Waste water from human habitations is harmful to the environment from numerous perspectives:
1. Spread of disease brought on by germs, infections and parasitic organisms.
2 Elimination of oxygen from the water of rivers or lakes which receive the waste-water
3. Poisoning of the lakes or rivers by chemicals and metals stemming from industry.
4. Enrichment of the natural waters by salts such as nitrates and phosphates which, then, cause unusual developments of algae and other plants, with unfavorable outcomes.
If neglected waste-water is enabled to get in a river, problems from the majority of these classifications can be anticipated. The seriousness of the issue will, naturally, depend upon the volume of effluent and the size of the receiving river.
In an extreme case, where the receiving body of water is the sea, waste-water from rather large cities, can be disposed of completely neglected. Remarkably, couple of problems are come across where this is done due to the big dilution factor included and the propensity of sea water to eliminate most organisms which trigger human illness.
Some people do not entirely consent to this statement however, in view of economic considerations, waste-water, consisting of sewage, continues to be gotten rid of off in this way by seaside cities in a lot of parts of the world.
Inland towns and cities, of course, do not always have the opportunity to get rid of off their waste in a large body of water. An interesting case is that of Calcutta where a large proportion of the sewage is passed along an open ditch for numerous miles before eventually reaching the sea. The authorities there do not concern this as an ideal option but alternatives are most likely to be extremely expensive.
Additional inland, the treatment procedures vary from complete (primary and secondary) measures to no treatment at all. Where there is little or no treatment, the damage done to the environment is bound to depend on the size of the population centres and the size of the river which is receiving the effluent.
Naturally, it is the size of the river, especially in the dry season, which is necessary. This goes against the opinion, in some cases, voiced that a flood- plain river Ganga can receive large amounts of contamination since it is all rinsed each rainy season.
This viewpoint may apply, to some level, to inorganic toxins such as some metals which need years to develop to harmful levels. One could, then, expect the flooding to decrease their accumulation in the river’s environment.
The scenario is quite different, nevertheless, with biological toxins. Here, we are dealing with infectious agents which can produce their impacts (in the spread of illness) within hours of getting in the drinking water.
Though the threat will be decreased, in the rainy season, due to dilution, this might be more than balanced out by the threat of contamination of drinking water by flood water.
One of the most apparent and instant impacts of contamination from a town or city sewage is the elimination of oxygen from the waters of the getting stream. Oxygen measurements upstream and, at some distance, from any sewage, inlet downstream, will show this quite clearly.
In fact, city effluents, which can be described as a suspension or option or organic products, and living organisms add to a heavy organic load. The natural product provides an endless supply of food for micro-organisms existing in the river.
Regrettably, in order to take in the natural material, most of these micro-organisms require oxygen which they consume at a much faster rate than its rate of diffusion into the river from the environment.
Therefore, the oxygen material is depleted, rendering it unsuitable for a lot of kinds of aquatic life. Nevertheless, if no more organically rich effluents get in the river, it will slowly recuperate and its oxygen content will go back to normal through the natural fortification mechanism for dissolved oxygen, i.e., diffusion. The ability to recuperate is, naturally, related to such elements as the size of the river, compared to the volume of effluent.
The foregoing conversation has concentrated mainly on dissolved raw material and its effects for dissolved oxygen in the water environment, which gets the effluent.
Many other materials significantly germs and liquified inorganic salts may also exist which can trigger problems in the environment. Techniques are understood, which can entirely purify waste water, even sewage, to such an extent that it can be safe for drinking.
Such procedures are, however, just justifiable in the case of a big city with a minimal supply of water, because the expense of the installation is very high. Also, expensive is the process for primary and secondary treatment, consisting of triggered sludge treatment and slack food digestion.
This involves the removal of almost all particles and raw material present however omits the liquified salts, a number of which are plant nutrients. Bacteria, however, endure this treatment in enough numbers to constitute a possible health hazard in effluent. The exact same applies to infections, in specific, the hepatitis virus.
Once again, nevertheless, capital costs are considerable and a required to make the plant function. Exceptions to this declaration are plants where utilized as fuel to power the machinery.
The dripping filter is a remarkably effective machine for dealing with drainage and sewage which has actually initially travelled through a primary settling tank. If properly created, it required no power input and the rotating arms of the sprinkler are moved by momentum of the water.
This needs a pressure of about 60 cms. The gravel bed, underneath the sprinkler, becomes colonized by a large number of organisms which effectively eliminate most of the organic matter. The effluent, nevertheless, after this procedure, will still include large quantities of plant nutrients. Capital expenses are likewise substantial and the capacity of the system is not large enough for huge neighborhoods.
The stabilization pond or oxidation pond is another approach of treatment. Compared with the methods explain above, these ponds have, somewhat, lower BODY loadings.
They count on the activity of micro-organisms in a large body of water, about 1 m deep. Specific usage is j made of microscopic plants. The raw material is first taken in by aerobic bacteria and oxygen is supplied from both the atmosphere and plants during the day.
The stabilization I pond works best where temperature levels are high and there is abundance of sunshine. Thus, their obvious advantage depends on India. The effluent can be quite low in organic matter however germs and parasite eggs stay an issue. This is a pity in view of the possible usage of the nutrient-rich water for watering.
The risk, still present, in the stabilization pond-effluent, can be considerably reduced by growing crop, not utilized as food, cotton or crops grown on trees, consisting of coco-1 nuts and citrus fruits. Much work of this kind has been performed by N.E.E.R.I. at Nagpur.
A good account of this has been offered by Sundaresan. The information of the rearing of edible fish, in the effluent from stabilization ponds, are also included. Other criteria for examining and comparing the efficiency of stabilization ponds in India are provided by Bopardikar and Dave and Jain.
The basic opinion seems to be that their low expense, ease of upkeep and possible I integration with some kinds of agriculture and fish production, makes the stabilization pond an useful choice.
However, extreme care will be necessary to make certain that the capacity I illness causing organisms and parasites are kept in control. The total treatment of drainage is typically divided into 3 stages.
These are called primary, secondary and tertiary treatments. The final level of pureness depends upon the economics of the scenario. It would naturally cost more to improve the water after the 2nd and 3rd stages so as to make the water suitable for drinking.
Waste water normally contains big quantities of drifting rubbish such as cans, fabric and wood. These bigger items are removed by metal bars which act like strainers as the water j moves underneath them in an open channel.
The velocity of the water is, then, decreased in a grit- settling chamber of a bigger size than the previous channel. This leads to most of the grit and sand settling at the bottom. Periodically, this settling chamber is disconnected from the primary system and the grit is removed by hand.
The smaller sized and lighter particles take longer time to settle under gravity. This slower procedure occurs in the primary sedimentation tanks. Such tanks are rather large and are typically circular with a bottom formed like a shallow cone.
At the bottom of the cone, the sediment or sludge is drained away by a horizontal pipeline. Rotating scrapers gradually scrape the sludge from the sloping sides, moving it slowly from the boundary to the centre where it is drained pipes off as described above.
The disposal of this primary sludge can be an issue because of its offensive smell. It likewise has a water material of over 95 percent. It needs to be dried prior to it can be gotten rid of on land.
Additionally, it might be digested by the approach described below under the heading “sludge food digestion”. The liquid effluent from the main sedimentation tanks has actually now lost over half of its initial suspended matter. This effluent might be drained pipes directly into a river or the sea if other factors to consider permit this. Secondary Treatment
: The suspended particles, staying after
main treatment, are too great to be gotten rid of by a simple sedimentation procedure. This would take far too long and much of the product is colloidal and would never settle down. Most of this material is, nevertheless, natural and this indicates that certain micro-organisms can consume it as food. The carbon chains of the big organic molecules are, thus,
broken down to smaller sized molecules such as carbon dioxide. This can be accomplished in a trickling filter or in an activated sludge digester. A big location of land is required for trickling filters and they, often, trigger problems since they draw in pests and release an unfavorable smell. They have the benefit; nevertheless, of requiring extremely little upkeep once they are working. They likewise run without electricity. Incoming waste water(after main treatment)is sprayed over circular filter beds by a turning boom. This is a pipe with holes along its length and the water emerges in horizontal jets. The reaction to these jets causes the boom to turn; hence, no additional power is required. The water is kept at the necessary pressure head by a kind of siphon
at the inlet. The filter bed is normally about 1.5 m deep and surrounded by a circular brick wall. The filter includes numerous combinations of stony material or perhaps plastic product.
The stones should, if possible, be round and in between 3 and 10 cms in diameter. Stones of irregular shape can, however, are utilized. Among the issues which might be faced, if the organisms, which grow on the stones, ultimately obstruct the filters
is too much effluent of high B.O.D. is used. If the B.O.D. is too high at particular times in the days it can be watered down by recalculating some of the low B.O.D. effluent which emerges from the bottom of the filter. The bottom of the filter must allow free entry of air, and, for this factor, it is usually offered with a floor of perforated tiles under which the incoming air
passes. This air makes its method up through the permeable filter-bed to the upper surface. It is essential to keep in mind that dripping filters, like other types of secondary treatment, require aerobic conditions. If there is absence of oxygen, the incorrect types of organisms would establish and harmful materials would discover their method into the last effluent. Under perfect conditions, the filter bed must supply a house for a wide array of organisms consisting of germs protozoa, fungi, worms and insects. The upper surface will likewise be colonized by algae.