Augmentation and Modernization of Water Treatment Plants in India

1. Introduction

Design and operation of water treatment plants in India have remained traditional with use of conventional treatment units and operation by untrained personnel. Most of the plants are quite old and have not been augmented due to lack of funds. Over the years, the demand of water has increased significantly, but the plants are being operated under overloaded condition resulting in unsatisfactory performance. A fact-finding survey by NEERI¹ revealed deteriorated condi­tions of water treatment plants in India during 1972 and the conditions have remained practically the same till now. Poor pre-treatment and non-availability of skilled person­nel for operating the plant make the situation worse, resulting in large and unpredictable changes in treated water quality.

2. Limitations of Slow Sand Filter

Slow sand filters have been used and are still being advocated by some to ensure filtrate quality because of practically no necessity of skilled manpower for operation and minimum requirement of power and mechanical devices. Though they may be suitable for rural areas and for small colonies having availability of ample space at low cost they cannot be considered for urban centres due to space limitation and cost of land. The rate of filtration in such units is too less as compared to rapid and multimedia filters and any modifications in slow sand filters cannot meet the urban requirements. Hence use of multimedia filters and that also through renovation of old rapid sand filters seems to be the most economical and effective solution.

3. Choice of alternative

It is observed that  the approach to solve this problem is dictated by established consulting firms and suppliers of plants who are reluctant to adopt new ideas. Naturally, the augmentation plans generally speak of installing new plants to cope up with increased demand rather than renovation of existing infrastructure to incorporate advanced treatment techniques and automation. As a result, old units remain unused or less efficient, occupy space and new units consume all the financial budget. The new plants also employ traditional rapid sand filters and are managed in the same old way with unskilled personnel and tend to become inefficient after the commissioning period and performance trials are over. A more in-depth analysis will reveal that old filter units can be transformed into modern treatment plants in less cost than constructing new large capacity filtration plants. More attention on operator training and running the plant as industry can achieve high performance with economy.

A review of technical journals and information available on internet search engines shows that that many new treatment technologies have been developed in recent past in the field of water treatment like use of poly-electrolytes as coagulant aids, tapered flocculation, Tube and plate settlers, dual, mixed and multimedia filters with variety of filter media. The capacity and performance of the existing water treatment plants can be enhanced significantly by incorporating these technologies with necessary modifications in units and changing operating procedures.

4. Improvements in Pre-filtration Units

Coagulation is the weakest link in treatment and improper coagulation is the main reason for high turbidity in treated water. Improvement of mixing arrangement and use of coagulant aids along with alum can render effective destabilization of colloids and assist in formation of flocs. Modifications in flocculation tank to achieve tapered flocculation by introducing baffles or compartments can improve the formation of large settelable flocs. The settling basins can be upgraded by fitting tube settler units. Culp and Culp have given detailed  information about installing tube settlers or lamella plate settlers in both circular radial flow settling tanks and horizontal flow rectangular settling basins to increase their overflow rate and efficiency.

4. Limitations of existing Rapid Sand Filters

Design of any filter is based on sus­pension characteristics, filter structure, operating parameters and expected filtrate quality. Due to uncontrolled alum dose, in­effective flocculation and short circuit­ing in settling tanks, the water ap­plied to the filters often has large concentra­tion of turbidity, with significant per­centage of large settleable flocs along­ with partially stabilized but unfloccu­lated colloids. This hampers the functioning of filters leading to early clogging, short filter runs and sometime cracking of bed leading to short circuiting. Improvement in coagulation, flocculation and settling by use of new techniques will eliminate these conditions.

The filters are operated by semi­skilled personnel and in some plants, even by coolies; as such, the control of filter operation is very poor. The head loss gauges, rate controllers and dis­charge measuring devices are out of order in most of the cases due to negli­gence. The backwashing is done on a routine time cycle, decided on the con­venience of shift duties. As a result the filter run is terminated only on the basis of time interval without consider­ing limiting head loss, turbidity of filtrate, etc. Any new design of the filter must take into consideration this lacuna in operation, which may not be altered unless skilled personnel are employed. Therefore the filter should be designed to give good filtrate quality and acceptable filtration rate during the entire filter run which should be a pre-determined time interval.

Most of the filtration plants are pro­vided with rate controllers and have submerged inlet flow conditions, thus limiting the standing water depth over the filter: medium. The structure of the filter does not provide any allow­ance for increasing the depth of filter medium, which is restricted to 0.6 to 0.75 m. The limiting head loss avail­able for filtration seldom exceeds 2.0 m, thereby preventing longer filter runs.

The current design practice in deve­loped countries aims at filtrate turbi­dity to be consistently below 0.2 FTU. However, the filtrate turbidity at such a low level, though desirable, is neither economically feasible under present conditions, nor essential from the point of view of acceptable drinking water standards which permit turbidity up to 5 FTU. Considering the techno-econo­mical feasibility, the filtrate turbidity of 1 FTU may be taken for design.

5. Conversion of Rapid Sand Filters into Multimedia Filters

The existing rapid sand filters form a bottleneck for up-gradation as its hydraulics depends on filter media and under drainage system where choice of alternatives is limited. Though coarse to fine grain gradation in dual and multimedia can solve surface clogging problem  faced in rapid sand filter and can give high rates of filtration, both inlet channel and under drainage system needs to be suitably modified to allow operation of existing filters at higher rates. Of all the high rate filters available, dual, multimedia and mixed media filters can be adopted easily for con­verting old filters. The multimedia filters, though more suitable, may not be practically feasible due to difficulty in the availability and cost of procur­ing and placing different filter media. Mixed media filters advocated by Culp and Culp² suffer from the same draw­backs.

6. Dual Media Filters

Dual media filters, though not truly coarse to fine graded, still pro­vide an effective and feasible alterna­tive. Due to non-availability of anthracite in India, various other materials like high grade bituminous coal (Param­shivam et al⁸ 1973, Ranade et al ^4,5,6 1975), crushed coconut shell (Kardile⁹ 1972), berry seeds (Bhole and Nashik­kar¹⁰ 1974) and kernels of stone fruits like apricots (Ranade and Agrawal¹¹ 1974) have been tried and were found to be suitable as coarse filter media.

Opinions differ regarding the desir­able amount of intermixing at the junction of coarse and fine media. Culp and Culp recommend significant intermixing to achieve ideal "coarse to fine" gradation and claim better filtrate quality and longer filter runs.¹² There is less control over the grading of filter media and if the gradation is selected to have significant intermixing there may remain large portion of fine mate­rial which may cause dense packing of intermixing layer, thus defeating the purpose of coarse to fine gradation. This suggests that some degree of intermixing is inevitable under present conditions but the design should aim at minimising it.

7. Conversion of Rapid Sand Filter into Coal-Sand Dual Media filter

Ample data^3-11 are available on the per­formance of dual media filters, both on pilot scale and field scale, it has been established that these filters can operate at high rates of filtration with consistent high removal efficiency of turbidity and bacteria. Use of such filters in existing water treatment plants would improve filtrate quality and augment the capacity at a rela­tively low cost. Such an exercise has been done successfully at Kanpur water works way back in 1975. Conversion of full scale rapid sand filter into coal sand dual media filter had conclusively proved that such augmentation can be done economically with twofold increase in filtration rate.

However, the idea was not pursued or adopted by water industry except in few sporadic cases. There have been number of success stories of converting old units to high rate modern treatment plants with significant space and cost saving in the world however in India these attempts have remained only at experimental level and have not been taken seriously and accepted by government officials and local authorities who are the decision makers.

8. Need of Modernization of Water Treatment Plants.

Everybody is aware that advances in technology have opened up new alternatives for better production and quality control. New micro controller based instrument gadgets and servo control process control units have revolutionized the chemical industry. Computerised  software systems for plants are designed to provide inventory management, data logging, operating instructions, trouble shooting routines and report generation for specific needs. It has been promptly employed in water and waste treatment plants in the west. This being the scenario in advanced countries, India has not yet initialized this process in environmental engineering field. make such  progress. Though India is leading in the development of  Instrumentation, Information technology and Management techniques they have not been translated in a crucial field like water treatment. If it is done then  the operation of the plant would become an easy and manageable process with complete control over quality and flexibility in operation in response to raw water quality and environmental changes.

Dnyandeep Infotech Pvt. Ltd., Sangli has launched a website www.envis.org to propagate this idea, train the personnel and provide advisory services in automation and system design of Water and Waste water Treatment Plants. Development of Environmental knowledge databases with compilation of human resources in Environmental Field available in India is aim of this website. Use of Information Technology for tackling Environmental Engineering problems is a challenging task with lot of potential both as regards Development and Employment Generation.

9. Conclusion

It is necessary to investigate economical but modern methods to augment existing water treatment plants taking full cognizance of the advances in research and development done so far in water treatment technology and new tools and techniques of Information Technology.

10. References

1. "Survey of Water Treatment Plants", Technical Digest No.3, CPHERI, Nagpur, (Jan 1971).

2. Culp G. L. and Culp R. L., "New Con­cepts in Water Purification", Van Nos­trand Reinhold Company, New York, (1974).

3. Conley, W. R., "High Rate Filtration", J.A.W.W.A. 64, 3, p. 203, (1972).

4. Ranade S. V., "Engineering and Theoreti­cal Investigations on Dual Media Filters using Indian Bituminous Coals", Ph.D. Thesis, .I.I.T., Kanpur, (July 1976).

5. Ranade S. V., Agrawal G. D. and Misra Y. D., "Conversion of Rapid Sand Filter into Dual Media Filter", J. Inst. Public Health Engrs., J., 2, p. 12, (1975).

6. Ranade S. V., Agrawal G. D. and Misra Y. D., "FulJ Scale Trials on Converted Dual Media Filter", J. I.W.W.A., (Octo­ber 1976).

7. "Manual on Water Supply and Treat­ment", Central Public Health and En­vironmental Engineering Organization, Government of India, (1977).

8. Paramsivan et al., "Bituminous Coal - ­A substitute for Anthracite in two Layer Filtration of Water", Indian J. Env. Health, 15, p. 178, (1973).

9. Kardile, J. N. (1972) "Crushed Coconut Shell as a New Filter Media for Dual and Multilayer Filters", J.I.W.W.A. 1, 1, p. 28, (1972).

10. Bhole A. G. and Nashikkar J. T., "Berry Seed Shell as Filter Media", J. Inst. o! Engrs 54, PH 2, p. 45, (1974).

11. Ranade S. V. and Agrawal G. D., "Use of Vegetable Wastes as a Filter Media" presented at the Conference on Engg. Materials and Equipment, The Associa­tion of Engineers, Calcutta (1974).

12. Brossman, D. R. and Malina J. F. Jr., "Intermixing of Dual Media Filters and Effects on Performanl;e", Technical Re­port EHE 72-4 CRWR 86, Env. Engg. Lab., University of Texas, Austin, Texas, U.S.A., (1972).

13. Ranade S. V. and Gadgil J. M. “Design of Dual Media Filters to suit existing Water Treatment Plants in India”, Journal of the I.W.W.A.VolXIII, No.1,p. 81-85 ( 1981)