3. Management of Water Resources

Water Management is the process of planning, developing, and managing water resources across all water applications, in terms of both quantity and quality^[9]. A good management system includes institutions, infrastructure, incentive and information systems. It seeks to maximize the benefits of water by providing optimum water quality for drinking water, sanitation, agriculture, energy generation and inland water transport. Alongside sustaining healthy water dependent ecosystems and protecting lakes, rivers and estuaries.
Water pollution is the most common problem faced in urban areas. The pollution level of water may be affected by different types of contaminants that can pollute water and render it unusable.

Water Treatment System

The water treatment processes are used to improve the quality of raw material up to drinking water quality. The main sources of drinking water include groundwater and surface water. The surface water treatment focuses on particle removal while groundwater treatment is focussed on removal of dissolved inorganic contaminants.

The process of surface water treatment includes the following steps^[10]:

• STEP 1: The raw water, on entering the treatment facility is allowed to pass through screens (bar screens, fine screens or micro screens) to remove the larger debris like plastic bags, twigs, bottles etc. This process is called ‘Screening’
• STEP 2: After screening, the water is sent to the grit chamber for the process of ‘Grit Removal’. Here, abrasive particles like sand and grit are removed by slowing down the flow of the water.
• STEP 3: Post grit removal, the water is then directed towards the primary sedimentation tank where the water flow is completely reduced and the water is allowed to stand still for a few hours. This allows the heavy suspended solids to settle down at the bottom of the sedimentation tank due to gravity. This process is called ‘Primary Sedimentation’ and the settled solid layer at the bottom is termed as ‘primary sludge’.
• STEP 4: The supernatant (water excluding the sludge layer) is then redirected for ‘Rapid Mixing’ process, where the water is vigorously stirred after addition of chemicals known as ‘Coagulants’. The coagulants destabilize the fine suspended solids resulting in the formation of larger particles called ‘flocs’.
• STEP 5: After the floc formation, the water is subjected to gentle stirring. This process is called ‘Flocculation’ where the flocs collide with each other forming larger clumps called ‘dense flocs’.
• STEP 6: The next step in the treatment is ‘Secondary Sedimentation’. The water is stagnated in the secondary sedimentation tank for few hours to facilitate the settling of the dense flocs forming ‘secondary sludge layer’

NOTE: Both primary and secondary sludge layers from the sedimentation process are sent for further treatment and dewatering.

• STEP 7: The water (excluding the sludge layer) is then transported to the filtration unit for ‘Filtration’. Here, the water is allowed to pass through a filter which contains layers of gravel, sand, activated carbon etc. based on the impurities in the water.
• STEP 8: The final step in the treatment process is ‘Disinfection’. The water is disinfected with the help of ‘chlorine, ozone or ultraviolet light’ to kill or inactivate the remnant harmful pathogens and microorganisms.

All these steps help to improve the quality of water and makes it suitable for drinking and other domestic use purposes
A schematic diagram of the water treatment process is shown in the* Figure below.*
For groundwater, the number of steps involved are relatively lower and include: Aeration, flocculation, sedimentation, recarbonation, filtration , disinfection and solid processing.

Wastewater Treatment Processes

The wastewater treatment plants are designed to provide primary, secondary and tertiary treatment of wastewater. The process of treating and reclaiming water from wastewater (any water that has been used in homes, such as flushing toilets, washing dishes, or bathing, and some water from industrial use and storm sewers) starts with the expectation that after it is treated it will be clean enough to re-enter the environment.

The process of the wastewater treatment comprises of the following steps^[11]:

• The primary treatment also known as physical treatment focuses on removal of physical impurities and results in ~60% removal of suspended or inorganic solids from the wastewater. It also removes the settleable organics. Various methods like screening, sedimentation etc. are used in this step.
• The secondary treatment also known as biological treatment is aimed to further treat the wastewater for more than 90% removal of solids and organics. Secondary treatment mainly removes biodegradable dissolved and colloidal organic matter with the help of microorganisms. In this treatment process, microorganisms are added to the wastewater and allowed to digest the organic matter in it. Commonly used secondary treatment processes include Activated Sludge Processes (ASP), Trickling Filters and Rotating Biological Contactors (RBCs) and Sequencing Batch Reactors (SBRs).
• The tertiary treatment comprises advanced treatment processes which further improves the quality of water. It involves several disinfection processes by addition of disinfectants like hypochlorite, ozone etc.

Zero Discharge Model:

The advancement of technology has led to many innovations in the field of wastewater treatment. One such innovation is the ‘Zero Discharge Model’. In this model, the treatment systems aid in efficient usage of water and help to reduce the wastage of water^[12]. The efficient wastewater treatment helps in 100% water recovery. Also, the recovered water can be reused. This reduces the dependency on the freshwater resources and also makes the industry/ organization environmentally compliant. Though its installation is expensive and the energy consumption is high, this technology helps to conserve water and is useful in many industries. Also, resource recovery is done from the solid sludge also. It is thus called as ‘Zero Discharge Model’