Good housekeeping is the least expensive means to reduce the overall burden on treatment and disposal. Loss of materials, solvent and product can be restricted by installing monitoring devices so that the process managers can be held responsible for spills and poor housekeeping practices. By adopting suitable process modifications, substantial reduction in wastewater generation can be achieved.
Substitution of organic solvent for water in synthesis and subsequent solvent recovery can reduce the quantity of wastewater generated. Barometric condenser systems can be a major source of contamination in plant effluent producing large volume of dilute waste stream.
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Steam jet ejectors and barometric condenser systems can be replaced with vacuum and surface condenser systems. Dust collector devices and vacuum type packing can reduce powder flying around in the tablet and packing sections.
Gaseous/Particulate Waste from Drug and Pharmaceuticals Industry:
Gaseous effluents like hydrogen chloride, hydrogen cyanide, sulphur dioxide, chlorine and solvent vapours are emitted from various processing units manufacturing basic drugs. Particulate emissions are predominant in the material handling section and in formulation units where the products are in dry powder form.
Various physic-chemical processes are employed for controlling the emission of gases as fumes before discharging through stack into the atmosphere.
Adsorption is a control process by which the gas molecules attach themselves on solid surfaces. Activated carbon, alumina, bauxite, silica gel and molecular sieves are common adsorbents. Adsorption is carried out either in fixed bed or moving bed. Thermal regeneration is generally employed for the regeneration of the adsorbants.
Absorption is a process in which a soluble gas is transferred from a gas stream into a liquid. The liquid phase dispersed system include packed column, wetted wall column, spray column, venturi scrubber or flooded disc scrubber.
The physical and chemical properties of the particulate as well as the size play an important role in the design of particulate control equipment. Various types of equipment for the particulate control are gravity settling chambers, cyclones, scrubbers, electrostatic precipitators and fabric filters.
Solid Wastes Management of Drug and Pharmaceuticals Industry:
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Treatment of solid wastes depends upon the nature and composition of the waste. The present disposal practice mainly consists of hauling solid wastes to off-premises land disposal. Little attempt has been made to salvage solid wastes for reuse or making by-products.
Reclamation possibilities include biological treatment of extracted botanical dregs to produce useful by-products and regeneration and reuse of filter materials. The reported solid wastes recycling consist of selling mycellium and biological sludge as high protein animal or plant feed supplements.
Toxic solid wastes from processes are to be incinerated inside factory premises. Radioactive wastes generated from research activities are to be sealed into special containers and disposed of in some designated area.
Solid wastes such as card-board boxes, packaging materials, glass and metal containers from damaged or defective batches warrants investigation for salvaging with necessary precautions.
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Specific suggestions for minimising solid wastes disposal problems are as follows:
Recovery of solids like spent catalysts, unreacted materials, side products etc. can be separated to reduce pollution load to the treatment plant. These can be separated, settled and reused.
Some of these possibilities are:
(i) Mycellium from antibiotic fermentation is non-toxic and a rich source of protein and vitamins. This can be dried and used as animal feed. It has very high BOD and as such necessary to isolate from wastewater to be treated in the effluent treatment plant.
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(ii) Volatiles in the by-products may be condensed and reused.
(iii) Exhaust gases in the fermentation process can be recovered and used as potential fuel source. For example – methane is a good fuel which is generated in anaerobic fermentation process.
(iv) Tar produced in some organic reactions like Friedel Craft’s acrylation and alkylation can be used as a cheap fuel source.
(v) Volatile raw materials and solvents can be separated by rectification and these can be recycled into the process.
Physical Treatment of Drug and Pharmaceuticals Industry:
The common physical treatments are plain settling, dissolved air floatation, adsorption, and solar evaporation.
These methods can be adopted individually or in combination depending upon the wastewater quality and quantity:
i. Plain Settling – Water insoluble compounds can be removed from the wastewater by plain settling. The settling characteristics can be improved with the addition of suitable coagulants. The system consists of a settling basin with adequate volume to provide sufficient settling time for the impurities.
ii. Dissolved Air Floatation – Suspended, colloidal and emulsified impurities can be removed from wastewater by air floatation technique. Air dissolved in the wastewater under pressure when released in the floatation tank forms bubbles which trap the lighter impurities and lift them to the surface. The materials form a floating layer which is removed by a skimmer mechanism.
iii. Adsorption – Activated carbon and activated clay are used for the adsorption of refractory chemicals which are either non-degradable or inhibit the degradation of other organic compounds. The process is carried out in columns or tanks. Carbon treatment can be employed as a polishing unit to further improve the quality of the biologically treated wastewater.
Summary of a study using activated carbon on biologically treated wastewater from an industry manufacturing basic drugs and microbial products is presented in Table 18.4.
iv. Evaporation Pond – When wastewater quantity is less and contains high organic and inorganic impurities, it can be disposed through solar evaporation. This system is feasible where adequate area is available. Area required for effective evaporation depends upon the local annual evaporation rate.
Primary Treatment/Chemical Treatment of Drug and Pharmaceuticals Industry:
Segregation of different waste streams is an important step for economic design of a treatment plant.
The following streams may be segregated for this purpose:
(i) Strong process liquors.
(ii) Streams containing cyanide, heavy metals, toxic chemicals.
(iii) Condensate and cooling waters.
(iv) Acidic and alkaline streams.
Various treatment alternatives for strong process liquors are incineration, solar evaporation and treatment by anaerobic filter. The toxic effluents either can be incinerated or treated by suitable technologies like carbon adsorption, ion exchange, chemical precipitation, reverse osmosis etc.
Condensate and cooling waters can be recycled and reused. The acidic and alkaline waste streams can be either treated separately with acid/alkali for pH correction or may be combined suitably with other waste streams.
The effluent containing chemical sludge, settleable solids and high oil concentration (over 50 mg/l) can be treated by coagulation, flocculation and settling after neutralisation. Coagulants like alum, FeSO4, FeCl3 etc. with/without poly-electrolytes can be used.
The coagulation process also breaks oil emulsions and nullifying the zeta potential. Pre-aeration for 2 to 3 hours by means of diffused air may help to bring down the BOD load of about 30 to 40%. Diffused aeration is known to bring oily and fatty matters in suspension form in the wastewater.
Secondary Treatment of Drug and Pharmaceuticals Industry:
Various factors are responsible to select a suitable treatment system, i.e. quality and quantity of influent to be treated, desired degree of treatment, site conditions, change of products and overall economics.
Secondary biological treatments employed are mainly aerobic and in some cases anaerobic followed by aerobic treatment. Trickling filter, extended aeration and conventional activated sludge systems are generally practised. Anaerobic filter and anaerobic lagooning are also being used for treatment of pharmaceutical industry wastewaters.
Anaerobic Filter and Lagooning of Drug and Pharmaceuticals Industry:
Anaerobic filter can operate with an influent COD concentration upto 2,000 mg/l for a period upto six months. The hydraulic retention time is 35 to 40 hours at an operating temperature of around 35°C. It can operate with an efficiency of COD removal upto 80% and BOD removal of 90 to 95%.
However, it is not suitable for shock loads of high suspended solids and sulphate concentration. It cannot operate at all climatic conditions in certain parts of the country. Anaerobic lagooning is not suitable for effluents having higher COD load and lesser biodegradability.
For these reasons, aerobic treatment systems are preferred to anaerobic systems which are described below:
i. Trickling Filter:
This is widely employed for treatment of effluents of pharmaceutical industry in India and abroad. The major advantage of trickling filter is that it is capable of handling higher shock loads of BOD and toxic waste materials than any other biological treatment system. It can function with a load variation of ± 20% without affecting the performance.
Recirculation is usually practised upto a ratio of 8: 1 with an input BOD load of about 2,500 mg/l. In pharmaceutical industry, the type and load of pollutants change widely depending on the local market demand. This aspect necessitates putting up additional appropriate treatment in the downstream of trickling filter.
ii. Conventional Activated Sludge:
Conventional activated sludge is commonly practised in pharmaceutical manufacturing industry. This requires lesser space compared to oxidation ditch or aerobic pond and easily operates with a high efficiency of BOD removal of more than 90%.
The dynamic behaviour of the process is complicated by the presence of mixed population of microbes, varying physical and chemical characteristics of organic loads, fluctuation of influent flow and limiting substrate concentration.
The presence of nickel in effluent has toxic effects on nitrifying bacteria in the activated sludge process. This system needs high rate of aeration and sludge recirculation.
iii. Extended Aeration:
Extended aeration treatment system has all the advantages of conventional activated sludge. In addition, it takes care of complete sludge stabilisation and remaining BOD in the sludge as well as in the wastewater. But the disadvantages are it can handle low organic load and unable to tackle shock loads of BOD fluctuations and toxic compounds.
It requires an aeration time of 35 to 40 hours. But the system is very suitable for treating effluent from a pharmaceutical formulation unit and bulk drug manufacturing unit. Since this unit will be in the downstream of the trickling filter, major portion of the shock loads of pollutants will be absorbed in the trickling filter.
iv. Tertiary Treatment:
Desired effluent quality is the basis for the selection of any treatment scheme. In most cases, pharmaceutical industry effluents are not suitable for land disposal for farming due to the presence of high concentration of dissolved salts.
Tertiary treatments are required to kill virus and bacteria and to remove other impurities like colour, bad smell etc. Chlorination and sand filtration may generally be practised for tertiary treatment.
v. Biological Treatment:
Various factors are responsible for the selection of biological treatment system, i.e., quality and quantity of wastewater to be treated, desired degree of treatment, site conditions and overall economics. Biological treatment systems employed for pharmaceutical wastes are mainly aerobic in nature.
In some cases where the organic loading is high, anaerobic treatment units are used prior to aerobic system. The widely used anaerobic treatment unit for pharmaceutical wastes is anaerobic lagoon and for aerobic treatment, trickling filter, aerated lagoon or aeration tank followed by clarifier are used.
Performance of Existing Treatment Systems of Drug and Pharmaceuticals Industry:
For the development of Minimal National Standards (MINAS), a number of existing treatment plants of bulk drug manufacturing as well as formulation units were monitored. The performance of selected treatment plants are presented in Table 18.5.
Cost of Wastewater Treatment of Drug and Pharmaceuticals Industry:
Capital cost and economics for operation and maintenance of the treatment plant are the deciding factors to opt for a treatment system. Various alternatives of unit processes may be practised for primary treatment, depending on raw waste characteristics and desired quality of final effluent.
The cost of secondary or biological treatment may be calculated on the basis of the following alternatives:
(i) Single stage biological treatment consisting of extended aeration or conventional activated sludge or trickling filtration.
(ii) Two stage biological treatment for BOD value above 1,500 mg/l, consisting of trickling filtration followed by extended aeration or conventional activated sludge process.
The capital costs include civil, mechanical, electrical and plumbing costs but no cost of excavation. The annual running cost of biological treatment is about 30% of the capital cost of biological treatment. Annual burden is equal to annual loan repayment installment plus annual running cost.