Zero effluent discharge in chemical processing

P. Ganesan, S.Hariharan, E.Praddeep & A.Prakash

Department of Textile Technology

PSG College of Technology

ganeshg007@gmail.com , shariharan108@gmail.com & epraddeep@hotmail.com

Abstract

The goal of this paper is to examine the potential for ecologically and economically sustainable to chemical processing including textile processing. This paper reviews technical and scientific literature on a wide range of factors that will influence the overall impact of discharge done by the various chemical processors (textile, paper, wood-pulp etc.) on its total environment. The emphasis is on efforts to achieve "Zero Discharge or Totally Effluent Free (TEF) mills. The chemical processing industry is one of those identified as a potential threat to the environment due to the discharge of toxic effluents that cause air, water and soil pollution.

Zero discharge system is meant to treat all the incoming effluent, leave nothing behind. However, practically this is not feasible since some waste is always generated in the treatment process. Therefore, the main aim is to recover usable materials such as water and salt from the effluent, and; minimize the generation of waste so that it can be safely stored on-site without the need for discharge into the environment.

Introduction

Till recently the objective of a textile wet processor was to administer the desired colour and finish to the textile material with scant regard to the environment. These days awareness of the need for protecting the environment has posed challenging problems to all the industries causing environmental pollution. The textile wet processing industry is one of those identified as a potential threat to the environment due to the discharge of toxic effluents that cause air, water and soil pollution.

These pollutants when discharged untreated pose a great threat to human health, aquatic life and vegetation. These problems may be minimized only if the effluent generated in a process house is reduced to the minimum possible level. So today the textile wet processors also realized about the characteristics of the effluent that they discharge out of their units and its impact on the ecology. So the Chemical & textile wet processors are implementing effective measures to control the generation of waste not only at the production stage but also in tackling the disposal or treatment of effluent

Precipro^Applications in Chemical Processing and Chemical Waste Water Recycling

(Zero Discharge possible by hauling away waste cake and sludge, if amount is small)

Waste water from different sections of the chemical processing plant is combined. They are brought into Blue Spring PrecipROzero discharge waste water recycling system. In the PrecipROsystem, the combined waste is separated into two streams: solid cake containing precipitated impurities and concentrated liquid sludge containing dissolved impurities. The two final waste streams are hauled away to designated off-site disposal sites. The recovered water which is purified by reverse osmosis is recycled back to the different sections of the chemical processing plant. Water recoveries are generally in the range of 85-98% depending on the TDS content of the waste water.

Features of this Application

Good for multiple process wastewater streams.
Good when waste water contains Total Dissolved Solids up to 5,000 mg/L
Can combine with waste streams from other waste water sources like fume scrubbers, cleanout waste.
Good when wastewater contains some toxic chemicals which must be de-toxified.
Watch for buildup of low molecular weight chemicals in the recycled water. Use activated carbon filter to remove them (Blue Spring Series AC ).
Not suitable for recovery of individual chemicals, Mixes up chemicals.
Not suitable when wastewater is concentrated

The advantages of the Blue Spring PrecipRO system are:

In most cases, there is no net discharge to the sewer or to the local environment. In other cases, the final discharge is absolutely minimum.
The final liquid sludge can be rendered non-toxic by a suitable pre-treatment if necessary.
The impurities being removed need not be totally insoluble in water. Even partial insolubility allows nearly 100% removals from the final liquid sludge.

Pilot scale fluidized bed steam reforming

DMR: Operates in a strongly reducing environment 1) Reductants are used to convert nitric acid, nitrates, and nitrites directly to nitrogen gas 2) Other reactants like clay may be added to convert radionuclides, alkali metals, sulfate, chloride, fluoride, phosphates, and nonvolatile heavy metals into a solid mineral product.

CRR: Operates in both reducing and oxidizing modes 1) Receives process gas and entrained fines from DMR 2) Converts residual NOx to nitrogen gas in lower reducing sections. 3) Converts carbon fines and residual organic gases to carbon dioxide and water vapor in upper oxidizing section.

OFF gas system:- 1) Off gas from the CRR (mostly nitrogen, water vapor, and carbon dioxide) is cooled, filtered, and monitored prior to being released to atmosphere. 2) No wet scrubber required to be MACT-compliant.

Impact of Catalysis in General

Catalysts are a big business and the chemical industry depends upon catalysts; People depend upon the chemical industry for our 21st century

1) 80 % of processes in chemical industry use catalysts.2) Catalyst sales in 2000 were worth 8 to 10 million USD. 3) Growth in catalyst sales is increasing, between 5 % and 10 % per year. 4) Turnover in industry using catalysts was about 14 trillion USD, which is equal to the gross domestic product of Italy. 5) The conversion of non-renewable resources (coal, raw oil, natural gas) uses catalysts.

Catalysts can have an enormous impact on the chemical industry and everyday life:

- Enable reactions to take place

- Make processes more efficient

- A 0.5 % to 1 % increase in selectivity can lead up to one million USD increase in operating profile

- Make processes environmentally friendly, economic, and safe

Main Objectives in Environmental Protection by Catalysis:-

a) Pollution prevention by developing energy-saving processes free of pollution formation.

b) Decreasing pollution by achieving higher selectivity in fuel and chemical manufacture

c) Decreasing pollution by developing new and improved catalytic processes for removal of pollutants.

d) Developing competitive processes for production of hydrogen, chemicals and energy sources, providing reduced CO2 production.

e) Research: production of major products with greater energy and feedstock efficiency and with improved environmental issues.

Where catalysis plays a major role in the future?

Reformulated fuels
NOx, SOx; CFCs, VOCs, CO, methane, automotive exhaust gases O₃, N₂O, CO₂
Byproducts from chemical industry
Odor control
Toxic waste gas purification

Driving forces:

Environmental concerns
More selective catalysts to improve yields and to reduce byproducts formation
Replacement of liquid acids and aluminum chloride with solid acids, based on zeolite chemistry or other amorphous acidified silica alumina.

Membrane Separation

As the cost of wastewater disposal increases more emphasis is being placed upon the recovery and recycling of valuable chemicals contained within these streams. Membrane technology is a more recent development that can be used in conjuction with extraction solvents to extend the range of conditions under which such processes are available.1 The separation of distillery grain stillage was carried out on the micro filtration and ultra filtration ceramic three-channel membranes with pore diameter range from 1.4 μm to 15 kDa. In separation sequence the ions were recovered from permeates by electrodialysis.4, 5. The process was evaluated from the point of view of the mass balance and the dynamics (total separation time, the decline of the filtration effort made on the ceramic membranes, fouling effect, etc.). With this process we try to get some advantages over the conventional process in terms of eliminating both land and energy costs for the wastewater treatment process and improving the quality of the discharge water.

Reverse Osmosis

When a permeable membrane separates a dilute solution, the osmotic pressure drives the water molecules from the dilute solution, through the membrane to establish equilibrium. This natural response is reserved in the reverse osmosis process, where the waste water containing dissolved salts are filtered through a semi-permeable membrane such as cellulose acetate at a pressure higher than the osmotic pressure.

Reverse osmosis is found to be successful and about 70-80 % colour can be removed regardless of the type of dye stuffs. Decolourisation in the range of 95-100 % has been achieved by the use of zirconium oxide/ polyacrylate membranes.

Use of Physico-chemical & Tertiary Polishing Treatment

This article explores an appropriate treatment scheme for removing the dyestuff and other impurities from the segregated dye effluent by adopting physico-chemical and tertiary polishing treatments. This process helps in achieving commercial zero hardness and low level of metal content in the recovered water, providing an excellent scope for its reuse in the dyeing process itself. The waste inorganic chemicals were also recovered in the concentrated form or in pure crystalline form and were reused in the dyeing operation. The fastness properties such as light, washing and rubbing of the yarn after dyeing with recovered water and salt have been found comparable to the original samples dyed using fresh chemicals and soft water The repeated recirculation does not cause any significant enhancement of TDS or metal content in the recirculated water. This helps in the indirect control of TDS limit for the remaining major segregated water as prescribed by the concerned pollution boards in its disposal into the outside environment, after repeated recycling.

Role of Pump in Zero-discharge

The pumps used in the recovery system behind this nickel/chromium plating operation must handle acidic and alkaline plating and cleaning solutions over a broad pH range, commingled chemical waste streams, and DI high purity water recovered from the ion exchange system.

A zero discharge resource recovery treatment system designed, built and installed by CASTion Corporation (Worcester, MA) and Columbia. This system is a custom-engineered Controlled Atmosphere Separation Technology (CAST) packaged concentrated wastewater and valuable chemicals recovery system. CAST can be furnished as a stand-alone wastewater and chemical recovery system, or as part of an integrated plant-wide program to minimize or completely eliminate costly disposal of hazardous waste or process effluent.

The turnkey wastewater and product recovery system has resulted in the following advantages:

All recovered wastewater is returned to the rinse baths, and plating solutions that are recovered are returned directly to the plating tanks.
Concentrated wastewater from the cleaning and plating lines have their own CASTion ion-recovery systems and are recovered as DI water and are then recycled for use in the rinse tanks.
98 percent of the nickel and chromic acid plating chemicals are recovered and re-used.
There is no discharge into sewer or air, so the company needs no permits from DEP, and is exempt from RCRA permits.
Six hundred pounds of chromium trioxide are recovered each week and returned to the plating tank. As a result of these changes and installation of the recovery systems.

This closed loop plating facility and the CASTion zero-discharge flash distillation wastewater and chemistry recovery system not only resulted in appreciable cost savings, but also brought the company the Governor of Massachusetts Green Seal award for service to the state in its drive to improve the environment.

Conclusion

It is imperative that, while the government wants to promote the economy, it should also support the remedial measures taken towards sustaining the economy through implementation of pollution control measures in the industry. Like two sides of a coin where one side reflects the value and other side exhibits the Ashoka pillar, which is the symbol of pride of nation the nation also has two sides; i) Economy; ii) Environment. If the environment is not taken care of, then the economy would vanish.

Though the industrial units should be held responsible for polluting the environment and delaying the implementation of the zero-discharge system. Since most of the industrialist were agrarian, and most of them have not had enough education, these people were unaware of environmental problems that could arise due to industrial pollution. The lack of awareness, have forced them to pay no attention towards environmental safety and sustainable development.

Under the situation, it is imperative that the State and Central governments take immediate steps for necessary intervention to help out the industry to implement Zero-discharge system compulsory in order to avoid further environmental degradation and provide environmental security, industrial growth.

References

Kirk-Othmer Encyclopedia Of Chemical Technology, "Adipic Acid", Vol. 1, 4th Ed., New York, Interscience Encyclopedia, Inc., 1991.
Handbook: Control Technologies For Hazardous Air Pollutants, EPA-625/6-91-014, U. S. Environmental Protection Agency, Cincinnati, OH, June 1991.
Prof. Riitta Keiski Green Engineering, Green Chemistry and Catalysis March 31st, 2004
Ind. Eng. Chem. Res. 2004, 43, 1999-2004
Dr. Gene Daniel Advance Process Development Process Science & Engineering Section November 2006
Kentis, S.E., Stevens, G.W. (2001) Chemical Engineering Journal 84, 149-159
Kim, J.S., Kim, B.G., Lee, CH. H., Kim, S.W., Jee, H.S., Koh, J.H., Fane a.G. (1997) Developement of clean technology in alcohol fermentation industry. J.Cleaner Pro., 5 (4), 263-267
Rajeshwari, K.V., Balakrishnan, M., Kansal, A., Lata, K., Kishore, V.V.N. (1999) State of the art of anaerobic digestion technology for industrial wastewater treatment. Renewable and Sustainable Energy Reviews 4 (2000), 135-156