JAR TESTING FOR DIRECT FILTRATION
The potential economy both in capital outlay and operating costs makes direct filtration an attractive treatment process. Although the decreased costs associated with reduced chemical consumption and reduced sludge load have been emphasized less than the initial capital economy in plant construction, they represent on-going savings that continue for the life of the plant. Pilot plant investigations are required in order to establish the design criteria for a direct filtration plant. However, pilot plant investigations should not be undertaken unless the raw water can be treated by direct filtration.
The procedure is the following:
| Step 1 | Determine the raw water turbidity and record. |
| Step 2 | Filter the raw water through Whatnan #40 filter paper and record. |
| Step 3 | Fill the four jars with raw water to the 2-liter mark and decide on dosages. |
| Step 4 | Measure out the coagulant and polymer doses. |
| Step 5 | With the Phipps & Bird Stirrer at maximum speed, pour in the coagulant and polymer (test to determine sequence); stir at maximum speed for 30 to 40 seconds. |
| Step 6 | With stirring continuing at about 50 rpm take a 200ml sample. |
| Step 7 | Filter through Whatman #40 filter paper (discard paper). |
| Step 8 | After 3 or 4 minutes of the stirring at 50 rpm take another 200 ml sample. |
| Step 9 | Filter this later sample through Whatman #40 filter paper (discard paper). |
| Step 10 | Read and record turbidities of all samples. |
| Step 11 | Plot data on arithmetic scale paper. |
Figure 13, Figure 14,
Eaxmple: Figure 15
Raw water – 37 NTU
Filtered – 10 NTU
| First Trial | Jars | 1 | 2 | 3 | 4 | 5 |
| Alum Dosages | 2 | 4 | 6 | 8 | 10 | |
| Filtered Turbidity NTU | 10 | 10 | 4 | 4 | 0.4 |
Second trial – Fec13 Dosages 2 4 6 8
Filtered Turbidity 8.4 2.2 0.35 0.20
Third trial – Cationic polymer
dosages 0.1 0.2 0.3 0.4
Filtered Turbidity 8.0 4.0 2.0 0.8
The result of this test is obvious in terms of effectiveness. The polymer is very efficient and wiU produce only a small amount of floc which portends weU for filter runs. The economics of the situation, however, might favor the FeCl3. This would depend on the location of the plant and delivered cost of each coagulant. A well designed dual media or deep, course sand filter would probably perform satisfactorily with any of the coagulants. Pilot filter testing therefore would determine the best and most economical.