Haddad, M., (2006). Evaluation Of Constructed Wetland

As Secondary Wastewater Treatment, Source For Tertiary

Wastewater Treatment; And Reuse System. ASCE and

World Water and Environmental Resources Congress In

Omaha, Nebraska, USA (May 21-25, 2006). The paper

Awarded Visiting International Fellowship

Evaluation of Constructed Wetland as Secondary Wastewater

Treatment, Source for Tertiary Wastewater Treatment; And Reuse

System

By: Marwan Haddad

Abstract

This paper describes an investigation into the treatment effectiveness and feasibility of

constructed wetland (CW) system as a secondary wastewater treatment system, as an

economic agricultural producer, and as a pretreatment phase for an ultrafitration/reverse

osmosis UF/RO tertiary treatment plant.

The treatment system consists of one vertical-flow infiltration CW cell (150 m2 in surface

area, 112.5 m3 in volume) and two settling basins (one before and one after the CW);

gravel, coastal sand, and almond shells were used as CW media. The CW was vegetated

with various plants including spineless cactus. Samples were analyzed for total plate

count, turbidity, total nitrogen, total phosphorus, total suspended solids, biochemical

oxygen demand, chemical oxygen demand, temperature, conductivity, and pH.

The CW operation indicated a significant reduction in influent water quality and proved

to be of suitable for smooth operation of the UF/RO pilot plant. High biomass growth

was observed on the spineless cactus and banana and little or negative growth was

obtained on other planted crops.

Keywords: Constructed Wetland, Wastewater treatment, Wastewater Reuse,

Environmental Management Systems for Agriculture, Palestine

Introduction

Wastewater collection and disposal in Palestine continues to be one of the most public

health and environmental hazards. However, the status of wastewater treatment and

collection services varies from one locality to another. Wastewater collection systems

are available in most of the cities of the West Bank and Gaza Strip with 50-85%

collection levels (Approximately 60% of the houses in the urban communities are

connected to sewage systems – PWA 2003).

Few wastewater treatment plants have been constructed in the past 10 years for a number

of cities in the West Bank and Gaza while untreated wastewater still flows in the wadis

from many other cities including major urban centers as the city of Nablus. However,

more than half of the population of the West Bank lives in more than 500 villages. Most

Marwan Haddad, Professor, An-Najah National University, Nablus Palestine, Tel. + 970-9-2381115, Fax

+070-9-2386982 , email: haddadm@email.com, haddadm@najah.edu

of these village lack wastewater collection systems and rarely have wastewater treatment

systems. In most of these villages, wastewater is disposed through cesspools. Due to the

spread of the rural population in the West Bank in a large number of villages and the high

cost of wastewater conveyance system, decentralized wastewater treatment plants are of

great value for the local population and are expected to be the only feasible alternative for

wastewater treatment in the West Bank.

The situation in the refugee camps can only be classified as very poor. Wastewater is

channeled into open drains until it flows into either a sewage network in a nearby city or

is simply transported to outside camp boundaries. Most of the Israeli settlements in the

West Bank have sewage networks and most of these settlements discharge the wastewater

into Wadis without any treatment.

Because there is very little wastewater treatment systems in rural areas of Palestine and

the economic situation is very bad, there is a high interest in testing and evaluating the

use of CW systems as a secondary treatment level benefiting from there low-cost, good

efficiency and minimum maintenance properties.

Current study will present and detail the results of the CW - UF/RO treatment and reuse

experiment indicating and emphasizing the lessons learned including costs, operation

and maintenance problems, and reuse and treatment efficiency.

Background

Wetlands have been used for secondary and tertiary wastewater treatment in different

parts of the world since the 1950s and research over the last half century has accumulated

much quantitative information on the performance of these systems (Verhoeven and

Meuleman 1999, Sukais and Tanner 2004),

Wetland beds contain plant species including cattails, reeds, bulrush, bamboo, blueberry,

cranberry, watercress, wild rice, alder, bald, cypress, river birch, swamp white oak, water

oak, white cedar, and black gum or tupelo (Wynn 2003).

Constructed wetlands (CW) for water pollution control are becoming an accepted

technology world-wide. Recent inventories have indicated that there are more than 7000

CW in Europe and North America, with the number increasing in central and south

America, Australia and Newzealand as well as Africa and Asia (Senzia et al 2002).

Although CW proved to be low in cost, easily managed, good for atural habitat, and good

in performance without the use of chemicals still some how controversial because there is

no agreed upon design criteria for the various CW systems (OEMC, 2001). In addition,

appropriate vegetation and uniform flow through the cells have been difficult to establish.

It was found that while data from some sources have indicated very good treatment

efficiencies, the performance of typical wetlands have been very erratic (Langston and

VanDevender, 1998).

Constructed wetlands are artificial wetlands. According to U.S. EPA (1993), a

constructed wetland is defined as “a wetland specifically constructed for the purpose of

pollution control and waste management, at a location other than existing natural

wetlands.”

Constructed wetlands are efficient at transforming pollutants such as nitrogen

phosphorus, suspended solids and biological oxygen demand found in wastewater, into

essential nutrients for plant growth or harmless bi-products. This was due to high level of

biological productivity created during filling and draining processes(Kadlec & Knight

1996).

Experience with infiltration wetlands in Europe has shown that systems loaded

with 800 PE:ha of domestic wastewater had a long-term removal capacity of

80–95% for COD and BOD, 99% for bacterial pollution; 35% for N; and 25% for

P. The removal of nutrients can be optimized up to about 50% for N and 40% for

P at these loading rates (Schierup et al., 1990; Meuleman, 1994).

Methods

A wastewater treatment system consisting of a vertical flow CW as a secondary level

and UF/RO pilot plant as a tertiary level was used.

The treated effluent was directed to various reuse schemes. The treatment and reuse site

is located in a land area of 1.8 ha on the eastern open wastewater channel about 13 km

east of the city of Nablus towards the Jordan Valley. Nablus is located on the northern

parts of the West Bank – Palestine. The West Bank is part of the Palestinian territory

under the administrative control of Israel. The population of the West Bank is estimated

at 2,304,825 (Palestinian Central Bureau of Statistics, 2003). The wastewater flow from

eastern parts of Nablus contains domestic and industrial liquid waste.

In this paper, the CW results only will be presented and discussed.

As shown in Figure 1 bellow, the treatment and reuse system consist of:

A diversion canal built of reinforced concrete transporting raw wastewater from

the open channel to a settling tank (50 cm wide and 50 cm deep),

A raw wastewater collection and settling tank built of reinforced concrete from

which settled wastewater is being pumped to a CW basin (4.5 m wide, 16,0 m

long, and 3.0 m deep),

A CW basin built of reinforced concrete where gravel, almond shells, and coastal

sand represent the media (5 m wide, 30m long, and 0.75 m deep, see Table 1).

The CW was vegetated with economic crops of local importance such as spineless

cactus, pecans, bananas, apricot, peaches, and apples.

A final settling tank built of reinforced concrete from which settled wastewater is

being pumped to UF/RO pilot plant or to reuse (5 m wide, 10 m long, and 2.0 m

deep),

A UF/RO pilot plant for tertiary treatment of wastewater

A 1.8 ha reuse site. The site has small green house (~60 m2), small open area for

vegetable growth (~250 m2), and the reminder mostly planted with various trees.

The hydraulic regime of the CW was vertical flow with intermittent wetting and draining.

The flow to the CW was introduced through a perforated PVC pipe located along the

upper-inner edges of the CW. After being filled the CW was allowed to drain at the

preset rate controlled by three check valves located at the lower end of the discharge side

(see Figure 1). CW filling was done twice per week. Due to controlled discharge and CW

size, variations in water movement and mixing in the CW was ignored. Between

September 2003 and September 2005, the average flow through the CW was 13.5 m3/day.

Flow characteristics are given in Table 1.

To assess treatment effects, wastewater was sampled once a week at several pointes

through the system in 2-year period. Samples were analyzed for total nitrogen, total

phosphorus, total suspended solids, chloride, biochemical oxygen demand, chemical

oxygen demand, temperature, conductivity, turbidity, and pH. All analysis were

conducted according to Standard Methods for the examination of water and wastewater

(APHA-AWWA-WEF, 1998).

Table 1 CW Characteristics and Operating Parameters of Importance

Characteristic or Parameters Unit Value

Bottom Length m 30

Bottom Width m 5

Bottom Slope to Outlet % 1.67

Surface Area m2 150

Mid-Length Depth m 0.75

Volume m3 112.5

Bed Porosity % 42

Effective Volume m3 47.5

Detention Time* days 3.5

BOD Loading* kg/m2-d 0.029

TSS Loading* kg/m2-d 0.063

Hydraulic Loading* m3/m

2-d 0.09

* = Average Measured During the Study

Figure 1 Wastewater Treatment and Reuse Site

To Reuse

To Reuse

UF/RO

CW

Settling

Basin 1 Settling

Basin 2

Perforated

PVC Pipe Diversion

Channel

Wastewater

Channel

Pump 2

Pump 1

Results and Discussion

Performance data were collected for two year period and a summary is presented in

Figures 2-a to 2-h and Table 2. Although the results include the UF/RO pilot plant

results, the following discussions will emphasize the CW only.

As shown in Figure 2, the BOD, TSS varied considerable over the two years including

clear seasonal variations. However, it was noticeable that these variation of various

quality parameters were relatively repeated in the second year (with small exceptions).

Very little maintenance works has been required for the CW over the two year period.

Maintenance issues included clearing openings of the perforated influent pipe

to prevent clogging, cleaning and/or harvesting of the wetland plants, and checking the

discharge valves. No problem was faced concerning mosquitoes and other insects.

It is apparent from the data collected that the CW was able to produce effluent with very

good quality.

Influent BOD concentrations to the CW were ranging between 130 and 540 mg/l with an

overall average of 319 mg/l which is considered high in western countries. This is due to

water scarcity and low dilution of waste. Average organic loading rate was 28.7

gm/m2/d. Effluent BOD concentrations to the CW were ranging between 20 and 190

mg/l with an overall average of 85 mg/l which is reasonable compared to influent

concentrations. Average BOD removal rate was 73.4%. Although BOD removal was

somehow uniform which gives reliability to the treatment process, BOD removal rate was

a little higher in summer months than winter months.

Influent TSS concentrations to the CW were ranging between 550 and 900 mg/l with an

overall average of 699 mg/l which is also considered high in western countries and due to

the same reason as for BOD. Average organic loading rate was 28.7 gm/m2/d. Effluent

BOD concentrations to the CW were ranging between 20 and 190 mg/l with an overall

average of 85 mg/l which is reasonable compared to influent concentrations. Average

BOD removal rate was 73.4%. Although BOD removal was somehow uniform which

gives reliability to the treatment process, BOD removal rate was a little higher in summer

months than winter months.

The pH difference between influent and effluent water to the CW was little ranging

between 7.2 – 7.4 in thee influent and about 7.3 in the effluent.

Average influent Chloride concentration to the CW was 330 mg/l with low removal rate

of 12%. Chloride concentrations were higher in summer in raw wastewater and in CW

effluent than winter probably due to dilution factor. This represent a typical secondary

treatment efficiency.

Average TPC removal was 99.2 % which still less than acceptable for unrestricted

irrigation water quality standards.

Reasonable average removal rates of TP (65.2%) , TN (48.6%) , and turbidity (62.5%)

were observed in the CW (See Table 2).

The performance of the UF/RO pilot plant was very good in term of effluent water

quality (see Figure 2 and Table 2). However, fouling of membranes started shortly after

the start of plant operation and continued allover the experimental period. Most of the

fouling was permanent despite the various methods used in cleaning the membranes. The

cost of treatment per meter cubic using the UF/RO was 5.65 US$, which considered very

high and unacceptable by local farmers. In addition to the need of cleaning chemicals, a

trained technician presence was obligatory every time the plant is operated and/or

maintained which resulted in increasing the cost of produced water.

Vegetative growth in the CW was good for cactus and bananas, while orchards trees

(apples, apricots, plum, and pecans) mostly dried by the end of the second season. The

growth of cactus in CW was steady positive all over the last two years of about 670

gm/m2 (presented in Figure 3). This indicate the advantage of CW in reusing raw

wastewater for small (as well as large system) and in producing fodder and fruit crop in

economic quantities such as spineless cactus.

Table 2 Average Performances of CW and UF/RO

Description Quality Parameter

TSS BOD COD Cl TN TP TPC Turbidity

CW

In

Out

Loading rate

% Removal

699

126

62.9

82.0

319

85

28.7

73.4

641

252

57.7

60.7

330

291

29.7

12.0

14.4

7.4

1.3

48.6

20.7

7.2

1.9

65.2

5 E-6

4.2 E-4

--------

99.2

48

18

-------

62.5

UF/RO

In

Out

% Removal

126

0

100

85

1-3

96-99

252

3-5

98-99

290

2-8

97-99

7.4

2-3

60-73

7.2

0

100

4.2 E-4

0

100

18

0-3

83-100

Loading Rate in gm/m2-d, In, Out in mg/l, TPC in #/100 ml, and Turbidity in NTU

Conclusions

In conclusion and based on the results of this study, CW proved to deliver:

Reasonable effluent quality but not complying with quality standards

Good in reuse

Cost is minimal

O&M costs are minimal and need no chemical use or high tech personal for O&M

And therefore, could be recommended as a secondary level treatment for small systems

such as rural communities and/or remote areas in Palestine and elsewhere. Combination

of CW with an additional extended treatment system is necessary to attain accepted water

quality standards.

The data collected indicated that vegetation of CW with spineless cactus and bananas was

successful and feasible while orchard trees were problematic.

Additional treatment of the wastewater using The UF/RO would provide excellent

effluent quality which is very suitable for any class of reuse, however fouling is a real

problem, flow dropped to 25-30% of original and cost for small systems is very high per

cubic meter produced and will not be accepted by farmers. Furthermore, O&M of UF/RO

pilot plant need to be conducted by specialized personal and time and material

consuming. Accordingly, such treatment system is not recommended for small

communities.

Acknowledgements

This study was conducted as part of a MERC project No. M22-006. The author would

like to acknowledge and thank MERC, the Palestinian Research Group, and the Grand

Water Research Institute for their support and cooperation in conducting this study.

References

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wastewater’, 20th edition, eds L. S. Clesceri, A. E Greenberg, A. D. Eaton, American

Public Health Association, American Water Work Association, Water Environment

Federation, Washington DC.

Kadlec, R. H., & Knight, R. L. 1996. Treatment Wetlands, Boca Raton: CRC Press,

Lewis Publishers.

Langston, J., and VanDevender, K., (1998). Constructed Wetlands: An Approach

for Animal Waste Treatment. University Of Arkansas, Division Of Agriculture,

Cooperative Extension Service Report, Found In http://www.uaex.edu, accesses June

2005.

Meuleman, A.F.M., 1994. Waterzuivering door moeras-systemen: onderzoek naar de

water- en stofbalansen van het rietinfiltratieveld Lauwersoog. RIZA Nota 94.011, 1–134.

OEMC, (2001). Colorado Governor’s Office of Energy, Management, and Conservation.

Colorado Constructed Wetland Inventory, Denver, March 2001.

Palestinian Central Bureau of Statistics . (2003). Press conference about the results of

Local Community Survey in the Palestinian Territory , September, 2003, Ramallah –

Palestine.

PWA, Palestinian Water Authority. (2003). Water Supply Status in Palestine. Accessed

on February, 2004 at http://www.pwa-pna.org/status/supply.php.

Schierup, H.H., Brix, H., Lorenzen, J., 1990. Wastewater treatment in constructed reed

beds in Denmark; state of the art. In: Cooper, P.F., Findlater, B.C. (Eds.), Constructed

Wetlands in Water Pollution Control. Pergamon Press, Oxford, pp. 495–504.

Senzia, M., Mashauri, A., and Mayo, W., (2002). Suitability of Constructed Wetlands

and Waste Stabilisation Pond in Wastewater. 3rd WaterNet/Warfsa Symposium 'Water

Demand Management for Sustainable Development', Dar es Salaam, 30-31 October 2002

Sukais, J., and Tanner, C., (2004). Evaluation of the Performance of Constructed Wetland

Treaing Domestic Wastewater in the Waikato Region, NIWA Client Report : HAM2004-

015 for Environment Waikato, Hamilton East , March 2004.

U.S. Environmental Protection Agency. 1993. Subsurface Flow Constructed

Wetlands for Wastewater Treatment: A Technology Assessment. EPA Report 832-R-

93-008.

Verhoeven, J., and Meuleman, A., (1999), Wetlands for wastewater treatment:

Opportunities and limitations. Ecological Engineering 12 (1999) 5–12

Wynn, J., (2003). Innovative And Alternative On-Site Treatment Of Residential

Wastewater. Prepared For TERRAFORMS, Athens, Ohio, September 2003.

Figure 2-a Suspended Solids Concentration in Raw Wastewater, CW, and UF/RO

Figure 2-b Chloride Concentration in Raw Wastewater, CW, and UF/RO

Ave = 699 mg/l

Ave = 126 mg/l

Ave = 0 mg/l

Chloride Concentration

0

100

200

300

400

500

600

700

8009/

3/20

03

11/3

/200

3

1/3/

2004

3/3/

2004

5/3/

2004

7/3/

2004

9/3/

2004

11/3

/200

4

1/3/

2005

3/3/

2005

5/3/

2005

7/3/

2005

Time

Cl

in m

g/l

Raw Wastewater Constructed Wetland UF/RO

Water Turbidity

0

10

20

30

40

50

60

70

9/3/

2003

10/3

/200

3

11/3

/200

3

12/3

/200

3

1/3/

2004

2/3/

2004

3/3/

2004

4/3/

2004

5/3/

2004

6/3/

2004

7/3/

2004

8/3/

2004

9/3/

2004

10/3

/200

4

11/3

/200

4

12/3

/200

4

1/3/

2005

2/3/

2005

3/3/

2005

4/3/

2005

5/3/

2005

6/3/

2005

7/3/

2005

8/3/

2005

Time

Tu

rbid

ity

[NT

U]

Constructed Wetland Effluent UF/RO Effluent Raw Wastewater

Ave = 85 mg/l

Ave = 319 mg/l

Figure 2-d BOD Concentration in Raw Wastewater, CW, and UF/RO

Figure 2-c Turbidity Levels in Raw Wastewater, CW, and UF/RO

Ave = 48 NTU

Ave = 18 NTU

Ave = 0-3 NTU

Ave = 641 mg/l

Ave = 252 mg/l

Ave = 3-5 mg/l

Total Plate Count (TPC)

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

9/3

/2003

11/3

/2003

1/3

/2004

3/3

/2004

5/3

/2004

7/3

/2004

9/3

/2004

11/3

/2004

1/3

/2005

3/3

/2005

5/3

/2005

7/3

/2005

Time

TP

C

Raw Wastew ater Constructed Wetland UF/RO

Ave = ~0 Ave = 42045

Ave = 5,050000

Figure 2-e Total Plate Count Concentration in Raw Wastewater, CW, and UF/RO

Figure 2-f COD Concentration in Raw Wastewater, CW, and UF/RO

Total Phosphouros

0

5

10

15

20

25

30

9/3

/2003

11/3

/2003

1/3

/2004

3/3

/2004

5/3

/2004

7/3

/2004

9/3

/2004

11/3

/2004

1/3

/2005

3/3

/2005

5/3

/2005

7/3

/2005

Time

TP

in

mg

/l

Raw Wastew ater Constructed Wetland UF/RO

Ave = 20.7 mg/l

Ave = 7.2 mg/l

Ave = 0.0 mg/l

Total Nitrogen (TN) Concentration

0

5

10

15

20

25

9/3

/2003

11/3

/2003

1/3

/2004

3/3

/2004

5/3

/2004

7/3

/2004

9/3

/2004

11/3

/2004

1/3

/2005

3/3

/2005

5/3

/2005

7/3

/2005

Time

TN

in

mg

/l

Raw Wastew ater Constructed Wetland UF/RO

Ave = 14.4 mg/l

Ave = 7.4 mg/l

Ave = 2-3 mg/l

Figure 2-g Total Phosphorous Concentration in Raw Wastewater, CW, and UF/RO

Figure 2-h Total Nitrogen Concentration in Raw Wastewater, CW, and UF/RO

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

30/8/200330/10/200325/2/200430/6/200430/8/200428/2/200530/5/200530/8/2005

Time

Figure 3 Change in CW of Cactus aboveground biomass with Time

Cac

tus

Bio

mas

s

us

Bio

mas

s in

Bio

mas

s in

ass

in g

m/m

2

gm

/m2

m2