filter construction manual

8/2/2019 Filter Construction Manual

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A8.0 Construction manual for a slow sand filter

How to construct an intermittent slow sand filter.


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TABLE OF CONTENTS

0.0 Introduction................................................................................. pg. 71

1.0 Description................................................................................... pg. 71

2.0 Essential Design Criteria.......................................................pg. 71-72

3.0 Supplies ........................................................................................ pg. 72

4.0 Construction................................................................................ pg. 73

4.1 Preparing the Barrel....................................................... pg. 74

4.2 Constructing/Installation of PVC Tubing .................... pg. 74

4.3 Washing the gravel and sand......................................... pg. 77

4.4. Final assembly................................................................. pg. X

5.0 First run and Operation ............................................................. pg. 80

6.0 Maintenance ................................................................................ pg. 80


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0.0 Introduction

This instruction manual will show how to build, operate and maintain an intermittent

filtration system. An intermittent filter is one that does not require continuous flow. This

allows for the user to filter water when needed. This particular filtration system includesan intermittent slow sand filter and a moringa seed flocculation tank. The filter process is

shown in Figure 1. The flocculation tank works to reduce the amount of suspendedparticles in the water before filtration. This is important because removing particlesgreatly reduces the amount of bacteria in the water and increases the life of the slow sand

filter. The slow sand filter uses a naturally occurring biofilm called a schmutzdecke to

aid in water filtration. It is important to know that the biofilm provides the mainmechanisms for filtration and maintaining the biofilm is the greatest concern.

1.0 Description

The slow sand filter described in this document will produce approximately 1.5 liters ofclean water per minute. The filter takes 2 or 3 people about 5 hours to construct. It

requires 3 weeks of operation to begin producing clean water. Many of the components

used in the construction of this filter may not be available in your area. We suggest

alternatives for some of the components throughout the manual. The design can bealtered as long as the essential criteria are met. In Nairobi, Kenya a filter with similar

attributes was constructed for around 15 US dollars, about 1050 Kenyan shillings.

2. 0 Essential Design CriteriaThe essential design criteria are the necessary components and filter requirements to

allow operation. Listed below are the Essential Design Criteria:

Figure 1: This figure shows the filtration process. Step 1 is flocculation of dirty water, add

ground moringa seeds and wait over night. Step 2 shows filtration of flocculated water.


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5. The dirty water travels through a 45 cm tall column of sand.6. The sand is prevented from leaving the barrel by a layer of small gravel.7. The top layer of sand remains under 2 cm of water between uses.8. The top layer is not disturbed when the dirty water is poured in.

3.0 SuppliesThe primary slow sand filter described in this document, as shown in Figure 1, can be

made from supplies list on the left of Table 1. An alternative filter can be constructedwith the supplies listed on the right of Table 1. Table 2 shows the supplies needed tobuild a flocculation tank. Included in the supply lists are the tools needed for

construction. It should be noted that the sand and gravel are listed in height

measurements. While you will not purchase sand and gravel by these measurement it ismeant to describe how tall the column of sand and gravel should be. The width of the

barrel used will determine the overall volume of sand and gravel required. As long as the

sand column is 45 cm deep and the gravel column is 10 cm deep all is well.

Primary Filter Supplies Alternative Filter Supplies

1. 1 ~55 gallon barrels with seal2. 5 ft of PVC tubing3. 45 cm washed sand4. 10 cm washed pea gravel5. Fine washed gravel6. Bulk head with washer7. PVC joint elbows, no threads8. PVC joint elbows (one end

threaded)

1. 1 ~100 liter barrels with seal2. 5 ft of PVC tubing3. 45 cm washed sand4. 10 cm washed pea gravel5. Fine washed gravel6. 2~ PVC joint elbows7. PVC glue8. End cap9. Knife

45 cm washed

sand

2 cm above

Pebbles to

prevent sand

Figure 2: Quarter-section of Slow Sand Filter showing essential criteria.


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9. Non-toxic PVC glue10.Ball Valve11.End cap12.Fine mesh bag or pillow case13.20 L bucket14.

Drill or knife15.Saw

16.6 mm screen, 60 cm x 60 cm

10.Saw11.Fine mesh bag or pillow case12.20 L bucket

Table 1: This table shows the supplies needed to construct the primary filter and an alternative

filter.

Flocculation Tank Supplies

1. 1 ~55 gallon barrel with seal

2. 2x Bulk head with washer

3. 2x Ball valve4. 2.5 ft of PVC tubing

5. 1 End cap

6. 1 PVC joint elbow, no threads7. Drill or knife

8. Saw

9. Non-toxic PVC glueTable 2: This table shows the supplies need to construct a flocculation tank.

4. 0 CONSTRUCTIONThe construction section describes, in detail, how to assemble the primary filter. Keep in

mind that an alternative assembly is possible as long as the minimum criteria are met. It

is advised to build the filter in the desired final location. Once the filter is constructed it

will be too heavy to move. It should be placed on level ground in a location where theflocculation tank can be elevated as seen in Figure 3.

Flocculation tank

Bio-Filter

Figure 3: Showing a good filter location with a

raised flocculation tank.


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4.1 Preparing the barrelPreparing the barrel consists of punching the necessary holes in the barrel and diffuser

plate. The diffuser plate fulfills the minimum criterion of "not disturbing the biological

layer." The diffuser plate allows the water to drip slowly into the barrel to avoid mixingof sand and water which disturbs the biological layer. The diffuser plate can be made out

of the plastic seal that comes with most barrels. If the barrel does not have a plastic sealthen a fine 2mm screen would be a good alternative. Using the components andequipment from Table 3a or 3b and following instructions below will complete barrel

preparation. In appendix A-1 an exploded view of the barrel, plastic seal (diffuser plate),

and vent can be seen.

Table 3: Table 2a shows the equipment and used to make the primary filter. Table 2b shows theminimum equipment and components required.

1. Drill (or cut) a hole 58 cm from the bottom ofthe barrel, big enough for the bulk head to fit

through. If a bulk head is not available, cutthe hole as close to the outside diameter of the

PVC tubing as possible.

2. To make the diffuser (Figure 4) cut 2-3mmholes 2 cm apart throughout the barrel seal.

(The diffuser prevents the dirty water pouredin from disturbing the biological layer this isvery important).

3. Drill of cut a hole in the center of the plasticseal/diffuser plate such that a small section of

PVC tubing can fit snugly without fallingthrough.

4.2 Constructing/Installation of PVC TubingThis section explains how to construct and install the internal PVC tubing. For the

primary filter we suggest using a bulk head to allow water to pass through the barrel wall.

If a bulk head is not available then a PVC pipe will work. If a PVC pipe is used insteadof a bulk head it is important to seal the hole around the PVC with silicone or PVC glue.

Below, in Table 3, are the required materials for constructing the primary filter and an

Table 3b

Equipment Materials

Knife Barrel w/

plastic seal

Table 3a

Equipment Materials

Drill Barrel w/plastic seal

Figure 4: Punching holes in the plastic seal to

make a diffuser plate. Also shown is the

installed bulkhead and ball valve.


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alternative filter. The exploded pipe assembly in Figure 5 shows the correct order andlayout of each piece included in the pipe assembly for the primary filter. Note that the

numbered parts in Figure 5 correspond to the part numbers in instructions. Figure 2

shows how the pipe assembly is situated in the bio-filter.

Table 3aEquipment Materials

Drill 5 ft of PVC tubing

Saw End Cap

PVC Glue PVC joint elbows

PVC joint elbows(one side female threads)

Bulk Head

Ball Valve

Table 3b

Equipment Materials

Knife 5 ft of PVC tubing

Saw End Cap

PVC Glue PVC joint elbows

PVC joint elbows(one side female threads)

Figure 5: Exploded view of piping system and bulk head

-

#3

#8 Elbow

that is


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4.2.1 Construction and installation of PVC tubing

1. Using the saw cut a section of PVC tubing that fits across the bottom of the barrelwith 3 cm of relief from both walls.2. Drill or cut 5mm diameter holes, 2-3 cm apart down the length of the tube. Dothis on four sides of the tube as seen on part #1 of Figure 5. This creates part #1.

3. Without gluing, attach unthreaded PVC elbow (#7) to the bottom PVC section(#1).

4. Using the rest of the PVC pipe attach the middle section (#2) to the elbow (#7).5. Place attached bottom and middle sections into the barrel as situated in Figure 2.

On the middle section, mark the point where the PVC tube touches the top of the

bulkhead hole.6. Using the saw cut the middle section where it is marked.7. Using the remainder of the PVC pipe cut a piece that is 15 cm long and install

into the center hole of the diffuser plate. This will act as a vent when pouring thewater of the diffuser plate.

8. To install the bulk head into the barrel use Figure 6 and follow steps a through d.Keep in mind that Figure 6 shows the order in which the bulk pieces fit together.

i. Placing the O-ring on the Threaded flange Slide part 6c (O-ring) downthe threaded portion of part 6b (threaded flange) until it is snug against the

flange.

ii. Slide part 6b through the hole you cut in the barrel, such that the threadscome from inside the barrel to outside the barrel. Ensure that the o-ring is

sandwiched between the threaded flange and the inside of the barrel wall.iii. Thread part 6d (nut) onto the threaded flange.iv. Thread part 6a into the threaded flange.

Note: If a bulkhead is not available then stop at step 6 and follow steps I - VI. If a

bulkhead is not available the PVC tubing will be installed in the same manner except

without the bulkhead, where the threaded elbow will pass through the barrel insteadof the bulkhead passing through the barrel.

9. Without gluing, attach the threaded PVC elbow (#8) to the top of the middlesection (#2), as shown in Figure 5. After installing the bulk head make sure the

elbow meets the inside of the bulk head.

a. If the elbow does not line up with the bulk head take the elbow off andtrim the middle section down until the elbow properly connects with thebulkhead.

10.After ensuring the pipe assembly will fit in the barrel and align with the bulkheadglue the end cap (#11), bottom section (#2), unthreaded elbow (#3), and middlesection (#2) in the order shown in Figure 5.

11.Place the glued pipe assembly in the barrel as seen in Figure 2. Attach thethreaded elbow (#8) to the bulkhead via part 6a.

12.Glue the middle section (#2) and threaded elbow (#8) together.


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13.Thread ball valve (#10) into the bulkhead.14.This completes the construction and installation of the PVC tubing. On the

middle section of the pipe mark the appropriate gravel and sand heights, 10cm

and 55cm respectively, from the bottom of the barrel.

I.

Glue the threaded elbow (#8) into the cut hole such that the threads are facing outand the unthreaded portion is facing down the barrel.II. After installing the threaded elbow make sure the middle section is the proper

length to fit in the elbow

a. If the pipe does not connect with the elbow properly, trim the pipe so it fitssnugly inside the elbow.

III. After ensuring the pipe assembly will fit in the barrel and aligns with the threadedelbow glue the end cap (#11), bottom section (#2), unthreaded elbow (#3), and

middle section (#2) in the order shown in Figure 5.IV. Place the glued pipe assembly in the barrel as seen in Figure 2 and glue middle

section (#2) to the threaded elbow (#8).

V.

Thread the ball valve (#10) into the threaded elbow (#8).

4.3.0 Washing the gravel and sandThis section will describe how to wash the sand and gravel. It is very important to washthe sand and gravel before using in the filter. If either the sand or gravel is not washed

the filter will produce cloudy water. The size of the sand and gravel is also important. It

is desirable to use gravel smaller than 6mm. A 6mm screen can be used separate smallrocks from larger rocks. If a 6 mm screen is not available one can pick 6 mm rocks by

hand. The sand should be medium grade construction sand.

Table 4a

Equipment Materials

Fine mesh bag or pillow case Sand

Water source Pea gravel

20 L

6 mm 60 cm x 60 cm screenTable 4: Table 4a shows the equipment and materials used to build the primary filter. Table 4b

shows the minimum material required to build the alternative filter.

Table 4b

Equipment Materials

Fine mesh bag or pillow case Sand

Water source Pea gravel

20 L

Figure 6: Exploded view of the bulkhead.


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1. Washing the pea gravela. Wash a quarter of a bucket of pea gravel in the mesh bag by running water

through the bag. This can be done by dipping the bag into the water

source. Repeat this process until the water coming off the rocks is clear(Figure 8) or nearly clear. If the gravel is very dirty this will take a long

time (up to 40 minutes per quarter bucket).b. Before adding the gravel to the barrel, make sure the barrel with tubingassembly is washed and the PVC glue is dry.

c. Repeat gravel washing process until there is enough gravel to fill thebarrel to the 10 cm mark

2. Washing the sanda. Apply the same washing process used for the pea gravel, stirring the sand

helps speed this process up.

b. Fill the barrel to the sand height mark of 55 cm.c. Clean one and a half more buckets full of sand (this will be needed later).

4.4.0 Building the flocculation tankThis step will explain and show how to build a flocculation tank. The flocculation tank iseasy to construct and requires only a few pieces. The Flocculation tank will use the

following tools and materials:

Figure 7: Clean sand or gravel yields clean water

leaving the bag.


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1. Cut a hole in the barrel wall 5cm above the bottom large enough for thebulkhead to fit through. Be sure the hole is high enough to provide groundclearance for the ball valve.

2. Install bulk valve in the same manner as step 7 of PVC installation section.3.

Install ball valve by threading it into the bulkhead.4. Cut another hole in the barrel wall 5cm above the bottom large enough for thebulkhead to fit through. This hole will be located directly opposite of the first

hole.5. Repeat steps 2 and 3 for the second hole.6. Attach thread adapter to one of the bulk heads.7. Cut two length of PVC that is half the width of the barrel. For the

primary design this is length is 27cm.8. Drill or cut holes in one length of pipe in the same manner as step 2 of the

PVC installation section.9. Using PVC glue attach the pipe which have no holes to bulkhead and thread

adapter assembly.

10. Glue elbow to the non holed pipe, thread adapter, bulkhead assemblyusing PVC glue.

11. Glue the other pipe, with holes, to the elbow such that rises up the barrel asseen in Figure 8.

12. Allow glue to dry before use.

Table 5

Equipment Materials

1x 55 gallon barrels with sealDrill or

Knife 3 ft of PVC tubing

Saw End CapPVC Glue PVC joint elbows

2x Bulk Heads

2x Ball Valves

Thread adapter

5 cm

Filth Drain

Flocculated

5 cm

Figure 8: Flocculation tank.


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5.0 First Run and Operation

Before operating the filter it is important to understand how the process works. The first

steps of producing clean water is a process called flocculation. Flocculation is a process

which removes suspended particles and is achieved by adding ground moringa seeds intodirty water. This will be done in the flocculation barrel. When the water is finished

flocculating there will be a layer silt at the bottom of the barrel, this is illustrated by theyellow layer in Figure 1. Once the flocculation process is complete silt can be drained.After draining the silt layer the cleaner flocculated water, illustrated in blue, can be

drained into the filter via flocculated water drain. Follow steps 1-8 to produce clean

water.

1. Fill up flocculation tank with dirty water, be sure ball valves are closed.2. Shell and grind moringa seeds, using 1 seed per liter, into a powder using a rock

or a mortar and pestle.3. Add a small amount of water to moringa powder such that a thick morninga paste

is created.

4.

Mix the moringa paste with the water in flocculation tank.5. Allow flocculation tank to sit overnight, approximately 8 hours, whileflocculation occurs.

6. When dirty water is flocculated drain the filthy water out though the filthy drain.7. Once the filthy water is drained the flocculated water can be drained into the

filter.

8. Repeat steps 1-7 for three weeks before testing water.The filter will not hold as much water as the flocculation tank. So water must be added

to the filter from the flocculation tank throughout the day. 80 to 100 L should be ranthrough the filter each day.

After running 80-100L of flocculated water though the filter for three weeks the watershould be tested for coliform (see water test kit instructions). Upon passing the

flocculation test the water can then be consumed.

The first days you run water through the filter, air bubbles escape from the sand, and the

sand height falls. Add the excess clean sand to ensure that the sand level meets the sand

height marked on the barrel.

6.0 MaintenanceMaintaining the filter requires minimum work. Most of the filter maintenance is

maintaining the biofilm. The most important aspect in maintaining the biofilm is whenone adds water. It is important to pour water over the diffuser plate so it drips slowly into

the filter. This will ensure no damage is done to the biofilm whenever water is added. If

the biofilm is destroyed then repeat first operation steps.

When the flowrate drops to an inconvenient level or below 0.25 liters per minute it is

time to clean the filter. A process called wet harrowing is used to clean the top layer ofthe filter.


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1. Close the ball valve.2. Pour 1 bucket into the barrel.3. Remove diffuser plate.4. With your hand slowly swirl the water in the filter. Be careful not to touch the

sand with your hand. The movement of the water loosens the accumulated dirt

and suspends it into the water.5. Remove the water with a cup.6. This process can be repeated until most of the dirt is removed. The flowrate

should increase considerably.


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Appendix

A-1

Barrel

Diffuser

Air Vent

Figure 3: This figure shows an exploded view of the

barrel, diffuser plate and vent.

filter construction manual

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