4 Waste water characteristics, disposal and discharge standards

J.S. Laura

epgp books

 

 

5.1 Introduction

 

Water is used for various purposes in domestic,commercial and industrial applications, resulting in change in the quality of the water. This water which has been affected by use and produced as a byproduct of such activities is termed as wastewater. The change in the water quality due to alteration in its characterics depends on how it has been used.The wastewater has to be reused or more commonly disposed by reintroduction into the environment. The wastewater based on its characteristics can be disposed either directly or after treatment. The most common methods for disposing are surface water discharge, subsurface discharge, and land application . However befor discharge the characteristics of the water and its quality have to meet the discharge standards for wastewater set by the authority. For the purpose of management,planning and regulating, the wastewater discharge and wastewater generation standards have also been formulated. These standards for the various types of industries in the manufacturing sector regulate the quality and quantity of the wastewater discharge.

 

5.2 Wastewater characteristics

 

Wastewater contains impurities in it, these impurities can be physical, chemical, biological or their combination. Waste water can be categorised into two; municipal wastewater and industrial wastewater. Wastewater from human dwellings is commonly termed as sewage (or domestic wastewater or municipal wastewater) where as wastewater from industrial units is termed as effluent. The sources of wastewater generation are diverse, the physical, chemical and biological impurities found in wastewater also vary accordingly. As industries are highly diverse in their types and processes thus producing waste of highly different characteristics. The industrial wastewater includes pollutants like remains of raw materials, impurities in raw material, intermediates chemicals, process byproducts, oils and final products. So industrial wastewaters cannot be treated easily by the normal method of treating domestic wastewater and specially designed methods or sequence of methods is necessary. In contrast the variation in impurities in municipal waste water is less as compared to that in industrial wastewater. The characteristics and pollutants of domestic and industrial waste water are discussed below.

 

Physical Characteristics

The physical characteristics can be felt by our senses. The main physical characteristics of wastewater include Turbidity, colour, odour and temperature.

 

Turbidity: The wastewater contains insoluble or suspended solids and the soluble compounds dissolved in water. The suspended or dissolved solids are responsible for turbidity of water. On average 50 % of the solids in an average wastewater are suspended.

 

Colour: Colour of waste water is used to assess the general water condition of the in waste water. Colour could be due to presence of various coloured compound, dyes, oils etc. or due to decomposition going on in waste water. Fresh waste water is generally light brown in colour, but after a few hours of decomposition the colour changes to light/medium grey. While the dark grey or black colour is indication of extensive bacterial decomposition under anaerobic conditions. Hydrogen sulphide (H2S) produced under anaerobic condition reacts with metals present in waste water and give dark coloured sulphides.

 

Odour: Foul smell is always offensive to peoples and disturbs them from distance. It is qualitative as well as quantitative physical quality of waste water and depends on concentration and types of volatile compounds and gases released by waste water. The various compounds and gases responsible for odour in waste water includes; Sulphur compounds (Sulphur dioxide (SO2), Hydrogen sulphides (H2S), Dibutyl sulphide), Ammonia (NH3), Amines, Phenolic compounds, Mercaptans, Acroleins, Fermentation products etc.

 

Temperature: Temperature varies from season to season, from one geographical region to another and from industry to industry. It is the extra heat carried by the waste water from the industrial processes. Heat is released as waste water by industries involving heating and cooling processes.

 

Radioactivity: Radioactive contamination is due to presence of radioactive substances in waste water. The radioactive material decays spontaneous and emit harmful ionising radiations. The radioactive contamination occurs due to accidental release of coolants containing radioactive waste, improper handling of such material or disposing of the waste in unscientific manner. Fukushima daiichi nuclear disaster is recent example of release of radioactive waste in water.

 

Chemical characteristics

 

Chemical impurities found in waste water can be divided into two types, inorganic and organic. A. Inorganic impurities: Inorganic impurities are those substances that do not contain carbon and are not derived from living things. These include minerals, inorganic salts, inorganic acids, alkalis, free chlorine, ammonia, and metals etc. The inorganic impurities also includes anions such as phosphates, sulphates, chlorides, nitrites, nitrates, cyanides and cations such as calcium, magnesium, sodium, potassium, iron, manganese, lead, mercury etc. They cause eutrophication of water bodies, increases dissolved solids content and can also be harmful to aquatic life. They also lead to the contamination of the surface and groundwater through runoff and percolation.

 

Table 5.2: Inorganic pollutant elements and their sources in waste water

 

 

Acids and alkalies: These generally affect the aquatic life of receiving water body. They also cause serious problem in operation of treatment units.

 

Toxic Substances: These include cyanides, sulphides, acetylene, phenols, ammonia etc. due to which flora and fauna of receiving waters is greatly affected. This may cause problems in the biological treatments of the wastewater.

 

  1. Organic impurities: Organic impurities are those substances that contain carbon and are derived from materials once living. They have high molecular weight. These deplete dissolved oxygen (DO) of stream and impose great load on secondary treatment unit. They Include carbohydrates, oils, fats, proteins, surfactants, pesticides, phenols, organic acids, grease and several other organic compounds etc. When the population of aerobic bacteria grows, they utilize more oxygen than is available in the river for degradation of organic matter. Now in oxygen depleted environment anaerobic bacteria start growing. They use oxygen bound to other inorganic pollutants like sulphates to degrade the organic matter and release other pollutants like hydrogen sulphides (H2S), organic acids, methane (CH4) and other nutrients. So one kind of pollutants are converted partly to the other kind.

                              Table 5.3: Organic chemicals and their sources in waste water

 

 

Pesticides: “Pesticides” is composite term that includes all chemicals that are used to kill or control pests. These include herbicides, insecticides, fungicides, nematocides and rodentocides. Oils: They hinder self purification as they remains floating on the surface and cause problem in oxygen diffusion.

 

Some of the organic species are persistent organic compound and do not degrade or degrade very slowly(Persistent organic pollutant, POPs). These include PCB, DDT, dioxins etc. Some of these POPs can be carried for many miles when they evaporate from water or land surfaces into the air, or when they adsorb to airborne particles.

 

The concentration of organic matter in wastewater is measured by the following parameters. Biochemical oxygen demand (BOD), is the oxygen equivalent of organic matter. It is determined  by measuring the dissolved oxygen used by microorganisms during the biochemical oxidation of organic matter. Chemical oxygen demand (COD), is the oxygen equivalent of organic matter. It is determined by measuring the dissolved oxygen used during the chemical oxidation of organic matter.

 

The water pollutants and the characteristics of waste water from some common industries are given in the table (5.4).

 

Biological Characteristics

 

Wastewater also contains various types of biological organisms . These organisms are mainly microbial in nature. These organism are both usefull as well as harmfull. They are usefull as they take part in the biological treatment of the waste water , illumination of pathogens but harfull as well as they cause diseses and eutrification of water bodies.

 

The microorganisms of concern in wastewater treatment are Bacteria, Fungi, Algae, Protozoa, Viruses, and pathogenic microorganisms groups.

 

Bacteria: They are the most abundant in terms of quantity and variety in the wastewater and are able to utelise the organic mater and minerals in the waste water for growth.

 

Some important bacteria:- Pseudomonas:- reduce NO3 to N2, So it is very important in biological nitrate removal in treatment works. Zoogloea:- helps through its slime production in the formation of flocs in the aeration tanks. Sphaerotilus natuns:Causes sludge bulking in the aeration tanks. Bdellovibrio: is a genus of Gram-negative, obligate aerobic bacteria. They  destroy pathogens in biological treatment. Acinetobacter: Store large amounts of phosphate under aerobic conditions and release it under an – anaerobic condition so, they are useful in phosphate removal. Nitrosomonas: transform NH4 into NO2 Nitrobacter: transform NO2- to NO3. Coliform bacteria:- The most common type is E-Coli or Echerichia Coli, (indicator for the presence of pathogens).

 

Fungi: Important in decomposing organic matter to simple forms.

 

Algae: Cause eutrophication phenomena. Cause taste and problems when decayed. Useful in oxidation ponds. Blue gree class of algae fix nitrogen.

 

Protozoa: Feed on bacteria so they help in the purification of treated waste water. However some of them are pathogenic.

 

Viruses: Viruses are a major hazard to public health. Some viruses can live as long as 41 days in water and wastewater at. They are responsible for diseases.

 

Pathogenic organisms: The main categories of pathogens are the Bacteria- Pathogenic E. coli Salmonella spp., Shigella spp,. Vibrio cholera. Viruses- Enteroviruse. Protozoa- Entamoeba histolytica and Helminthes- Ascaris Lumbricoides, Taenia saginata, Trichuris trichiura,

 

 

5.3 Disposal and discharge standards

 

The wastewater generated from the various sources as a byproduct has to be discharged from the site by certain methods. The waste water is as per regulations is to be treated befor discharge. The wastewater treatment is done to the extant that the treated water characteristics should meet the certain standards. These standards which regulate the quality of the water that can be discharged into various sources are the discharge standards.

 

The three methods of water disposal after treatment are generally employed,1. Discharge into surface waters 2. Discharge on to land and 3. Discharge into the subsurface. Central government of India in its Environmental (protection) rules 1986, ( Rule 34a, schedule-VI, part A) has made rules in respect of standards for discharge of waste water in four different areas. These areas are

  • – 1) Inland surface water (rivers, lakes, streams, pools and springs), Public Sewers (sewerage system), Land for irrigation (drains and canals) and Marine coastal areas (area near the sea and ocean). Discharge and generation standards for discharge of environmental pollutants in effluents are given in table 5.5 and 5.6.

 

 

Table 5.5 Discharge parameters and standards.

 

you can view video on Waste water characteristics, disposal and discharge standards

References

 

  1. Muttamara, S., 1996. Wastewater Characteristics. Resources, Conservation and Recycling, 16(1-4):145-159. https://doi.org/10.1016/0921-3449(95)00052-6
  2. Wastewater characteristics and effluent quality parameters. FAO Corporate Document Repository. http://www.fao.org/docrep/t0551e/t0551e03.htm
  3. Water and waste water Engineering, NPTEL. http://nptel.ac.in/courses/105106119/5.
  4. Wastewater characteristics, Licenced to plumb, CPC40908 certificate iV in plumbing and Services. https://www.dlsweb.rmit.edu.au/toolbox/plumbing/toolbox12_01/units/cpcpdr4001a_sanitary/00_gr oundwork/page_004a.htm.
  5. Water quality Characteristics. http://echo2.epfl.ch/VICAIRE/mod_2/chapt_2/main.htm.
  6. Characteristics of water- Physical, Chemical and biological. https://theconstructor.org/environmental-engg/characteristics-of-water-physical-chemical-biological/4735/.
  7. Talling J.F. (1976) Water Characteristics. In: Rzóska J. (eds) The Nile, Biology of an Ancient River. Monographiae Biologicae, vol 29. Springer, Dordrecht. https://doi.org/10.1007/978 -94-010-1563-9_39