Sewage treatment is mostly chemistry. The clothes you are wearing are made largely of synthetic fibres and are coloured by synthetic dyestuffs. The medicine you may have taken was produced by chemists. The radio and television you had on contain electronic devices made by chemists, as does your cassette recorder and its tape. The fuel your train, bus or car used was made by a chemist, and so was most of the material the vehicle was made of.
Chemistry controls the environment.
Water has to be kept clean, the air has to be safe, crops must be kept clean, and the fertilisers and sprays must be safe for everyone except the pests. Chemists do the analyses which tell us how it is all happening, and chemists have to find solutions to the problems that come up. Your chemistry degree can help you to get into this world. You will probably start by doing a Ph.D, most of which are about some piece of abstract chemistry. The methods you learn in your three years tackling these problems will be the methods you will use when you work for a pharmaceutical firm, an oil company, or an environmental agency.