ORIGINAL PAPER Preliminary surface topographical characteristics of biofilms attached on drip irrigation emitters using reclaimed water Yunkai Li • Bo Zhou • Yaoze Liu • Yinguang Jiang • Yiting Pei • Ze Shi Received: 9 December 2011 / Accepted: 24 February 2012 Ó Springer-Verlag 2012 Abstract Drip irrigation is the most effective and reliable method for reclaimed water irrigation. Emitter clogging is the bottleneck to restrain the application and popularization of reclaimed water drip irrigation technology, and some researchers have reported that this was tightly related to the formation of biofilms in the irrigation system. We selected reclaimed water treated with cyclic activated sludge system (CASS) and four kinds of labyrinth emitters in cusp-shaped saw-tooth, rectangular straight-tooth, arc-shaped saw-tooth and arc-angular straight-tooth and studied the surface topographical characteristics of biofilms in different posi- tions of reclaimed water drip irrigation emitters with the 3D white-light scanning interferometer (WLSI). The results showed that biofilms in different positions of units were different with each emitter while showing the largest thickness in water-side tooth-tip zone ( [ 20 lm); the bio- film thickness in the same monitoring sites inside one unit segment gradually decreased along the flow direction, while the flow at the inlets was much larger than that at the outlets; comparing the head, middle and tail parts, the biofilm thickness at the inlet and outlet showed the largest in the tail part, followed by the middle and the head parts. This can be explained by the equilibrium relation between hydrodynamic behavior and the transportation of nutrient and particles inside the emitters. The water-side tooth-tip zone of the first unit in the last emitter was selected to monitor surface topographical characteristics of biofilms, and its biofilm thickness also could be used as the indicator for evaluating the characteristics of surface topography. These results were aimed to provide references to explain the emitter clogging mechanism of reclaimed water drip irrigation as well as its technological application and popularization. Introduction Irrigating with reclaimed water has been widely used to alleviate the global water shortage (Asano et al. 2007). Although the quality of the reclaimed water reaches basic standards of irrigation, it still contains a certain number of pollutants. Hence, excessive and inappropriate use of reclaimed water for irrigation may harm plants, soil, envi- ronments of surface water and groundwater, and human health. Drip irrigation was regarded as the most effective and reliable pattern for reclaimed water irrigation (Adin and Sacks 1991; Ravina et al. 1992, 1997; Capra and Scicolone 2004, 2005; Liu and Huang 2009). The emitter is one of the key components of the drip irrigation system. However, due to its narrow flow path of 0.5–1.2 mm, it can be easily clogged by pollutants like suspended particles, chemical deposits and microorganism, which may eventually com- promise the whole irrigation system (Li et al. 2006). Reclaimed water contains a large number of suspended Communicated by T. Trooien. Yunkai Li, Bo Zhou and Yaoze Liu equally contributed to this paper. Y. Li (&) B. Zhou Y. Liu Y. Pei Z. Shi College of Water Resource and Civil Engineering, China Agricultural University, Beijing 100083, China e-mail: [email protected]Y. Li State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China Y. Jiang Beiqijia Sewage Treatment Plant, CPWAB, Beijing 102209, China 123 Irrig Sci DOI 10.1007/s00271-012-0329-1
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ORIGINAL PAPER
Preliminary surface topographical characteristics of biofilmsattached on drip irrigation emitters using reclaimed water
Yunkai Li • Bo Zhou • Yaoze Liu • Yinguang Jiang •
Yiting Pei • Ze Shi
Received: 9 December 2011 / Accepted: 24 February 2012
� Springer-Verlag 2012
Abstract Drip irrigation is the most effective and reliable
method for reclaimed water irrigation. Emitter clogging is
the bottleneck to restrain the application and popularization
of reclaimed water drip irrigation technology, and some
researchers have reported that this was tightly related to the
formation of biofilms in the irrigation system. We selected
reclaimed water treated with cyclic activated sludge system
(CASS) and four kinds of labyrinth emitters in cusp-shaped
where dx and dy denote the pixel distances along x-axis and
y-axis, respectively.
Results and analysis
Surface topographical characteristics of biofilms
inside the flow path unit
The topographical characteristics of surface biofilm in
these four types of flow path are shown in Figs. 4, 5, 6 and
7, and the analysis of the 3D topographical characteristics
is summarized in Table 3.
As shown in Figs. 4, 5, 6 and 7 and Table 3, the biofilm
thickness was 7.70–29.58 lm in cusp-shaped saw-tooth
flow path, 4.53–23.21 lm in arc-shaped saw-tooth flow
path, 5.29–21.03 lm in rectangular straight-tooth flow path
and 4.47–28.91 lm in arc-angular straight-tooth flow path.
Obvious differences were between the monitoring sites. All
four types of flow path showed that the biofilms thickness at
water-side dedendum zone (site 4, [20 lm) were much
(a)
(b)
(c)
1 2 3
4 5
6 7
1 23
4 5
6 7 8 9 10
11
12
13
14
16
15
17
8 1 2
3 45
6 7 8
(d)
1 23 45
6 7 8 9
10
12
11
13
Fig. 3 Monitoring sites of biofilms. a Cusp-shaped saw-tooth flow path. b Arc-shaped saw-tooth flow path. c Rectangular straight-tooth flow
path. d Arc-angular straight-tooth flow path
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larger compared to other monitoring sites. In addition, site 4
exhibited the largest Sq, Sy and Sdr. Three types of flow
path— cusp-shaped saw-tooth, arc-shaped saw-tooth and
rectangular straight-tooth—showed that the biofilm thick-
ness at main flow deformation zone (site 3) was the smallest,
while the arc-angular straight-tooth flow path had a different
result. The water-reverse-side dedendum zone (site 5)
showed the second largest biofilm thickness. The biofilm
thickness of water-reverse-side dedendum zone (site 5) was
larger than that of water-reverse-side tooth-tip zone (site 2),
while the biofilm thickness of water-side tooth-tip zone (site
1) was between those of sites 3 and 4. The biofilm thickness
of the arc-shaped straight-tooth flow path was obviously
larger than the other three types of flow path.
Fig. 4 Surface topographical characteristics of biofilms in cusp-shaped saw-tooth flow path unit. a Site 1. b Site 2. c Site 3. d Site 4. e Site 5
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Changes in the topographical characteristics of biofilms
in the flow path unit segment
Figures 8, 9, 10 and 11 show the biofilm topographical
characteristics at sites which were analogous to the water-
side tooth-tip zone (site 1), inside the units of the four types
of flow path. In the figures, the unit shown is the closest to
the flow outlet. The analysis of the topographical
characteristics of biofilms inside different units in unit
segment along with the flow direction is shown in Table 4.
The biofilm thickness was 9.68–13.55 lm for cusp-
shaped saw-tooth flow path, 5.52–16.75 lm for arc-shaped
saw-tooth flow path, 5.81–11.89 lm for rectangular
straight-tooth flow path and 4.73–9.56 lm for arc-angular
straight-tooth flow path. In summary, the biofilm thickness
gradually reduced from the inlet to the outlet of the flow
Fig. 5 Surface topographical characteristics of biofilms in arc-shaped saw-tooth flow path unit. a Site 1. b Site 2. c Site 3. d Site 4. e Site 5
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path by 28.6, 66.3, 51.3 and 50.5 %, respectively. However,
we did not observe any obvious regularity in Sq, Sy and Sdr.
Changes in the topographical characteristics of biofilms
inside multilevel unit segments
Figure 3b, d shows the multilevel unit segments of two
flow paths. The topographical characteristics at sites which
were analogous to the water-side tooth-tip zone (site 1) are
shown in Figs. 12 and 13. The biofilm topographical
characteristics are summarized in Table 5, from which we
found that the biofilm thickness was 3.59–11.75 lm for the
arc-shaped saw-tooth flow path and 4.86–8.64 lm for the
arc-angular straight-tooth flow path. These results indicated
that the thickness of biofilms at multilevel unit segments
gradually reduced by 69.4 and 43.8 % from the inlet to the
Fig. 6 Surface topographical characteristics of biofilms in rectangular straight-tooth flow path unit. a Site 1. b Site 2. c Site 3. d Site 4. e Site 5
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outlet of the flow path. However, we did not observe any
obvious regularity in Sq, Sy and Sdr.
Changes in the topographical characteristics of biofilms
at the inlet and outlet of the flow path
Table 6 shows the biofilm topographical parameters at the
inlets and outlets of emitters with different flow paths. At
the inlets, the biofilm thickness was 6.65–9.12 lm for cusp-
shaped saw-tooth flow path, 5.25–9.26 lm for arc-shaped
saw-tooth flow path, 6.50–9.99 lm for rectangular straight-
tooth flow path and 4.71–8.53 lm for arc-angular straight-
tooth flow path, while at the outlets, the biofilm thickness
were 4.11–7.36, 2.34–7.08, 5.15–7.74 and 3.09–7.25 lm
correspondingly. Compared to the inlets, biofilm thick-
nesses at the outlets were reduced by 28.6, 34.5, 23.2 and
Fig. 7 Surface topographical characteristics of biofilms in arc-angular straight-tooth flow path unit. a Site 1 b Site 2. c Site 3. d Site 4. e Site 5
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20.6 %, respectively. Furthermore, the reduction rate of the
biofilm thickness at the head, middle and tail parts of the
experimental system gradually decreased in all types of
emitters except the rectangular straight-tooth one. Mean-
while, the biofilm thickness at the inlets and outlets of the
emitters increased from the head to the middle and to the tail
part of the system. Compared to the head part, the inlet
biofilm thickness at the tail part of the system increased by
27.1, 43.3, 34.9 and 44.3 % for the four types of emitters,
respectively, while the outlet biofilm thickness increased by
44.2, 66.9, 33.5 and 57.4 %. In addition, the inlet biofilm
thickness showed lower levels of Sq, Sy and Sdr compared to
the outlet. However, there was no observable difference in
principle among the emitters at the head, middle and tail
parts of the monitoring system. When the average flow rate
was reduced to 90 %, analysis of the samples increased by
1.4–10.7, 2.3–14, 3.2–12 and 2.5–16 %, respectively,
compared to the first batch of samples, while showing
similar regularities of biofilm changes for the emitters at
different positions of the system and at the inlets and outlets
of the emitters. Furthermore, the increasing rate of biofilm
thickness at the outlets was higher than for the inlets.
Table 3 3D topography parameters of biofilms in different positions of different types of flow path unit
Number Flow path type Site 3D topography parameters