performance study of different addition of stabilizers_in 50% dry sludge

Performance Study of Different Stabilizers Addition on 50% Dry

Sludge from Water Treatment Plant (WTP) of Taiaupeba to Use as

Compacted Material in Earthwork Ditches

Rita Moura Fortes & Joo Virgilio Merighi Department of Civil Engineering, Mackenzie Presbyterian University,

Rua Maranho, 101, apto 72 So Paulo SP Brazil Research Group of CNPq Mackenzie Sistemas Virios (Roads Systems) [email protected]; [email protected];

Dante Ragazzi Pauli; Marco Antonio L. Barros; Magda H. de Carvalho; Nlson Csar Menetti SABESP - Companhia de Saneamento Bsico do Estado de So Paulo. [email protected]; [email protected];

[email protected]; [email protected]

lvaro S. Barbosa; Benicio Bibiano Bento LENC Laboratrio de Engenharia e Consultoria Ltda [email protected]; [email protected]

ABSTRACT: This present paper is a report from a research that has been carried since 2005

in the Mackenzie Presbyterian University. This research takes part of the CNPq Research

Group denominated Sistemas virios (Roads Systems) for use of the sludge from the water disposal treatment in pavement construction as sub-base or roadbed reinforcement. The study

presents and discuss the performance of the 50% dry sludge, with 3 to 5% of Portland cement

lime or micro granular lime weight addition, looking for an inert material, as defined in the

Brazilian Standard (NBR 10004: 2004), attending to the technician-economic-environmental

viability with potential to use in workmanships of earthwork ditches.

KEY WORDS: Pavement, Laboratory Tests, Dry Sludge, Recycling Materials, Earthwork

Ditches, Stabilizer.

1. INTRODUCTION

So Paulo is the fourth most populous city in the world, and the largest in the southern

hemisphere. Almost 11 million people live within its 1,530 square kilometers, according to

the year 2000 Census.

The So Paulo Metropolitan Area includes, besides the city itself, 38 other municipalities.

As in any great metropolis, the population density is quite high and in many cases, it is

difficult to know where the city ends. Having that in mind, the region is home to 20 million

people, many from all over Brazil and the world (CIDADE DE SO PAULO, 2009).

In many cases, it is found at least six public concessionaires companies associated with municipality activities. In downtown, under a plenty of pavements, there are telephonic

cables, gas, energy line, TV cable, petroleum, water and sewage disposal facilities, etc. The

local water and sewage disposal facilities concessionaire, named Companhia de Saneamento Bsico do Estado de So Paulo (SABESP), is present in 366 municipalities of the So Paulo State, to provide better quality of life for more than 26.7 million people. This corresponds to

60% of urban population of So Paulo, being responsible for the management of the water

2

distribution and sewer system (Companhia de Saneamento Bsico do Estado de So Paulo,

2010 (a)) (FORTES et al., 2006(a)).

Considering the emergencies services motivated by innumerous repairs, SABESP has a lot

of pavement recuperation to cover holes. The execution of this type of repair involves special

cares because they need to repair and to finish the service as soon as possible.

A planning contemplating all different concessionaries and the city hall is practically

unachievable for many reasons. It is common that, after a rehabilitation or construction of an

urban pavement, a concessionaire intervention occurs, because it is impossible to foresee

workman-ships emergencies that need a ready fix by the concessionaire. Many proposals have

been presented in the direction of managing these problems, developing management tools of

the pavements, searching to reduce the negative impact of these workmanships, but so far,

none has shown effectiveness (FORTES et al., 2008).

These repairs are more than 1,500 potholes per day (over than 550,000 per year), due to the

water or sewage disposal outflow (FORTES et al., 2005).

It has to be considered that the water or sewage disposal outflow, the soil used in the

earthwork ditches isn`t suitable to be reused, since it is saturated or contaminated, needing to

be removed and substituted (FORTES, 2006 (b)). This fact creates the necessity of searching

soils deposits, a task which is becoming almost unachievable considering that the exploration

of the available deposits are more difficult because of the environmental protection.

On the other hand, the process used in Water Treatment Plants (WTPs) removes suspended

particles from the water by sedimentation and filtration processes, resulting in waste

production (GUERRA; ANGELIS, 2005). The sludge from the water or sewage disposal

treatment is considered a solid residue which the final destination has been hardly questioned.

The Brazilian standard NBR 10004 - Solid waste Classification (2004) classify it in different danger levels and defines that this residue must be treated. Considering the risks to

the environment and to the public health, this Brazilian standard also stabilizes the criteria for

final deposition. The development of a sustainability technology for the utilization of this

material is significant and vital.

The sludge from Taiaupeba is, according to Brazilian standard NBR 10004 (2004),

classified as Classroom IIA - No Inert. It means that the residue is not considered dangerous.

This research intends to study the technician-economic-environmental viability for the

improvement of the dry sludge generated by the water treatment plant (WTP) of Taiaupeba,

searching the stabilization of this material to use as compacted soil in earthwork ditches.

2. TAIAUPEBA WATER TREATMENT PLANT (WTP)

The WTP of Taiaupeba is located in Suzano municipality, near So Paulo: city. It produces

almost 16,000 kg of dry sludge per day, which are taken to sanitary landfills. Nowadays,

almost 3,000 m of dry sludge is disposed by Taiaupeba, for the second stage, approximately

5,000 m of dry sludge (28,000 kg per day).

The Alto Tiet Producing System was conceived in stages because of its complexity.

Taiaupeba was projected in five modules of m/s each. In March of 1992 was implanted the

first stage with nominal productive capacity of 5 m/s. Nowadays WTP operates with the

nominal capacity of 10 m/s, treating on average 9.8 m/s that they supply about 3.5 million

resident people of the Great So Paulo east region. In figure 1 an aerial sight is showed.

3

Figure 1. Aerial sight of Taiaupeba Water Treatment Plant.

The CAB spat (Alto Tiet Producing System) is a Society of Specific Purpose (SPE)

created in 11/04/2008, having for shareholders the Galvo Company and the environmental

CAB.

The administrative PPP between the CAB spat and the SABESP will do that the number of

people attended by Taiaupeba WTP increases the 3.5 to 5 millions, in other words, 15 % of

the Metropolitan Region of the So Paulo State population. That will be possible by the

enlargement in the Alto Tiet Producing System, the drinkable water production grows 10

m/s to 15 m/s.

Nine counties in the metropolitan region will benefit from the expansion of the Taiaupeba

WTP: Aruj, Biritiba-Mirim Ferraz de Vasconcelos, Itaquaquecetuba, Mogi das Cruzes, Po,

Salespolis, Suzano and So Paulo (East Zone). Currently, WTP receives water from five

dams that integrate the Alto Tiet Producer: Paraitinga, Ponte Nova, Biritiba-Mirim, Jundia

and Taiaupeba, which together boast a total capacity reservation of 513 million m.

The currently operation system is composed basically of two consolidation type rotating

drum with 60 m/h and capacity centrifugal condensation of 30 m/h each one. This system of

sludge condensation and dewatering processes produces daily about 60 tons of dehydrated

sludge with in medium 18% of total solid. Figure 2 illustrates the condensed and dewatering

sludge.

4

Figure 2 Condensed and dewatering (a); transportation of sludge (b)

Sludge drying process reduces mass and volume of the product, making its storage and trans-

port (FLAGA, 2005). This residue is transported and deposited into two waterproofed landfill

cells, for dewatering to obtain almost 50% (or more) of the total possible dry solids (DS)

concentration (Companhia de Saneamento Bsico do Estado de So Paulo, 2010 (b)). The pos

dewatering sludge is illustrated in figure 3.

5

Figure 3 Dewatering sludge localization (a) Drying process (b)

3. SCOPE OF THE RESEARCH

This research is being developed in mutual cooperation between the SABESP and the

Mackenzie Presbyterian University, with the contribution of the LENC (a technological and

consultant company) in the execution of the physical and chemical characterization tests. This

deal was signed on February, 14th, 2008, when SABESP organized a Sustainability and

Innovation Public Audience about one of most controversial subjects: the final destination of

the sludge generated in the water treatment process (Companhia de Saneamento Bsico do

Estado de So Paulo, 2008 (a)).

In the chemical tests, SABESP attended the recommendations of Brazilia Standard NBR

10006: 2004. Several tests were made at different concentrations of alkaline material that

searching with these residues of WTP to become inert. The concentrations ranging between 3

and 5% of alkaline material: micro granular lime and Portland cement. From the practical

point of view it was made two tests than originally planned with 14 and 21 days of dry sludge

in contact with alkaline materials. The results indicated that the best solution for the sludge

Taiaupeba has characteristics of inert environmental point of view is the treatment of solid

with a mixture of micro granular lime or portland cement a total concentration of 5% weight.

It was also made complete chemical tests as recommended by the Brazilian Standards to

dry sludge, and with addiction of 3 or 5% portland cement or microgranular lime for 14 and

21 days and was obtained a classification class IIA (no inert) because of the presence of some

metals as aluminum, manganese. The solid waste is considered non-hazardous waste.

6

In the physical characterization, the dry sludge was classified as A-2-4 with NL and NP

Atterberg limits and this classification didn`t change for: pure dry sludge with 50% or 85% of solids content; with addition of 3% or 5% of hydrated lime or portland cement or micro

granular lime. The specimens were compacted with the normal energy Proctor according to

NBR 7182 (1986) and was cured in the moist room. The specimens were molded in different

situations: with mixture and immediate compacting or after 3 or more days of cure, as

discriminated in table1.

In this research the samples were: dry sludge (50% of solids content), dry sludge (50% of

solids content) with 3% weight of portland cement and the compactation after 14 days of

cure, dry sludge (50% of solids content) with 3% weight of portland cement and the

compactation after 21 days of cure, dry sludge (50% of solids content) with 5% weight of

portland cement and the compactation after 14 days of cure, dry sludge (50% of solids

content) with 5% weight of portland cement and the compactation after 21 days of cure, dry

sludge (50% of solids content) with 3% weight of micro granular lime and the compactation

after 14 days of cure, dry sludge (50% of solids content) with 3% weight of micro granular

lime and the compactation after 21 days of cure, dry sludge (50% of solids content) with 5%

weight of micro granular lime and the compactation after 14 days of cure, dry sludge (50%

of solids content) with 5% weight of micro granular lime and the compactation after 21 days

of cure.

The cylindrical specimens have been molded as determined by the Brazilian Standard Test

Method (DNER ME 202: 1994) (Figure 4) and carried through the determination of the

compressive strength test (Brazilian

standard NBR 12025: 1990) and

determination of the tension

strength of cylindrical specimens

submitted to diametrical

compression (NBR7222:

1994), as a

recommendation of Little et al.

(2000). The compressive

strength was determined to

1, 3, 7, 14, 21 and 28 days age and

the diametrical compression

was determined to 14, 21 and 28

days age;

It was also used the CBR and the Mini CBR test, that is similar to the CBR (California

Bearing Ratio), different in terms of the specimen size obtained through a compactation

procedure called the mini Proctor. The molds have a diameter of 50 mm and a volume of 100

ml. The sample mass is 250g, and the maximum grain diameter is 2 mm. The diameter of the

penetration piston (plunger) is 16 mm, while the loading machine has a capacity and speed of

4.5 kN and 1.25 mm/min, respectively. There are two compactation rammers used for

compaction: (a) standard energy rammer weighing 2.27 kg, height of drop 305 mm, blows -

10 total or 5 per side and (b) the intermediate energy rammer weighing 4.5 kg, height of drop

305 mm, blows - 12 total or 6 per side. Soaking time is 24 hours. If not soaked, expansion can

be determined as in the CBR test. This test is used in the MCT methodology (FORTES,

MERIGHI, 2003).

7

Figure 4 Specimen Molded

For each determination of CBR, mini CBR, compressive strength and tension strength, the

results presented in table 1 are the average of six specimens tested.

It is observed that this material is composed by 66.1% of sand, 30.7% of silt and 3.2 of

clay.

Table 1 Results of physical tests

8

1 day

(***)

3 days

(***)

7 days

(***)14 days 21 days

28 days

(***)14 days 21 days 28 days

1 51.0 - - - - - - - - - - 12.0

2 43.3 - - - - - - - - - - -

3 26.4 0.20 0.60 0.90 - - 0.76 - - 0.02 - 25.0

4 33.1 0.50 0.80 0.60 - - 1.04 - - 0.07 - 24.9

5 35.9 0.21 0.46 0.66 - - 0.94 - - 0.003 - -

6 33.3 0.28 0.55 0.84 - - 1.05 - - 0.03 - -

7 32.6 - - - - - - - - - - 18.0

8 29.7 0.51 0.50 0.53 - - - - - - - 23.6

9 27.5 0.76 0.67 0.75 - - 1.20 - - 0.12 - 25.2

10 28.6 - - - 0.13 0.15 - 0.037 0.04 - 8,0 6,0

11 28,0 0.21 - - 0.02 - - 6,0 6,0

12 29.4 - - - 0.31 - 0.08 - 7,0 7,0

13 29.5 - - - 0.22 - - 0.03 - - 9,0 9,0

14 30.5 0.38 - - 0.10 - 7,0 7,0

15 28.5 - - - 0.20 - - 0.023 - - 10,0 9,0

16 28.2 - - - 0.25 - - 0.047 - 8,0 7,0

17 29.1 - - - 0.22 - - 0.03 - - 8,0 7,0

18 29.3 - - - 0.32 - - 0.083 - 7,0 6,0

1 Sludge with 3% of hydrated lime - mixture and immediate compacting (50% of solids content) **

2 Sludge (85% of solids content) **


4 Sludge with 3% of portland cement - mixture and immediate compacting (85% of solids content) **

5 Sludge with 3% of hydrated lime - after 3 days of cure (85% of solids content) **

6 Sludge with 3% of portland cement - after 3 days of cure (85% of solids content) **

7 45% of soil + 50% of sludge + 5% of hydrated lime - mixture and immediate compacting (50% of solids content) **


9 Sludge with 5% of portland cement - mixture and immediate compacting (85% of solids content) **

10 Sludge pure (50% of solids content)

11 Sludge with 3% of portland cement compacted after 14 days of cure (50% of solids content)




15 Sludge with 3% of micro granular lime compacted after 14 days of cure (50% of solids content)




speci

men

Maximum

Dry Unit

Weight

(kg/m3)

Optimum

Moisture

Content

wo(%)

Compressive strengths (MPa)mini

CBR

(%)

satured

Tension strength (MPa)

1210

1250

1410

1410

870

1290

1380

1370

1210

1220

1250

1230

1240

1220

1290

1200

1221

1220

mini

CBR

(%) wo

* Determination of the tension strength of cylindrical specimens submitted to diametrical

compression (FORTES et al., 2008)

** (FORTES et al., 2006(b))

*** (FORTES et al., 2009)

In figures 5, 6 and 7 are presented the mini CBR, Compressive strengths and the tension

strength of cylindrical specimens submitted to diametrical compression graphics, respectively.

mini CBR (%)

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Sample

Min

i C

BR

(%

)

mini CBR (%) wo

mini CBR (%) satured

Figure 5 Mini CBR and CBR

CBR

0,0

2,0

4,0

6,0

8,0

10,0

12,0

10 11 12 13 14 15 16 17 18

Sample

CB

R (

%)

CBR without imersion (wo)

CBR with 4 days imersion

9

Figure 6 Compressive strengths (MPa)

Figure 7 Tension strength of cylindrical specimens submitted to diametrical compression

graphics

3.3. Discussion of results

The Taiaupeba sludge with 85% of solids content stabilized using 5% of hydrated lime,

according to the NBR 10004 (2004) classification change of Class IIA - No Inert to Inert, in

other words, the addiction of the hydrated lime allows its utilization as compacted soil in

earthwork ditches (FORTES et al., 2009).

In case of the dry sludge with 50% of solids content, the best results in the chemist point of

view occurred with cement and micro granular lime concentration with 5% weight, but to

evaluate what each one contributed to the best result we believe that the cement was not

effective for neutralize the manganese effect but had the best results for color, turbidity and

pH stable in all samples - little variation.

The increase of the mechanics strength with bigger additions of air binder, discloses,

according to Nez et al (2005), the occurrence of a cementation. The values taken for the compressive strength and tensile strength for diametrical compression are acceptable for its

use in earthwork ditches.

It is important to point out that the use of the dosage with addition of 45% of soil plus 50%

of sludge and 5% of hydrated lime, it is relatively important to take into account the

mechanical behavior presented in a better performance, beyond presenting a lesser expansion

value. Not only does this new dosage brings the advantage to mix this material with soil, but

also diminish the heavy mineral presence that can be presented in the sludge, even so the

classification has given to Classroom II A- no inert.

10

Bandeira, Merighi e Fortes (2008) had presented an analysis through the use of the

computational program of finite elements ANSYS, of the structural behavior of airport

pavements, considering an aircraft with maximum load of 540 kN (aircraft EMB 195), with

pressure of application of the tire of 1,083 MPa and wheel load of 125 kN, they obtained 0.5

MPa as the compression strength in 100 mm of depth and tension strength from the triple state

of tensions of 0.01 MPa.

Analyzing all the studied dosages it is verified that the same ones had presented better

values that one, so it is possible to conclude that on the point of view of the mechanical

characteristics, this material can be used in earthwork ditches, or in layers of sub-base of

airport pavements, therefore they attend the recommendation of the support capacity (superior

to 20%) and expansion values less than 1.0%, beyond the values of compression and tension

strengths.

In this last dosage carried out, it was obtained inferior values that in the previously, due to

the use of dry sludge with 50 % of solids content and it was used microgranular lime. We also

have to consider that the samples were been prepared by the WTP, packed and sent to the

laboratory to be tested, and in the previous dosages, the addition was carried out by the

laboratory itself, besides the dry sludge was used with 85 % of solids content.

If the results obtained in this research are compared with presented ones from the PCA

(2003) for clay stabilization with portland cement addition, where the authors searched ten

types of different soils, and had found a value of 0.19 MPa to compression strength for A6

soil (8) without no portland cement addition, being that with 3% of portland cement in

weight, the value passed to 1.44 MPa and with 5% for 2.22 MPa to the 7 days of age, one

checks that they are coherent.

The results obtained with addition portland cement have been more promising than the

ones obtained with addition of hydrated or micro granular lime in terms of resistance.

However, considering that the samples stabilized with this last binder had presented

acceptable values, its use is very interesting, being a kind of air binder and does not require

care in its stockage, allowing its preparation foresaw.

CONCLUSION

Little et al. (2000) affirmed that the reactions between the hydrated lime and the soil are

complex. The pozzolan reaction that occurs between the air binder and the silica and/or

aluminum of the soil is the solution for an effective and durable stabilization of it. This

affirmation strengthens that when adding the hydrated lime or Portland cement to the sludge,

its chemical composition is modified, thus, will be carried through chemical analyzes to verify

the changes in the composition of the mixture considering the recommendations of Brazilian

standard NBR 10004 (2004).

The new steps of this research contemplate to repeat these tests adding micro granular lime

or Portland cement, but mixing in the laboratory, carrying out the chemical and mechanical

analysis and after applying the better performance in an experiment in field in earthwork

ditch. All these mixtures will be carried through chemical analyses.

The proposal of the mixtures with micro granular lime or Portland cement addition study,

cure and posterior compacting, inhabits in the preparation easiness that can occur in a plant or

the seedbed. The material previously would be prepared, excusing the constructor to add/to

dose the binder in the hour to apply, what will prevent losses, beyond providing a bigger

technological and quality control of the material to be used in earthwork ditches.

The authors are motivated by the promising results, and feel that this research contributes

for the environment and sustainability point of view because of rehabilitate a residue

11

conferring the necessary quality for its application in civil constructions. They really believe

in the technician-economic-environmental viability of this technology.

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