Article

Calcium Reduction Using Variations of Thickness and Retention Time of Cocoa

Shell Activated Carbon

Afidatul Muadifah^1*, Arif Santoso1, Khoirul Ngibad², Rahma Diyan Martha¹, Siti Nurriyatul

Kholifah¹

¹Department of Pharmacy, STIKES Karya Putra Bangsa, Tulungagung 66291, East Java, Indonesia

²Department of D3-TLM, Universitas Maarif Hasyim Latif, Sidoarjo 61257, East Java, Indonesia

Abstract

High levels of hardness can lead to increased cases of kidney stones. Hardness levels can be reduced by

using activated carbon from the cocoa rind as an adsorbent. The purpose of this research was to

determine the variation of activated carbon thickness and optimum retention time in reducing the

calcium content of dug well water, to determine the percent decrease in calcium ion levels at the

optimum variation, and to determine the significance of the difference in the decreased in calcium levels

between the treatment groups. The research method used the principle of adsorption of activated

carbon from cocoa shells to calcium ions, which are activated by KOH. There were ten treatment samples

with different variations of activated carbon thickness and retention time. The results showed that the

thickness of activated carbon of 60 cm with a retention time of 50 minutes had the optimum ability to

reduce the calcium content of dug well water. The percentage decrease in calcium levels reached 89,041

% with a decreased concentration of 234 ppm. The result of the statistical test showed a significance

value of 0,05. The conclusion of the research is that activated carbon of cocoa shells can reduce calcium

levels to the levels of soft water hardness, with variations in activated carbon thickness and retention

time having a significant effect.

Keywords: activated carbon; calcium; cocoa; retention time; spectrophotometer UV-Vis

Graphical Abstract

*

Corresponding author

Email addresses: afidatul.muadifah@stikes-kartrasa.ac.id

DOI: 10.22437/chp.v7i1.24768

Received 14 April 2023; Accepted 3 July 2023; Available online 30 July 2023

(https://creativecommons.org/licenses/by/4.0 )

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Chempublish Journal, 7(1) 2023, 42-53

The high level of hardness requires an effort to

improve public health by applying a method that

works to reduce hardness levels. One effective

method is the adsorption process using cocoa

shell activated carbon. Some studies on activated

carbon used as an adsorbent include the use of

activated carbon from palm shells as a filtration

medium for physical characteristics of water

covering turbidity, odor, pH and taste. The use of

palm shells and corn cobs as a heavy metal

Introduction

Water is a natural resource that has an important

role in the continuation of life, so it is necessary

to have water quality parameters ^[1]. There are

several factors that can affect water quality, such

as geological conditions, aquifer properties,

lithology and soil type ^[2]. One factor that can

reduce water quality is the geological condition of

an area (Jahanshahi & Zare, 2016). An area with a

limestone rock composition will potentially have

high water hardness levels ^[3]. Based on the

absorber in batik waste ^[7], adsorption of lead

[8]

metal (Pb) from its solution using corn cobs

,

Regional

Environmental

Status Report

of

the use of adsorbents from cocoa shells

(Theobrema cacao L.) to reduce chemical oxygen

demand in palm oil mill effluent ^[9], study of the

adsorption of hazelnut shell charcoal (Aleorotes

moluccana) on Iron (III) and Lead (II) ions ^[10], the

effectiveness of activated carbon from kluwek

(Pangium edule) fruit shells and coffee bean

shells (Coffea arabica L.) on CO and CO gas

adsorption on the absorption of CO gas and Pb

particles from motor vehicle emissions ^[11], the

use of cocoa shell activated charcoal (Theobrema

cacao L.) as an absorber of lead metal in used oil

^[12], the use of cocoa fruit shells as an adsorption

medium for iron (Fe) and manganese (Mn) metals

in well water ^[13], and the effectiveness of using

cocoa shell waste charcoal (Theobrema cacao L.)

Tulungagung Regency in 2007, 40% of the total

area of Tulungagung Regency is composed of

limestone. This allows high levels of calcium in

water sources. According to Ministry of Health

Regulation RI ^[1], the maximum limit of water

hardness level with the function as consumption

water is 500 mg/ml. The high level of hardness

that exceeds the maximum limit can affect public

health, namely cardiovascular cases ^[4]. Further,

[1]

Ministry of Health Regulation RI number 492

states that diseases that can be caused by hard

water are cardiovascular disease (blockage of

heart blood vessels) and urolithiasis (kidney

stones). Based on Jain et al. (2010) hardness

levels above 300 mg/ml can increase the risk of

kidney stones with long-term consumption. From

several statements that support the cause of the

increase in cardiovascular cases, Tulungagung

Regency recorded cases of hypertension in 2016

reaching 21,214 cases which ranked fourth out of

the ten most common diseases ^[5]. The high

number of cases is due to a trigger factor, namely

high hardness levels. In accordance with

research conducted by Kristina (2013) in

Semarang, it is known that there is a relationship

between the hardness of dug well water (p-value

= 0.001) with the incidence of kidney stones in the

community in the working area of the Margasari

Health Center, the results showed that dug well

water with high hardness is a risk factor for

kidney stone disease (OR = 4.795). Another study

conducted by Bobihu in Gorontalo (2012)

showed that the hardness level of drinking water

for people with urinary tract stones was 1375.172

mg/L, while the hardness level of drinking water

sources for people without urinary tract stones

to reduce water hardness, salinity and organic

[14]

compounds

.

The adsorption process is an

event of substance absorption on a solid surface

with an attractive force ^[15]. The occurrence of the

ion absorption mechanism causes activated

carbon to be able to reduce hardness levels. The

utilization of cocoa shell as activated carbon is

based on the content of organic compounds in it.

Cocoa shell contains 23-54% cellulose^[16]while

cellulose is composed of 44.44% carbon. The high

carbon content in cocoa shells can produce

activated carbon with good quality. In previous

studies, tests have been carried out related to the

utilization of cocoa shell activated carbon

including as a lead metal sorbent ^[12], iron and

manganese metal adsorption ^[13], and reducing

total hardness ^[14]. This study was conducted to

determine the effectiveness of cocoa shell

activated carbon in reducing calcium levels in dug

well water based on activated carbon thickness

and retention time.

was 429.7415 mg/L ^[6]

.

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Chempublish Journal, 7(1) 2023, 42-53

The ability of cocoa shell activated carbon to bind

metal ions, especially calcium, is expected to

reduce water hardness levels so as to improve

water quality which in turn can improve the

quality of public health.

series of the population of dug wells in the

village. Sampling points in the dug wells were

taken from five spots in the well.

The simulator used is a series of pipes with

adsorption media arrangement. There are three

simulators with different thickness of activated

carbon used.

Experimental Section

Materials

Cocoa shell carbonization^[13]

The materials used include dug well water as a

sample, cocoa shell activated carbon, murexide

indicator (ACS), 96% ethanol (ACS), NaOH

(EMSURE), KOH (Merck) and CaCl₂.2H₂O (Merck).

Carbonization is done by a simple method of

burning cocoa shells in a closed furnace. The

carbonization process lasts for 2 hours in an

airtight place. To obtain an airtight condition,

treatment is given by covering the surface of the

furnace with wet banana stem fronds, then

covering it again using a cloth, and the outermost

layer is covered with soil while the hole cavity that

can still be penetrated by the burning smoke is

Instrumentation

The instrument used to test calcium levels using

a UV-Vis spectrophotometer brand Inesa UV-Vis

N4S to increase accuracy with a high degree of

precision.

covered with clay ^[17]

.

Procedure

Activation of cocoa shell carbon^[18]

The research method is experimental with

quantitative identification of the decrease in

calcium levels. Several stages were carried out as

follows.

The activation process of cocoa shell carbon is

carried out chemically with a 5 M KOH solution

soaked for 24 hours in a tightly closed container.

then filtered and washed using distilled water

until a neutral pH is obtained. The last stage was

oven drying at 200 °C for 2 hours. Based on SNI

Sample and simulator preparation^[13]

The sample used is dug well water taken from

one of the houses in Bulus Village, Tulungagung

Regency. Based on the profile of Bulus Village,

geographically Bulus Village is located right on

the border of Tulungagung Regency and

Trenggalek Regency (Figure 1), topographically

located in the lowlands with an altitude of 100 m

from sea level with an administrative area of

148,290 Ha. Sampling is a complete random

(Standar

Nasional

Indonesia—Indonesian

National Standard) 06-3730-1995 on technical

activated charcoal, good quality powdered

activated charcoal has a maximum moisture

content of 15%, a maximum volatile substance

content of 25%, a maximum ash content of 10%

and a minimum carbon content of 65% ^[19]

.

Figure 1. Map of Bulus village, Bandung sub-district.

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Chempublish Journal, 7(1) 2023, 42-53

Preparation of the simulator^[13]

The simulator used comes from a paralon pipe

with a length of 150 cm and a diameter of 2

inches which is assembled in such a manner.

Then the preparation of adsorption media is

carried out. The media that functions as

adsorption is activated carbon which is arranged

according to thickness variations.

d. Standard curve determination

From 1000 ppm of calcium standard solution, 3

variants of concentration were made, namely 10,

100, and 200 ppm. Each concentration was put in

a 50 mL volumetric flask. Each volumetric flask

was added with 1 mL of murexide solution then

a small amount of distilled water. After that, 2 mL

of 0.1 N NaOH was added and then distilled

water was added until the limit mark. The

solution was mixed until homogeneous then put

into the cuvette and the absorbance was read at

the maximum wavelength, with the linear

Adsorption process

The adsorption process is differentiated by the

thickness of activated carbon and the retention

time of water with activated carbon. There are

three variations of activated carbon thickness

used, namely 40, 60, and 80 cm. While the

retention time variations are 30, 40, and 50

minutes.

regression equation y = bx + a ^[20]

.

e. Determining calcium content in dug well

water

1 mL of dug well water sample was taken and put

into a 50 mL volumetric flask. 1 mL of murexide

solution and enough distilled water were added.

Then, 2 mL of 0.1 N NaOH was added to distilled

water until the limit mark. The solution was

shaken until homogeneous then put into a

cuvette and the absorbance was read at the

Calcium level test

Calcium level test was conducted on the control

group and test group after treatment. The test

was

carried

out

with

using

the

a

UV-Vis

spectrophotometer

murexide indicator in an alkaline environment.

addition of

maximum

determined with 3 replications.

wavelength.

The

levels

were

a. Preparation of murexide solution

The preparation of the solution was carried out

by weighing 50 mg of murexide and then

dissolved in 10 mL of distilled water, so that a

concentration of 0.5% was obtained. Next, 25 mL

of ethanol was added.

Analysis of results

To see the significant difference in calcium

content reduction between treatment groups,

statistical analysis is needed. The statistical

analysis used the Kruskal-Wallis comparative test

to see the difference between variations in

activated carbon thickness and retention time on

the decrease in calcium levels in the sample,

followed by the Mann-Whitney Post Hoc test.

b. Preparation of calcium standard solution

Calcium standard solution will be utilized with a

level of 1000 ppm. The preparation of the

solution was by dissolving 50 mg of CaCl2.2H2O

with distilled water up to 50 mL so that a

concentration of 1000 ppm was obtained.

Before

comparative

conducting

test,

the

normality

Kruskal-Wallis

test was

a

performed, requiring normally distributed data if

both variables or at least one variable had a

p>0.05 value.

c. Determination of maximum wavelength

From a standard solution with a concentration of

1000 ppm, 1 mL was taken and put in a 50 mL

volumetric flask. Then 1 mL of murexide solution

and a little distilled water were added. After that,

2 mL of 0.1 N NaOH was added and then distilled

water was added until the limit mark. The

solution was mixed until homogeneous then put

in a cuvette and the absorbance was read at a

Results and Discussions

Sample and test media preparation

Sample selection was based on a complete

randomized series from the population of dug

wells in Bulus Village.

wavelength between 400-800 nm ^[20]

.

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Chempublish Journal, 7(1) 2023, 42-53

The sampling technique was done with a

polypropylene (PP) plastic bucket that had

previously been rinsed using water from the

same dug well as the sample. In Indonesia, the

standard requirements for sample containers

that can be used are made of glass or

Tulungagung Regency. The dehydration stage

was done by drying the cocoa pods with the help

of sunlight. The carbonization stage was carried

out by burning in a closed furnace. The

carbonization process was conducted for ±2

hours to produce perfectly burned carbon. The

carbon formed was cut into pieces and then

activated. The dehydration and carbonization

process are shown in Figure 3.

polyethylene plastic (PE) or polypropylene (PP) or

[21]

Teflon (Poly Tetra Fluoro Ethylene, PTFE)

.

Samples were taken ± 20 cm below the water

surface by visual means. Sampling points are at

five spots of the well. Samples taken as much as

20 L were then placed in the same plastic

container to be homogenized.

Activation of carbon

The activation process uses a chemical activation

method. Chemical activation is the process of

breaking the carbon chain in organic compounds

with the help of chemicals. The activating agent

used was a 5 M KOH solution. The selection of

KOH as an activating agent is based on research

conducted by Nurfitria et al.^[24]that KOH is a good

chemical activator for carbon because it can

increase the surface area up to 3000 m2/g. The

activation process was carried out by soaking the

pieces of cocoa shell carbon with 5 M KOH

solution for 24 hours. After being soaked, it is

then washed with distilled water until the pH is

neutral, then continued with an oven at 200 °C

for 2 hours. The results of curing are in the form

of activated carbon that is black, odorless, has a

smooth, shiny surface, is more fragile and lighter.

The simulator used is a series of PVC pipes with a

diameter of 2 inches equipped with a faucet at

the bottom of the pipe in a vertical position. The

inside of the pipe is set up with adsorption media

in the form of cocoa shell activated carbon as per

the thickness variation used. The results of the

media arrangement are presented in Figure 2.

Carbonization of carbon shells

Carbonization is a method to obtain charcoal or

carbon as the main product ^[22]. Referring to the

research of Shofa^[23], the carbonization process is

divided into two stages, namely dehydration and

carbonization. Cocoa shell waste used as media

was taken from a plantation in Bulus Village,

Empty space

Activated Carbon

Faucet

(b)

(a)

Figure 2. a) Simulator dan (b) Scheme of the inside of the simulator.

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Chempublish Journal, 7(1) 2023, 42-53

(a)

(b)

Figure 3. Processes of (a) Dehydration dan (b) Carbonization.

standard solution of CaCl2.2H2O in 1000 ppm.

The 1000 ppm standard solution was diluted by

pipetting 1 mL into a 50 mL volumetric flask and

then adding 1 mL of murexide solution and 2 mL

of 0.1 N NaOH solution. The addition of murexide

solution to the standard solution formed a brick

red color then the addition of NaOH formed a

concentrated burgundy color. The addition of 0.1

N NaOH will form a solution with a pH of 12-13 so

that the solution is in a stable state to form a

complex. Then distilled water is added to the limit

mark so that a burgundy-colored solution is

formed.

Preparation of test media

The test media used is an arrangement of

activated carbon as an adsorbent. The simulator

circuit with adsorbing agent was divided into

three media based on the difference in activated

carbon thickness of 40, 60 and 80 cm.

Measurement of the density of the activated

carbon pieces was done visually.

Adsorption process

The adsorption process was carried out without

repetition in each treatment. The sample

adsorbed in each simulator is equalized in

volume of 2 L. The filtering results in each

treatment produce black colored water. This is

due to the ability of activated carbon to bind

calcium ions chemically by forming a suspension

The prepared solution was put into a cuvette and

the absorbance was read in the wavelength

range of 400-800 nm. The absorbance readings

were repeated three times in the visible area. The

reading results obtained a maximum wavelength

of 507 nm with an average absorbance of 1.340.

The spectra of the calcium standard solution

formed are shown in Figure 4.

in the sample so that a black color is produced

[25]

.

The adsorption process begins with the

movement of adsorbate molecules towards the

surface and diffuses on the surface of the

adsorbent pore forming covalent bonds and

ionic bonds ^[26]

.

Standard curve set up

Calcium standard curve was made using three

concentration variations of 10, 100, and 200 ppm

diluted from 1000 ppm calcium standard

solution. Then each concentration was added 1

mL of murexide solution and 2 mL of 0.1 N NaOH

solution and then marked using distilled water.

The solution was homogenized then put into a

cuvette and the absorbance was read at a

wavelength of 507 nm.

Calcium level test

Calcium level test was conducted on the negative

control group and treatment group with three

repetitions.

Determining the maximum wavelength

Determination of the maximum wavelength is

done by measuring the absorbance of the

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Chempublish Journal, 7(1) 2023, 42-53

Figure 4. The spectra of the calcium standard solution.

Absorbance readings at each concentration

variation were repeated three times. The results

of the standard curve absorbance will be shown

in Table 1.

the concentration of calcium in the sample. From

the standard curve formed, a linear regression

equation y = 0.0015x + 0.4438 was obtained with

a value of R2 = 0.864.

Table 1 shows the absorbance value of each

Determining calcium content in dug well water

variation

concentration.

of

calcium

There

standard

an

solution

increase in

Calcium content was determined on 10 samples

consisting of 1 negative control group sample

and 9 treatment group samples. Each sample

was prepared for absorbance reading. 1 mL of

each sample was taken and placed in each 50 mL

volumetric flask and then added 1 mL of

murexide, 2 mL of 0.1 N NaOH and marked with

distilled water.

is

absorbance value as the concentration of the

solution increases. The average absorbance

results will be presented in the form of a curve

shown in Figure 5. Figure 5 shows the calcium

standard curve obtained from the absorbance of

various calcium concentrations. Presentation

with a standard curve aims to acquire a linear

regression equation that will be used to calculate

Tabel 1. The standard curve absorbance.

Absorbance

Calcium

Average Abs.

R3

concentration

R1

R2

10 ppm

0.422

0.668

0.725

0.420

0.665

0.716

0.429

0.659

0.716

0.424 ± 0.005

0.664 ± 0.005

0.719 ± 0.005

100 ppm

200 ppm

Notes:

R: replication

Abs.: absorbance

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Chempublish Journal, 7(1) 2023, 42-53

Ca Standard Curve

0,8

0,6

0,4

0,2

y = 0.0015x + 0.4438

R² = 0.864

0

50

100

150

200

250

Concentration (ppm)

Figure 5. Ca Standard Curve.

The absorbance reading of each sample was

done in three repetitions which will be presented

in Table 2. Table 2 presents the average

absorbance data of the treatment samples

conducted in three replications. Based on the

absorbance value, the negative control group has

an absorbance value of 0.838 while the

activated carbon and retention time influence

reducing calcium levels.

Based on the average absorbance data, the

calculation of calcium concentration levels and

the percentage decrease in levels in each

treatment was carried out. The results of the

calculation

of

calcium

concentration

and

treatment

group

shows

a

decrease

in

percentage reduction are presented in Table 3.

absorbance. This means that the thickness of

Tabel 2. Sample Absorbance.

Treatment

Absorbance

R2

Calcium Level

Average Abs.

(ppm)

Thick (cm) RT (minute)

R1

R3

30

0,688

0,570

0,842

0,784

0,613

0,483

0,565

0,516

0,576

0,828

0,690

0,567

0,843

0,790

0,611

0,487

0,564

0,518

0,577

0,831

0,703

0,585

0,908

0,809

0,638

0,485

0,586

0,543

0,577

0,854

0,694 ± 0,008

0,574 ± 0,01

0,875 ± 0,04

0,794 ± 0,01

0,621 ± 0,02

0,484 ± 0,002

0,572 ± 0,012

0,526 ± 0,015

0,577 ± 0,001

0,838 ± 0,014

166,800

86,800

287,467

233,467

111,467

28,800

85,467

54,800

88,800

262,800

40

60

80

40

50

30

40

50

30

40

50

Control (-)

Notes:

Thick: Thickness of activated carbon

RT: retention time

R1: 1^streplication

R2: 2^ndreplication

R3: 3^rdreplication

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Chempublish Journal, 7(1) 2023, 42-53

Tabel 3. Calcium level and level decrease percentage.

Thick

(cm)

RT

(menit)

Ca Concentration

(ppm)

Concentration Decrease

(ppm)

%

Decrease

K -

0

262,800

0

30

40

50

30

40

50

30

40

50

166,800

86,800

287,467

233,467

111,467

28,800

85,467

54,800

88,800

96

36,530

66,971

-9,386

11,162

57,585

89,041

67,478

79,148

66,210

40

176

-24,667

29,333

151,333

234

60

80

177,333

208

174

Notes:

Thick: thickness of activated carbon

RT: retention time

Based on Table 3, there are eight samples from

the treatment group that have decreased

calcium levels when compared to the negative

control group. The negative control group has a

calcium level of 262.800 ppm, indicating that the

water is classified as hard. According to Sutrisno

(2007) water is classified as hard if it has calcium

presence of CaO content in cocoa shells allows

the release of Ca ions in the sample so that the

calcium content of the treatment sample is

higher than the negative control. This is in

accordance with the statement of Bujawati (2014)

that if the activated carbon is saturated, there will

be a re-release so the sample after treatment

levels of 150-300 mg/L ^[27]

.

shows an increase in hardness ^[15]

.

Furthermore, Table 3 also shows that the

thickness of activated carbon at 40 cm with

variations in retention time has an optimal

reduction rate at a retention time of 40 minutes.

The 30-minute retention time has a decreased

level below the 40-minute retention time; this is

due to the lack of contact time between the water

sample and activated carbon so that the calcium

adsorption process is not optimal. While at a

retention time of 50 minutes there was an

At a thickness of 60 cm, activated carbon with

variations in retention time has an increase in

reducing calcium levels. With variations in

retention time of 30, 40 and 50 minutes, there

was an increase in the reduction of calcium levels

by 11.162%, 57.585% and 89.041%, respectively.

In accordance with research conducted by

Bujawati (2014) which compared the thickness of

activated carbon, the optimum thickness was

obtained at a thickness of 60 cm with an increase

increase

in

calcium

concentration

when

in the ability to reduce as the retention time

[15]

compared to the negative control. This is likely to

occur due to the saturation of activated carbon

against the binding of calcium ions. Referring to

the quality standard of technical activated

charcoal of SNI 06-3730-1995, the absorption

capacity of carbon is ≥750 mg/g. The increase in

hardness levels is a result of several factors, one

of which is the mismatch between the ratio of

activated carbon thickness and retention time to

the volume of sample adsorbed. In addition, the

prolonged.

A similar research conducted by

Ristiana et al. (2009) on the effect of activated

carbon thickness on hardness reduction showed

the results of a decrease in hardness levels at a

thickness of 60 cm activated carbon by 71.54%

[28]

.

While another research conducted by

Nurullita et al. (2010) which compared the effect

of contact duration showed an increase in the

percent reduction in levels as the contact

duration increased ^[4]

.

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Chempublish Journal, 7(1) 2023, 42-53

Tabel 4. Statistical test significance value.

Treatment

Comparative Treatment

P

Meaning

RT 30 Thick 40

RT 30 Thick 60

RT 30 Thick 80

RT 40 Thick 40

RT 40 Thick 60

RT 40 Thick 80

RT 50 Thick 40

RT 50 Thick 60

RT 50 Thick 80

0,050

0,275

0,050

0,046

Significant

Not Significant

Significant

K-

Notes:

Thick: thickness of activated carbon

RT: retention time

Similar research was conducted by Lustiningrum

(2013) by comparing the effect of the length of

contact of activated carbon on the decrease in

hardness levels. The results showed that the

longer the contact time, the lower the hardness

calcium levels with variations in activated carbon

thickness and retention time. The optimal

variation is obtained at a thickness of 60 cm and

a retention time of 50 minutes with a percent

decrease reaching 89.041% or 234 ppm.

levels ^[29]

.

Conclusions

Meanwhile, at a thickness of 80 cm with

variations in retention time, the optimal

reduction rate is reached at 40 minutes with a

percent reduction of 79.148%. The 50-minute

Variations in activated carbon thickness and

retention time can reduce calcium levels of dug

well water with optimal results at 60 cm activated

carbon thickness with 50 minutes retention time.

Percentage decrease in levels reached 89.041%

with a concentration decrease of 234 ppm and

has a significance value ≤0.05. Further research

on the effectiveness of cocoa shell carbon can be

done by considering the weight of carbon, the

need to characterize activated carbon with SEM

or determination of functional groups with FT-IR,

and the need for comparison with the control

group +.

retention time shows

a

decrease in the

percentage of calcium content reduction. This is

due to the saturation of activated carbon at a

retention time of 50 minutes. This is in

accordance with the research by Masitoh and

Sianita (2013) that increasing the retention time

above the optimal time causes an insignificant

decrease in calcium levels, because the active

side of the activated carbon reaches a saturated

condition so that the adsorption ability decreases

^[30]. The decrease in calcium levels with variations

in activated carbon thickness and retention time

has a significance value of ≤0.05 as shown in

Table 4.

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Tentang Persyaratan Kualitas Air Minum, Pub. L.

No. Nomor 492/Menkes/Per/IV/2010, 1 (2010).

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variation of activated carbon thickness and

retention time has an influence on the ability to

reduce calcium levels of dug well water which is

significantly different. This is as shown in Table

4.3 regarding the percentage of decrease in

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