"Water – Let us awake to a National priority" Desalination and Sewage water Treatment Recycling

Overview

India is critically poised for a high growth rates spanning between 7-9% in the next few decades. This growth propensity is likely to bring about an all around change in the dynamics of the priority fixation in country, in general. Almost all the sectors of economy are bound to be affected on account of this step expected growth trajectory on a sustained basis.  While on the one hand, there are initiatives being taken, strategically, to keep the energy basket full, for sustaining/maintaining this growth momentum, there are several other problems at hand, which, need to be combated with vigor and vision. It is often stated, that the next war is not going to be fought with weapons but on water. This over statement only underlines the criticality associated with development of water initiatives, to sustain and support the growth momentum and the overall vision of the country.

Present Scenario and Potential

India faces a turbulent water future. Unless water management practices are changed – and changed soon – India will face a severe water crisis within the next decade. Managing utilizable water for domestic and industrial applications is fast becoming a major challenge to India as demand is growing rapidly due to population and economic growth. Continuous water scarcity woes have made the water management issue to be classified as one of the top problems that could impact India's growth story. 

Increasing water use is a fact of life in many and may be broadly classified into three consumption sectors: agricultural, industrial and domestic. According to UNDP’s World Water Development Report, 2018, domestic consumption accounts for only eight per cent of the total consumption and agricultural consumption accounts for about 70 per cent of the total freshwater abstraction. However, it is predicted that both these users will be outdone by industry in future as water consumption by industries is increasing at a much higher rate as compared to other sectors. In fact, in the high income countries, industrial water use already accounts for as much as 59 per cent of the total fresh water consumption; almost twice the amount used in agriculture.  

Although current industrial withdrawal of water in developing countries is relatively low in comparison to developed countries, this is expected to increase in comparison to other sectors of the economy as well as in absolute terms since these countries are expected to have higher growth in industrial production in the near future. Industrial water use is closely linked to the economy of a country, as GDP increases, so will industrial water consumption.

The Ministry of Water Resources and the Central Pollution Control Board and World bank all claim that industrial water use in India will grow at a rate of 4.2 per cent per year, rising to about 225 billion cubic meter by 2025.  Barring minor differences in estimates almost all the agencies concur that industrial water use in India is quite significant and is growing at a fast pace. Industrial use of water has a direct bearing on the country’s economy. This implies that as the GDP increases, there will be a corresponding increase in water use by Indian industries.

Fresh water & drinking water scarcity is higher in coastal regions in comparison to the interior parts of India; in coastal areas, the groundwater is saline and not suitable for drinking. Therefore, desalination of sea water becomes an ideal solution to bridge the widening gap between growing water needs of industrialization/urban population and scarcity in supply in major coastal cities in India. 

The chart given below depicts the water requirement in major coastal cities in India.

In India, around 20 major cities are on the coast line and the water requirement for all these cities in 2008 stood at 6,267 million liters per day (MLD). The coastal cities experiencing tremendous growth are Mumbai, Chennai, Surat, Kolkata, and Vizag. Around 93 percent of the total water requirement from coastal cities is from these five cities. The rest is with cities such as Cochin, Bhavnagar, Kozhikode, Mangalore, Kakinada, Tuticorin, and others. The projected water requirement for all coastal cities in 2026 is estimated to be 23,607 MLD a whopping increase of 4 fold.

Major industrial zones, which are flourishing along the Indian coast, are Vishakhapatnam, Kakinada & Krishnapatnam in Andhra Pradesh; Cuddalore, Kanchipuram Chennai in Tamil Nadu; Kochi in Kerala; Mangalore in Karnataka; Ratnagiri & Sindhudarg in Maharashtra; Dahej & Mundra in Gujarat; Paradip in Orissa; and Haldia in West Bengal. Major industrialization in a cluster would put an extra stress on the existing fresh water infrastructure in that region, and in such a scenario, industries would have no choice but to look for alternate source of water to meet their needs.

Similarly across India water scarcity is being noticed. The rivers are drying up, Irrigation, Potable water all seem to be a concern. A two fold approach is required to be adopted to not only obviate and find a solution to this major problem which is already beginning to reveal its fangs.

1.   For the Coastal Belts Ro Based Desalination has to be a way to look into a long term solution

2.   Across the country Sewage water treatment and recycling for Industrial and Service water requirements has to be resorted to

3.   River water and ground water and from other water bodies may be used predominantly for potable purposes

Desalination in Coastal Belt

Simulating a conservative scenario that, by 2026, around 20 percent of the water requirement in coastal cities is met by desalination, India would require considerable investments. The total installed capacity that would be required to meet 20 percent of the total water demand in coastal cities by 2026 is estimated to be 4,721 MLD. Without any doubt, this is a gargantuan task requiring strong political will at all levels of governments, in addition to promoting private sector participation. The factors that support the establishment of desalination projects in major coastal cities are:

• Population explosion and growing water needs.
• Rapid Industrialization by setting up of SEZ (Special Economic Zones), PCPIR (Petroleum, Chemical, Petrochemical Investment Regions) and MPP (Mega Power Projects), etc.
• Fresh water requirement by industries competing with the drinking water requirement of the growing population
• Faster extraction from groundwater and surface water resources than the rate of replenishment
• Contamination of groundwater tables and surface water bodies

Sea Water Desalination - RO based Technology

There are many proven desalination technologies available. However, only the reverse osmosis (RO) membrane process and the distillation (multi stage flash-MSF, multi effect distillation-MED and mechanical vapor compression-MVC) processes have achieved commercial large-scale application. We will for the moment restrict ourselves to a brief discussion on Reverse Osmosis process only

Reverse Osmosis (RO)

Reverse osmosis is a membrane separation process in which pure water passes from the high-pressure seawater side of a semi-permeable membrane to the low pressure permeate, or “pure” water, side of the membrane. In order to overcome the natural osmotic process (migration of pure water from a solution of low concentration into a solution of higher concentration in order to balance the osmotic pressures), the seawater side of the system has to be pressurized to create sufficiently high net driving pressure across the membrane.

In practice, the seawater can be pressurized to pressure as high as 70-80 bars. RO systems require stringent feed water pre-treatment in order to protect the membranes from effects such as scaling and fouling, including biological fouling. The extent of pre-treatment requirement depends on a variety of factors, such as seawater composition and temperature, seawater intake, membrane materials and recovery ratio.

Usually the pre-treatment consists of the filtration and the addition of anti-scalants, dispersants to inhibit precipitation and the growth of micro-organisms. The use of micro, ultra and nano filtration is becoming increasingly important as a potential pre-treatment alternative to the conventional pre-treatment processes in order to achieve higher flux in RO membranes. High salt rejection and good high pressure operation qualities of current membranes permit the economical operation of seawater RO plants in single-stage systems. In recent years, seawater RO based desalination has become most commercially viable process applicable on a large scale.

Reverse Osmosis (RO) Process Schematic:

Various studies performed at various points of time have indicated that cost of desalinated water from RO systems is lower than those from alternate technologies for instance thermal desalination systems.

 

Recent developments in RO technology have led to significant cost savings both in capital and operating costs. The significant reduction in cost for RO system over last decade has become possible because of continuous reduction in cost of RO membranes and developments in RO membranes manufacturing processes resulting in energy efficient membranes. Energy consumption has become considerably lower than thermal desalination, making RO less sensitive to high-energy costs. Because of the cost economics in favour of RO desalination system under present scenario, more and more users are opting for RO systems for sea water desalination. Some of the other important points, which go in favour of RO desalination systems, are listed below:

1)Cost of RO desalinated water increases with increase in TDS (total dissolved solids) levels in the feed sea water. The cost economics in favor of RO desalination is high in Indian conditions (with TDS values of 35,000 to 40,000 ppm in Indian sea) as compared to middle east (with TDS values of 45,000 ppm in Arabian sea)

2) The capital and operating costs of seawater desalination plants have decreased significantly in real terms over the last decade due to:

• Capital costs: process design improvements; membrane performance development and lower cost per m2; manufacturing methods and increased volume; increased competition.
• Operating costs: process performance; membrane life; energy efficiency improvements; inter-stage boost pumping; improved chemicals; reduced corrosion; energy recovery devices.

While in the past decade, considerable growth has taken place across the country, it is unfortunate, that several pockets of the country still remain deprived of potable water. Besides, India being an agrarian country, the need for water for agricultural purposes cannot be under emphasized. Several ideas, including the superb initiative of inter linking of rivers have been purported over a period of time. However, the problem of economically arriving at a logical and sustainable solution has eluded hitherto. What is actually required is a holistic and viable solution for catering to across the board problems in various domains and sectors of the Economy.

This being so, it is important to divide the problem in smaller initiatives, viz. water requirements for the industrial usage, water requirement for city and village sustainability and water requirement for agricultural produce. All these sectors are of vital importance and perhaps, absolutely essential, to lend a helping hand to the growth momentum of the country.

While the subject is vast and warrants solutions on several fronts, the problem needs to be addressed sequentially. In this article we will concentrate on Sea water Desalination and Sewage water management and recycling. Water  for industrial usage is identified as a prime focus for arriving at a sustainable solution for water supply to meet the requirements of Industry. The Incidental benefits to the other sectors will accrue alongside.

Peninsular India – A Huge Opportunity for Desalination

While the country is confronted with several problems, there is a blessing in disguise, in respect of the fact, that India is a Peninsular country, surrounded by ocean along three major contours of its entire geographical landscape. Proximity to sea water itself, provides an opportunity to examine the feasibility of a techno-economic solution for addressing the country’s water problem to a large extent. It was this very fact, that provided an avenue of evolving a viable technical solution, which to start with, could serve the interests of the mega industries, and gradually, be developed further to cater to the other sectors, as well. A prime motive for looking into the subject a little more closely, was the fact that the around the world several initiatives have already been taken up successfully, to provide potable/industrial water with sea water as feed.

Overview

Several mega projects in the Refineries, Petrochemicals, Fertilizers, Steel and Non Ferrous metallurgy, mega power plants are envisaged around the various parts of the country. Most of these projects are heavily investment driven and also require substantial quantities of treated water for their sustenance.  

Various initiatives with zero discharge have been incorporated in almost all the mega facilities to minimize the requirement of fresh water. However, given the scale and size of the Projects, water requirements continue to remain substantial inspite of recycling.

Industrialization in India is at an all time high, with every state inviting Industries to set up their units in their state. Several of these regions are located along various coasts of India. With limited fresh water available and ever increasing demand for domestic drinking water supply, State Governments are finding it extremely difficult to supply fresh water to these industries. Even if limited quantity of fresh water is being supplied by the state municipalities to industries, the cost of water supply is very high. Rivers are running dry and the problem of water management is only becoming more and more complex by the day.

The Industries which consume the major quantity of water for their process use are Refineries, Petro chemical units, Power plants & Fertilizers. Major grass-roots or expansion projects in these industries are expected in next 5-10 years in the coastal regions. Existing industries in these areas in coastal regions primarily uses fresh water for process requirements which is a huge burden on the already scare water resources of the state. In case a good & consistent high quality fresh water (having total dissolved solids, TDS typically less than 200 mg/L) is made available to these industries in adequate quantity, one of the major problems of the state and the Industry can be resolved. Besides, an alternate source of water will to a large extent enable restoring the ground water table and the gradual replenishment of the rivers to the extent that the Industrial water is secured through alternate means.

A brief study reveals that the peninsular India can be divided into several Industry led consumption centers for which, a holistic solution can be provided for sourcing and organizing water to major Industries. 

RO Modules

From the above estimated data on the fresh water requirements for the identified clusters, four standard desalination plant modules are proposed to cover all the modules and to produce fresh water having total dissolved solids (TDS) less than 200 ppm. The four modules could be standardized to produce 7500 m3/hr, 5000 m3/hr, 2500 m3/hr and 1250 m3/hr of fresh desalinated water respectively.  These could be strategically located with connectivity to the consumption centers through a pipeline network.  The standardization would enable expansion in modules and repetition of facilities to not only help in meeting the requirements, but also to enable keeping the costs of services competitive.

Proposition

Based on the estimated consumption levels in the various Industrial clusters multiple RO units of various capacities can be installed accounting for the following:

1.   Water intake facility for each of the modules to be located, as close as possible to the sea shore, with the intake of the water taken sufficiently from depth in the sea to ensure that water quality of sustainable composition could be obtained.

2.   The intake pump heads may be adjusted, such that, usage of either GRE/GRP or cement lined Carbon Steel Pipes is possible. 

3.   The Desalination facilities could be located in close proximity of habitat for availing the grid power connectivity. Solar Thermal Facilities could be envisaged to keep the power costs low and on larger scales to meet the Industrial and society requirements.

4.   The Desalination facility based on Membrane process could comprise of an upstream ultra filtration unit, followed by Membrane Units for recovery of treated water permeate with TDS of the order of 200 mg/l maximum.

5.   The Desalination reject of high TDS streams to be pumped back to the sea, at least a Kilometer further from the intake point for proper dispersion of the reject in the sea.

6.   The permeate from the Desalination Plant may be pumped through Carbon Steel Pipeline networks, to the nearest cluster of the identified zone.

7.   All the RO Plants conceived in modules could be utilized for add on capacity as and when required in future.

8.   As the Desalination Plant capacity is enhanced upwards of  5000 M3/hr and 7500 M3/hr, the effective price of the RO water can be rationalized taking benefits of economies of scale

9.   For the solar Thermal Plant the requirement of the DM water could be achieved by adding tertiary RO modules to improve the quality of water. A mixed bed chamber could be provided downstream of the same to maintain the conductivity of the DM water to be utilized for solar steam generation

Economics

Based on an internal study depending upon several assumptions the price of the water RO water could range between Rs 30- Rs 42/M3. The critical area is always the cost of Power. With the solar power prices dropping asymtotically in the times to come, even further advantage of the reducing costs will accrue. Industry, which has the capacity to pay, could be encouraged to use this water. 

Municipality waste Recycling

As has been the case with most of natural resources, on water front too India is inadequately placed. India, home to 16% of world’s population has only ~2.5% of worlds land mass and about 4% of world’s water resources at its disposal. Precipitation in form of snow and rain provide fresh water to India. However most of this fresh water is drained into seas and oceans. Addling issue actually has notng to the agony is uneven rainfall, depriving certain sections of country from fresh water availability, which further constrains the existing water resources. With almost fixed water/depleting fresh water disposal, it is felt that some urgent interventions (some of which are prevalent globally) are required to tackle this problem on war footing basis as are outlined below:

a)   Utilizing treated Municipal Sewage Waste Water for Domestic/Industrial purposes. All the treated water should be put through a final treatment in RO for generating high quality water for Industry. The Reject from the Ro system could be controlled in TDS such that, it remains suitable for irrigation purposes. This way almost all the sewage water could be optimally utilized enabling the ground water table to restore some normalcy. The rivers too would begin to look healthier

b)   The central issue alongside is that the Sewage Treatment capacity in the country itself is very low and requires quick up-gradation. Wherever the capacity has been created the technology and the maintenance of the plants has been another Major issue on account of which the recycling issue has not achieved the kind of attention that it deserves

The western world and the high income countries have amply demonstrated as to how important it is to maintain the Sewage Treatment systems commensurate with requirements for ensuring a proper water balance in the ecological set up. Huge benefits accrue out of the recycling of the Municipality driven Sewage water treatment and recycling:

• Water Availability Reduction in load in water bodies which are stressed due to discharge of untreated water
• Reduced utilization of treatment equipment at consumer end
• Monetization of water resources
• Employment generation
• Aligning with GOI vision of swach bharat

a)   Utilization of treated MSW for construction purposes

Utilization of treat MSW water for construction purposes would not only help monetize the treatment plant but also offload constrained fresh water supply system.

Treated municipal waste recycling, particularly, from the land locked locations, must be looked into as an important foray.  Somewhat akin to the model discussed above  for the Sea Water Desalination Plants the same can be utilized in the municipality waste recycling as well.

Directional Study

1.   It is assumed that treated sewage waste from municipalities would be available for recycling for Industrial and service water usage.

2.   It is also assumed that such projects would be land locked. Consequently, the reject usage must be carefully designed such that the Ro reject can be used for irrigation purposes

3, Considering a front end TDS of about 750 an MBR treatment system may be considered to develop the flow scheme.

4.   It may be ensured that the reject from the plant under all the circumstances/options is always below 2100 TDS, such that, the same can be disposed either through rivers, rivulets or to be used for irrigation. Typically 40-45% of the feed sewage quantity, is expected to be disposed through the reject route.

5.   Membrane based permeate from the recycle plant has been restricted to 160 TDS, which, can be utilized for distribution to various industrial consumers as well as used as  service water.

6.   Somewhat similar to the study for the sea water desalination unit, four separate modules for permeate recovery of 1250 M3/hr, 2500 M3/hr, 5000 M3/hr and 7500 M3/hour can be considered. These sizes of the plant are very demonstrative of the various varieties and sizes of the Projects that one can encounter across the board in sewage water treatment/recycling.

7.   Solar power can be used to keep these plants operational with appropriate grid back up.

8    Magnitude

From the various Published literature it is inferred that the total waste Water System capacity for the class 1 cities about 500 odd in the country and inferences from the same could be broadly as below

Surely the above itself serves as an important resource for augmenting the depleting water resources of the country

 9    Economics

Treated water price between Rs 20-Rs 35 can be foreseen. Large industrial clusters could be utilized to use this thereby easing the dependence on ground water and fresh water sourcing from natural bodies

Conclusion

Non-availability of fresh water, depletion of underground water due to its misuse and the rising cost of fresh water due to differential water tariffs for industrial, domestic and agriculture use of water in coastal Indian cities are the prime reasons for persuading industries to look at large scale desalination plants to meet their fresh water demand at competitive rates. Desalination of seawater must be encouraged in a big way as an alternative source to full-fill growing water demand in coastal India. Coastal states like Tamil Nadu, Gujarat, and Andhra Pradesh, Kerala, Orissa and West Bengal, Maharashtra must take advantage of sea water desalination to meet water demand.

The total Industrial water recovery from the clusters as well as the Sewage Treatment plants provides a per annum potential as below:

Clearly, Desalination and sewage water treatment and recycling will secure a large part of the Industrial projects in the coastal and the landlocked areas areas besides significant quantity of water would be available for irrigation purposes as well. This will help in the revival of water tables and also return some health to the depleting rivers across the country besides leading their cleaning as well. This will provide a boost to the Ecological balance of the Nation and restore confidence in a society which is beginning to get worried with the implication arising of scarcity of water in general!