Before deciding on the most economic form of treatment for wastes it is important to make a factory survey. The information should include the water volume, the organic and solids loading, range of pH variation, nutrient level, temperature fluctuation, and the presence of any toxic compounds. It will also be necessary to consider company finance policies, the site location and government legislation for waste disposal (see also Chapter 11).
In the majority of fermentation processes it is impossible to dispose of effluents at zero cost. Whether the waste is incinerated, dumped on waste land, or discharged to sewers, rivers or tidal waters, some expenditure will be necessary for treatment that ensures that minimal harm is done to the environment.
Since the 1980s the European Community has adopted a number of Directives to reinforce earlier legislation for the protection and improvement of inland and marine water quality. The standards of these Directives and consent for discharge are implemented in the United Kingdom through the monitoring of the National Rivers Authority and the water companies in England and Wales, the River Purification Boards in Scotland and the Department of the Environment in Northern Ireland (Brown, 1992). Costs to meet the requirements of these Directives will need to be included in process costings.
The various alternative disposal procedures may be compared using economic considerations. Pape (1977) claimed that the cheapest treatment method was controlled dumping, followed by waste incineration or dumping in salt mines. The most expensive method was biological degradation in a waste-water-treatment plant. The last method has often to be used because the effluents usually contain only a few percent of organic matter which would be costly to separate, concentrate and incinerate.
The possibility of direct disposal of pharmaceutical waste into the sea is now very restricted, especially if the waste is untreated, even though many of the large fermentation plants in the United Kingdom are in coastal locations. In 1972, Jackson and Lines stated that a pipeline of over 2.8 km overland and 2.8 km on the sea bed at a cost of £350,000 would be needed to dispose of 3000 dm3 day"1 of untreated antibiotic waste. The other options are to discharge the effluent direct to the sewers and pay a charge, to treat the waste in the plant, or to operate a combination of the two. Sewage works' charges for treating effluents have increased 1000% in less than 5 years in some instances (Forage, 1978). Those plants which treat all or part of their effluents have discovered that energy costs have risen and sludge disposal is more costly and difficult. Ripley (1979) estimated the costs for a treatment plant for a whisky distillery producing 4,500,000 dm3 year"1 of proof whisky to have a capital cost of £75,000 and operating costs of £9000 year"1. Power was calculated at 0.9 kW kg"1 of BOD removed while dosage of nutrients was £0.03 kg"' of effluent BOD.
Avermectin is an antihelmintic compound produced by Streptomyces avermitilis (Omstead et al., 1989). During development of this compound it was recognized that it was very potent and could have a potential impact on aquatic fauna. All possible exit streams from the process at the factory, both fermentation and downstream purification, are therefore captured and chemically degraded. In this case, environmentally safe waste treatment is a major component in production costs. An alternative method for disposing of wastes of this type would be to absorb all waste streams in a suitable material and incinerate this and solid wastes at an appropriate temperature (see also Chapter 11).
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