Question

Draw flow sheet diagram and explain the process of industrial waste water treatment.

Answer 1

• The main objective of wastewater treatment is to allow domestic and industrial effluents to be disposed of without any danger to human health or the natural environment. The type of treatment required depends on the application of water. The wastewater from industrial, commercial and residential areas is collected through a network of underground pipes (sewers) and is then transported through sewerage systems to treatment plants. The conventional water treatment procedure involves mechanical, physical, biological and chemical methods to remove solids, organic matter and, sometimes, nutrients from wastewater. The wastewater treatment procedure in order of the treatment level is as follows:
• Preliminary treatment: The objective of preliminary treatment is the removal of coarse solids and other large materials often found in raw wastewater. Removal of these materials is necessary to enhance the operation and maintenance of subsequent treatment units. The primary method consists of screens, grit chamber, and oil-grease trap.
• Primary treatment: Primary treatment involves the removal of settleable organic and inorganic solids by sedimentation, and the removal of materials that will float (scum) by skimming. Sedimentation tanks are made either in circular or rectangular and the settled solids are normally removed from the bottom of tanks as sludge. Sedimentation may also be done by adding chemical coagulants.
• Secondary treatment: In the secondary treatment, residual organics and suspended solids are removed from the effluent from primary treatment. In most cases, secondary treatment involves the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes. Common processes include the activated sludge processes, trickling filters, oxidation ditches, and rotating biological contactors.
• Tertiary treatment: Tertiary and/or advanced wastewater treatment is employed when specific wastewater constituents such as suspended solids, BOD, dissolved solids, toxic substances and plant nutrients which cannot be removed by
  secondary treatment must be removed. This treatment involves electrodialysis, disinfection, filtration methods like reverse osmosis, ultrafiltration, etc.

Diagram of waste water treatment procedure

• Treatment of industrial waste water: The treatment procedure for industrial waste water is the same and consists of the preliminary, primary, secondary and tertiary treatments. The nature of the pollutant determines the type of treatment employed for industrial waste water. For example, waste water from dairy and food industries require biological treatment, metal plating industrial waste are chemically treated. Many industrial wastes may even require neutralization prior to chemical or biological treatment methods.