How Wastewater Treatment plants work

industrial wastewater treatment process steps and industrial wastewater management treatment and disposal process lecture notes
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Global good practices in industrial wastewater treatment and disposal/reuse, with special reference to common effluent treatment plants Central Pollution Control Board (Ministry of Environment & Forests, Govt. of India) Table of Contents   Executive Summary ............................................................................................................................................ 1  1.  Introduction ............................................................................................................................................. 3  1.1  Background and evolution of CETP ................................................................................................... 3  1.2  Status of cetps in India .......................................................................................................................... 4  1.3  CETPs’ Performance ............................................................................................................................. 5  1.4  Need for this study ................................................................................................................................ 5  1.5  Rationale for selection of industry for case studies .......................................................................... 5  2.  An Overview of Effluent Treatment Technologies............................................................. 6  2.1  Preliminary treatment ........................................................................................................................... 6  2.2  Primary treatment ................................................................................................................................. 7  2.3  Secondary treatment ............................................................................................................................. 8  2.4  Tertiary treatment................................................................................................................................ 10  2.5  Best Available Techniques (BAT) for wastewater treatment ......................................................... 11  3.  Methodology .......................................................................................................................................... 13  3.1  Scope of the study ............................................................................................................................... 13  3.2  Methodology & Approach ................................................................................................................. 13  4.  Textile Industry. ......................................................................................................................................... 15  4.1  Introduction ......................................................................................................................................... 15  4.1.1  Environmental issues of textile industries ....................................................................... 15  4.1.2  Global Scenario in Textile Industries ................................................................................ 16  4.2  Effluent Treatment System ................................................................................................................. 19  4.3  Best Available Technology (BAT) ..................................................................................................... 22  4.4  Textile Case studies ............................................................................................................................. 23  4.4.1   Overview of Common Effluent Treatment Plant (CETP, Tirupur) .............................. 23  4.4.2   Case study of Germany Plant ............................................................................................ 27  5.  Tannery Industry ....................................................................................................................................... 30  5.1  Tannery industry process ................................................................................................................... 30  5.2  Best Available Technology (BAT) in Tannery sector ...................................................................... 31  5.2.1  Global Senerio ...................................................................................................................... 31  5.2.2  Indian Senerio ...................................................................................................................... 31  5.3  Tannery Case studies .......................................................................................................................... 32  5.3.1   Italy CETP ............................................................................................................................. 32  5.3.2  Netherland ETP (TANEFTREAT) ..................................................................................... 35  5.3.3  SWEDEN ETP ...................................................................................................................... 37  5.4  Indian Tannery case‐study ................................................................................................................. 38 5.4.1  CETP at Vaniambadi, Tamil Nadu ................................................................................... 39  5.5  Combined wastewater treatment ...................................................................................................... 41  5.6  Conclusion ............................................................................................................................................ 41  6.  Pharmaceuticals ......................................................................................................................................... 42  6.1  Pharmaceutical Industry .................................................................................................................... 42  6.2  Effluent characteristics ........................................................................................................................ 42  6.3  Treatment process ............................................................................................................................... 43  6.4  Case of wastewater treatment in United Kingdom ........................................................................ 43  6.4.1  Effluent Characteristics ....................................................................................................... 43  6.4.2  Selection and introduction to treatment technology ...................................................... 43  6.4.3  Treatment scheme for AstraZeneca effluent plant ......................................................... 44  6.5  Case of wastewater treatment of in India, Patancheru CETP ....................................................... 47  6.5.1  Wastewater Treatment........................................................................................................ 49  6.5.2  Improving the process control through new technologies ............................................ 51  6.5.3  Results ................................................................................................................................... 52  7.  Electroplating Industry ................................................................................................................... 53  7.1  Effluent characteristics ........................................................................................................................ 54  7.2  Effluent Treatment Process ................................................................................................................ 54  7.3  Best Available Techniques (BAT) ...................................................................................................... 55  7.4  Specific case studies using BAT ......................................................................................................... 56  7.4.1  Case Study of CETP in Ludhiana ...................................................................................... 56  7.4.2  Nevada Goldfieldsʹ Wastewater Treatment System ....................................................... 57  7.4.2  Innovative case study, Massachusetts .............................................................................. 57  7.5  Economic Cost Analysis ..................................................................................................................... 58  7.5.1  Ion exchange case study ..................................................................................................... 58  7.5.2  Estimation of cost ................................................................................................................ 58  7.5.3  Savings in ion exchange ..................................................................................................... 59  7.5.4  Payback period of Ion exchange ........................................................................................ 59  7.6  Conclusion ............................................................................................................................................ 60  8.  Sludge Management .......................................................................................................................... 62  8.1  Introduction ......................................................................................................................................... 62  8.2  Methods of sludge treatment ............................................................................................................. 62  8.2.1  Sludge treatment ................................................................................................................. 63  8.2.2  Sludge disposal and use options ....................................................................................... 66  9.  Key Findings .......................................................................................................................................... 69 Annexure 1 Project Questionnaire .................................................................................................... 71  References.   ................................................................................................................................................... 72  List of Tables Table 1.1 Effluent treatment capacity of cetps in different states of India ................................................... 4  Table 2.1 Waste Minimization Potential in various selected Industries ..................................................... 12  Table 4.1Typical Characteristics of Textile Wastes in the manufacturing processes ................................ 16  Table 4.2 Production statistics for India ......................................................................................................... 18  Table 4.3 State-wise distribution of textile industries ................................................................................... 19  Table 4.4 Performance of Treatment System for Wash Water ..................................................................... 21  Table 4.5 Filtration spectrum of different membranes ................................................................................. 22  Table 4.6 Characteristics of effluents of Shivasakthi Textile Processors, Tirupur .................................... 25  Table 4.7 Average reduction of BOD, COD, TDS, Na, Cl of cetps in Tirupur ........................................... 25 Table 4.8 O&M cost of wastwater treatment .................................................................................................. 27  Table 4.9 Influent, effluent characteristics & Regulatory standard Germany plant no 1 ......................... 28  Table 4.10 Percentage removal of BOD, N and P in German Plant Number 1 ......................................... 28  Table 5.1 Tannery Wastes – Typical Characteristics ..................................................................................... 30  Table 5.2 Influent characteristics ..................................................................................................................... 33  Table 5.3 Effluent characteristics ..................................................................................................................... 35  Table 5.4 Influent characteristics ..................................................................................................................... 39  Table 5.5 Treated effluent quality from membrane bioreactor .................................................................... 40  Table 5.6 Quality requirement for water recovered from RO system for reuse ........................................ 40  Table 5.7 Performance evaluation in terms of wastewater treatment ........................................................ 40 Table 5.8 O & M cost of treatment processes ................................................................................................ 40  Table 6.1 Inlet parameters ................................................................................................................................. 48  Table 6.2 Outlet parameters ............................................................................................................................. 48  Table 6.3 Performance of PETL during 1994 to October 2010. .................................................................... 52  Table 7.1 Characteristics of waste water ......................................................................................................... 54  Table 7.2 Comparison of influent and effluent technology.......................................................................... 57  Table 7.3Overall comparison of chemical recovery techniques .................................................................. 60  Table 7.4Selected Metal recovery Techniques & Methods for Types of Plating ....................................... 61  Table 8.1 Sludge management processes ........................................................................................................ 63  Table 8.2 Comparison of Indian and Global scenario in terms of sludge management .......................... 65  Table 8.3 Sludge disposal and use methods ................................................................................................... 66 List of Figures   Figure 2.1 Wastewater Treatment Process ....................................................................................................... 6  Figure 3.1 Approach of the study .................................................................................................................... 14  Figure 4.1 Schematic diagram of advanced treatment for recycling of textile dyeing wastewaters. ..... 26  Figure 4.2 Flow diagram of conceptual zero discharge in textile dyeing unit .......................................... 26  Figure 4.3 Wastewater treatment plant scheme Germany plant no 1 ........................................................ 29  Figure 5.1 Simplified process flow diagram of the tannery effluent treatment plant in Netherland..... 36  Figure 5.2 Treatment Scheme of the tannery effluent treatment plant in Sweden .................................. 38  Figure 6.1 Treatment scheme for AstraZeneca effluent plant, United Kingdom.. .................................... 45  Figure 7.1 Schematic diagram representing input and output in an electroplating processing unit ..... 53    Executive Summary Rapid industrialization is adversely impacting the environment globally. Pollution by inappropriate management of industrial wastewater is one of the major environmental problems in India as well, especially with burgeoning small scale industrial sector in the country. To address the pollution coming out from industries, adoption of cleaner production technologies and waste minimization initiatives are being encouraged. Common Effluent Treatment Plants (CETPs) are considered as one of the viable solution for small to medium enterprises for effective wastewater treatment. However, many of the operating CETPs are not performing optimally due to various technical and managerial reasons. This study has made an attempt to understand the issues related to the operating CETPs and provide information related to Best Available Techniques (BAT), along with economic feasibility. The study has taken four prominent industrial sectors in the country, i.e. textile, tannery, pharmaceuticals and electroplating. For each of these sectors case studies which have adopted the BAT have been reported. The textile industry is a water intensive sector and produces effluent with high levels of TSS and BOD. In the present report, a case study of a treatment plant in Germany is presented. The textile and clothing industry in Germany has oriented towards high quality and innovative products. This treatment plant is based on activated sludge process designed on low food-to-microorganism (F/M) ratio. The BOD is reduction is about 97%. Indian textile industries are also willing to upgrade technology and adapt technology to the Indian context. Many of the larger companies have already access to BAT. The report also documents a case study of Tirupur, Tamil Nadu, where zero liquid discharge (ZLD) system has been implemented. The BOD reduction is up to 98% and the Total Dissolved Solids (TDS) reduction is up to 97%. The water recovered has very low hardness, which is always demanded in textile sector for an improved finish and better quality dyeing. Tannery sector in India has seen some advances in adoption of BAT, like adopting Zero Liquid Discharge (ZLD) technology by practicing reverse osmosis. Many countries are following the process of mixing tannery industry effluent with municipal waste water after some treatment for removal and recovery of heavy metals from the effluent. Some of the commendable case studies from Italy, Sweden and Netherland have been documented which efficiently remove nitrogen and sulphur from the effluent, along with main parameters COD. Special treatment to remove nitrogen from the effluent is generally not practiced in India. The reported Indian case study from Vaniambadi, Tamil Nadu is using BAT. Its performance has been analysed based on its trial operation results. Pharmaceutical sector in India has taken a major leap after 1970. The pharmaceutical industry produces effluent having high concentration of organic matter. The high COD values and refractory nature of some organic compounds present are characteristics of pharmaceutical effluent. The report documents a case study of AstraZeneca effluent plant at Avlon Works, Avonmouth, United Kingdom. This plant has adopted anox Moving Bed Bio Reactor (MBBR) process which is a robust system followed by chemical phosphate removal and a Dissolved Air Flotation (DAF) plant. The plant uses plastic Bio carriers media which have high internal surface area and allow the biofilm to grow protected within these engineered plastic carriers. A case study of pharmaceutical sector in Patancheru CETP, Andhra Pradesh, India is also reported. In this plant the effluent is mixed with sewage to improve biological treatment amenability. The inlet parameters are regularly monitored and 1 non-compliant tankers are rejected and sent back to the industries for further treatment of the effluent. This CETP has UF membrane bio reactor based treatment and the treated effluent is further polished at a public STP at Amberpet. Electroplating sector discharges effluent with heavy metals like chromium and nickel. BEST Available Technologies (BAT) insists on recovering the metals and recycling the water. Technologies used for this purpose are Reverse Osmosis (RO), Ion-exchange, and Electro- dialysis and evaporation, etc. Documented case study from CETP in Ludhiana (India) is a Zero Liquid Discharge (ZLD) plant. Recovered water is reused by textile units. An innovative case of a Massachusetts company providing reagent based extraction of metals from effluent in a simple and cost effective manner is also reported. Based on the analysis, ion-exchange is evaluated to be effective in terms of efficiency and applicability. It is inferred that for each case, with its unique set of issues, different technological solutions are needed. Moreover, technological solution is not the only factor. A survey was conducted with CETP operators and other stakeholders and it was concluded that operation and management issues plays an equally important role. In India, even though several CETPs have implemented latest and advanced technologies, but issues like, operation and maintenance, untrained staff, intermittent power supply, high operation cost, inappropriate design capacity, inadequate penalties for non-compliance, lack of regular monitoring of inlet and outlet parameters etc. are some major issues for the underperformance of CETPs. Therefore to solve the problem a holistic approach that take into account use of viable technologies as well as the support mechanisms and good management and business models, is required. 2 1. Introduction This chapter discusses evolution of Common Effluent Treatment Plants (CETPs) in Indian context and their performance evaluation. A section in the report also presents the rationale for selecting industry sectors for this study, in particular to understand the best case studies. Since CETP case studies are not widely available, the study also discusses the treatment technologies in ETPs for various industries. 1.1 Background and evolution of CETP The process of industrialization is adversely impacting the environment globally. Pollution due to inappropriate management of industrial wastewater is one of the major environmental problems particularly in India. With burgeoning numbers of Small Scale Industries (SSIs), concern towards the ever increasing volume of the effluent generated has tremendously increased. The volume of effluent generated by a cluster of SSIs at times surpasses the volume of wastewater generated by a single large industry. Also due to lack of space, technical manpower, and often finances, individual SSI cannot install and operate captive wastewater treatment plant, which constraints their ability to control pollution. To address the pollution coming out from industries, adoption of cleaner production technologies and waste minimization initiatives are being encouraged across the globe. Developing economies have encouraged small scale industries for employment generation although they are known to be highly polluting. Common Effluent Treatment Plants (CETPs) are considered as one of the viable solution for small to medium enterprises for effective wastewater treatment. In India, Ministry of Environment and Forest (MoEF) in 1991 initiated an innovative financial support scheme for CETPs to ensure growth of the small and medium entrepreneurs (SMEs) in an environmentally compatible manner. The provision of the scheme for fund is as follows; • Central Government matching grants-25% of the project capital cost (this has been increased to 50% since 2012) • State Government subsidy- 25% of the project capital cost • Loans from financial institutions- 30% of the project capital cost, and • Contribution from the SMEs-20% of the project capital cost While initially the scheme was launched for first ten years, but considering the need, it was extended further. Accordingly the MoEF instructed various State Pollution Control Boards (SPCBs) to examine the possibilities of establishing CETPs in various industrial estates in the respective states. In India more than 150 CETPs have been set up so far under this scheme. The concept of CETP was adopted as a way to achieve end-of-pipe treatment of combined wastewater to avail the benefit of scale of operation. In addition, the CETP also facilitates in reduction of number of discharge points in an industrial estate for better enforcement by environmental regulatory agencies and the investment of substantial government finances in the CETP scheme was justified on the basis of potential benefits in terms of pollution reduction and environmental improvements. 1 The main objective of establishing CETP is : • To reduce the treatment cost for individual units while protecting the environment.  • To  achieve  ‘Economies  of  scale’  in  waste  treatment,  thereby  reducing  the  cost  of  pollution abatement for individual factory.  • To minimize the problem of lack of technical assistance and trained personnel as fewer  plants require fewer trained personnel.  • To solve the problem of lack of space as the centralized facility can be planned in  advance to ensure that adequate space is available.  • To reduce the problems of monitoring for the pollution control boards.  • To organize the disposal of treated wastes and sludge and to improve the recycling  and  reuse  possibilities  as  once  individual  units  are  required  to  pay  for  waste  treatment/disposal, they tend to adopt means to reduce waste generation.  1.2 Status of CETPs in India In the Indian context, given the small investment in establishing SMEs, provision of individual effluent treatment plants is not feasible due to high capital and operating cost. The disposal of treated effluents is also problematic as every individual industry cannot reach the water body through pipeline nor can it purchase land for inland irrigation. MoEF therefore instructed the various SPCBs to examine the possibilities of establishing CETPs in various industrial estates. In response to the directive issued by the Central government, the State governments started identifying the locations for establishing CETPs. Work carried out in this context till 1990 was very limited. Till 1990, India had only one CETP in Jeedimetla near Hyderabad (Andhra Pradesh). Till 2005, around 88 CETPs had been established across the nation. The number of CETPs rose to more than 150 by the year 2011. Table 1.1 Effluent treatment capacity of CETPs in different states of India (in MLD) Sl. No.  State  CETPs  in  Combined  CETPs in 2011  Combined  4  13.5  1.   AP  3  12.75 13  211.8  2.   Delhi  11  133.2 1 26   374  3.   Gujarat  16  156.3 9  48.3  4.   Haryana  1  1.1 7  7  5.   Karnataka  2  1.3 2 25   186.9  6.   Maharashtra  11  63.25 1  0.9  7.   MP  1  0.9 5  6.9  8.   Punjab  2  1.535 11  117.2  9.   Rajasthan  8  57.7 44  148  10.   Tamil Nadu  29  71.15 7  56.3  11.   UP  3  44.4 1  20  12.   WB  1  10 153  1191  13.   Total  88  559.770 1 2 Two CETPs contribute to a final CETP (FETP), One CETP contributes to another CETP 1 Performance Status of Common Effluent Treatment Plants in India, CPCB, 2005 4 It can be seen on Table 1.1 that even though Tamil Nadu has the highest number of CETPs, Gujarat treats the highest amount of wastewater. Tamil Nadu has the distinction of being the state that has the maximum number of CETPs. This is due to large concentration of small scale garment and the leather processing units. Delhi, Maharashtra, Rajasthan and Uttar Pradesh also have a large number of CETPs and also treat a high volume of wastewater. 1.3 CETPs Performance The technologies used in various CETPs all over India have been built on the best available 2 technology . In many cases, the CETPs have been upgraded to adopt better technology, but the overall performance of the CETPs in many cases is sub optimal. Central Pollution Control Board (CPCB) evaluated the performance of 78 operating CETPs in the year 2005 3 and came out with a status report with following main observation: • Unsatisfactory performance of CETPs is largely due to poor operation & maintenance.  • Meeting the design inlet quality to the CETPs that inter alia depends on effluent quality  from contributing industries is key to achieving the standards for CETP effluent quality.  • High TDS in the raw influent reaching CETPs, and as a result in treated effluent of  CETPs, is a widespread problem.  The CPCB report had suggested that the performance of CETPs has been largely unsatisfactory because of poor operation and maintenance therefore the SPCBs should conduct their regular monitoring of CETPs and take action against wilful defaulters. It further reiterated the fact that the SPCBs are required to prescribe specific set of pre- treatment standards for influent to CETP from each industrial sector and enforce them diligently. The report also recommended for need for area specific approach to tackle the problem of Total Dissolved Solids (TDS). Attempt should be towards reduction in use of TDS contributing chemicals in industries by adopting cleaner production technologies and recovery and recycling of chemicals from the waste streams. 1.4 Need for this study In view of the underperformance of CETPs in India, this study has been envisioned to find and document global best practices of wastewater treatment in specific context of CETP. For this study industry specific cases have been analysed and documented in the report, along with some good sludge management and disposal practices. 1.4 Rationale for selection of industry for case study Textile processing is the leading industry in terms of number of CETPs. This is followed by tanneries, which can be considered as the second highest industrial type in reference to number of CETPs catering to them. Based on this analysis, these two industries types have been taken up along with other two key industry types i.e. pharmaceuticals, and electroplating. Each of the four selected industry sectors are described in the upcoming chapters which details out the associated problems in terms of effluent characteristics, Best Available Techniques (BAT), and some case studies exemplifying the adoption of BAT. 2 Waste-water treatment technologies: A general review., United Nations, 2003 3 Performance Status of Common Effluent Treatment Plants in India, A CPCB report, 2005 2. An Overview of Effluent Treatment Technologies This chapter discusses in brief various treatment technologies involved in the process of wastewater treatment. In-depth knowledge of all these technologies and factors regulating the treatment mechanism is important for better management of CETPs or ETPs. Wastewater depending on its characteristics is subjected to different treatment options. Basic wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and, sometimes, nutrients from wastewater. General terms used to describe different degrees of treatment, in order of increasing treatment level, are preliminary, primary, secondary, and tertiary and/or advanced wastewater treatment. These are described below in brief. Figure 2.1 Wastewater Treatment Process 2.1 Preliminary treatment Preliminary treatment is required to remove the coarse solids and other large materials from raw wastewater. Removal of these materials is necessary to enhance the operation and maintenance of subsequent treatment units. A number of unit operations are engaged in the preliminary treatment of wastewater to eliminate undesirable characteristics of wastewater. The operations include use of screens and grates for removal of large materials, comminutors for grinding of coarse solids, pre-aeration for odour control. Sometimes pH correction and removal of oil & grease is also done. At times, member industries do preliminary treatment in their premises, before sending the effluent to CETP for further treatment. If preliminary treatment or pre-treatment is taken up by individual member industry, it improves the performance of CETP. 6 2.2 Primary treatment Primary wastewater treatment, at times, is the first step in the wastewater treatment process or it may be the second step after the preliminary treatment. It involves physical separation of suspended solids from the wastewater using primary clarifiers. This process is helpful in reduction of total suspended solids (TSS) and associated biochemical oxygen demand (BOD) levels and prepares the waste for the next step in the wastewater treatment process. The objective of primary treatment is to remove of settleable organic and inorganic solids by sedimentation and removal of materials that float (scum) by skimming. Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD ), 50 to 70% of the total suspended 5 solids (TSS), and 65% of the oil and grease are removed during primary treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected. The effluent from primary sedimentation units is referred to as primary effluent. Primary treatment ensures satisfactory performance of subsequent treatment units. Sedimentation chambers are the main units involved but various auxiliary processes such as fine screening, flocculation and floatation may also be used. The second step may be chemical treatment (generally with lime and alum) which is sometimes preceded by flocculation. The purpose is to remove metals by precipitation but it also removes some associated colloidal BOD. The process generates chemical sludge. The primary treatment involves various physical-chemical processes: • Flocculation-It is a physico-chemical process that encourages the aggregation of coagulated colloidal and finely divided suspended matter by physical mixing or chemical coagulant aids. Flocculation process consists of a rapid mix tank and a flocculation tank. The process involves mixing of wastewater stream with coagulants in a rapid mix tank, which is then passed on to the flocculation basin where slow mixing of waste occurs which allows the particles to agglomerate into heavier more settleable solids. Either mechanical paddles or diffused air facilitates better mixing. The different types of chemicals used in coagulation include inorganic electrolytes, natural organic polymers and synthetic poly electrolytes. The selection of a specific chemical depends on the characteristics and chemical properties of the contaminants. • Sedimentation- This process is aimed to remove easily settleable solids. Sedimentation chambers may also include baffles and oil skimmers to remove grease and floatable solids and may include mechanical scrapers for removal of sludge at the bottom of the chamber. • Dissolved Air Floatation- Use of bubbles in this process is required to raise the suspended particles in wastewater up to surface level and hence make it easy for their collection and removal. Air-bubbles are introduced into the wastewater and attach themselves to the particles, thus causing them to float. This process of diffused air flotation can be used to remove suspended solids and dispersed oil and grease from oily wastewater. Wastewater is pressurised and contacted with air in a retention tank. The pressurised water that is super-saturated with air is passed through a pressure- reducing valve and introduced into at the bottom of floatation tank. As soon as pressure is released the super-saturated air begins to come out of solution in the form of fine bubbles. The bubbles get attached to suspended particles and become enmeshed in sludge flocs, floating them to surface. Float is continuously swept from the surface and sludge may be collected from the bottom. Addition of certain coagulants increases the oil removal efficiency of DAF units. • Clarification- Clarification system uses gravity to provide continuous, low cost separation and removal of particulate, flocculated impurities and precipitates from water and generally follow the processes which generate suspended solids such as biological treatment. In a clarifier, wastewater is allowed to flow slowly and uniformly, permitting the solids to settle down. The clarified water flows from the top of the clarifier over the weir. Solids get collected at the bottom and sludge must be periodically removed, dewatered and safely disposed.   Chemical Treatment Processes Chemical treatment may be used at any stage in the treatment process as and when required (preferably before biological treatment as it removes toxic chemicals which may kill the microbes). Mainly used methods are- • Neutralization- Incoming untreated wastewater has a wide range of pH, and it is difficult to treat wastewater with such a high variability of pH. Neutralization is the process used for adjusting pH to optimize treatment efficiency. Acids such as sulphuric or hydrochloric may be added to reduce pH or alkalis such as dehydrated lime or sodium hydroxide may be added to raise pH values. Neutralization may take place in a holding, rapid mix or an equalization tank. It can be carried out at the end of the treatment also to control the pH of discharge in order to meet the standards. • Precipitation- For removal of metal compounds from the stream of wastewater, precipitation is carried out in two steps. In the first step, precipitants are mixed with wastewater allowing the formation of insoluble metal precipitants. In the second step, precipitated metals are removed from wastewater through clarification and/or filtration and the resulting sludge must be properly treated, recycled or disposed. pH is an important parameter to consider in chemical precipitation. Metal hydroxides are amphoteric in nature and their solubility increases towards higher or lower pH. Thus, there is an optimum pH for hydroxide precipitation for each metal. Wastewater generally contains more than one metal. Therefore, selecting the optimum treatment chemical and pH becomes more difficult and involves a trade-off between optimum removal of two or more metals. Various chemicals used for this process are lime, sodium hydroxide, soda ash, sodium sulphide and ferrous sulphate. Normally, hydroxide precipitation which is effective in removing metals like antimony, arsenic, chromium, copper, lead, nickel and zinc. Sulphide precipitation is used in removing mercury, lead, copper, silver, cadmium etc. 2.3 Secondary treatment This process involves decomposition of suspended and dissolved organic matter in waste water using microbes. The mainly used biological treatment processes are activated sludge process or the biological filtration methods. Biological treatment processes mainly used for secondary treatment and are based on microbial action to decompose suspended and dissolved organic wastewater. Microbes use the organic compounds as both a source of carbon and as a source of energy. Biological treatment can be either aerobic where microbes require oxygen to grow or anaerobic where microbes grow in absence of oxygen or facultative where microbes can 8 grow with or without oxygen. Micro-organisms may be either attached to surface as in trickling filter or be unattached in a liquid suspension as in activated sludge process. Activated sludge process- It is a continuous flow, aerobic biological treatment process that involves suspended growth of aerobic micro-organisms to biodegrade organic contaminants. Influent is introduced in the aeration basin and is allowed to mix with the contents. A suspension of aerobic microbes is maintained in the aeration tank. A series of biochemical reactions in the basin degrade the organics and generate new bio mass. Micro- organisms oxidize the matter into carbon dioxide and water using the supplied oxygen. These organisms agglomerate colloidal and particulate solids. The mixture is passed to a settling tank or a clarifier where micro-organisms are separated from the treated water. The settled solids are recycled back to the aeration tank to maintain a desired concentration of micro-organisms in the reactor and some of the excess solids are sent to sludge handling facilities. To ensure biological stabilization of organic compounds, adequate nutrient levels of nitrogen and phosphorous must be available to the bio mass. The key variables to the effectiveness of the system include: a) Organic loading which is described as food to micro-organism ratio (F/M) ratio or Kg of BOD applied daily to the system per Kg of biological solids in aeration tank. F/M ratio determines BOD removal, oxygen requirements and bio mass production. Systems designed and operated at lower F/M provide higher treatment efficiency. b) Sludge retention time (SRT) or sludge age is the measure of the average retention time of solids in the system and the SRT, similar to F/M ratio, affects the degree of treatment, oxygen requirements and the production of waste sludge. Systems designed and operated at higher SRT provide higher treatment efficiency. c) Oxygen requirements are based on the amount required for biodegradation of organic matter and the amount required for endogenous respiration of micro-organisms. Various modifications in activated sludge process are possible by changing one or more of the key parameters. Sequential batch reactor is a form of the activated sludge process where aeration, sedimentation and decantation processes are performed in a single reactor. Biological filters - These filters are biological reactors filled with media which provide a surface that is repeatedly exposed to wastewater and air and on which a microbial layer can grow. The two most common types of biological filters are; a) Trickling Filters: In trickling filters treatment is provide by a fixed film of microbes that forms on the surface which adsorbs organic particles and degrades them aerobically. Wastewater is distributed over a bed made of rock or plastic and flows over the media by gravity. b) Rotating Biological Contractor: A rotating biological contactor (RBC) consists of a series of discs about 40% of the area is immersed in waste water and the remainder of the surface is exposed to atmosphere, provide a surface for microbial slime layer. The alternating immersion and aeration of a given portion of the disc enhances growth of the attached micro-organisms and facilitates oxidation of organic matter in a relatively short time and provides a high degree of treatment. Anaerobic Treatment Systems- These processes are slower than aerobic degradation and when sulphur is present, obnoxious hydrogen sulphide gas is generated. Though the capital cost is high, part of it can be compensated by recovery of bio gas. They are not so commonly used in wastewater treatment systems for CETPs except as a means for sludge stabilization. 2.4 Tertiary treatment Tertiary treatment may include a number of physical and chemical treatment processes that can be used after the biological treatment to meet the treatment objectives. It is the next wastewater treatment process after secondary treatment. This step removes persistent contaminants that secondary treatment is not able to remove. Tertiary treatment is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment. Tertiary treatment is used for effluent polishing (BOD, TSS), nutrient removal (N, P), toxin removal (pesticides, VOCs, metals) etc. Tertiary treatment can also be extensions of conventional secondary biological treatment to further stabilize oxygen-demanding substances in the wastewater, or to remove nitrogen and phosphorus. Tertiary treatment can also involve physical-chemical separation techniques such as activated carbon adsorption, flocculation/precipitation, membranes filtration, ion exchange, de-chlorination and reverse osmosis. Advanced treatment processes which generally constitute of or are part of the tertiary treatment may also sometimes be used in primary or secondary treatment or used in place of secondary treatment. Some of the common tertiary treatment processes are described below: • Granular Media Filtration- Many processes fall under this category and the common element being the use of mineral particles as the filtration medium. It removes suspended solids mainly by physical filtration. Two common types of these granular media filers are a) Sand filters are the most common type which consists of either a fixed or moving bed of media that traps and removes suspended solids from water passing through media. b) Dual or multimedia filtration consists of two or more media and it operates with the finer, denser media at the bottom and coarser, less dense media at the top. Common arrangement is granite base at the bottom, sand in the middle and anthracite coal at the top. Flow pattern of multimedia filters is usually from top to bottom with gravity flow. These filters require periodic back washing to maintain their efficiency. These processes are most commonly used for supplemental removal of residual suspended solids from the effluents of chemical treatment processes. • Membrane Filtration– This technique is used to separate particles from a liquid for the purpose of purifying it. In membrane filtration, a solvent is passed through a semi- permeable membrane. The membrane's permeability is determined by the size of the pores in the membrane. The size of the pores has to be carefully calculated to exclude undesirable particles, and the size of the membrane has to be designed for optimal operating efficiency. The result is a cleaned and filtered fluid on one side of the membrane, with the removed solute on the other side. Microfiltration, ultrafiltration and nano-filtration are examples of membrane filtration techniques. • Reverse Osmosis Systems– This is also a membrane separation method that is used to remove several types of large molecules and ions from solutions through application of pressure to the wastewater on one side of a selective membrane. The result is that the 10 contaminant is retained on the pressurized side of the membrane and the treated waste water is allowed to pass to the other side. • Ion Exchange – Ion exchange is a process of exchange of ions between two electrolytes or between an electrolyte solution and a complex. Ion Exchange can be used in wastewater treatment plants to swap one ion for another for the purpose of demineralization. There are basically two types of ion exchange systems, the anion exchange resins and the cation exchange resins. It can be used for softening, purification, decontamination, recycling, removal of heavy metals from electroplating wastewaters and other industrial processes, polish wastewater before discharging , removal of ammonium ion from wastewaters, salt removal, purify acids and bases for reuse, removal of radioactive contaminants in the nuclear industry, etc. • Activated carbon– Activated carbon is used in a large range of applications in tertiary waste water treatment. Powdered as well as granular activated carbons are used for the purpose of de-chlorination of organic compounds. Organic compounds in waste water are adsorbed on to the surface of the activated carbon. A number of factors affect the effectiveness of the activated carbon. These include pore size, composition and concentration of the contaminant, temperature and pH of the water and the flow rate or contact time of exposure. Activated carbon can be applied on a broad spectrum of organic pollutants and is typically used to remove contaminants from water such as pesticides, aromatic compounds such as phenol, adsorbable organic halogens, non- biodegradable organic compounds, colour compounds and dyes, chlorinated/ halogenated organic compounds, toxic compounds, compounds that normally inhibits biological treatments, oil removal in process condensates, halogens, especially chlorine that oxidises downstream processes and organics that have the potential to foul ion exchange resins or reverse osmosis membranes. • Ultraviolet (UV) Disinfection – This technique is primarily employed as a disinfection process that inactivates waterborne pathogens without use of chemicals. Additionally, UV is also effective for residual TOC removal, destruction of chloramines and ozone. Design of the actual treatment system for a CETP involves selection of alternative processes based on the ability of individual treatment processes to remove specific waste constituents. 2.5 Best Available Techniques (BAT) for waste water treatment BAT refers to ‘best’ in relation to techniques, means the most effective in achieving a high general level of protection of the environment as a whole; ‘available techniques’ means those techniques developed on a scale which allows implementation in the relevant class of activity under economically and technically viable conditions, taking into consideration the costs and advantages, whether or not the techniques are used or produced within the state, as long as they are reasonably accessible. ‘Techniques’ includes both the technology used and the way in which the installation is designed, built , managed, maintained, operated and decommissioned. The scope of BAT reference document of European Commission on wastewater and waste gas treatment and management in the chemical sector comprises: • Application of environmental management systems and tools • Application of the treatment technology for wastewater and waste gas as it is commonly used or applicable in the chemical sector, including the treatment technology for wastewater sludge, as long as it is operated on the industry site • Identification of or conclusion on best available techniques based on the two preceding items, resulting in a strategy of optimum pollution reduction and, under appropriate conditions, in BAT-associated emission levels at the discharge point to the environment. And the definition of best available techniques is - "best available techniques" shall mean the most effective and advanced stage in the development of activities and their methods of operation which indicate the practical suitability of particular techniques for providing in principle the basis for emission limit values designed to prevent and, where that is not practicable, generally to reduce emissions and the impact on the environment as a whole. One of the BAT measures is Waste Minimization proves. Waste Minimization can be subdivided in the following major ways: • Process Modification (PM)  • Equipment Modification (EM)  • Material Substitution (MS)  • Reuse / Recovery / Recycle (RRR)  • Housekeeping (H)  Table below present potential of waste minimization is some of the important selected industrial sectors. Table 2.1 Waste Minimization Potential in various selected Industries Industry Type  PM  EM MS RRR H Agrochemicals    Bulk  drugs    Pharmaceuticals  Chemical    Metal finishing    Paper      Manufacturing  Petrochemical    Tannery    Source: Bastock et al (1994) and Gardener et al (1987) low, medium, high Process modification does not mean for the complete process line, normally individual activities in processes are modified to alter the inputs or outputs. Industries such as tannery and metal where processes are uncomplicated it might be relatively easy to modify the process, but the same might not be feasible for large industries.           12 3. Methodology This chapter of the report presents the approach adopted for carrying out this study. 3.1 Scope of the study • Documentation of the global best practices in industrial waste water technologies for primary, secondary as well as tertiary treatment and best treated effluent disposal/reuse practices, with special reference to the technologies/practices adopted in common effluent treatment plants (CETP) technologies. • Analysis of costing and economic viability of those technologies in India. 3.2 Methodology & Approach For the study, effluent treatment processes for few selected industries like • Textile, • Tannery, • Electroplating, • Pharmaceuticals Based on the industry type selected, extensive literature review and few site visits were carried out. During the site visits, CETP & ETP operators and members of industrial estates were interviewed using a structured questionnaire (Annexure 1).  Literature on wastewater treatment technologies specific to Effluent Treatment Plants (ETPs) and CETPs of these selected industries was reviewed for both Global and Indian context. The documented case studies are presented in subsequent chapters which define the BAT adoption process, capacity, influent characteristic, treatment technology used, effluent characteristics, sludge management, regulatory norms and cost issues of the selected ETPs and CETPs. Some of the selected case studies have been economically analysed to understand the economic feasibility of a particular technology. The report does not only restrict to the technical issues but also has taken an attempt to look at managerial and regulatory issues attached to performance of CETPs. Selected Industries Literature Review & Survey Treatment schemes‐ETP & CETP Cost estimates analysis Key findings Figure 3.1 Approach of the study                     14 4. Textile Industry 4.1 Introduction The textile industry is one of the oldest industrial sectors in the world. Textile industries consume large volume of water and chemicals for wet processing of textiles. The effluents from textile units have various types and qualities of wastewater. The wastewater from printing and dying units in a textile plant are often rich in colour, containing residues of colouring agents and chemicals, and needs appropriate treatment. The integrated textile industry is engaged in production of yarn, fabric and finished goods from raw fibres. Initially, raw fibres are transformed into yarn, thread or webbing. Then the yarn is converted into fabric in looms. Fabric is then dyed or printed to convert into finished product. In short, process flow is fibre manufacturing, yarn manufacturing, fabric production and finishing processes. Textile manufacturing units use natural and synthetic fibres, different chemicals as raw materials and other utilities such as water, energy and labour. 4.1.1 Environmental issues of textile industries The textile industry is water and labour intensive and produces pollutants of different forms. The manufacturing operation also generates vapours during dyeing, printing and curing of dye or colour pigments. Dust emission is associated with fibre processing. Other than these process operations, textile mills have wood, coal or oil fired boilers and thermic fluid heaters which are point emission sources. Major environmental issues in textile industry result from wet processing. Wet processes may be carried out on yarn or fabric. The transformation of raw cotton to final usable form involves different stages. The various important wet processes involved in the textile industry are as follows: • Sizing / Slashing: This process involves sizing of yarn with starch or polyvinyl alcohol (PVA) or carboxy methyl cellulose (CMC) to give necessary tensile strength and smoothness required for weaving. The water required for sizing varies from 0.5 to 8.2 litre / kg of yarn with an average of 4.35litre / kg. • Desizing: The sizing components which are rendered water soluble during sizing are removed from the cloth to make it suitable for dyeing and further processing. This can be done either through acid (sulphuric acid) or with enzymes. The required water at this stage varies from 2.5 to 21 L /Kg. with an average of 11.75 • Scouring  /  Kiering:  This  process  involves  removal  of  natural  impurities  such  as  greases, waxes, fats and other impurities. The desized cloth is subjected to scouring.  This can be done either through conventional method (kier boiling) or through modern  techniques (continuous scour). Kiering liquor is an alkaline solution containing caustic  soda, soda ash, sodium silicate and sodium peroxide with small amount of detergent.  The water required for this process varies from 20 – 45 L/ Kg. with an average of 32.5  • Bleaching: Bleaching removes the natural colouring materials and renders the cloths  white. More often the bleaching agent used is alkaline hydrochloride or chlorine. For  bleaching the good quality fibre, normally peroxide is used. The chemicals used in  peroxide  bleaching  are  sodium  peroxide,  caustic  soda,  sulphuric  acid  and  certain  soluble oils. The water and chemical requirement and the effluent generation normally 

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