2021/224

Evaluation of replacing river sand by Manufactured (M) sand as filter media in sludge drying beds

4 Poster Track: Applied Research » 4 Innovative technology aspects

Speaker: Sagar Dattatray Patil

Summary – for publication in conference brochure:


Sand mining is a direct cause of erosion and impacts the local ecosystem and habitat. Therefore, in 2013, the Government of India banned illegal sand mining from river beds. As a result, use of Manufactured (M) sand has increased in construction and other sectors. However, its applicability is yet to be explored in wastewater & sludge treatment. M sand has many advantages over river sand, viz. lesser cost, easier availability & less harmful impacts on the environment. These advantages, coupled with its characteristics and performance in treatment, are the key factors for considering its applicability in sludge treatment (sludge drying beds).

Introduction, methods, results and discussion:


1. Introduction

Sand media is an integral part of water, wastewater and sludge treatment. It is used in treatment processes, such as filtration, adsorption, biological degradation etc. This study is aimed at understanding the use of M sand as filter media in (two types of) Sludge Drying Beds, specifically Un-Planted & Planted Drying Beds (UDB & PDB) where river sand is used as filter media.

Manufactured sand OR Crushed Stone sand (IS 383-1970)

  • Production of M sand generally involves crushing, screening and washing the source material (Granite/Basalt) in controlled environments. Therefore, it's quality & physical properties can be controlled as per requirement.
  • M sand is free from organic & soluble contents.
  • Particle size: 0.075-4.75 mm | Shape: Angular & rough

Technology overview

Sludge Drying Bed (SDB) is a shallow basin filled with filter media, usually sand & gravel. It is used for sludge treatment in wastewater treatment plants and also in Faecal Sludge (FS) treatment. It dewaters sludge by draining through filter media & by evapotranspiration to give percolate (liquid) and dried sludge as by-products.

 

Typical sand layers in SDBs (from top to bottom)

Un-planted Drying Bed (UDB)

Planted Drying Bed (PDB)
•0.3-1.2 mm fine sand for 150 mm
•5-8 mm fine gravel for 75-100 mm
•12-20 mm medium gravel for 75-100 mm
•30-50 mm coarse gravel for 100-150 mm
•0.3-1.2 mm fine sand for 200-300 mm
•5-8 mm fine gravel for 100 mm
•12-20 mm medium gravel for 200-250 mm
•30-60 mm coarse gravel for 100-150 mm

 

2. Methods

Experimental Setup

Four lab-scale models had been developed,

  1. UDB with river sand
  2. UDB with M sand
  3. PDB with river sand
  4. PDB with M sand

Features of lab-scale models are,

  • Sand media layer in UDB & PDB (at top) as150 & 200 mm respectively
  • The diameter of models: 0.6 m
  • FS feeding depth in UDB & PDB: 150 & 100 mm respectively
  • FS feeding frequency UDB & PDB: 12-15 day

 

3. Results

Comparison: Characteristics of M sand and vs. river sand

Parameter

Unit

Criteria

River sand

M sand

Shape

-

Sub-angular to round

Sub angular

Sub-angular to Angular

Colour

-

-

Brown

Whitish grey

Effective grain size

mm

0.3 to 1.2

89.2 %

88.5

Specific Gravity

-

-

2.58

2.61

Bulk density

g/cc

-

1.55

1.47

Porosity

%

-

66.45

43.68

Coefficient of Uniformity

-

3-5

2.79

3.13

Silt Content

%

< 6

0.56

1.12

Hydraulic Conductivity

m/s

10-3 to 10-4

3.2 × 10-4

4.3× 10-4

 

 

Performance evaluation and comparative study of lab-scale models of UDB & PDB

 

Parameters

Unit

Inlet

Percolate (monitored up to 72 hrs.)

UDB

 

River

M

River

M

Total Suspended Solids (TSS)

mg/L

13,800-46,500

3-188

7-103

10-84

4-43

Fixed Solids (FS)

mg/L

9,447-30,843

1,093-2133

723-1,733

1,007-2,757

1,040-2,443

Total Solids (TS)

mg/L

28,690-81,760

1,307-4,453

843-2,640

1,407-4,803

1,497-5,477

Biochemical Oxygen Demand

mg/L

5,000-10,000

30-40

25-30

20-25

15-20

Chemical Oxygen Demand

mg/L

14,800-54,800

166-410

110-383

84-312

121-221

E-Coli

MPN/

100 ml

54,000

9,300-21,000

1,500-7,500

2,300-3,600

1,500-2,900

Turbidity

NTU

-

4-69

6-60

8-62

4-26

Quantity of percolate

%

100

25-52

35-50

45-50

40-55

Dried sludge

Moisture content (%)

64-68

62-70

 

Weight (Kg)

3-4

3.3-4

 

 

 

Conclusions and implications:


1. Conclusions

  1. The quality of percolate is better in drying beds with M sand than those with river sand and Moisture content
  2. in drying beds with M and river sand is quite similar.
  3. Vegetation growth in PDB with M sand is lesser than that of PDB with river sand.
  4. It is safe to say that M sand can be used instead of river sand; and will reduce the cost of filter media in drying beds by 30 - 40%.

2. Implications

Given the findings from the study, M sand is now being used as a filter media in two more projects, that are under construction,  in the Indian states of Madhya Pradesh and Chattisgarh. In these locations, the cost of M sand is approximately 40% less than the cost of river sand. Along with cost, the availability of river sand becomes itself is a supply problem - either due to illegal mining or due to inaccessibility when the river bed gets flooded. Hence, in such scenarios, M sand can be considered as an alternative to river sand in unplanted and planted drying beds - saving the environment, reducing costs, reducing procurement delays and also improving treatment efficiency. 

Relevant references:


Eliason J. 2002 Rule development committee issue research report Draft Sand media specifications Washington state department of health
IWA publishing 2014. Faecal Sludge Management. London UK
UN-HABITAT 2008. Constructed Wetlands Manual. UN-HABITAT Water for Asian Cities Programme Nepal Kathmandu
Wang et al. (2007). Drying Beds 10.1007/978-1-59259-996-7_13
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