Water pollution in India is posing a significant threat to human health. Large volume of unprocessed wastewater is being discharged by industries into fresh water sources, resulting in frequent outbreaks of waterborne diseases and environmental degradation. While the overall investment potential of the Indian water sector is estimated to be about $130 billion by 2030, the total water and wastewater treatment market alone would be worth about $420 million, with an annual growth rate of 18%. The Wastewater treatment industry in India is definitely looking to grow rapidly in the coming years.
TECHNICALLY, WASTEWATER treatment process comprises chemical, biological and physical treatment. Various chemicals are used at the initial stage to oxidize the soluble organic compounds. Chemical reactions are much faster than the biological process as the latter requires huge retention time that allows live biomass (Bacteria, Bio-phage, Protozoa, Rotifers, or Fungi) to produce thousands of extracellular enzymes suitable to degrade the remaining organic matters coming out or un-oxidized compounds from a chemical reaction.
There are several biological processes as well, which are being used for wastewater treatment. The process implemented depends on the nature of pollutants and on the stringent discharge norms laid down by Pollution Control Boards. Clear understanding is essential for selecting suitable biological processes and we need to understand the nature of effluent to be treated and the end use of the treated effluent.
The biological process is selected based on the nature of raw materials being used in the manufacturing process of the products like, organic solvents, fats, alcohol, humic acid, tannins, dyes and intermediates , All manufacturing ingredients (API) among others. Such manufacturing products require more retention time in order to complete degradation process. Therefore, it is advisable to adopt the combination of biological processes like, moving bed bioreactor (MBBR) with Activated Sludge Process (ASP) or Moving Bed Bio Reactor (MBBR) with Sequential batch reactor (SBR). These combinations are also economically viable. However, ASP though is proven biological process may become expensive in Capital expenditure (CAPEX) & operating expenses (OPEX).
Significance
The biological process becomes an imperative and integral part of the wastewater treatment for municipal as well as industrial purposes. Each of the pollutants in the form of Biochemical oxygen demand (BOD) or chemical oxygen demand (COD) requires selective enzymes that are being secreted outside the cell of biomass. The process gets completed by a series of such selective enzymes over a designed period of retention time. This leads to significant reduction in BOD or COD by biological process in comparison to the chemical treatment. Moreover, selection and the combination of biological processes have a greater advantage over conventional treatment processes.
In terms of both operational as well as capital costs for thermal oxidation, the biological process is far superior to other processes like chemical treatment. More is the chemical utilization, more is the sludge production. This makes the total treatment expensive and questionable too. It is, therefore, essential to select and make the biological process much stronger with an aim to eliminate chemical treatment.
Types of biological processes
Membrane Bio-Reactor – The advanced biological process called ‘Membrane Bio-Reactor’ (MBR) is being implemented on a huge scale these days. Although it avoids ultra-filtration (UF) for the downstream membrane process, there are several disadvantages of this sophisticated technology and therefore it becomes limited.
Moving bed Bio-reactor ( MBBR): The process follows the same principal as of trickling filters in early 80’s and 90’s centuries. The thin bio-film is developed on some HDPE/PVC media and will not generate Mass liquor suspended solids (MLSS) as observed in other biological processes like ASP/ SBR/MBR etc.
The developed bio-film contains 90-92% of biomass that is composed of bacteria, rotifers, planktons among others and has a long age. The bio-film degrades organic matter as a source of carbon and energy and the process of degradation reaches up to 90-95%. The end user can expand the capacity of production without any additional civil units in effluent treatment with MBBR as a biological process. It also requires 45% lesser foot print as compared to the foot print required by other biological processes.
[box type=”shadow” ]The developed bio-film contains 90-92% of biomass that is composed of bacteria, rotifers, planktons among others and has a long age.[/box]
In few cases, a combination of aerobic processes like, MBBR and Integrated Fixed Film Activated Sludge (IFAS) will have better impact as compared to other biological processes, although the latter process requires lower capital cost and mainly applicable when the stringent norms of amonical nitrogen and other nutrients like phosphorous are required to be maintained.
Activated Sludge Process – The ‘Activated Sludge Process’ (ASP) is a proven process that has been in practice for well over a century. However, ASP may not be a suitable process where the discharge norms are more stringent.
Several advanced biological processes are adopted when such stringent norms are to be adhered to. Selection of the process is also based on the end use of treated water. The conventional processes like, ASP or ‘Sequential Batch Reactor’ (SBR) that have been proven for municipal wastewater treatment may not be suitable for many industrial applications.
Anaerobic Processes – The biodegradation processes gets hampered at several stages because of two major reasons – increase in hydraulic load and thus increase in organic load simultaneously. In such a scenario, the selection of biological process becomes very important. The process selected should be one that can handle such abnormal shock loading. In many cases, the anaerobic process like ‘Upflow Anaerobic Sludge Blanket’ (UASB) fails due to lack of an understanding of the parameters. Therefore, the application of UASB becomes limited. It is common practice everywhere to promote and implement UASB for the effluent contains higher COD/BOD load but it is very much essential to understand other important parameters which hamper any of the three stages of biomethanation completely.
Selective Bacterial Culture-The concept of selective bacterial culture adopted for seeding purposes would not be successful for a long term. This is primarily because in biodegradation, one organic compound will produce thousands of other metabolites everyday till the end product H2O and CO2 are formed. Each of the products synthesized during the chain of biodegradation processes requires selective enzymes and these selective enzymes will be extra-cellular produced by selective bacteria only. Therefore, the start-up process in any of the biological process is a skill that will successfully work if proper bacterial or biomass growth phase is well understood and maintained scientifically. It is also proven that longer the age of biomass, the higher is the degradation capacity. The pollutants which are slow degrader need to be treated by MBR, where the biomass concentration is always > 8000 ppm, or by a series of MBBR or with MBBR/ASP combination.
It is observed in many cases that higher the Total Dissolved Solids (TDS) concentration more is the danger for biological process. However, it is always advisable to understand the hardness of wastewater rather than TDS. We have two National Patents on textile dye bath effluent treatment wherein the conventional ASP is working at a very high pH of 11-12 while leaving the treated effluent from secondary clarifier at pH of 7.8-8. This is because of the alkalophilic bacterial mass wh
ich was naturally enriched and cultivated in the aeration tank.
The concept is eliminating chemical treatment completely and therefore chemical sludge becomes ‘zero’. However, the waste biomass generated from the aeration tank contains very high calorific value as good as of Indian lignite.
Dr. Vijay Kaluskar Vice President – Business Operations (Industrial Segment) Ikos GAIA Infra Pvt. Ltd
Powdered Activated Carbon – The application of ‘Powdered Activated Carbon’ (PAC) in the aeration tank is the most proven technology that avoids shock loading during the process and help biomass to self sustain under nutrient starved conditions like, continuous less feed and effluent lacking nutrients accidently in the existing effluent treatment plant. It is observed that powered activated carbon (PAC) ranging from 80-200 micron and the selection will be carried on based on the nature of effluent to be treated.
The biological process is significant in treating wastewater effectively. The various processes and techniques not only save time, but also make the task cost efficient. Always focus on short listing and working out three to four feasible processes. It is important to compare and analyze all the options independently. This practice will prove beneficial as this will enable you to understand the processes and implement the same in your projects effectively, thereby, avoiding mismanagement.