Haddad, M., (2006). Evaluation of Performance and

Operational Costs for a Pilot UF/RO Wastewater

Treatment And Reuse Plant. Arab Water World (AWW)

magazine, Vol. 3, No. 4, May 2006.

Evaluation of Performance and Operational Costs for a Pilot UF/RO

Wastewater Treatment And Reuse Plant

By: Marwan Haddad

Abstract

A two and half-year wastewater treatment and reuse study was conducted at a reuse site

near Nablus, Palestine. The overall objective of the research was to evaluate the treatment

effectiveness and feasibility of using new wastewater treatment approaches to produce

high quality –more reliable effluent from secondary or conventionally treated municipal

wastewater. The treatment system consists of (a) a primary settling basin (4.5 m wide,

16,0 m long, and 3.0 m deep), (b) a vertical-flow infiltration CW cell (150 m2 in surface

area, 112.5 m3 in volume) followed by a settling basin and (c) an UF/RO pilot plant.

Maintenance, operational , and chemical input costs for system operation were tacked.

Water samples were collected bimonthly at influent and effluent points for each treatment

stage and analyzed for total plate count, turbidity, total nitrogen, total phosphorus, total

suspended solids, biochemical oxygen demand, chemical oxygen demand, temperature,

conductivity, and pH.

The study found that 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 and Reuse, Ultra

filtration/Reverse Osmosis, 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).

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

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

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

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

There has been continuous and significant growth in fresh water demand in the Middle

East and due to limitations in water supply availability, water scarcity is sharpening with

time in this region. Consequently attention is being directed towards reusing treated

municipal wastewater as a potential supplementary water source to agricultural as well as

domestic and industrial uses. Dissolved constituents and biological contamination in

conventionally or secondary treated effluents were considered among the most important

obstacles for safe reuse either in agriculture or in other sensitive sectors.

During the last few years strong emphasis was given to the development and testing of

new treatment approaches to produce high quality effluent from secondary or

conventionally treated municipal and industrial wastewater. These developments and

testing have resulted in the use of ultrafitration (UF) in wastewater treatment. UF is a

form of filtration that uses partially permeable membranes to preferentially separate

different fluids or ions. UF does not require high energy to perform the separation. UF is

capable of concentrating bacteria, some proteins, some dyes, and constituents that have a

larger molecular weight of greater than 10,000 daltons. UF is typically not effective at

separating organic streams (Osmonics, 2002). Four treatment approaches or directions

were identified in the use of UF following secondary treatment processes:

(a) using (UF) as a tertiary treatment process by it self,

(b) using (UF) as tertiary or post treatment process in combination with sand

filters or, ozone treatment, or micro-filtration,

(c) using (UF) as pretreatment process in combination and before reverse osmosis

(RO) , and

(d) using pre-filtration then ultrafitration (UF) followed by RO as three stage

treatment process.

The most applied and tested treatment approach found in literature was that of using (UF)

as pretreatment process in combination and before reverse osmosis (RO). RO is a

technique of cross-flow filtration that uses composite polyamide membranes to remove

molecules of dissolved salts, metals and certain dissolved organics. This approach was

proven to be technically reliable and cost viable approach (Sierka et al 1997, Hoof et al

1999 and Mignani et al 1999).

Capital cost was reported and estimated to range from 0.29 US$/ m3-day for systems

with 430 m3/day to 0.11 US$/ m

3-day for systems with capacity of over 20,000 m

3/day

(Bates and Cuuozzo, 1999). Reported operational costs of various UF treatment systems

were in the range of 0.1 to 0.27 US$/m3 (Hoof et al, 1999).

UF reported results indicate reductions in water suspended solids from 1600 to 3.5 mg/l,

in COD from 416 to 12 mg/l and in BOD from 469 to 5 mg/l and fecal bacteria removal

was close to 100% (Abdessemed et. al., 1999).

Plant with capacity from few m3/day as pilot and lab scale plants to small scale plants

with capacity of 432-1480 m

3/day to large scale treatment systems of 375,000 m

3/day

were also reported (Gagne, 2004).

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.

The site has small green house (~60 m2), small open area for vegetable growth (~250

m2), and the reminder mostly planted with various trees.

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.

As shown in Figure 1 bellow, the treatment 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.

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

with hydraulic loading of 0.09 m3/m

2-d and a detention time of 3.5 days. The flow to the

CW was introduced through a perforated PVC pipe located along the upper-inner edges

of the CW. The BOD and TSS loading rates were 0.029 and 0.063 kg/m2-d, respectively.

The inlet depth was 0.50 m and the outlet depth of 1.0 m with bottom slope to outlet of

1.67%. 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.

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

through the system in two and half 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).

The UF/RO plant was bought from NIROSOFT-Carmeal and the system was delivered to

the reuse site near Nablus on a flat truck. The plant was compact on a stainless steel

frame (1.20 m wide, 3.00 m long, and 1.60 m high). The plant was equipped with flow

and pressure meters, valves, pumps and pipes. It included the following unit processes:

UF (one NIROSOFT RM10 membrane) to remove fine particles

RO (one Filmtec FT30 UF element) to remove very fine particles,

microorganisms, and dissolved salts and organics.

The UF , Nirosoft RM10-8 element has Molecular Weight Cut Off (MWCO) of 20 k

Dalton. The element has a length of 1016 mm, diameter of 200 mm and membrane active

area of 37.1 m2. The design rejection rate is 88-93%.

The RO FT30 element has the following characteristics:

Volume in vessel = 0.2 m3

Volume in pipes = 0.11 m3

pH range 1-11

Cleaning rate ~3 m3/hr

The UF/RO pilot plant was first operated with clean water to check for proper operation

and then was operated with CW effluent. Reject flows generated by the UF/RO

processes were discharged to the raw wastewater open channel. Differential Pressure

(ΔP) was measured across each stage of the array of pressure vessels.

Membranes were cleaned with NaOH solution during the first month of operation then

and due to fouling a combination of alkaline (0.1%, NaOH, pH 12 , 27oC) followed by

acidic solution (0.2%, HCl-pH 2, 27 oC) cleaning was used. Cleaning was conducted for

the first time after two weeks of operation then it was conducted weekly or every 25

hours of operation for about 25-30 min.

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

Figure 2 Schematic diagram of the UF/RO pilot system.

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.

Figure 2 present the history of pilot plant fouling. As presented in Figure 2, during the

first 250 hours of operation, flow rate dropped from about 400 l/hour to 170 l/hr or about

60%.

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

Membrane Pilot Treatment Plant Cost/m3

Cost Element Cost in US$

Capital Depreciation 15 yrs (0.72 $/m3)

Energy (Diesel Generator) 1$/hr (2.50 $/m3)

Operation and Maintenance

Equipment

Labor Cost (700$/month)

0.02$/m3

2.33 $/m3

Cleaning chemicals (HCL &NaOH) Cost 0.015 $/m3

Total Cost per m3 5.59

UF/RO pilot plant is producing water of finest quality suitable for all kind of irrigation

classes. However, the plant is limited by the fouling phenomena which leads during

filtration continuous decrease of the

permeate flux.

The continuing pilot plant operation, so far, is due to the good constructed wetland

effluent quality (low turbidity and about neutral pH).

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.

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

Ave = 699 mg/l

Ave = 126 mg/l

Ave = 0 mg/l

Ave = 85 mg/l

Ave = 319 mg/l

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

UF/RO Effluent Flowrate as a function of Operational Time

0

50

100

150

200

250

300

350

400

450

0

101

176

251

326

401

476

551

626

701

776

851

926

1001

1076

1151

1226

1301

1376

1451

1526

1601

1676

1751

1826

1901

1976

2051

2126

2201

2276

2351

2426

2501

2576

2651

Operational Time in Hours

Flo

wra

te i

n l

/hr