Water is a paradoxical commodity; it seems free and plentiful, yet its supply is under tremendous strain. Use of potable water has more than doubled over the past 50 years, and many fear that we are coming close to a frightening breaking point, a world where chronic water shortages for farmers, businesses and people is the norm. Access to clean water has emerged as a critical issue affecting economic activity, development, and business around the world. Increasing regulatory pressures, climate change, aging and failing infrastructure, growing focus on social responsibility, and concern for environmental are forcing organizations to reassess the impact of water management on their economic wellbeing.
In India, population growth and overall economic development are expected to lead to an increase in water usage across sectors. Available resources are likely to be overexploited with a rise in the consumption of water for irrigation, industrialization and infrastructure growth. Industry bodies are encouraging companies by recognizing their proactive implementation of sustainable water management programs and large Indian companies are investing in multiple water management initiatives across their operations. In a large developing country such as India, the links between water consumption across sectors complicates water management and rapid industrialization and unplanned urban growth is resulting in the generation and discharge of large quantities of wastewater into existing water bodies. This untreated wastewater is leading to increased pollution and depletion of clean water resources.
Godrej & Boyce has achieved 'Zero Discharge', since 2010, for its industrial activities by effectively treating and recycling of industrial effluent generated through various activities. A total of around 15 lakh liters/day of treated waste water is recycled back for use in Process in Pre-Treatment (PT) line after treatment through RO systems, RMC production and Landscaping applications. By making use of recycled and ground water for our cooling applications we have reduced the use of about 3 lakh liters/ day of good potable water which was lost due to evaporation and drift. If this is not enough, we are using recycled water for new constructions as for production of ready mix concrete. The everyday requirement of 2-3 lakh liters/day of water for RMC production at two plants is sufficed by recycled water.
Godrej & Boyce has not only taken various initiatives in our manufacturing units, but also in our residential colonies in Vikhroli. One among the many is the construction of sewage and recycling plant with a distribution network for using it for flushing of toilets in our residential colonies, which reduces about 5 lakh liters/ day of good potable water use. Other very significant initiative which has been taken is the Rainwater Harvesting.
As a part of our on-going efforts, Godrej decided that the Godrej IT Park Project, 02, Godrej Business District which is a part of our Vikhroli Township. The plant recycles 100% of Sewage Water generated from the building by reusing the same for its flushing, gardening and landscaping requirements after adequate level of treatment in a Sewage Treatment and Recycling plant. This project has also received LEED certification for achieving the required green standards.
An overview of the process:
- The treatment procedure used in this project was a 'completed mixed aeration system', which uses submersible non-clog sewage pumps to pump the sewage from the collection sump. The pumped sewage is then taken to an overhead holding tank before it is drained by gravity to an open RCC basin to be treated biologically by highly efficient diffused aeration system.
- After a certain period of aeration, the sewage settles down and can be decanted and collected in a decantation tank from where it is pumped through a filter package consisting of pressure sand filter and activated carbon filter. These are then sent to the treated water storage tank after disinfection by sodium hypochlorite. After that, tank chlorination is done to this treated water by using hypochlorite solution for disinfection.
- Unlike commonly used aeration sewage treatment plant, this process utilizes the same tank for aeration and as well as settlement purpose, thereby doing away with a separate civil structure for the settling tank and also the settling tank machinery and return sludge pumps. Also, the variation in the flow rate creates malfunctioning in conventionally designed settling tank of regular extended aeration process. As a result, during maximum sewage flow rate there is a carryover of the sludge together with the treated effluent thereby causing higher BOD in treated sewage.
Detailed characteristics and functions of each of the units of the STP:
- Screen: The Sewage is drained to raw Sewage Collection tank through Bar Screen Chamber with Manual Bar Screen. Here coarse suspended solids are removed. The Bar Screen Chamber is common to all the incoming streams of raw sewage coming to the STP.
- Raw Sewage Collection Tank: The Sewage after removal of coarse suspended solids is collected in this tank. This Raw Effluent Collection tank is equipped with compressed air aeration grid to maintain aerobic condition and avoid any settling of solids in the tank.
- Aeration Tank:
- The properly and homogenously mixed sewage from Raw Sewage Collection Tank is alternately pumped to the Aeration Tanks. Aeration Tank maintains optimum MLSS by retaining active biomass for biodegradation of organics. Air is supplied using fine bubble membrane type diffusers.
- The aeration tanks are used alternately to ensure continuous operation of the system and to handle shock loads. In the same tank after certain period of aeration, settling also takes place. An MLSS of 2500 ppm is maintained in the Aeration Tanks.
- Decantation Tank: The clear supernatant from Aeration tank after settling is decanted by opening decantation valve into Decantation tank. This also acts as a holding tank before pumping through the filter package. Alum is added to the treated sewage in the Decantation tank from the Alum tank by gravity.
- Alum Tank: Placed over the Decantation tank RCC slab, this tank is used to prepare Alum solution from powder alum for dosing into the treated water collected in Decantation tank. Alum from this tank is dosed by gravity to the treated sewage for coagulation of suspended impurities so that the same are removed when pumped through Filter package for tertiary treatment.
- Treated Water Tank: The treated and disinfected effluent from Activated Carbon Filter is collected in this tank before pumping it for gardening application.
- Sludge Tank: Excess Sludge from the bottom of the Decantation tank is collected in this tank before pumping it through the Filter press for dewatering.
- Multi-grade Sand Filter: The water from Treated Water Tank is pumped under pressure through the Multi-grade Sand Filter for removal of residual suspended solids. The filtered water is passed through Activated Carbon Filter.
- Activated Carbon Filter: The residual organics from the treated wastewater are removed in the Activated Carbon Filter. The treated wastewater is then disinfected in the treated water tank before use.
- Filter Press: The sludge from the Decantation Tank is dewatered with the Filter Press. Sludge will be pumped to the Filter Press using Filter Press pumps.
We at Godrej have turned the threat of water scarcity into an opportunity for discovering and implementing innovative ideas for management of this most critical resource in the most efficient manner. With our in-house experience and expertise we think we are now positioned to offer the benefit of this knowledge aided by our technical knowhow to external entities as well, who are eager to embark on this journey of water efficiency.
To quote Ban Ki-Moon, Secretary General, United Nations, from his speech at The World Economic Forum in 2008, "As the global economy grows, so will its thirst. This is not an issue of rich or poor, north or south. All regions are experiencing the problem of water stress. There is still enough water for all of us… but only so long as we keep it clean, use it more wisely and share it fairly."
This case study has been co-authored by Mr. Rumi Engineer, Head of Green Buildings at Godrej Green Building Consultancy Services & Head of Energy Conservation, Godrej & Boyce Ltd. and Ms. Tejashree Joshi, Asst. General Manager, Environmental Engineering Services.