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| 1. Greenfield or new water treatment plants based on Tube Settler technology / clarifiers read more... |
| 2. Single or multimedia gravity filter beds. read more... |
| 3. Complete water treatment systems and Water supply schemes read more... |
| 4. Augmentation or retrofit of existing plants for capacity or quality up-gradation read more... |
5. Mass application of small capacity standardized plants
read more... |
| 6. Sewage Treatment Plant. |
| 7. Project Management Consultancy. (PMC).. |
| 8. Civil, Structural, Electrical & Automation Engineering design & drawings. |
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| Research Paper & Presentation |
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| Case studies
Augmentation of the Nasik Road Plant of M.W.S.S.B.
From 8 MLD to 30 MLD |
| By – Dr. J. N. Kardile |
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Accordingly it was decided to generate additional clarified water of 18.08 MLD (26.26
MLD- 8.18 MLD by existing clariflocculator) by utilizing the existing steel tanks in the
campus. By this time, however, the plant constructed in 1920 was not in use but the steel
plates of the tanks were still in good condition. Out of the three steel tanks (1920) the
tank which was located between the two, was converted into tube settling tank. Each tank
which was located between the two was converted into tube settling tank. Each tank has a
diameter of 12.5m and a height of 4.60m. Thus the detention time provided for flocculation
was about 30-35 mm. Flocculation was achieved by providing a series of perforated
partitions to promote re-contacts for coagulated water. As the water passes in horizontal
direction through the partitions, alternate increase and decrease in the velocity creates the
requisite velocity gradients for effective slow mixing. These partitions consisted of outer
mild steel frame. Half cut rigid PVC pipes (dia. 80 mm) were fixed in a vertical position on
the frame. The vertical gap between the two adjoining pipes is about the same as the pipe
diameter. The partition frames were placed at gradually increasing distance of 0.30m to
1.0m in the direction of flow.
The other two circular tanks were converted into tube settling tanks with surface
loading rate of 4200 lph/sqm. For draining of sludge, multiple hoppers were constructed in
masonry in two annular rings to restrict the height. At the centre of the tank, RCC circular
well was constructed with a separation slab at mid-height. The bottom half thus was a
feed well which received flocculated water and distributed it by radial perforated pipes in
the clarification zone. Top half of the well collected clarified water by similar radial pipe
collection arrangement. To convey the clarified water to filters, a pipe was laid connecting
the collection well to filter beds. The tube modules with tube size of 50mm x 50mm and
tube length of 600mm were placed 1.0m below the FSL of the tank. The modules were
supported on a frame work of mild steel sections. Movement of material and people during
modifications was managed by cutting an opening of 1.5m x 1.5m through side plate near
the ground level. To increase longetivity of structure, all tanks were lined from inside by
brick mortar.
The three existing RCC rapid sand gravity filter beds (plant constructed in 1952)
were converted into dual media filter beds to filter 26.26 mld of settled or clarified water
flow. The rate of filtration from old beds was increased from 3000 lph/sqm to 8750 lph/
sqm. In one of the filter beds, the false bottom nozzle type under-drain system was replaced
with lateral and manifold system. The height of the central wash gullet was increased by
0.60m, to accommodate media expansion. New cross-troughs were constructed for uniform
collection of wash water. The filtration media consisted of crushed coconut shell (sieved
between 1.0mm to 2.0mm) and quartzite sand (E.S. 0.45mm, U.C. 1.6) with supporting
layers of graded gravel. The other two filter beds were retained with false bottom type
under-drain with media depths of 0.4m, 0.4m, and 0.4m respectively as above. The inlet,
outlet and backwash water header pipes were required to be re-laid with larger sizes.
As the old backwash water tank inadequate in capacity, a new tank of 300 cum
capacity was constructed to wash dual media beds. Area of each filter bed is 42.0 sqm. Hard
wash at the rate of 700 lpm/sqm for 10 mm necessitated provision of backwash water tank
of mentioned capacity. The rate of flow controllers in the existing beds were removed and
were replaced by manual control. The dial type indicators were replaced by manometric
tubes for measurement of head loss. Rate of flow mechanisms were replaced by float and
linear gauges.
A new inlet works of capacity 26.26 MLD, comprising a stilling chamber, mixing weir
and mixing channel were constructed to receive raw water from the rising main. Alum
solution is fed just downstream of weir for instant mixing. The flow is then divided into
two streams, 18.08 MLD feeding the retrofitted tube settling tanks and 8.18 MLD feeding
the existing clariflocculators. The above described units were part of a newly constructed
multi-purpose chemical house. It had chemical storage room and offices on the ground floor,
chemical dosing tanks on the first floor and wash water tank of capacity 300 cum above
that.
The raw water turbidity of river Darana goes as high as 1000 NTU to 2000 NTU
during flash floods in the monsoon. The operators are able to maintain settled water
turbidity in the range of 5 NTU to 10 NTU and filtered water turbidity less than 1 NTU.
Being a completely non-mechanical treatment system, operation and maintenance expenses
are low. Due to application of new techniques, the augmented plant complex was completed
at nearly one-half the cost of a new plant of similar capacity. |
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