After reading this article you will learn about Waste Water:- 1. Characteristics of Waste Water 3. Treatment Process of Waste Water.
Characteristics of Waste Water:
According to their characteristics, waste water can be distinguished into two categories:
(a) Domestic waste water and
(b) Industrial waste water.
(a) Domestic Waste Water Characteristics:
The characteristics of waste water are physical, chemical and microbiological components (total solids, temperature, pH, colour, odour, carbohydrates, proteins, fats, BOD, heavy metals, sulphur, bacteria, algae, virus etc.). In domestic waste water specific toxic and hazardous compounds may exist, i.e. phenols and toxic organics.
(b) Industrial Waste Water Characteristics:
Each industry is individual. It is not possible to enumerate wastes from all industry types as many wastes are specific lo particular industries, Industrial waste water vary considerably in their nature and toxicity.
Treatment Processes of Waste Water:
Urban waste water is primarily organic in content. A significant number of industries including pharmaceuticals, chemical and food processing industries have high organic waste loads, so that the main treatment processes are geared towards organic removal. In a typical treatment plant, the waste water is directed through a series of physical, chemical and biological processes, each with a specific waste load reduction work.
The processes include the following stages:
(b) Primary treatment
(c) Secondary treatment’
(d) Tertiary treatment.
(a) Pre-treatment of Waste Water:
Pre-treatment is the process or sum of processes that is the conventional method of waste water treatment. Through this system, the removal and disintegration of gross solids, the removal of grit and the separation of storm water are accomplished. Oil and grease are also removed at this stage of treatment.
The stages of waste water pre-treatment processes are shown here:
(b) Primary Treatment of Waste Water:
Primary treatment is often called sedimentation, clarification or settling system. This is the unit process where the waste water is allowed to settle for a period in a settling tank or reservoir. The waste water is passed through a specially constructed sedimentation tank at such a velocity that the fine solids settle out of suspension by gravity.
The benefits of primary waste water treatment are:
(i) Regulation of suspended solids
(ii) Reduction in BOD
(iii) Reduction in the amount of waste activated sludge
(iv) Removal of floating material
(v) Finally, partial equalization of flow rates and organic load.
(c) Secondary Treatment of Waste Water:
After primary treatment the settled waste water enters a specially designed reactor where it is mixed or exposed to a dense microbial population or microorganisms under aerobic conditions.
The secondary waste water treatment systems are categorized as:
(i) Suspended growth systems;
(ii) Attached growth systems;
(iii) Dual process systems.
(i) Suspended growth systems:
It is defined as those aerobic processes that achieve a high microorganism concentration through the recycle of biological solids.
(ii) Attached growth systems:
It allows a microbial layer to grow on the surface of the media while exposed to the atmosphere from where it draws its oxygen. The microbial layer is sprayed with the waste water.
(iii) Dual process systems:
It utilizes two-stage arrangements of fixed film and suspended growth processes with the principal objective of achieving very high quality effluent standards,
(d) Tertiary Treatment of Waste Water:
The principal methods are:
(i) Prolonged settlement in lagoons, irrigation in grassland or via percolation areas (for land treatment).
(ii) Straining through a fine mesh or filtration through sand or gravel.