Abstract

Decentralized systems play a big role in wastewater treatment in rural areas. The aims of this study are to address the wastewater treatment and disposal problems for rural districts of Istanbul, to discuss the efficiencies of currently operated systems and to offer new appropriate wastewater treatment systems for small communities having a population up to 5,000. The management and final disposal alternatives for sludge generated in septic tanks are also discussed within the scope of this study. A sequencing batch reactor (SBR) system serving 2,500 people and a hybrid constructed wetland system serving 500 people are presented as case studies. A thorough evaluation based on the capacity and performance of the existing wastewater treatment systems in rural districts revealed that a number of these systems are not operating at their optimum. Improperly constructed sewer lines receive a lot of infiltration and inflow (I & I) after rainfall events, decreasing treatment performance and causing operational difficulties. Natural treatment systems such as constructed wetlands prove a viable alternative in these communities, especially for villages with populations less than 500 people.

INTRODUCTION

Istanbul is the most important industrial and commercial center of Turkey, with a current population around 15 million. The annual population growth rate of Istanbul (∼2.1%), as the average for the last 5 years, is approximately 1.5 times the overall population growth rate of Turkey (∼1.4%) (Ozturk & Altay 2015). Municipal infrastructure of wastewater in Istanbul is not as well developed as its water supply system. A sanitary sewer system serving 98% of the population with a length of ∼14,000 km exists in Istanbul (ISKI 2017). A part of the existing sewer system is a combined system, and mainly bears significant amounts of stormwater. The wettest months in Istanbul are January and December, while the driest months are June and July. The sewer system overflows from time to time during intense precipitation, resulting in surface water pollution at a local level with health risks for the community.

Decentralized systems play a big role in wastewater treatment in small communities (Engin & Demir 2006; Libralato et al. 2012). In Istanbul, wastewaters from rural populations of between 500 and 5,000 inhabitants are treated using individual septic systems, packaged biological treatment systems, low-cost stabilization ponds on-site, conventional activated sludge systems, or in some cases with advanced biological treatment systems that remove nutrients (Ozturk & Altay 2015). There are currently 66 small wastewater treatment plants (WWTPs) with capacities ranging from 125 to 1,730 m3/day in rural districts of Istanbul. Of these, 41 are located in the European side of the city and 25 are located in the Asian side (Figure 1, Table 1).

Table 1

List of small wastewater treatment plants (WWTPs) in Istanbul

NameYear startedCapacity (m3/d)
European side Terkos advanced SBR WWTP 2000 1,730 
Akalan package WWTP 2008 400 
Belgrat package WWTP 2008 50 
Kestanelik conventional WWTP 2010 500 
Örcünlü conventional WWTP 2010 250 
Yazlik conventional WWTP 2012 250 
Subasi conventional WWTP 2012 250 
Canakca conventional WWTP 2010 500 
İzzettin conventional WWTP 2010 500 
10 Oklali conventional WWTP 2011 500 
11 Boyalik conventional WWTP 2011 250 
12 Ihsaniye conventional WWTP 2011 500 
13 Basakkoy conventional WWTP 2010 250 
14 Beyciler conventional WWTP 2013 1,000 
15 Binkilic conventional WWTP 2014 1,000 
16 Ciftlik conventional WWTP 2014 1,000 
17 Karaburun conventional WWTP 2014 2,000 
18 Karaca conventional WWTP 2014 1,000 
19 Yali conventional WWTP 2014 1,000 
20 Degirmenkoy conventional WWTP 2014 2,000 
21 Sayalar conventional WWTP 2014 500 
22 Cayirdere conventional WWTP 2014 500 
23 Hallacli conventional WWTP 2014 500 
24 Danamandira conventional WWTP 2014 500 
25 Aydinlar conventional WWTP 2014 500 
26 Gumuspinar conventional WWTP 2014 500 
27 Karamandere conventional WWTP 2014 500 
28 Zekeriyakoy conventional WWTP 2016 4,000 
29 Cakil conventional WWTP 2016 1,000 
30 Incegiz conventional WWTP 2016 1,000 
31 Dursunkoy conventional WWTP 2016 500 
32 Dagyenice conventional WWTP 2016 500 
33 Hisarbeyli conventional WWTP 2016 500 
34 Orencik conventional WWTP 2016 500 
35 Gokceali conventional WWTP 2016 500 
36 Elbasan conventional WWTP 2016 500 
37 Ovayenice conventional WWTP 2016 500 
38 Akoren conventional WWTP 2016 500 
39 Buyukkilicli package WWTP in progress 400 
40 Buyukcavuslu package WWTP in progress 1,000 
41 Silivri Kadikoy package WWTP in progress 800 
Asian side 42 Geredeli Village conventional WWTP 2013 250 
43 Kabakoz Village conventional WWTP 2013 250 
44 Sofular Village conventional WWTP 2013 250 
45 Alacali Village conventional WWTP 2013 250 
46 Dogancali Village conventional WWTP 2013 500 
47 Kurnakoy Village conventional WWTP 2013 250 
48 Cumhuriyet Village conventional WWTP 2013 500 
49 Uvezli Village conventional WWTP 2013 250 
50 Satmazli Village conventional WWTP 2013 500 
51 Suayipli Village conventional WWTP 2013 250 
52 Degirmencayiri Village conventional WWTP 2013 250 
53 Omerli conventional WWTP 2008 500 
54 Agva advanced membrane WWTP 2010 4,000 
55 Komurluk conventional WWTP 2008 125 
56 Sahilkoy conventional WWTP 2011 250 
57 Imrenli conventional WWTP 2012 250 
58 Karakiraz conventional WWTP 2012 250 
59 Kocullu conventional WWTP 2012 250 
60 Kervansaray conventional WWTP 2012 250 
61 Yenikoy conventional WWTP 2008 200 
62 Ogumce conventional WWTP 2010 200 
63 Orucoglu constructed Wetland 2009 125 
64 Huseyinli Village conventional WWTP 2013 2,000 
65 Resadiye Village conventional WWTP 2013 2,000 
66 Poyraz conventional WWTP 2017 250 
NameYear startedCapacity (m3/d)
European side Terkos advanced SBR WWTP 2000 1,730 
Akalan package WWTP 2008 400 
Belgrat package WWTP 2008 50 
Kestanelik conventional WWTP 2010 500 
Örcünlü conventional WWTP 2010 250 
Yazlik conventional WWTP 2012 250 
Subasi conventional WWTP 2012 250 
Canakca conventional WWTP 2010 500 
İzzettin conventional WWTP 2010 500 
10 Oklali conventional WWTP 2011 500 
11 Boyalik conventional WWTP 2011 250 
12 Ihsaniye conventional WWTP 2011 500 
13 Basakkoy conventional WWTP 2010 250 
14 Beyciler conventional WWTP 2013 1,000 
15 Binkilic conventional WWTP 2014 1,000 
16 Ciftlik conventional WWTP 2014 1,000 
17 Karaburun conventional WWTP 2014 2,000 
18 Karaca conventional WWTP 2014 1,000 
19 Yali conventional WWTP 2014 1,000 
20 Degirmenkoy conventional WWTP 2014 2,000 
21 Sayalar conventional WWTP 2014 500 
22 Cayirdere conventional WWTP 2014 500 
23 Hallacli conventional WWTP 2014 500 
24 Danamandira conventional WWTP 2014 500 
25 Aydinlar conventional WWTP 2014 500 
26 Gumuspinar conventional WWTP 2014 500 
27 Karamandere conventional WWTP 2014 500 
28 Zekeriyakoy conventional WWTP 2016 4,000 
29 Cakil conventional WWTP 2016 1,000 
30 Incegiz conventional WWTP 2016 1,000 
31 Dursunkoy conventional WWTP 2016 500 
32 Dagyenice conventional WWTP 2016 500 
33 Hisarbeyli conventional WWTP 2016 500 
34 Orencik conventional WWTP 2016 500 
35 Gokceali conventional WWTP 2016 500 
36 Elbasan conventional WWTP 2016 500 
37 Ovayenice conventional WWTP 2016 500 
38 Akoren conventional WWTP 2016 500 
39 Buyukkilicli package WWTP in progress 400 
40 Buyukcavuslu package WWTP in progress 1,000 
41 Silivri Kadikoy package WWTP in progress 800 
Asian side 42 Geredeli Village conventional WWTP 2013 250 
43 Kabakoz Village conventional WWTP 2013 250 
44 Sofular Village conventional WWTP 2013 250 
45 Alacali Village conventional WWTP 2013 250 
46 Dogancali Village conventional WWTP 2013 500 
47 Kurnakoy Village conventional WWTP 2013 250 
48 Cumhuriyet Village conventional WWTP 2013 500 
49 Uvezli Village conventional WWTP 2013 250 
50 Satmazli Village conventional WWTP 2013 500 
51 Suayipli Village conventional WWTP 2013 250 
52 Degirmencayiri Village conventional WWTP 2013 250 
53 Omerli conventional WWTP 2008 500 
54 Agva advanced membrane WWTP 2010 4,000 
55 Komurluk conventional WWTP 2008 125 
56 Sahilkoy conventional WWTP 2011 250 
57 Imrenli conventional WWTP 2012 250 
58 Karakiraz conventional WWTP 2012 250 
59 Kocullu conventional WWTP 2012 250 
60 Kervansaray conventional WWTP 2012 250 
61 Yenikoy conventional WWTP 2008 200 
62 Ogumce conventional WWTP 2010 200 
63 Orucoglu constructed Wetland 2009 125 
64 Huseyinli Village conventional WWTP 2013 2,000 
65 Resadiye Village conventional WWTP 2013 2,000 
66 Poyraz conventional WWTP 2017 250 
Figure 1

Locations of small wastewater treatment plants in rural districts of Istanbul.

Figure 1

Locations of small wastewater treatment plants in rural districts of Istanbul.

As can be seen from Table 1, existing small wastewater treatment plants are predominantly designed as conventional activated sludge systems. There is only one natural treatment system designed as a hybrid constructed wetland system. 33 of the small WWTPs are located in drinking water basins. These need to be upgraded to advanced biological treatment for efficient removal of nutrients and emerging organic contaminants.

The aims of this study are to address the wastewater treatment and disposal problems for rural districts of Istanbul, to discuss the efficiencies of currently operated systems and to offer new appropriate wastewater treatment systems for small communities having a population of up to 5,000. A sequencing batch reactor (SBR) system serving 2,500 people and a hybrid constructed wetland system serving 500 people are presented as case studies within the scope of this paper.

CASE STUDY AREAS

Terkos Advanced Biological Wastewater Treatment Plant (WWTP) and Orucoglu Constructed Wetland (CW) are selected to be presented as case studies in this paper. Terkos Advanced Biological WWTP is located in the northern part of the European side of Istanbul near Terkos Lake (Figure 1). It has a capacity of 1,730 m3/day and has been designed as two parallel sequencing batch reactors (SBR), which is a fill-and draw activated sludge system for wastewater treatment.

Orucoglu CW is located on the Asian side of Istanbul near Omerli Reservoir (Figure 1). Orucoglu CW system consists of two parallel horizontal subsurface flow wetlands (HSFWs) with a total surface area of 500 m2, and three vertical subsurface flow wetlands (VFWs) with a total surface area of 250 m2. The system has been operated without effluent circulation with an option to activate effluent circulation when necessary (Ayaz et al. 2008).

METHODS

Monthly or weekly samples were collected from the small wastewater treatment plants operated by Istanbul Water and Sewerage Administration (ISKI). Influent and effluent parameters were measured in ISKI laboratories according to Standard Methods (APHA 2012). Statistical analyses were done using version 25 of the IBM SPSS software Package (IBM, Armonk, New York, USA).

RESULTS AND DISCUSSION

Average monthly performance data for the Terkos WWTP are given in Table 2. Average removal efficiencies for chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total suspended solids (TSS) were 68%, 81% and 80%, respectively. As for the nutrients, 49% total nitrogen (TN) removal and 61% total phosphorus (TP) removal was achieved.

Table 2

Average monthly performance data for the Terkos Advanced WWTP in 2017

COD (mg/L)
BOD5 (mg/L)
TN (mg/L)
TP (mg/L)
TSS (mg/L)
InfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluent
January 35 19 16 12.7 9.2 0.4 0.1 43 14 
February 88 23 37 18.3 11.8 1.1 0.4 137 
March 77 27 40 17.0 7.9 1.0 0.2 42 12 
April 59 20 30 14.0 7.0 1.9 1.0 60 
May 116 38 62 14.5 10.6 2.0 1.0 63 13 
June 173 33 75 11 12.6 6.8 1.5 0.4 133 
July 123 44 72 24 16.4 6.9 2.1 0.8 120 18 
August 124 50 62 21 13.4 8.2 2.0 0.6 69 15 
September 194 77 102 15 17.3 7.5 2.5 1.5 134 49 
October 116 28 76 16.4 5.1 2.2 1.5 43 17 
November 90 22 51 14.7 5.2 1.6 0.4 58 
December 102 17 45 12.3 4.2 1.3 0.5 81 11 
COD (mg/L)
BOD5 (mg/L)
TN (mg/L)
TP (mg/L)
TSS (mg/L)
InfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluent
January 35 19 16 12.7 9.2 0.4 0.1 43 14 
February 88 23 37 18.3 11.8 1.1 0.4 137 
March 77 27 40 17.0 7.9 1.0 0.2 42 12 
April 59 20 30 14.0 7.0 1.9 1.0 60 
May 116 38 62 14.5 10.6 2.0 1.0 63 13 
June 173 33 75 11 12.6 6.8 1.5 0.4 133 
July 123 44 72 24 16.4 6.9 2.1 0.8 120 18 
August 124 50 62 21 13.4 8.2 2.0 0.6 69 15 
September 194 77 102 15 17.3 7.5 2.5 1.5 134 49 
October 116 28 76 16.4 5.1 2.2 1.5 43 17 
November 90 22 51 14.7 5.2 1.6 0.4 58 
December 102 17 45 12.3 4.2 1.3 0.5 81 11 

As can be seen from Table 2, the influent water is classified as low strength most of the time, especially when there is rainfall. The reason for this is improperly constructed sewer lines which receive a lot of inflow and inputs from groundwater after rainfall events. In Terkos basin, stormwater and wastewater are collected separately and sewer pipes are laid at a depth range of 2.8 to 4.5 m below ground level, while the local groundwater table around the serviced area is between 3 and 9 m below ground level (ISKI, unpublished). This makes the sewer pipes prone to groundwater seepage. The combined plot of maximum daily flow in each month and the Cumulative Deviation from Mean (CDFM) of monthly rainfall between 2015 and 2017 indicates that the maximum flow is responding to the rainfall pattern (Figure 2). Hence, the design capacity of 1,730 m3/day is exceeded most of the time during rainfall events. Similar problems exist in several of the WWTPs listed previously.

Figure 2

Monthly variation of maximum daily flow and Cumulative Deviation from Mean (CDFM) of monthly rainfall between 2015 and 2017 in Terkos Advanced WWTP.

Figure 2

Monthly variation of maximum daily flow and Cumulative Deviation from Mean (CDFM) of monthly rainfall between 2015 and 2017 in Terkos Advanced WWTP.

Inflow and Infiltration, commonly referred as ‘I&I’, is a frequently seen problem in wastewater treatment systems around the world (Weiss et al. 2002; Staufer et al. 2012; Pawlowski et al. 2014). Inflow is defined as the clean water entering sewer pipes at direct points such as manhole covers and roof drains connected to sewer pipes. Infiltration, on the other hand, refers to the water that enters sewer pipes mostly from groundwater seeping through pipe joints or faulty locations along the pipe (EPA 2014). As a result, operational difficulties arise, treatment performance decreases and cost of operation increases due to higher energy demand and use of chemicals (Karpf & Krebs 2011). If necessary actions to mitigate this problem are not taken, the impacts are expected to become more severe as the infrastructure ages and deteriorates. To tackle this problem, ISKI is planning to rehabilitate existing sewer lines with proper internal sealing. Beside sewer pipes, manholes can also be structurally rehabilitated. There have been successful applications of poured-in-place concrete linings for manholes (EPA 2014). Old and leaky manhole covers should be replaced with watertight covers as they can be significantly contributing to I&I.

Dilution of wastewater due to I&I also affects sludge amount and quality. There have been occasions during sampling where no sludge was generated due to washout. Average sludge generation was estimated as 43.2 g dry solids per population equivalent (PE) per day assuming 0.12 kg COD contribution per person per day. The current practice is using mobile dewatering equipment to process the generated sludge and transport it to the big WWTPs where they are combined and go through final disposal at municipal solid waste landfills. Landfill disposal is not considered as a sustainable practice in the EU and many other countries any more (Kalderis et al. 2010). Hence, transporting sludge as supplementary fuel to licensed cement factories after thermal drying, biosolids composting and incineration alternatives have been evaluated by ISKI. Three incineration plants are currently planned for the disposal of WWTP sludge in the long run.

In recent years, natural treatment systems such as constructed wetlands have been increasingly used for wastewater treatment in small communities across Europe and North America (Kadlec & Wallace 2009; Wu et al. 2015). Compared to conventional treatment systems, their low construction cost, less energy demand, relatively easy operation and maintenance makes them suitable for wastewater treatment in rural areas (Wu et al. 2015).

Orucoglu constructed wetland system was designed as a hybrid system consisting of a septic tank followed by horizontal subsurface flow wetlands (HSFWs) and vertical subsurface flow wetlands (VSFWs) (Ayaz et al. 2008). The purpose of this design is to achieve effective nitrogen removal through nitrification and denitrification. As the water percolates through the pulse-loaded VSFW via unsaturated flow, oxygen is transferred to the wetland bed, allowing nitrification. In contrast, HSFWs operate under anoxic conditions and promote denitrification (Kadlec & Wallace 2009). Average monthly performance data for the Orucoglu constructed wetland during 2017 are given in Table 3.

Table 3

Average monthly performance data for the Orucoglu constructed wetland in 2017

COD (mg/L)
BOD5 (mg/L)
TN (mg/L)
TP (mg/L)
TSS (mg/L)
InfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluent
January 47 12 12 10.0 6.0 0.9 0.5 58 21 
February 86 24 43 28.1 15.8 1.9 1.5 29 
March 171 41 120 20 29.0 16.0 2.2 2.3 32 10 
April 220 64 125 24 47.2 28.2 3.2 2.1 63 14 
May 285 109 95 46 65.0 42.6 4.9 4.4 106 40 
June 329 159 170 80 43.4 50.5 4.7 5.6 296 37 
July 280 122 195 64 60.5 46.7 5.7 5.1 138 19 
August 288 111 161 55 52.5 45.4 4.7 4.6 134 15 
September 672 155 418 83 83.7 64.1 4.8 3.8 322 30 
November 94 46 47 17 24.4 17.2 1.9 2.0 31 
December 129 24 35 17.8 8.8 1.4 0.7 32 12 
COD (mg/L)
BOD5 (mg/L)
TN (mg/L)
TP (mg/L)
TSS (mg/L)
InfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluentInfluentEffluent
January 47 12 12 10.0 6.0 0.9 0.5 58 21 
February 86 24 43 28.1 15.8 1.9 1.5 29 
March 171 41 120 20 29.0 16.0 2.2 2.3 32 10 
April 220 64 125 24 47.2 28.2 3.2 2.1 63 14 
May 285 109 95 46 65.0 42.6 4.9 4.4 106 40 
June 329 159 170 80 43.4 50.5 4.7 5.6 296 37 
July 280 122 195 64 60.5 46.7 5.7 5.1 138 19 
August 288 111 161 55 52.5 45.4 4.7 4.6 134 15 
September 672 155 418 83 83.7 64.1 4.8 3.8 322 30 
November 94 46 47 17 24.4 17.2 1.9 2.0 31 
December 129 24 35 17.8 8.8 1.4 0.7 32 12 

Average removal efficiencies for COD, BOD5 and TSS were 67%, 72% and 77%, respectively. As for the nutrients, 30% TN removal and 15% TP removal was achieved. In a hybrid constructed wetland system, if HSFWs are used before VSFWs, effluent recirculation is recommended to supply nitrified effluent to the HSFW system for denitrification. It has been shown that effluent recirculation enhances nitrogen removal (Ayaz et al. 2012; Vymazal 2013; Ávila et al. 2017). Hence, the TN removal performance of Orucoglu constructed wetland can potentially improve if the system is operated with effluent circulation.

When the constructed wetland system first started operation in 2009, the TP removal rate was reported to be 54% (ISKI, unpublished). The decrease in TP removal as the treatment system gets older is a typically seen phenomenon in wetland systems. Adsorption to sediments and filter material is the major TP removal mechanism in constructed wetlands (Kadlec & Wallace 2009). As the adsorption sites become saturated with time, TP removal efficiency rapidly declines unless the filter material is renewed each time. Thus, if efficient and continuous phosphorus removal is required, an additional treatment step such as chemical phosphorus removal might be an option.

More recently, hybrid wetland systems having free surface flow (FWS) wetlands have become more common. Inclusion of FWS wetlands together with VSFWs and HSFWs have been shown to improve TN removal efficiencies (Vymazal 2013). FWS wetlands can also improve TP removal efficiencies and keep their TP removal efficiency for a longer time, as they provide a wider sediment surface for adsorption and have more plants for phosphorus uptake. Hence, implementation of FWS wetlands within hybrid systems is recommended where there are no space constraints.

Besides mitigating the current I&I problem with the existing systems, ISKI plans to increase the number of constructed wetlands and package WWTPs with SBRs and upgrade the conventional WWTPs to advanced WWTPs for nutrient removal. Future research will focus on cost-effective design and integration of natural treatment systems for small communities that do not have access to main sewer lines.

CONCLUSIONS

  • A thorough evaluation based on the capacity and performance of the existing wastewater treatment systems in rural districts revealed that a number of these systems are not operating at their optimum.

  • I&I is a frequently seen problem, decreasing treatment performance and causing operational difficulties.

  • Natural treatment systems such as constructed wetlands after septic tanks prove as a viable alternative in rural districts of Istanbul.

  • Implementation of FWS wetlands within hybrid systems is recommended where there are no space constraints.

REFERENCES

APHA/AWWA/WEF
2012
Standard Methods for the Examination of Water and Wastewater
, 22nd edn.
American Public Health Association/American Water Works Association/Water Environment Federation
,
Washington, DC
,
USA
.
Ávila
C.
,
Pelissari
C.
,
Sezerino
P. H.
,
Sgroi
M.
,
Roccaro
P.
&
García
J.
2017
Enhancement of total nitrogen removal through effluent recirculation and fate of PPCPs in a hybrid constructed wetland system treating urban wastewater
.
Science of The Total Environment
584–585
,
414
425
.
Ayaz
S.
,
Akça
L.
,
Güneş
K.
&
Baban
A.
2008
Treatment of Domestic Wastewaters in Wetlands for Reuse-Application in Sile Orucoglu Village
.
TUBITAK-Marmara Research Center, Project No. 505G227
,
Turkey
.
Ayaz
S. Ç.
,
Aktaş
Ö.
,
Fındık
N.
,
Akça
L.
&
Kınacı
C.
2012
Effect of recirculation on nitrogen removal in a hybrid constructed wetland system
.
Ecological Engineering
40
,
1
5
.
Engin
G. O.
&
Demir
I.
2006
Cost analysis of alternative methods for wastewater handling in small communities
.
Journal of Environmental Management
79
(
4
),
357
363
.
EPA
2014
Guide for Estimating Infiltration and Inflow
.
United States Environmental Protection Agency
.
ISKI
2017
Istanbul Water Administration's Annual Progress Report
.
Istanbul
(in Turkish)
.
Kadlec
R. H.
&
Wallace
S. D.
2009
Treatment Wetlands
.
CRC Press
,
Boca Raton, FL
.
Libralato
G.
,
Volpi Ghirardini
A.
&
Avezzù
F.
2012
To centralise or to decentralise: an overview of the most recent trends in wastewater treatment management
.
Journal of Environmental Management
94
(
1
),
61
68
.
Ozturk
I.
&
Altay
D.
2015
. Water and Wastewater Management in Istanbul
. In:
UNESCO HQ International Conference on Water, Megacities and Global Change
,
Paris, France
.
Pawlowski
C. W.
,
Rhea
L.
,
Shuster
W. D.
&
Barden
G.
2014
Some factors affecting inflow and infiltration from residential sources in a core urban area: case study in a Columbus, Ohio, Neighborhood
.
Journal of Hydraulic Engineering
140
(
1
),
105
114
.
Staufer
P.
,
Scheidegger
A.
&
Rieckermann
J.
2012
Assessing the performance of sewer rehabilitation on the reduction of infiltration and inflow
.
Water Research
46
(
16
),
5185
5196
.
Weiss
G.
,
Brombach
H.
&
Haller
B.
2002
Infiltration and inflow in combined sewer systems: long-term analysis
.
Water Science and Technology
45
(
7
),
11
19
.
Wu
H.
,
Zhang
J.
,
Ngo
H. H.
,
Guo
W.
,
Hu
Z.
,
Liang
S.
,
Fan
J.
&
Liu
H.
2015
A review on the sustainability of constructed wetlands for wastewater treatment: design and operation
.
Bioresource Technology
175
,
594
601
.