Wastewater Treatment Furthering the Course of Water: Best Practices for Effluent Treament
Water is the source of all life. This article explains various technologies to recycle and reuse water / wastewater – with experiences, hints and best practices to further the course of your water treatment – essentially, making this scarce resource go the extra mile...
The importance of water in all aspects of life is not lost on anyone, least of all, on India’s rapidly developing industry. This has in turn affected the growth of the water industry. Growing urbanization and industria-lization, coupled with over-exploitation of water resources is expected to push growth in the water and wastewater management market in the years to come, but industry participants are worried that existing poor infrastructure and pricing mechanisms may hamper the path.
A growing population has also contributed to the need to create a strong and sustainable water and wastewater infrastructure for the country. It is thus obvious that supply of clean water and effective treatment of wastewater generated across India are crucial for sustainable development in the country. The water and waste water management industry encompasses multiple techniques for the treatment of water and to overcome water scarcity and conserve water resources. Some of these technologies are listed here under:
Water treatment technologies
- Conventional system Conventional treatment consists of coagulation, flocculation, clarification, and filtration, followed by disinfection at the pre and post stage of treatment. Conventional treatment is often preceded by presedimentation tank. The benefit of using conventional systems is that it reduces the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi; and a range of dissolved and particulate material derived from surfaces water sources.
- Tube settler / Lamella settler system Tube settlers are used for clarification purposes. This increases the settling capacity of circular clarifiers and/or rectangular sedimentation basins by reducing the vertical distance - a floc particle must settle before agglomerating to form larger particles. Clarifiers equipped with tube settlers can operate at 2–4 times the normal rate of clarifiers without tube settlers.
Wastewater Treatment Technologies
- Conventional activated sludge process (ASP) This is a suspended growth process used for municipal wastewater treatment. The activated sludge plant involves wastewater aeration tanks with microbial suspension, solid-liquid separation, clarifier, discharge of clarified effluent, wasting of excess biomass, and return of remaining biomass to the aeration tank.
- Extended aeration activated sludge process Extended aeration is the modification of activated sludge process (ASP) and operates in the endogenous phase, the production of cell matter which is producing a minimum of excess sludge to be wasted from the system. The range of F/M‘s to use is that which produces the least BOD5 and suspended solids in the effluent while producing sludge with good settling characteristics.
- Moving media bio-reactor (MMBR) MMBR technology employs thousands of polyethylene biofilm carriers operating in mixed motions, within an aerated wastewater treatment basin. Each individual bio carrier increases productivity through providing protected surface area to support the growth of bacteria within its cells. It is this highdensity population of bacteria that achieves high-rate biodegradation within the system, while also offering process reliability and ease of operation. This technology has the advantage of providing cost-effective treatment with minimal maintenance.
- Sequential batch reactor (SBR) Sequencing batch reactor (SBR) is an activated sludge process. It operates in a true batch mode with aeration and sludge settlement both occurring in the same tank. The major differences between SBR and conventional continuous-flow, activated sludge system, is that the SBR tank carries out the functions of equalization, aeration and sedimentation in a time sequence rather than in the conventional space sequence of continuous-flow systems. In addition, the SBR system can be designed with the ability to treat a wide range of influent volumes whereas the continuous system is based upon a fixed influent flow rate. Thus, there is a degree of flexibility associated with working in a time rather than in a space sequence. The operating principles of a batch activated sludge process, or SBR, are characterized in five discrete periods: Anoxic fill, aerated fill, react, settle, decant.
- Membrane bio-reactor (MBR) A membrane bioreactor or MBR is an activated sludge process that utilizes a physical barrier, the membrane, to filter contaminants from wastewater. Utilizing submerged membranes eliminates the need for secondary clarification and tertiary filtration. By decoupling the activated sludge process from the settling characteristics of suspended solids (MLSS), the footprint of a wastewater treatment process can be halved or more. In addition, a MBR is ideally suited for biological nutrient removal (BNR) applications as coagulated metal salts are easily filtered and captured phosphorous can be collected as waste activated sludge (WAS).
- Up-flow anaerobic bio-reactor (UASB) In the UASB process, the whole waste is passed through the anaerobic reactor in an up flow mode, with a hydraulic retention time (HRT) of only about 8-10 hours at average flow. No prior sedimentation is required. The anaerobic unit does not need to be filled with stones or any other media; the up-flowing sewage itself forms millions of small ‘granules‘ or particles of sludge which are held in suspension and provide a large surface area on which organic matter can attach and undergo biodegradation. A high solid retention time (SRT) of 30-50 or more days occurs within the unit. No mixers or aerators are required. The gas produced can be collected and used if desired. Anaerobic systems function satisfactorily when temperatures inside the reactor are above 18–20°C. Excess sludge is removed from time to time through a separate pipe and sent to a simple sand bed for drying
- Trickling filter/bio-tower Trickling filter is an attached growth process i.e. process in which micro-organisms responsible for treatment are attached to an inert packing material. Packing material used in attached growth processes include rock, gravel, slag, sand, redwood, and a wide range of plastic and other synthetic materials.
Wastewater Recycling Technologies
- Rapid gravity sand filtration Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals—typically salts of aluminum or iron. Water and flocs flow through the filter medium under gravity or under pumped pressure and the flocculated material is trapped in the sand matrix.
- Ultra-filtration membrane technologyUltra-filtration (UF) is the process of separating extremely small particles and dissolved molecules from fluids. The primary basis for separation is molecular size – particles ranging from 1,000 - 1,000,000 molecular weight are retained by ultra-filtration membranes.
Kirloskar Brothers Ltd has been at the forefront of the water industry and has executed several plants based on the above technologies. The 30 MLD sewage treatment plant (STP) for the Steel Authority of India, Bhilai, which is one of the largest recycling treatment plants in India, is based on extended aeration technology. Through this plant, colony sewage is recycled and used for the processes of the steel plant.
Similarly, sewage recycled from a 8.5 MLD STP for the Vadodara Municipal Corporation is now used for gardening purposes, while a 4 MLD STP for the Hyderabad Urban Development Authority (HUDA) helped in lake reclamation. On water treatment, the company has constructed several plants. A 125 MLD plant, based on conventional technology is supplying water to Coimbatore city, whilst plants at Meenad and Pattuvam, based on lamella clarifier technology (90 and 73 MLD respectively) have been constructed for the Kerala Water Authority (KWA). Bhopal in Madhya Pradesh also has a 195 MLD water treatment plant.
A 12.5 MLD STP based on moving media bioreactor for Karad Municipal Council, Maharashtra and a 20.5 MLD STP based on sequential batch reactor at Sanand, for the Ahmedabad Municipal Corporation, are also underway.