Public Health Engineering Department

Digha has turned out to be one of the favourite destinations where a causal day tripper wishes to visit repetitively in a bid to “drink life to the lees” for some time while shoving out the mundane activities that fatigues the human intellect to the nadir of restiveness.

 However with rising population and inrush of inbound tourists Digha’s tryst with hygiene turned out to be a major cause of an impending environmental hazard which will have serious ramifications on the entire coastal ecosystem adjacent to Digha. In the Digha area because of growing population, large urban tourist influx and construction of hotels and restaurants the problems of sanitation related waste management and treatment including construction of a sanitary landfill along with vermi-compositing facility, construction of underground sewer lines and a sewage treatment facility are required to be addressed.

 Presently raw sewage from the existing buildings whether residential, commercial, hotels etc. are treated in individual septic tanks as on-site sanitation and final effluent of septic tanks are discharged either through individual soak pits or directly into the existing surface drains. As a result the flows in the surface drain become septic sullage or septage which is not at all desirable in such a popular beach resort. The situation become more aggravated as some hotels and holiday homes violate the regulations set by the Environment Department, Govt. of West Bengal, by disposing their sewage into the surface drain without any treatment. Discharges from these surface drains are disposed to the sea directly causing public health hazards along the shore line which requires adequate treatment to protect receiving waters from oxygen depletion and ecological damage. Considering the same Environment Department, Govt. of West Bengal felt the need of preparation of a Sanitary Sewerage Scheme for Digha beach resort which will be constructed by the Public Health Engineering Directorate, Govt. of West Bengal and will be maintained under Digha Sankarpur Development Authority (DSDA).

A flashback of not so remote period will entail the fact behind the wobbly and asymmetrical scenario of the incumbent sanitary sewage scheme at Digha.  The Sanitary Sewerage Scheme for Digha was sanctioned earlier in the year 1996 for an estimated cost of Rs. 4.09 crores considering a design population of 17,000 in the design year 2011. After laying of about 1825 mtr. sewer line some problems of sand boiling were faced in some places and work was suspended, temporarily, in the year 1997. To overcome such problem re-design of the entire system was done in 1999 to safeguard against sand boiling problem and suspended work resumed in the year 2000. Based on the re-design a considerable part of the work was completed within the sanctioned amount of Rs. 4.09 crores. However as the entire sewer network had been re-designed it was not possible to execute all works of the scheme within the sanctioned amount due to cost escalation and other allied corollaries. Accordingly, revised estimate was prepared subsequently and it was proposed to execute the work in 2 phases. Value of the revised estimate was Rs. 12.51 crores comprising of works for Phase-I and Phase-II. Estimated amount for Phase-I works was proposed as Rs. 8.89 crores and for Phase-II works was Rs. 3.62 crores. But the said revised estimate was not sanctioned and as a consequence, works remains suspended till now for want of requisite fund.

 Under the stated circumstances and considering the necessity to improve the hygienic condition as well as to maintain the environmental standard of the popular beach resort the renovation work of the suspended Sanitary Sewerage Scheme of Digha area has been considered as one of the pilot investment scheme under ICZM Project to be executed by Public Health Engineering Directorate.

Objective of the Proposed Sewerage System

With the growing population the management of solid waste turned out to be a critical affair as if untreated wastewater is allowed to accumulate, the decomposition of the organic matter it contains can lead to the production of large quantities of mal-odorous gases. In addition the untreated wastewater usually contains numerous pathogenic or disease-causing microorganisms that dwell in the human intestinal tract. It also contains nutrients, which can stimulate the growth of aquatic plants, and it may contain toxic compounds. For these reasons, the immediate and nuisance-free removal of wastewater from its sources of generation, followed by treatment and disposal, is not only desirable but also necessary for the society to improve the hygienic condition as well as to maintain the environmental standard of the area. The ultimate goal - wastewater management - is the protection of the environment in a manner commensurate with economic, social, and political concerns.

The objective of the sewage treatment is to stabilize decomposable organic matter present in the sewage so as to produce an effluent and sludge which can be disposed of in the environment without causing health hazards or nuisance. Health hazards are also created due to the bacteriological contamination in the underground water and also to the surface water bodies. Therefore, treatment of Sanitary Sewage in the Digha area becomes essential to safeguard the health hazards of the people of the area as well as to the visiting tourists and also for the protection of the coastal ecosystem of the popular beach resort.

Proposed Project Component:

In the renovation work of the present scheme, different diameter sewer lines are to be laid except sewer lines constructed earlier. In the proposed system, the sewer network of 18,646 meter length of different diameters will collect sewage from the entire command area and will transmit the same to the Sewage Treatment Plant. Out of total sewer line, a length of 6,496 meter of different diameter sewer lines were laid earlier according to the initial sanction and remaining 12,150 meter sewer lines of different diameter are to be laid as per proposed renovation work. Sewer lines already constructed earlier are to be cleaned thoroughly to make those lines functional as those lines are lying idle for quite a long time.

 Sewage from residential houses, hotels, different Institutions, commercial and other establishments will be collected through different manholes of different sizes to be provided at regular intervals, as per requirement, within the sewerage network. Manholes will be provided within the sewer network at an interval of 30 mtr. or less based on requirement. Considering the necessity from the engineering perspective it has been proposed to construct ordinary manholes, junction manholes, drop manholes and flushing manholes at different locations within the sewerage network. Provision of flushing manholes at the head of sewer have also been kept for flushing the system once or twice a day to wash away deposited solids of the sewer. Manholes to be provided within the sewerage network will also act as inspection manholes and will also be utilized for inspection, cleaning and other purposes at the time of operation and maintenance.

 As the soil condition is not favourable for laying sewer along deeper level, due to sand boiling problem in some areas, it was decided to lay sewer comparatively along shallower depth to facilitate easy construction. Accordingly provisions for 4 Sewage Lifting Stations have been made at suitable locations adjacent to sewerage network system. Out of which 3 Sewage Lifting Stations have already been constructed earlier as per initial sanction and the remaining 1 Sewage Lifting Station is to be constructed under the proposed renovation work. Besides Sewage Lifting Stations provision of 2 main Sewage Pumping Stations has also been made in the present renovation work to facilitate pumping of accumulated sewage into the Sewage Treatment Plant. Out of these 2 Sewage Pumping Stations one has already been constructed earlier and the other Sewage Pumping Station will have to be constructed under the present renovation scheme.

The sewerage network of the proposed renovation scheme has been designed in such a way so that these Sewage Pumping Stations can function independently. Accumulated sewage of these pumping stations will be pumped separately and will be collected in a collection chamber before entering into the sewage treatment plant and will then be distributed uniformly from the collection chamber to the treatment ponds.

The treatment process to be adopted for the present scheme has been decided after comparative study of advantages and disadvantages among several treatment technologies available now-a-days and after such comparative study it has been decided that waste stabilization pond comprising of anaerobic, facultative and maturation pond will be the best option for treating sewage of Digha Township. The degree of treatment to be provided has been decided by comparing the raw waste water characteristics with respect to the required standard of final effluent to be discharged according to the set provisions. Main advantage of this process is that this process does not require any mechanical equipment for operation and as a result no electrical energy will be required for the plant operation which in the process will drastically cut down the operational cost. But the main disadvantage of the process is that it requires large area of land but as the land is available free of cost from Digha Sankarpur Development Authority (DSDA) waste stabilization pond has been selected for the treatment of sewage of Digha Township. Waste stabilization pond is also the simplest of all waste treatment technologies available for sewer waste water because of its simplicity and reliability of operation. A stabilization pond is simply a shallow body of water contained in an earthen basin exposed to sun and air.

The total estimated cost of the renovation work of Digha Sanitary Sewerage Scheme comes to `35.59 crores comprising of costs related to civil works as well as mechanical/electrical works. This cost also includes charges for service connection as well as cost of trial run coupled with operation and maintenance costs for the initial 3 years after commissioning of the project.

Execution of the present scheme will be done through turnkey contracts with provision of 3 years operation and maintenance by the executing agency including performance guarantee after successful commissioning of the entire system. Thereafter, the scheme will be handed over to the Digha Sankarpur Development Authority (DSDA) for operation and maintenance.

Along with the aforementioned sewage network PHED is supposed to construct a building within in the adjacent areas of Hospital at Digha. The proposed building will serve multiple purposes as it will have allotted room spaces for discharging administrative duties and responsibilities, laboratory, staff quarters, rest shed, stores, etc.  An internal pathway along with street lighting and fences embedded with bushes and shrubberies surrounding the building will be put together. As ICZM Project is an environmental project the proposed building will be based on LEED green building rating system. The target is to achieve Platinum certification provided by LEED rating system. A building with Platinum certification means it has taken care of the sustainability issues by recognizing the performance in five key areas of human and environmental health:

·         sustainable site development

·         water efficiency

·         energy efficiency

·         materials selection

·         indoor environmental quality

Operation & Maintenance Planning

Operation and maintenance cost of the scheme after initial 3 years has been assessed as `1.80 crores including cost of manpower and electricity charges which will guide the DSDA to decide upon the policy of operation and maintenance. Based on the policy of operation and maintenance DSDA has to finalize appropriate tariff structure to be recovered from the consumers. For the purpose of recovery of operation and maintenance cost from consumers DSDA also has to finalize suitable cost recovery mechanism. In addition, DSDA has to create a separate cell for the operation and maintenance of the entire system.

Maintenance work generally consist of good "house-keeping" which mainly entails regular weed and grass trimming and other usual measures to prevent mosquito breeding. Floating scums and mats will also have to be removed. Regular visits by an operator will be there to ensure that the waste stabilization ponds are operating satisfactorily. When the characteristic green colour of a pond changes to grey, brown or pink, it is generally a sign of overloading and anaerobic conditions, often accompanied with mal-odours. When this occurs as a result of temporary overload, the wastewater will have to be by-passed for some time to allow the pond to restore itself. Repeated occurrences can be corrected by taking more permanent measures such as enlarging the existing ponds to cater to increased load. Occasionally, embankments may need dressing once every few years. Desludging of ponds will also be necessary at suitable intervals as per requirement.

In this regard, regular and periodic samplings at different points are to be done for a clear assessment of the performance of the entire system. Installation of a simple measuring weir in the inlet chamber will be there to assess whether flow conditions have changed or BOD or other characteristic of the wastewater or both have changed.