Industrial Effluents

Whereas the nature domestic wastewater is relatively constant, the extreme diversity of industrial effluents calls for an individual investigation for each type of industry and often entails the use of specific treatment processes. Therefore, a thorough understanding of the production processes and the system organization is fundamental.

There are four types of industrial effluents to be considered:

1. General manufacturing effluents: Most processes give rise to polluting effluents resulting from the contact of water with gases, liquids, or solids. The effluents are either continuous or intermittent. They even might only be produced several months a year (campaigns in the agriculture and food industry, two months for beet sugar production, for example). Usually, if production is regular, pollution flows are known. However, for industries working in specific campaigns (synthetic chemistry, pharmaceutical and allied chemical industries), it is more difficult to analyze the effluents as they are always changing.
2. Specific effluents: Some effluents are likely to be separated either for specific treatment after which they are recovered, or to be kept in a storage tank ready to be reinjected at a weighted flow rate into the treatment line, such as pickling and electroplating baths, or spent caustic soda.
3. General service effluents: These effluents may include wastewater (canteens, etc.), water used for heating (boiler blowdown, spent resin regenerants), etc.
4. Intermittent effluents: These must not be forgotten; they may occur from accidental leaks of products during handling or storage, from floor wash water and from polluted water, of which storm water may also give rise to a hydraulic overload.

For the correct design of an industrial effluent treatment plant, the following parameters must be carefully established (IWT 1999):

1. Types of production, capacities and cycles, raw materials used
2. Composition of the make‐up water used by the industrial plant
3. Possibility of separating effluents and/or recycling them
4. Daily volume of effluents per type
5. Average and maximum hourly flows (duration and frequency by, type)
6. Average and maximum pollution flow (frequency and duration) per type of waste and for the specific type of pollution coming from the industry under consideration, since it can seriously disturb the working of certain parts of the treatment facilities (glues, tars, fibers, oils, sands, etc.)

In the starch industry, starch is extracted from tubers of manioc and potatoes. A wet process is used to extract starch from the richest cereals (wheat, rice, corn). The general pollution of this process is shown in Table 3.5. The nature of the effluents depends on the specific treatments used on the raw materials after common washing.

The effluents are rather acidic which is due to lactic fermentation or to sulphitation process in white sugar manufacture (pH 4–5). When a wet technique is used to extract starch, the pollution comes from the evaporation of water and it is made up of volatile organic acids. A notably soluble protein‐rich pollution may come from the glucose shop. The general wastes of potatoes processing is presented in Table 3.6.