BACKGROUNDIt is well known that of the entire sewage generated in India, only about a quarter is treated. The rest is discharged untreated, allowing it to mix with various water bodies and cause severe pollution. This has been the case over the last few decades, with no significant improvement, despite the Government of India’s assurances to eliminate the wide gap between treated & untreated sewage.As such, the sewage treatment is within the purview of local municipal bodies. Every year, all of these bodies allocate funds for treatment plants in their budgets. Irrespective of this, the existing sewage treatment plants (STPs) either operate at capacity or are completely shut down, resulting in the release of large quantities of raw sewage into water bodies.When such a situation persists for a number of years, one wonders about the reasons for the same. Apart from government apathy, there must be some other angle to this status..POSSIBLE REASONS FOR UNDER CAPACITY SEWAGE TREATMENT:OPERATIONS OF EXISTING STPs:Usually, operations of STPs are outsourced & contract is awarded to the lowest bidders. This situation overlooks the possibility of technical incompetence in the operation of STPs.Moreover, the minuscule surplus of operating cost left with STP contractors (after various adjustments) is insufficient to correctly operate the existing STPs. This is why only a fraction of input sewage is treated & rest is released as such.Apart from the above, the burgeoning population within STP jurisdiction creates extra sewage generation over & above the input capacity of the existing STP. This extra sewage cannot be accommodated within the operating capacity of the existing STP & the same is released untreated into water bodies..CREATION OF NEW STPs:The long, drawn-out process of budgeting, sanctioning, tendering, etc., in municipal bodies takes a very long time to create new STPs. In the meantime, the sewage being generated has to be released into water bodies without treatment. The planned capacity is exceeded in the intervening period.The same bureaucratic procedure fails to provide extra land required for the establishment of new STPs.As regards existing STPs, providing extra land to augment the capacity is next to impossible. The burgeoning population growth has already occupied the land surrounding the existing STP.Land costs have tremendously increased & hence it is economically impossible to acquire new land..These are the salient features that prevent municipal bodies from providing complete and foolproof sewage treatment without causing water pollution. Unless this administrative procedure is radically changed, the same state of affairs will continue. Hence is the reason to look for something better..EXISTING TECHNOLOGIES: There are mainly three technologies adopted in existing sewage treatment. 1. Activated Sludge Process2. Moving Bed Biofilm Reactor (MBBR)3. Membrane Bio-Reactor (MBR).Some variations are adopted, but the basic technologies are the three above. However, the implementation of these technologies more & less keeps the limitations in municipal administration the same. Thus, in terms of STP technology as well, there is room for further evolution..OPERATIONS OF EXISTING STP TECHNOLOGIES: .The scheme involves an aeration tank, in which BOD is destroyed. If the aeration tank is modified by adding plastic floating media to enhance surface area while keeping all other conditions the same, then the scheme is called MBBR. It enhances the rate of destruction of BOD. Now, if membranes are kept immediately after the aeration tank or are immersed in the aeration tank, then the scheme is called MBR. Apart from the elimination of suspended solids i.e. MLSS, membranes do not do anything else. Membranes only produce higher-quality treated water, since they cut off all substances larger than the membrane pore size. Usually, microfiltration-type membranes (or sometimes ultrafiltration types) are used in MBR. .Overall, the four basic stages of sewage treatment remain the same, as illustrated in Diagram 2. They are viz., Primary, Secondary, Tertiary Treatments, followed by sludge management..NOVEL PROCESS FOR SEWAGE TREATMENT: Now, I have decided to look for something out of the box in devising something new in sewage treatment. I thought about whether it is necessary to aerobically degrade the BOD/COD in sewage. What if I decide to skip aeration altogether & simply somehow eliminate BOD/COD from the scheme & treat sewage differently? Only reverse osmosis/ nanofiltration membranes can separate dissolved BOD/COD from the sewage. All other membranes, such as ultrafiltration or microfiltration, allow most of the dissolved BOD/COD in sewage to pass..After preliminary trials, I focused on Reverse Osmosis membranes and decided to use them for our purpose. Given the robust characteristics of Plate & Tube Reverse Osmosis (PTRO) membranes, I decided to use them immediately after primary treatment. Primary treatment provided me with raw filtered sewage, on which PT-type RO membranes performed well, and I could produce 90%+ permeate water suitable for construction or irrigation. The RO membranes after primary treatment split the raw filtered sewage into two streams, viz., 90%+ of the original volume as reusable water permeate & 10% of the original volume as reject. Regarding the reject, in which almost all the BOD/COD was trapped, we considered subjecting it to anaerobic digestion. (In the traditional STP, anaerobic digestion is performed in sludge management anyway.) The output of anaerobic digestion is a fertiliser..Now, if one refers to Diagram 2, the entire secondary & tertiary stages are eliminated by the insertion of RO membranes as above. It also eliminates the need for aeration, sludge generation & sludge management. This proposed method will significantly reduce the STP's footprint. Thus, land requirement will be reduced. Secondly, since aeration is eliminated, the need for monitoring MLSS & meticulously managing STP operations will be eliminated too. The reason for sludge generation is eliminated. Thus, in this new type of STP scheme, no sludge will be produced..POSSIBLE CHARACTERISTICS OF NOVEL METHOD OF STPPOSSIBILITY OF AVOIDING SLUDGE GENERATION.POSSIBILITY TO REDUCE LAND REQUIREMENT.POSSIBILITY TO REDUCE ELECTRICITY REQUIREMENT.POSSIBILITY OF ENERGY GENERATION.POSSIBILITY OF FERTILIZER GENERATION.Since there is no aeration, there will be no generation of suspended solids or sludge. The basic reason for the sludge generation will be eliminatedWith reference to Diagram 2, the two most significant stages, viz., secondary & tertiary stages, are eliminated. Hence, it will significantly reduce the land requirement.Since aeration is eliminated, electricity requirements will decrease; however, this reduction will be partially offset by the electricity required to operate the RO unit..After the raw filtered sewage is treated by RO, the RO reject will undergo anaerobic digestion. Although biogas generation will be insignificant, the digestate output will be a fertiliser. The government of India has recognised the digestate of anaerobic digesters as a fertiliser. It is rich in nitrogen & phosphorus. [3].SALIENT FEATURES:Our novel membrane process is instantaneous. It immediately produces recycled-grade water without aeration.It can also be retrofitted to existing STP.It is quickly assembled in a few weeks in the field to expedite sewage treatment.This process will require less power since aeration is not needed. Skilled manpower is required for maintenance. (Unskilled workers can be trained in a short period.).Beauty of this process is that it instantaneously starts producing recycle grade water. (There is no need to wait for development of optimum MLSS.)The existing STPs can be retrofitted with this process system. They too can start producing recycle grade water immediately. Suitable short training can be provided to unskilled workers, so that they can carry out operations & maintenance..POSSIBLE BUYERS OF THE NOVEL SYSTEM:Municipal bodies, which wish to either increase the capacity of the existing STP or to set up a new STP.Large industrial establishments with their own stop units.Power and fertiliser units that buy sewage to augment their water requirement with treated sewage.Government industrial and military establishments having their own STPShips in the naval, commercial and tourism sectors.Pilgrimage centres.Exports to other countries. .ASSURANCES FROM NOVEL SEWAGE TREATMENT:Shortest time set up of STP units.Immediate recovery of reuse quality water at 90% of original volume.Reliable output water quality.Low power cost STP.Low maintenance cost STP. Lowest footprint STP.Enables the use of saved land for other commercial or housing purposes.REASONS FOR INVESTMENT IN NOVEL STP:Customers save a significant amount of time in setting up STP.Customers save in costly urban land cost.Customers can augment the capacity of existing STP units. Saves the cost of a new STP. Saved land can be used/sold for construction purposes.Customers save on operating costs by reducing electricity.Meets the obligation from the irrigation department to put back reusable quality water into the canal/river.Recovered water supports the water supply to needy farmers.Process of STP does not depend on constant monitoring of the biological process. The PTRO unit can be leased for a finite period, saving capex.CURRENT STATUS: This process requires the development of certain parameters in the pilot plant. Efforts to that effect, are undertaken with the technical collaboration with Rochem Separations Systems (I) Pvt. Ltd., Bandra, Mumbai, INDIA. The preliminary results are very promising. Further development is underway at R&D dept. of Rochem, Mumbai. The trials are conducted on 20m3/day capacity PTRO unit..About the AuthorSince 2012, Dr. Harshvardhan M. Modak has been semi-retired while consulting for various companies. He was President of Rochem Separations Systems (India) Pvt. Ltd. from 1999 to 2012, significantly contributing to the company's growth. From 1992 to 1999, he worked as a Corporate Advisor, driving strategic change for national and multinational firms. As CEO of the Distillery Division at Western Maharashtra Development Corporation from 1987 to 1992, he improved operational efficiency. He was also a Professor at Vasantdada Sugar Institute from 1985 to 1987 and a Senior Scientist at Reckitt & Colman from 1982 to 1985. Dr. Modak's career began as a Technical Expert at Blue Star Ltd. from 1980 to 1982. He has consistently demonstrated a commitment to growth and innovation throughout his career.
