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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
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| 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
Hajira, Dist. Surat, Gujarat |
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This case study reflects on a quantitative and qualitative enhancement of existing surface water treatment plant of capacity 69.6 MLD (18.39 MGD,US). The plant is located at Hazira, Gujarat State, India and is part of a Petrochemical complex of one of India's largest and most reputed firms, M/s Reliance India Ltd.
The source of raw water is a river 'Tapi', from which water is pumped over 16 km to storage ponds near the plant. The plant consisted of two Solids contact Clarifiers and six Rapid Sand Gravity Filters constructed in RCC. The treated water was used for Cooling Tower make-up, as feed to Demineralization for process and power, utilities and drinking.
The plant capacity was enhanced up to 128.4 MLD (33.92 MGD) with minimum possible modifications and new structures, since the entire plant was on piles due to pre-dominant black cotton soil strata. In the process the finished water quality in terms of Turbidity, TOC and Colloidal Silica (in that order of preference). The potential to form the DBPs is to be kept as low as possible.
The new Inlet Works was constructed to facilitate proper sequencing of pre-oxidant, primary coagulant and polymers and to ensure efficient mixing to prepare coagulated water prior to flocculation. The Inlet Works consisted of a Receiving Chamber, Flow Measuring weir, Mechanical rapid mix chamber and a flow splitter box.
Each Clarifier was 29.50m in diameter with a side water depth of 5.0m. It was decided to discard the existing solids contact mechanism (radial turbine in a draft tube) primarily because internal re-circulation of algae laden sludge was not desired in the process after augmentation. It was retrofitted by tube settlers in a form of an annular ring, separated by a carbon steel circular baffle partition. The inside of the concentric portion worked as a flocculation zone after addition of four paddle Flocculators supported from the fixed bridge. The tube settlers were designed for surface loading rate of 6000 lph/sqm (2.46 gpm/sqft). The detention time (Dt) available for the flocculation was 27 min. The existing scrapper mechanism with a central drive were retained as it was. The flow path of water was same as in the existing unit. Other major modifications included suspending circular baffle from the fixed bridge, support for modules and placing of radial collection troughs in the clarification zone..
The existing six Rapid sand gravity filters, (5 working + 1 standby) each was having an area of
106 sqm and side water depth of 3.0m were converted to Dual Media Filters. The rate of
filtration adopted was 10350 lph/sqm (4.24 gpm/sqft). Crushed coconut shell with specific
gravity 1.4 was used as the coarse media; silica sand with specific gravity 2.6 was the fine
media. The existing rate control mechanism was defunct and therefore the battery was converted
to variable declining rate control operation. The modifications involved replacement of all port
gates/valves with higher sizes. The height of central gutter was rearranged including provision of
new cross-troughs to take care of media expansion during backwash. Existing laterals were
replaced to ensure uniform distribution of air and water during backwash and to reduce the head-
loss. The existing manifold pit was enlarged to accommodate the filter backwash water flow
hydraulics. As a part of renovation, all filter operations were automated , through individual
operating consoles and actuators.
Interconnecting channels/conduits between the units were enlarged or supplemented, to limit the
total head-loss to an allowable extent for enhanced flow. Existing bypass arrangements were
modified prior to execution so that each stream consisting of one Clarifier and three Filters could
be isolated, one at a time for retrofit. The modifications to each stream took time of 6.0 months.
The work was started in fair weather season from first week of November 2005. The activities
were planned in such a way that complete shutdown requirement was limited to 4-5 hours for
the entire plant.
Chlorine and Chlorine-di-oxide were dosed as pre-oxidants to neutralize algae. The primary
coagulant was Polyaluminium Chloride (PAC), supplemented by a Cationic Polymer During the
trial run the clarified water turbidity was consistently less than 5 NTU and filtered water quality
less than 0.50 NTU. This process generated minimum sludge.
Retrofit of the process units and dosing scheme was evolved from a view to keep the Capital cost
and Operation & Maintenance cost low. The capital cost of the augmentation was about INR 60
million (USD 1.35 million) which is about 65% of the cost of a new plant of same capacity.
Apart from the obvious advantages, there was saving in the land cost and manpower, had a new
plant been constructed.
The location of this treatment plant in the Petrochemical complex is the only green zone in the
entire area (16 sq.km). Augmentation of existing plant avoided the destruction of flora and fauna.
This was the key issue in adopting appropriate simple yet innovative technological advances can
ensure harmony between the man and nature.
Performance
The plant was commissioned in the month of July. Turbidity of raw water was generally less
than 15 NTU. The dosing consisted of pre-chlorination (2-4ppm), Poly Aluminum Chloride (20-
25 ppm), Cationic polymer (0.50ppm). The clarified water turbidity was consistently less than 2-
4 NTU and filtered water turbidity was less than 0.40 NTU. Filter aid was not used during the
trials. Average Filter service cycle was 72 hours. The TOC of raw water was very low (less than
3 ppm) and 20-25% reduction was achieved in the process. Further tests are proposed in the
summer months, when TOC is likely to increase. Provision for dosing Potassium Permanganate
and Anionic Polymer was made but was not required during the trial period. The colloidal silica
reduction was 50% for inlet value of 3-4 ppm. The residual chlorine at filter outlet achieved was
0.5 to 1.0ppm as per the required norms of this industry.
Trouble Shooting :
The scrapper rake tip speed of the original clarifier equipment was very high.
This fact The simultaneous operation of flocculators and rake made the flocs to rise in the tube
clarification zone. This required the mechanism to be suitably altered to reduce rake speed.
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