Every fermentation plant utilizes raw materials which are converted to a variety of products. Depending on the individual process, varying amounts of a range of waste materials are produced. Typical wastes might include unconsumed inorganic and organic media components, microbial cells and other suspended solids, filter aids, waste wash water from cleansing operations, cooling water, water containing traces of solvents, acids, alkalis, human sewage, etc. Historically, it was possible to dispose of wastes directly to a convenient area of land or into a nearby watercourse. This cheap and simple method of disposal is now very rarely possible, nor is it environmentally desirable. With increasing density of population and industrial expansion, together with greater awareness of the damage caused by pollution, the need for treatment and controlled disposal of waste has, and will, continue to grow. Water authorities and similar bodies have become more active in combating pollution caused by domestic and industrial wastes. Legislation in all developed countries now regulates the discharge of wastes, be they gas, liquid or solid (Fisher, 1977; Hill, 1980; Masters, 1991; Brown, 1992). In the U.K., much of the legislation pertaining to waste disposal and pollution is embraced by the Environmental Pollution Act 1990 (HMSO, 1990, 1991). Futher information on legislation and environmental policy can be found in the following texts; Haigh (1990), Tromans (1991) and Hughes (1992).
With liquid wastes, it may be possible to dispose of untreated effluents to a municipal sewage treatment works (STW). Obviously, much will depend on the composition, strength and volumetric flow rate of the effluent. STWs are planned to operate with an effluent of a reasonably constant composition at a steady flow rate. Thus, if the discharge from an industrial process is large in volume and intermittently produced it may be necessary to install storage tanks on site to regulate the effluent flow. In some locations, municipal sewers are not available or the effluent may be of such a composition that the wastewater treatment company or regulatory authority requires some form of pretreat-ment before discharge to its sewers. In these cases an effluent-treatment plant will have to be installed at the factory. Whatever the pollutant load of the liquid effluent, its discharge to a sewer will be a cost centred activity, and will incur charges from the treatment company.
Normally, fermentation effluents do not contain toxic materials which directly affect the aquatic flora or fauna. Unfortunately, most of the effluents do contain high levels of organic matter which are readily oxidized by microbial attack and so drastically deplete the dissolved oxygen concentration in the receiving water unless there is a large dilution factor. This can be shown by the oxygen sag curve in Fig. 11.1. Different aquatic species have varying tolerances to depleted oxygen levels, and as a consequence some species will die off in specific stretches of the receiving water, and in other regions a different population capable of growth at lower oxygen levels will develop.
Effluents may be treated in a variety of ways, as will be outlined later in this chapter. In a number of processes it may be possible to recover waste organic material as a solid and sell it as a by-product which may be an animal feed supplement or a nutrient to use in fermentation media (Chapter 4). The marketable by-product helps to offset the cost of the treatment process. It is now recognized that water is no longer a cheap raw material (Chapters 4 and 12), hence there are considerable advantages in reducing the quantities
used and in recycling whenever it is feasible (Ashley, 1982). Obviously the introduction of good 'housekeeping' will lead to reductions in the volume of water used and the volume of effluent for treatment and final discharge. Recycling and reuse of materials, waste minimization, waste reduction at source and integrated pollution control are now very important factors to consider in the design and operation of any manufacturing facility, and may be the subject of new legislation in this field (Laing, 1992; Donaldson, 1993; McLeod and O'Hara, 1993).
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