ABSTRACT
Moving forward to the seventeenth century, an early problem of sizable towns was the disposal of raw sewage into rivers. In the late seventeenth century John Evelyn wrote a diary that records, among other things, problems of pollution. In nineteenth century Victorian London the Thames River was filthy, stinking, and without fish. As discussed in Chapter 4, organic waste has a high biological oxygen demand, and this can lead to the deoxygenation of water and the death of fish (Figure 4.4). In time, this problem came to be resolved, at least in part, by the treatment of wastewaters in sewage plants. Organic residues were broken down and treated sewage subsequently discharged into rivers. This practice was largely successful, but in some places, e.g., the Thames estuary in London, there remained something of a problem even into the 1950s. Oxygen levels remained low, and the worst affected reaches were unable to support fish (Mellanby 1967). With time, however, sewage treatment practices have been refined in Western countries, and the quality of freshwater of rivers has improved. This has been an important issue with seaside resorts that once discharged raw sewage into the sea, making it unhealthy for people to swim. Standards have become stricter in recent years in the European Union, where bathing beaches are graded according to the water quality of the sea. There has recently been considerable improvement in sewage treatment to ensure that seawater is clean enough for bathing.
