Water is a vital resource for the sustenance of human life and activities. Rapid urbanization, climate changes and growing needs have put an ever increasing pressure on freshwater resources. The Indian water scenario is grim and is expected to be water stressed by 2025 as per a recent report of UN. The industrial usage of water is presently pegged at around 8% of the total fresh water available and is expected to go up to 10% by 2025. The Industries also generate large amount waste water as a consequence of the processes employed. Short supply of water especially to Industries would have a negative impact on the economic growth rate and hence water recycling has become imperative for their sustenance and growth. Burgeoning cities have created greater demand for supply of water and also generate a large amount of waste water which if discharged without any form of treatment into water bodies may harm the aquatic life and the environment. Hence waste water management has become the need of the hour.
Waste water management may be defined as the processes adopted to manage effluent water either for reduction of pollution in water before discharge to water bodies or for its reuse. Thus waste water management is not only a science but also an art. Numerous technologies are available for waste water treatment and choosing the appropriate technology is a very important aspect of Waste water management.
Municipal waste water treatment processes involve primary treatment processes which include physical-Chemical processes such as sedimentation, flocculation etc., secondary treatment processes which include biological units such as activated sludge or trickling filters, tertiary treatment which includes processes for disinfection. Waste water treatment for Industrial applications may involve treatment processes specifically designed to remove contaminants that are present in the industrial effluents. Examples of typical industrial waste water treatment include sorption, membrane filtration, precipitation and pH adjustment. There has been a constant endeavor amongst the water professionals to innovate new technologies with the basic aim of reducing the reaction time, plant foot prints and cost of treatment. The present trend is the use of Membrane Bio Reactors (MBR) and Zero Liquid Discharge (ZLD) systems.
The major innovations in the waste water management are:
- De-centralized treatment plants: These are treatment plants specific to small communities/condominiums/buildings and are not connected to the main waste water treatment system. Such designs permit the community to utilize the waste water by recycling and help in conservation.
- Satellite Water reclamation plants: They remove flow from nearby sewers to produce reclaimed water close to the use area and thus avoids in laying of pipelines and pumping systems to return the reclaimed water to the use areas from central treatment plants.
- Membrane separation technologies: It involves the separation of liquids from solids using Ultrafiltration, Microfiltration or Reverse osmosis technologies. The water produced is so clean that it is potable, though most of the applications of reclaimed water are for grey water and irrigation use. These technologies are becoming increasingly popular as the cost of the membranes is showing a downward trend.
- Biodiesel from fats, oil and grease in waste water: Fats, oil and greases are collected from waste water and converted to biodiesel through esterification and hydrogenation. This is becoming increasingly popular in Europe and Canada.
- Electricity and heat from co-generation: Biogas fueled co-generation systems allows waste water facilities to utilize energy from treatment process itself. Co-generation produces electricity and hot water from biogas, a naturally occurring byproduct of sludge dewatering. The electricity produced can be used to supply power to anaerobic digesters in the plant thereby offsetting electricity purchases.
- Electricity from sewage powered fuel cells: Methane from sludge dewatering plants can be converted in Biogas or to Hydrogen which can be used in direct fuel cells.
- Water source heat pumps: Water-source heat pumps are being used in Japan to extract residual heat energy from wastewater, after treatment and before discharge by outfall. Similar heat extraction technology is now developing for extracting heat from wastewater in sewer pipelines. Wastewater temperatures average around 16 degrees Celsius. This heat can be used as an energy resource.
Apart from above innovations, Waste water management also includes processes and strategies for their reuse so as to reduce the dependency for fresh water supplies. The major shift seen in the recent past is the adoption of Zero Liquid discharge systems wherein the waste water treated is reused and not discharged to public sewers or water bodies. The technologies employed include Ultra filtration, Reverse Osmosis and Evaporation. Further considerable work is being done the world over to develop more effective materials used in the technologies with aim of reducing costs and improve treated water parameters and also improve the efficiency of the existing technologies by adopting different configurations.
To conclude, technologies associated with waste water management are constantly evolving and are the main focus of a large number of scientists, technologists and water professionals the world over and it has their constant endeavor to provide waste water treatment solutions meeting the exacting requirements of each the segment be it municipal waste water or industrial waste water. Waste water management is thus being viewed as an essential activity in environmental protection and water conservation.