SW2 Poppy Sri Lestari 15304007

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THE CHOOSING OF SLUDGE TREATMENT INSTALLATION SYSTEM

ALTERNATIVES

FOR BADAK SINGA WATER TREATMENT PLANT

PEMILIHAN ALTERNATIF SISTEM INSTALASI PENGOLAHAN LUMPUR

IPAM BADAK SINGA

Poppy Sri Lestari1)

and Mindriany Syafila2)

Department of Environmental Engineering FTSL-ITB, Jl. Ganesha 10 Bandung 401321) [email protected]

2)[email protected]

Abstract : Badak Singa is one of Water Treatment Plant in Bandung’s Municipality Water Companies (PDAM

Bandung). In processing its drinking water, residue is produce. The residue contains such materials as

muddiness-causing sludge to the raw water, organic and non-organic solidity, alga, bacteria, viruses, colloids,

and other chemical substances either naturally formed or as coagulant precipitated during the process of

producing drinking water. Residue coming from the process of producing drinking water, until recently is still flown to the public water supply (Cikapundung River). This residue disposing activity has affected not only the

Cikapundung River’s biota but also its aesthetic aspect. Currently, Indonesian Government has issued Regulation No. 16, 2005, in which under item 3 of the article 9, it is stipulated that the waste produced from any

processing must be treated before it is drained. Thus, we need sludge treatment system which doesn’t only fulfill

the regulation, but also decrease the influence for Cikapundung River, and increase quality of the environment.

The units for sludge treatment are going to be made. There are three processing steps, those are thickening,conditioning, and dewatering. The best alternative option is done by considering treatment effectiveness and

present value annual cost. From these considerations, the sludge treatment system with gravity thickener,

chemical conditioning, and belt filter press is chosen. The sludge treatment system can fulfill economical aspect

and availability of land. The total cost for building the sludge treatment system is about 5.7 billion rupiahs.

Key words: Badak Singa, residue, sludge treatment system, belt filter press

Abstrak : Badak Singa merupakan salah satu Instalasi Pengolahan Air Minum dari Perusahaan daerah yang

mengolah air minum di Kota Bandung (PDAM Bandung). Dalam hasil pengolahan air minum ini tentudihasilkan residu berupa lumpur yang mengandung material-material seperti material penyebab kekeruhan

pada air baku, padatan organik dan anorganik, alga, bakteri, virus, koloid, dan bahan-bahan kimia baik itu

yang secara alami terdapat pada air baku atau bahan kimia yang ditambahkan sebagai koagulan dan

terpresipitasi di proses. Residu dari pengolahan air bersih IPAM hingga saat ini masih dibuang kembali ke

perairan umum (Sungai Cikapundung). Pengaruhnya terhadap Sungai Cikapundung dapat dikategorikan

menjadi dua yaitu pengaruh estetika dan pengaruh terhadap biota air di dalamnya. Saat ini, Indonesia telah

memiliki peraturan khusus tentang residu dari IPAM. Peraturan yang berlaku saat ini di Indonesia yaitu

Peraturan Pemerintah Nomor 16 Tahun 2005. Pada pasal 9, ayat 3, disebutkan bahwa limbah akhir dari proses

pengolahan wajib diolah terlebih dahulu sebelum dibuang ke pembuangan akhir. Oleh karena itu, diperlukan

suatu sistem pengolahan lumpur di IPAM Badak Singa ini, yang selain dapat memenuhi peraturan yang

berlaku, juga diharapkan dapat mengurangi pengaruhnya terhadap sungai Cikapundung, serta dapat

meningkatkan kualitas lingkungan di sekitarnya. Direncanakan unit-unit pengolahan lumpur yang akan

digunakan terdiri dari tiga tahapan proses, yaitu thickening, conditioning dan dewatering. Pemilihan alternatif terbaik dilakukan dengan melihat efektifitas pengolahan dan present value annual cost. Dari pertimbangan-

pertimbangan ini maka dipilih sistem pengolahan lumpur yang terdiri dari gravity thickener, chemical

conditioning dan belt filter press yang memenuhi baik aspek ekonomi maupun ketersediaan lahan. Total biaya

yang diperlukan untuk membangun sistem pengolahan lumpur ini adalah sekitar Rp.5,7 milyar.

Kata kunci : Badak Singa, residu, sistem pengolahan lumpur, belt filter press



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INTRODUCTION

Badak Singa is one of Water Treatment Plant in Bandung’s Municipality Water

Companies (PDAM Bandung). In processing its drinking water, residue is produce. The

residue contains such materials as muddiness-causing sludge to the raw water, organic and

non-organic solidity, alga, bacteria, viruses, colloids, and other chemical substances either

naturally formed or as coagulant precipitated during the process of producing drinking water.

In the process of producing drinking water, mud is resulted. This mud is called

sludge. This sludge is categorized as chemical waste because it contains inert. There are

various kinds of sludge produced as a result of the process of producing drinking water. They

contain such substances, such as alumina (Al2O3), SiO2, Fe2O3, CaO, and MgO.

The concern towards the regulation about residue coming from the process of

producing drinking water in developed countries has recently been increasing. For example,

Public Law 92–500 and the Water Pollution Control Act Amendment 1972 categorize sludge

resulted from the process of producing drinking water as industrial waste (Kawamura, 1991).

Residue coming from the process of producing drinking water, until recently is still

flown to the public water supply (Cikapundung River). This residue disposing activity hasaffected not only the Cikapundung River’s biota but also its aesthetic aspect.

Currently, Indonesian Government has issued Regulation No. 16, 2005, in which

under item 3 of the article 9, it is stipulated that the waste produced from any processing must

be treated before it is drained.

The residue resulted from drinking water treatment installation system can be formed

into, what is know, cake shape, which can be benefited other purposes. For example, it can be

used as a mixture in soil or clay liner, as landfill, and other such as fertilizer, brick (batako),

and other value added materials.

Based on above–mentioned background, it is necessary that Badak Singa Water

Treatment Plant design a sludge treatment installation system to reduce the sludge in its

drinking water production.There are several factors that influence a sludge treatment installation system. They

are, among others: the characteristics of sludge, amount of sludge produced, type of

treatment, and economic cost.

By designing its sludge treatment installation system, it is expected that Badak Singa

Water Treatment Plant can achieve three objectives. The first is the objective of meeting the

required regulation about waste treatment. The second one is the objective of reducing the

negative effects resulted form its drinking water production. The third is the objective of

improving the environmental quality around the company.

BASIC PRINCIPLES OF DESIGN

Generally, the lifetime of a sludge treatment installation unit of a water company

depends on the sludge treatment installation system the company uses. In relation with the

sludge treatment installation unit of Badak Singa WTP, one time period construction should be applied since the capacity of its long-term drinking water will not change.

Sludge from Badak Singa WTP comes from pre-sedimentation tank, four accelators

and four flocculation-sedimentation tanks. The sludge coming from the pre-sedimentation

tank can then be drained to the river because it contains only particles in sand grain and

gravel size. As with the sludge coming from both the accelators and flocculation-

sedimentation tanks is alum mud, which has to be treated before it is drained.

The volume of raw water that goes to the water treatment installation of Badak SingaWTP is 1,400 – 1,600 litter/second. Table 1 contains data of volume rate of raw water in



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three months both in rainy season and dry season in the year 2007. It was assumed that the

data represented one year water production.

Table 1. Raw Water Quantity of Badak Singa WTP(PDAM Bandung, 2007)

Season MonthQ

(litter/second)

Rainy Season

Oct 1,527.64

Nov 1,511.80

Dec 1,509.87

Dry Season

May 1,569.28

June 1,575.84

July 1,590.23

Average 1,547.44

Maximum 1,590.23

Raw water that goes to the water treatment installation of Badak Singa WTP contains

little mineral, nutrient substance, total hardness, alkalinity, chloride, and low sulfate. Toxic

substance and crude metal are the least amount among the materials contained in the rawwater, or they are below the minimum standard. Thus, treatment is not needed.

Based on the secondary data, the characteristics of raw water from water treatment

installation unit of Badak Singa WTP in which PAC dosage is added and muddiness of the

water on the site are shown in the Table 2 below.

Table 2. PAC Dosage and Muddiness of Raw Water

Season MonthPAC Dosage

(mg/l)

Turbidity

Rates (NTU)

Turbidity

Max. (NTU)

Rainy Season

Okt 19.12 75.01 157.01

Nov 27.15 184.18 449.94

Des 30.97 132.99 300.77

Dry Season

Mei 17.11 69.97 116.85

Juni 16.87 56.93 99.63

Juli 14.59 66.93 146.33

Average 20.97 97.67 211.76

Maximum 30.97

The turbidity rates and maximum are fluctuated during a year 2007. From the Figure

1, we can see that in Badak Singa Water Treatment Plant, the maximum turbidity is happened

in July, while it is the dry seasons. Until, the design will use the average turbidity without

considering the seasons.

Average Turbidity of Badak Singa WTP (2007)

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30

day

T u r b i d i t y

( N T U )

October

November

December

May

June

July

Maximum Turbidity of Badak Singa WTP (2007)

0

500

1000

1500

2000

2500

3000

3500

0 5 10 15 20 25 30

day

T u r b i d i t y

( N T U )

October

November

December

ma y

June

July

Figure 1. Turbidity of Badak Singa WTP (2007)

The quantity of sludge from the water treatment for drinking is also influenced by

additional dose of coagulant and muddiness of raw water. Before the processing at the Badak



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Singa WTP, raw water must go through reservoir tank and pre-sedimentation tank first until

the sludge that will be processed is faded sludge, and the amount of float must be reduced by

SS sludge in pre-sedimentation tank.

The most used coagulant in the drinking water treatment is alum. Commercial alum

has a molecular weight of 594 and contains two moles of aluminum, each with a molecular

weight of 27. Therefore, alum is about 9.1 percent aluminum (54/594). The resulting

aluminum hydroxide species (Al2O3 . 3H2O) has a molecular weight of 132, and therefore, 1

mg/L of aluminum will produce 4.89 mg of solids (132/27), or 1 mg/L of alum added to

water will produce approximately 0.44 mg/L of inorganic aluminum solids (0.091 × 4.89)

(Cornwell, 1999 in the Letterman, 1999).

Coagulant that is used in Badak Singa WTP is Poly Aluminum Chloride (PAC). The

PAC dose conversion to be solid will depend on kind of PAC that is used. PAC consists of

PAC solution and Al2O3. The mixture that is used to be met is about 30.9 percent of Al 2O3.

That amount equals to 16.4 percent of aluminum, until 1 mg of PAC (as PAC) will produce

0.8 mg of solid (0.164 x 4.89).

The important thing in the calculation of sludge float is the SS value (suspended solid)

correlated with muddiness value. The b coefficient has a value among 0.7-2.2 (Cornwell,1987). The determining of b value is to compartmentalize the SS value against muddiness. In

this case, the value is just a muddiness value, until the determining of b value is 0.9. The

consideration is based on the muddiness at field which has high deviation standard, until the

average and maximum SS value is actually smaller than the muddiness value recorded at

field.

The calculation of sludge float amount uses the equations such as below (Cornwell,

1999 in the Letterman, 1999; Metcalf & Eddy, 1991):

Qsludge =SslPs

W

w ρ (1)

W = 8.34 Q (0.8Al + SS + A) - W prased (2)

SS = b TU (3)

W prased = Y/Yo x Q x SS x 1,000 L/m3 x 10-6 mg/Kg x 86,400 s/day (4)

n

AsQ

nv

Yo

Y /1

/11

−

+−= (5)

Explanation:

Qsludge = sludge generation amount (m3/day)

W = sludge production (lb/hari)

ρw = water density (Kg/m3)

Ssl = sludge specific gravity

Ps = % solid that is produce

Q = influent discharge (mgd)

Al = dry alum faded dose (mg/L) (as 16.4 % Al2O3)

SS = suspended solid of raw water (mg/L)

b = suspended solid ratio and the turbidity among 0.7–2.2 (Cornwell et all.,1987)

TU = raw water turbidity (NTU)

W prased = production of sludge in pre-sedimentation tank (Kg/day)A = additional chemical matters, such as polymer, clay or active carbon of powder

(mg/L)



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Y/Yo = the isolation efficient in pre-sedimentation. The condition of tank is assumed

really good (n = 1/8)

n = the coefficient for tank condition is really good

Q/As = surfacing loading (m/s)

v = speed under surface loading (m/s)

By using the equation 1-5, we find the sludge generation amount like in Table 3.

Table 3. The Sludge Generation of Badak Singa WTP

CapacityQ raw water

(mgd)

PAC dosage

(mg/L)

Turbidity

(NTU)

Wprased

(kg/hari)

Wsludge

(kg/hari)

Qsludge

(m3/hari)

Average 35.33 20.97 87.90 5,995.24 7,884.15 237.36

Maximum 36.31 30.97 190.58 13,119.68 16,225.14 488.48

The sludge that is produced from WTP is primary sludge from SS sediment. This SS

is a floc that is produced after additional coagulant such as PAC in flocculation and accellator

unit.

Thus, the controlling of sludge is only done in some parameters related to design

need. The controlling result of WTP sludge characteristic can be seen in Table 4.

Table 4. Sludge Characteristic of Badak Singa WTP

No. Parameter Unit Sed1

I Sed II Acc2

I Acc III

1 pH - 6.21 6.22 6.07 6.06

2 TemperatureOC 25 25 25 25

3 TS mg/L 31,396 17,816 73,876 9,844

4 TDS mg/L 740 484 432 260

5 TSS mg/L 30,656 17,332 73,444 9,584

6 VSS/TSS - 0.3 0.3 0.3 0.31unit sedimentasi

2unit Accelator

ALTERNATIVE SYSTEMThe sludge treatment units that will be used consist of three processing steps, those

are thickening, conditioning, and dewatering

1. Thickening (Metcalf & Eddy, 1999)

Thickening is the treatment process for increasing solid concentration of sludge by

separating the part of its water fraction. The volume reduction that is have through the

thickening is really important for the next step of sludge treatment such as dewatering,

digestion, drying or incinerating

The purposes of volume reduction are:

• Reducing the capacity of tank and the amount of equipments needed

• Reducing the amount of chemical for conditioning

• Reducing the amount of heat for digestion

• Reducing the amount of fuel for incineration.

In the large installation where sludge has to move in the far distance, then the sludge

volume reduction will impact to the reduction of pipe and pump size. Otherwise, in the small

installation, the minimum pipe size with minimum flow rate in the pump will be the limit

until the thickening will not be needed.



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2. Conditioning (Metcalf & Eddy, 1999)

Conditioning is useful to decrease the water content of sludge. One of the methods that

commonly used is chemical conditioning. The use of chemical to condition sludge for

dewatering is economical because of the increased yields and greater flexibility obtained.

Chemical conditioning results in the coagulation of the solids and release of the absorbed

water. Conditioning is done before the mechanical dewatering process.

The chemicals that commonly used for conditioning are lime, FeCl3, alum and organic

polymer.

3. Dewatering (Metcalf & Eddy, 1999)

Dewatering is a physical (mechanical) unit operation used to reduce the moisture content

of sludge for one or more of the following reasons:

o The costs for trucking sludge to the ultimate disposal site become substantially lower

when sludge volume is reduce by dewatering.

o Dewatered sludge is generally easier to handle than thickened or liquid sludge.

o Dewatering is required normally prior to the incineration of the sludge to increase the

energy content by removal of excess moisture.o Dewatering is required before composting to reduce the requirements for supplemental

bulking agents or admendments.

o In some cases, removal of the excess moisture may be required to render the sludge

odorless and nonputrescible.

o Sludge dewatering is required prior to landfilling in monofills to reduce leachate

production at the landfill site.

Based on kinds and characteristic of sludge that will be processed, there are three

alternatives of sludge treatment system.

* Gravity Thickener Conditioning Belt Filter Press

* Gravity Thickener Conditioning Solid Bowl Centrifuge* Gravity Thickener Sand Drying Bed

All alternatives will use gravity thickener unit for thickening. Although there are

some kinds of thickener at market, the water Company exclusively uses gravity thickener

(Cornwell, 1999 in the Letterman, 1999). This is because the consideration of alum sludge

characteristic such as flock which is easier to be settled than to be filled by using thickener

flotation unit. Thus, the alternative must be dewatering unit which consists of centrifugation,

belt filter press and sand drying bed.

Gravity Thickener Gravity thickener is a first step that is commonly used in the residue treatment

process. Generally, the process happened in Gravity Thickener unit can be described as theisolation process of water from sludge by thickening solid through sedimentation process.

Gravity sludge thickeners are generally circular settling basins with either a scraper

mechanism in the bottom, or equipped with sludge hoppers. They may be operated as

continuous flow or as batch “fill-and draw” thickeners. For continuous flow thickeners, thesludge normally enters the thickener near the center of the basin and is distributed radially.

The settled water exits the thickener over a peripheral weir, or trough, and the thickened

sludge is drawn from the basin. For tanks equipped with a scraper mechanism, the scraper is

located at the thickener bottom and rotates slowly. This movement directs the sludge to the

draw-off pipe near the bottom, center of the basin. The slow rotation of the scraper

mechanism also prevents bridging of the sludge solids.

In the operation, a sludge blanket put on thickener to defend sludge concentration.The operational variable consists of sludge volume ratio, which is volume in sludge blanket



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divided by volume thickened sludge per day (among 0.5-20). The depth of sludge blanket is

among 2–8 feet (0.6–2.4 m). The gravity thickener that is designed and operated well can

produce 2–6 % of alum sludge. Gravity thickener equals to sediment tub which has a function

of increasing sludge solid content by separating liquid. The concentration level has variation

from 2–3 times of solid concentration at sludge in influent. The solid concentration must be

reached less than 10 % (Qasim, 1985).

Chemical Conditioning The dewatering process often depends on conditioning process. The main aims of

conditioning is to increase the characteristic of sludge physic until water can be easily

separated from sludge, to increase sludge structure to ease drying and dismissal of water, to

increase recovery solid from the process (for example, to reduce the solid fraction amount

that is gone during the separation of water from solid), and to minimize the dewatering time

(process cycle times). Conditioning is commonly used for the dewatering process

mechanically.

One of the conditioning ways is to add chemical matter or chemical conditioning. The

chemical water that is used is reagent non organic or polyelectrolyte. Every chemical reagenthas different efficiency level in the making of flock and its size. For example, reagent non

organic can produce granular flocks while polyelectrolyte produces more volume flocks.

Belt Filter Press Belt Filter Press is continuous-feed sludge-dewatering devices that involve the

application of chemical conditioning, gravity drainage, and mechanically applied pressure to

dewater sludge. The application of belt filter press to dewater the alum sludge has done in the

United States. The system will result cake with solid concentration among 30–40 % with

good conditioning previously. The capital and land use for this system generally smaller than

for pressure filter sludge system (Metcalf & Eddy, 1991).

The Belt filter press system consists of sludge-feed pumps, the polymer addingequipment, conditioning tank, belt filter press, sludge cake conveyor, and supporting system

(wash water pump and air compressor). Some variables that influence effectiveness of

equipment are characteristic of sludge, method and type of chemical conditioning, press that

is used, configuration of machine, center of belt, width of belt, and speed of belt. For safety,

ventilation is needed to make H2S and other gas out.

Belt filter presses use a combination of gravity draining and mechanical pressure to

dewater sludge. A typical belt filter press consists of a chemical conditioning stage, a gravity

drainage stage, and a compression dewatering stage (Cornwell, 1999 in the Letterman, 1999).

The dewatering process starts after the feed sludge has been properly conditioned;

usually with polymer. The slurry enters the gravity drainage stage, where it is evenly

distributed onto a moving porous belt. Readily drainable water passes through the belt as theslurry travels over the full length of the dewatering stage. Typically, 1 or 2 minutes are

necessary to allow for the filtrate separation in the drainage stage.

Following gravity drainage, the partially dewatered sludge enters the compression

dewatering stage. Here, the sludge is “sandwiched” between two porous cloth media beltswhich travel in an S-shape path over numerous rollers. Both belts operate under a specific

tension, which induces dewatering pressure onto the sludge. The S-shape path the sludge

follows creates shear forces, which assist in the dewatering process. The compressive and

shear forces acting on the sludge increase over the length of this dewatering stage. The final

sludge cake is removed from the belts by blades.

The precise of sludge conditioning will be the critical consideration to get the best

result of dewatering. The dosage of polymer will be determined by the type of sludge thatwill be treated, as seen in the Table 5.



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Tabel 5. The Dosage of Polymer of various sludge for Dewatering Belt Filter Press and Solid

Bowl Centrifuge (Metcalf & Eddy, 1991)

Type of sludgePolymer dose (Kg polymer/1,000 Kg solid)

Belt Filter Press Solid bowl Centrifuge

Primary 1–4 0.5–2.5

Primary and waste activated 2–8 2–5

Primary and trickling filter 2–8 -

Waste activated 4–10 5–8

Anaerobically digested primary 2–5 3–5

Anaerobically digested primary and air

waste activated

1.5–8.5 2–5

Aerobically digested primary and air

waste activated

2–8 -

Centrifugation

Centrifugation of sludge is basically a shallow-depth settling process enhanced byapplying centrifugal force. The basic physical principle of centrifugal force is that a moving

body tends to continue in the same direction. Centrifugation enhances settlement of the

solids. In conventional settling tanks, the solids are acted on by the force of acceleration due

to gravity ( g ). In centrifugation, the applied force is r ω2, where r is the distance of the

particle from the axis of rotation and ω is the rotational speed. In modern centrifuges, r ω2

may be 1,500 to 4,000 times the value of g.

The major type of centrifuge used for the dewatering of water plant sludge is the

scroll-discharge, solid-bowl decanter centrifuge. The solid-bowl centrifuge (also called scroll

or decanter centrifuge) is a horizontal unit that utilizes a scroll conveyor inside the centrifuge

bowl. The unit is fed continuously with the solids settling against the bowl wall. The scroll

rotates at a slightly different speed than the bowl and conveys the dewatered sludge to thesmall end of the centrifuge where it is discharged. The water is directed from the central axis

of the centrifuge toward the centrifuge’s large end where it is discharged. The water exits

through adjustable weirs (level rings), which also control the pool depth (Cornwell, 1999 in

the Letterman, 1999).

Sand Drying BedSand drying beds were initially developed for dewatering municipal wastewater

biosolids, but they have since been used to dewater residuals from water treatment plants.

Drainage (percolation), decanting, and evaporation are the primary mechanisms for

dewatering. Following residuals application to the drying bed, free water is allowed to drain

from the residuals into a sand bottom from which it is transported via an underdrain system

consisting of a series of lateral collection pipes. This process continues until the sand is

clogged with fine particles or until all the free water has been drained, which may require

several days. Secondary free water can be removed by decanting once a supernatant layer has

formed. Decanting can also be utilized to remove rainwater that would otherwise hinder the

overall drying process. Water remaining after initial drainage and decanting is removed by

evaporation over a period of time necessary to achieve the desired final solids concentration.

Several variations on sand drying beds are currently in use, and Rolan (1980)

proposed the following classification categories:

1. Sand drying beds. These are conventional rectangular beds with sidewalls and a layer of

sand or gravel with underdrain piping. These are built with or without the provisions for mechanical removal of the dried residuals and with or without a roof or greenhouse-type

covering.



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2. Paved rectangular beds. These have a center sand drainage strip, with or without heating

pipes, buried in the paved section and with or without covering to prevent rain incursion.

The paved bottom beds are referred to as solar drying beds.

3. Drying beds with a wedge-wire septum. These incorporate provisions for an initial flood

with a thin layer of water followed by introduction of liquid residuals on top of the water

layer, controlled formation of cake, and provisions for mechanical cleaning.

STUDY RESULT AND DISCUSSION The three treatment alternatives above are based on the consideration such as;

o The existence does not give bad influence to the environment generally and the WTP

area particularly.

o Lands, materials, and workers to develop the sludge treatment unit

o Fee for development, operation, and maintenance of the sludge treatment unit (these

must fulfill economical aspect).

The treatment alternative is based on annual cost, which compares three treatment

alternatives according to the amount of first investment and also fee for operating andmaintaining that it’s needed. The parameter of comparison is equivalent annual cost which is

counted according to Present Value Annual Cost. As the investment will fall of prices in the

future, so it is multiply first with the discount rate which is depend on the discount factor

values. The values of discount factor depend on the project.

Discount rate =t i)1(

1

+

The most economical alternative is the alternative which has the smallest Equivalent

Annual Cost. The Equivalent Annual Cost is the totaling of:

o Depreciation, the shrinkage value which is the part of the benefit that has to be eliminated

every year as long as the economical project or equipment period, until the donation

reflects the amount of investment. The purpose of the shrinkage is to maintain theinvestment level, until if the economical project period is over, the same level of

investment can be redone. The depreciation is a fictive cost, not included the calculation

of capital cost value, so that the depreciation is added to annual cost to calculate the cash

flow. Because the depreciation is the annual cost that has to be paid, then the value is

taken from investment value (capital cost).

o Return On Investment (ROI), is the interest level which is determined and to be the

annual cost that is calculated based on the economical project period.

o Variable Cost, is the annual cost that has to be expended because the activity of a project

is calculated based on the economical project period.

With calculating all the factors above, it means all the cost for construction (fixed

cost) and for the operational and maintenance (variable cost) from each of the sludge

treatment alternatives has been covered, until we can compare all three annual costs. The

alternative which has the smallest Present Value of Annual Cost is the most economical

alternative.

The estimation of annual investment, operational and maintenance cost, with Present

Value Equivalent Annual Cost for all the sludge treatment alternatives is shown in the Table

6.

Tabel 6. Recapitulation of Total Present Value Annual Cost Analysis Cost (Rp) Alternative I Alternative II Alternative III

Construction/investment cost 3,203,881,980 3,512,525,250 8,561,932,730

Operational & maintenance cost 36,407,520 44,891,520 25,920,000

Total Present Value Annual Cost 5,772,091,691 6,427,675,523 13,997,637,467



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From the calculation is obtained that the alternative I has the smallest Total Present

Value Equivalent Annual Cost. Until, it is concluded that alternative I is the most economical

alternative.

The other consideration include treatment loading aspect such as large amount of

sludge float, sludge composition which is a sludge primer and technical aspect such as land

availability, construction implementation technical ease, operational and maintenance, also

material supplying and worker in the construction and operational the treatment units. The

most important aspect beside the economical aspect is the availability of land. The land that is

available is about 6,000 m2, until only the alternative with requirement of land under 6,000

m2 which can be considered as the selected alternative. From the Table 7 below, we can see

that only the Belt Filter Press and Solid Bowl Centrifuge that can comply with the limitation

of land. And the smaller one is the Solid Bowl Centrifuge. Then we have to compare between

them which one is comply not only with the limitation land and economical aspect but also

other technical consideration and the environment as shown in Table 8.

Table 7. The Necessity of Land for each Alternative

Alternative of the Unit unit The necessity of landBelt Filter Press m

2402

Solid Bowl Centrifuge m2

175

Sand Drying Bed m2

8,348

Table 8. The Comparison between Belt Filter Press and Solid Bowl Centrifuge

(Metcalf & Eddy, 1991)Belt Filter Press Solid Bowl Centrifuge

Less complex mechanically and easier to maintain Skilled maintenance personnel required

Minimal effort required for system shutdown Continuous system, so high energy required

High-pressure machine are capable of producing very dry

cake

Moderately high suspended-solids content in

centrateEnvironment : Less noisy The machine is so loud

CONCLUSION

From the result of calculation of economical aspect, technical, environment and

operational consideration, the selected alternative is alternative I, which consist of gravity

thickener, conditioning and belt filter press that will be used as sludge treatment system for

Badak Singa Water Treatment Plant.

References

Government Regulation Number 16 Year 2005 about Developing of Drinking Water Supplying SystemMetcalf and Eddy. 1991. Wastewater Engineering Treatment: Treatment, Disposal, and Reuse. Singapore:

McGraw-Hill, Inc.

Susumu, Kawamura. 1991. Integrated Design of Water Treatment Facilities. New York: John Willey & Sons,

Inc.

Qasim, Syed R. 1985. Wastewater Treatment Plant, Planning, Design, and Operational . New York: College

Publishing.Letterman, R.D. 1999. Water Quality and Treatment - A Handbook of Community Water Supplies (5th Edition)

USA: McGraw-Hill.

Cornwell, D. A., M. M. Bishop, R. G. Gould, and C. Vandermeyden. 1987. Water Treatment Plant Waste

Management. Denver: CO:AWWARF.

SW2 Poppy Sri Lestari 15304007

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