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Deepak Fertilizers and Petrochemicals Corpn. Ltd. (DFPCL) is one of the largest producers of industrial chemicals, Sulphur Bentonite & Nitro Phosphates in India.. DFPCL is only manufacturer of Iso Propyl Alcohol in India. It is the largest manufacturer of Technical Prilled Ammonium Nitrate in India. DFPCL's manufacturing plant is located at Taloja, Raigad. It is accredited with the prestigious ISO 9001:2000 and OHSAS 18001:2007. The total sale for agri - business stood at Rs. 576.8 crores and total revenue for chemical segments stood at Rs. 811.49 crores in 2008 - 09. The net profit for the year 2008 - 09 was Rs. 148.7 crores. The products manufactured by DFPCL are:
Agri - Products and services
Nitro Phosphate fertilizers
NPKs, Water soluble, Micro - nutrients and Bio - mixes (outsourced products)
Farmer consultancy Services through Mahadhan Saarrthie Centre.
Produce management (fruits and vegetables)
Low density Prilled Ammonium Nitrate
Ammonium Nitrate Solution
High density Prilled Ammonium Nitrate
Concentrated Nitric Acid
Strong Nitric Acid
Dilute Nitric Acid
Iso Propyl Alcohol
Effluent Treatment Plant:
The effluent treatment plant is designed to treat the effluent coming from different areas of the plant. The treatment of different effluents varies with the type of effluent.
2. Sources and Quality of Effluent:
The effluent comprising from various sections of plant mainly comprises of floor washings, spillages, scrubbed liquors etc. The effluent can mainly be classified into two types : those containing nitrogenous pollutants such as ammonical nitrogen and nitrate nitrogen and those containing phosphate pollutants.
The Ammonium Nitro - Phosphate plant and Tank Farm area are the major source of pollution containing pollutants such as phosphates, ammonical nitrogen and nitrate nitrogen. On the other hand Ammonia (NH3), LDAN (Low Density Ammonium Nitrate) and WNA (Weak Nitric Acid) plants discharge ammonical nitrogen and nitrate nitrogen.
The Raw Effluent Quality provided by DFPCL is:
NH4Â - N
NO3 - N
4 - 11
4 - 8
4 - 10
6.5 - 8
4 - 8
3. Raw Materials and Utilities Required:
a. Raw Materials:
Specified Raw Effluent Quality and quantity.
Caustic Soda 46% as Caustic Lye.
Acid (96% H2SO4)
Electric Power - single and three phase
The Treatment facilities provide entail a number of unit operations enumerated below:
Physio - Chemical Treatment
Physio - Chemical Treatment:
The wastes from ANP plant and tank farm area are combined together in existing holding tank CT - 1. These wastes are treated for removal of phosphates. The raw effluent is first pumped to Reaction tank - 1 where MOL is added to raise and maintain pH at 9.
The reacted waste then enters clariflocculator where in calcium phosphates precipitates are settled.
The clear effluent stream from clariflocculator then overflows into Reaction tank - 1.
Other nitrogenous plant wastes namely Ammonia plant floor washings, NH3 plant waste, LDAN plant and WNA plant waste are collected together in holding tank CT - 3 from where they combine with partially treated waste in Reaction tank - 2A. Here caustic soda solution is further added to raise the pH to 11. The pH corrected waste is then pumped to NH3 stripper which is similar to a standard cooling tower. At a pH of 11 most of ammonium ion are present as free NHÂ3 in dissolved state in waste water. The waste is pumped to top of stripper tower into a distribution system located below the induced draft fan. This distribution helps in maintaining uniform flow of water over entire cross section. The space below the distribution is packed with PVC tubes. These tubes help to break waste water into small droplets thus increasing surface area which helps release of ammonia gas. The IP fan at the top of the tower draws up air through the tower countercurrent to the falling waste water and ammonia rich air is exhausted from reduced NH3 level (around 80 % removal is expected in stripper 1) is then allowed to flow to Reaction tank - 2B where the pH is re - corrected for any drop that might occur in stripper - 1 back to pH of around 11. The waste is pumped to stage - 2 NH3 which is similar in design to stage - 1 stripper. In this stage balance NH3 is stripped out.
In this stage a stripping efficiency of 80% is expected. The treated water collected in basin of stripper stage - 2 is pumped to RT - 2.
The waste water flowing from the stripper is now ready for second step of the treatment. In this step all nitrates broken down to harmless end products. This is achieved by biological means. For denitrification step, a two step process has been provided there is a denitrification tank provided with mixers followed by clarifiers. From stage - 1 clarifiers effluent flows to denitrification tank - 2 where residual nitrate is broken down to nitrogen. This tank is followed by a second stage Denite clarifier. The underflow stages from each stage of denitrification tank are recycled back to the respective Denite tank. The biomass in denite tanks are kept in suspension by means of low speed agitators. The agitators are located in such a manner that entire contents are agitated. MeOH is provided as Carbon source. This is provided as methanol waste (fusel oil) from methanol plant.
The effluent tank from Denite classifier - 2 flows to polishing tank NT - 1 where O2 is introduced from air to increase the DO level to around 4 - 5 mg/l. At the same time N2 dissolved in effluent is stripped out.
Chemical sludge precipitating from the clariflocculator underflow is taken to centrifuge pump, From here sludge is pumped to centrifuge provided (1 working and 1 standby). The mother liquor from centrifuge flows by gravity back to process while cake is collected in trolley and disposed (sold) off.
The excess of sludge from two denitrification tanks is withdrawn from clarifier underflow and sent to sludge drying beds.
5. Explanation of various stages involved in process:
Physio - Chemical Treatment:
As can be seen from above table section - 2, effluent streams emanating from various plants have different composition. Some of these constituents cannot be treated biologically but are readily applicable to chemical treatment. This calls for segregation of waste water.
The waste waters from ANP plant and tank farm area contain high concentration of phosphates apart from ammonical nitrogen and nitrate nitrogen. Phosphates are removed by chemical treatment and gravity sedimentation.
The phosphates readily react with hydrated lime to form insoluble carbon phosphates. This precipitates, along with the settling solids, are represented by gravity sedimentation.
2(NH4)3PO4 + 3 Ca(OH)2 Ca3(PO4)2 + 6 NH4OH
Once these contaminants are eliminated from the effluents, this stream can be mixed with the waste waters from NH3Â, LDAN, and WNA plant. The composite stream is then treated for removal of nitrogenous pollutants.
Ammonical nitrogen can be removed from water by volatilization of gaseous NH3 into the air. The rate of transfer can be enhanced by converting most of ammonical compounds to gaseous NH3 at high pH.
In waste water ammonium ions exist in equilibrium with ammonia as represented by following equation:
NH3 + H2ÂO NH4+ + OH-
At a pH of 7 ammonium ions (NH4+) in true solution are present. At a pH of 12, ammonia exists in solution as a dissolved gas. In range of pH of 7 to 12, ammonium ions and ammonia gas co - exist. As pH is increased above 7 equilibium shown in above reaction is shifted to the left in favor of NH3 gas which can be removed from liquid, by aeration. The amount of base required to regulate the pH is governed by initial pH.
After ammonium ions have benn converted to ammonia gas there are 3 basic factors that will affect the transfer of NH3 from waste water to surrounding atmosphere:
The surface tension of air water interface.
The driving force resulting from difference in NH3 concentration in water and the surrounding air.
Temperature of waste water.
The objective of biological treatment is to remove oxygen consuming matter from waste water and reduce, oxidize or stabilize it to desired degree for safe disposal of effluent into receiving stream.
In a biological process BOD represents food for micro - organisms. This food will be attacked by heterogenous and varying mass of micro - organisms, all of which occur in natural body of earth and water. Both plant and animal form of micro - organism are required to do this work and relative number will vary depending on reacting conditions. The matrix of micro - organisms and extracellular products is referred to as biological sludge.
The first product of reaction is cellular matter which under equilibrium conditions is thought as excess of sludge. In the process of excess of food, the organisms will grow and multiply. This increase in population is synthesis part of reaction. While part of reactants are converted through synthesis to biological culture, another part is completely oxidized to end product. The aerobic reaction produces CO2, HÂ2O and NH3. It is through this latter reaction that micro - organisms gain their energy for existing.
Food + Micro - organisms + O2 Cellular matter + Energy + CO2 + HÂ2O
The above reaction can be accomplished both aerobically and anaerobically. The choice between the process is determined by type and complexity of the process water and the desired end products.
The waste water after NH3 stripping is left with nitrates which need to be destroyed prior to discharge of water. Here again biological treatment are found to be viable.
Biological denitrification can be defined as a process by which micro - organisms reduce nitrate ions to nitrogen gas. A relatively large no. of bacteria can accomplish this including Achromobacter, Bacillus, Brevibacterium, Enterobacter, Lactobacillus, Micrococcus, Paracalobactrum, Psuedomonas spirallum. These bacteria accomplish nitrate reduction by a process known as nitrate dissimilation whereby nitrates or nitrites replace O2 in respiratory process of organisms under anoxic conditions. This organisms can use either nitrates or oxygen as terminal electron acceptor while oxidizing organic matter is termed as heterotropic bacteria. This process occurs through series of complex reactions catalyzed by enzymes.
First nitrate is reduced to nitrite through transfer of two electrons from the substrate, producing energy for all synthesis in second step nitrite is reduced to N2. This two step process is termed as dissimilation. General reaction is:
NO3- + organic matter + Microbes N2 + H2O + CO2
As seen from above reaction a carbon source is required for reaction. Most waste water by the time they reach denitrification stage are deficient in carbonaceous matter. Thus in most cases methanol, due to its easy biodegradability is added as carbon source. This can be represented by following reaction
Nitrate to Nitrite: 6NO3- + 2CH3ÂOH 6NO2- + 4H2O + 2CO2
Nitrite to Nitrogen: 6NO2- + 3CH3ÂOH 3N2 + 3H2O + 3CO2 + 6OH-
In practice 25 to 30 % of amount of methanol required for energy is required for synthesis.
6. Efficient Utilization of raw materials:
Environment management not only involves safeguarding the environment but also effectively utilizing raw materials to
Calculating acid alkali requirements
Acid / Alkali requirements cannot be calculated theoretically and have to be computed based on laboratory tests.
This is done by carrying volumetric analysis. This involves adding acid / alkali of specific strength to sample. Gradually add an acid to lower the pH or an alkali to increase the pH till sample pH reaches desired value. Note the quantity added.
Assume: sample volume = 1 liter
Acid / alkali consumed = 25 ml
Solution strength = 10%
Therefore acid / alkali required = 25 ml/ lt
Therefore plant dosing rate = 25 x Flow rate (m3/hr)
Calculating Methanol (MeOH) requirement:
1 mg NO3 - N - 2.47 mg MeOH
1 mg NO2 - N - 1.53 mg MeOH
1 mg DO (Dissolve Oxygen) - 0.87 mg MeOH
Flow to Denit. Tank in m3/day - a
NO3 - N conc. in mg / l - b
NO2 - N conc. in mg / l - c
DO conc. in mg / l - d
MeOH (kgs / day) = 2.47(b*a / 1000) + 1.53 (c*a / 1000) + 0.87 (d*a / 1000)