników Sanitarnych: Szklarska Poreba, Poland, 2008; pp. 165–172.
7.
Bober, B.; Bialczyk, J. Determination of the toxicity of the freshwater cyanobacterium Woronichinia naegaliana
(Unger) Elenkin. J. Appl. Ecol. 2016,29, 1355–1362.
8.
Piontek, M.; Czy˙zewska, W. Influence of cyanobacterial bloom on freshwater biocoenosis. Use of bioassays
for cyanobacterial microcystins in toxicity assessment. CEER 2017,24, 47–68. [CrossRef]
9.
He, X.; Liu, Y.-L.; Conklin, A.; Westrick, J.; Weavers, L.K.; Dionysiou, D.D.; Lenhart, J.J.; Mouser, P.J.; Szlag, D.
2016 Toxic cyanobacteria and drinking water: Impacts, detection and treatment. Harmful Algae
2016
,54,
174–193. [CrossRef] [PubMed]
Toxins 2019,11, 285 13 of 13
10.
De Almeida, C.R.; Spiandorello, F.B.; Giroldo, D.; Yunes, J.S. The effectiveness of conventional water treatment
in removing Ceratium furcoides (Levander) Langhans, Microcystis sp. and microcystins. Water SA
2016
,42,
606–611. [CrossRef]
11.
Roegner, A.F.; Brena, B.; Gonz
á
lez-Sapienza, G.; Puschner, B. Microcystins in potable surface waters: Toxic
effects and removal strategies. J. Appl. Toxicol. 2014,34, 441–457. [CrossRef]
12.
Ibrahim, W.M.; Salim, E.H.; Azab, Y.A.; Ismail, A.-H.M. Monitoring and removal of cyanobacterial toxins
from drinking water by algal-activated carbon. Toxicol. Ind. Health 2015,32, 1752–1762. [CrossRef]
13.
Nada, T.; Damjana, D.; Zorica, S.; Dragana, L. Cyanotoxins in Serbia and Water Treatment Procedures for
their Elimination. Geogr. Pannon. 2012,16, 155–163.
14.
Matsushita, T.; Nakamura, K.; Matsui, Y.; Shirasaki, N. Effect of growth phase of cyanobacterium on release
of intracellular geosmin form cells during microfiltration process. Membr. Water Treat.
2015
,6, 225–235.
[CrossRef]
15. Pizzi, N.G. Water Treatment, 4th ed.; American Water Work Association: Denver, CO, USA, 2010; pp. 45–47.
16.
Piontek, M.; Czy ˙zewska, W.; Mankiewicz-Boczek, J. The occurence of cyanobacteria blooms in the Obrzyca
River catchment area (Poland), a source of drinking water. Pol. J. Environ. Stud.
2017
,26, 1191–1201.
[CrossRef]
17.
The Polish Parliament, Warszawa, Poland, 2002.Regulation of the Minister of Environment 2002 w sprawie wymaga´n,
jakim powinny odpowiada´c wody powierzchniowe wykorzystywane do zaopatrzenia ludno´sci w wod˛e przeznaczon ˛a do
spo˙zycia (on the Requirements to be Met by Surface Waters Designated to Supply Drinking Water for the Human
Population) [Dz.U. nr 204 poz. 1728].
18.
Kobos, J.; Błaszczyk, A.; Hohfeld, N.; Toru ´nska-Sitarz, A.; Krakowiak, A.; Hebel, A.; Sutryk, K.; Grabowska, M.;
Toporowska, M.; Kokoci´nski, M.; et al. Cyanobacteria and cyanotoxins in Polish freshwater bodies. Oceanol.
Hydrobiol. Stud. 2013,42, 358–378. [CrossRef]
19.
World Health Organization (WHO). Guidelines for Drinking Water Quality, 4th ed.; WHO: Geneva,
Switzerland, 2011.
20.
Jakubowska, N.; Zagajewski, P.; Gołdyn, R. 2013 Water Blooms and Cyanobacterial Toxins in Lakes. Pol. J.
Environ. Stud. 2013,22, 1077–1082.
21.
Kom
á
rek, J. Problems in cyanobacterial taxonomy: Implication for most common toxin producing species.
In Workshop: Freshwater Harmful Algal Blooms: Health Risk and Control Management, Rome, Italy, 17 October
2000; Melchiorre, S., Viaggiu, E., Bruno, M., Eds.; Istituto Superiore Di Sanità: Rome, Italy, 2002.
22.
Piontek, M.; Grochowiecka (Czy˙zewska), W. Choice of methods for toxicological studies on the basis of
hydrobiological analysis of blue-green in the water intakes. Chem. Rev. 2008,87, 2–6.
23. Pawlik-Skowro´nska, B.; Toporowska, M. Blooms of toxin-producing Cyanobacteria—A real threat in small
dam reservoirs at the beginning of their operation. Oceanol. Hydrobiol. Stud. 2011,40, 30–37. [CrossRef]
24.
Lawton, L.A.; Marsalek, B.; Padis
á
k, J.; Chorus, I. Determination of cyanobacteria in the laboratory. In Toxic
Cyanobacteria in Water. A Guide to Their Public Health Consequences. Monitoring and Management, 1st ed.;
Chorus, I., Bartram, J., Eds.; Taylor &Francis: London, UK; New York, NY, USA, 1999; pp. 347–367.
25. Komárek, J.; Komárkowa, J. Diversity of Aphanizomenon-like cyanobacteria. Czech Phycol. 2006,6, 1–32.
26.
Kom
á
rek, J.; Zapom
˘
elow
á
, E. Planktic morphospecies of the cyanobacterial genus Anabaena=subg.
Dolichospermum—1. Part: Coiled types. Fottea 2007,7, 1–31.
27.
Kom
á
rek, J.; Zapom
˘
elow
á
, E. Planktic morphospecies of the cyanobacterial genus Anabaena=subg.
Dolichospermum—2. Part: Straight types. Fottea 2008,8, 1–14.
28. Hindák, F. Atlas of Cyanophytes; Veda: Bratysława, Slovakia, 2008.
29.
Jurczak, T.; Tarczy´nska, M.; Izydorczyk, K.; Mankiewicz, J.; Zalewski, M.; Meriluoto, J. Elimination of
microcystins by water treatment process—Examples from Sulejow Reservoir, Poland. Water Res.
2005
,39,
2394–2406. [CrossRef] [PubMed]
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