4.1 Water

4.1.1 Waste-water Standards

Standards are a management tool. One aspect of good management is to focus efforts and interests exclusively on actions necessary to achieve specific objectives. In the course of monitoring and implementation, it is envisaged that the experience so gained, will help in the review of such parameters, and at the same time add more to the list. The list and reasons for choosing the parameters are shown below:
(i) pH
(ii) Total suspended solids (TSS)
(iii) Biochemical oxygen demand (BOD)
iv) Chemical oxygen demand (COD)
(v) Kjeldahl nitrogen
(v) Total phosphorus
(vi) Heavy metals, include: lead, mercury, cadmium, arsenic, nickel, copper, cobalt, aluminium, zinc,
barium.

Reasons for Selecting there Parameters:

(i) pH

The pH, is a term used universally to express the intensity of acid or alkaline condition of a solution. In waste-water, pH has a special significance in the sense that, it must be controlled within a range favourable to particular organisms involved. Furthermore, chemical processes for coagulation of waste-water, precipitation of heavy metals, draining of the settled sludge and oxidation of certain toxins ions, for example, cyanide from waste-water require pH to be controlled within rather narrow limits.

The pH of fresh domestic sewage is slightly more than that of the water supply for use by the community; however, the onset of septic conditions may lower the pH further. Industrial waste-water may have extreme fluctuations in pH levels depending upon the nature of the manufacturing processes, raw materials and chemicals involved. For these reasons and
because of the fundamental relationship that exist between levels of pH (acidity and alkalinity), it is important to include this parameter in the standard for effluents.

(ii) Total suspended solids

Solids found in effluents may be classified as suspended, dissolved, colloidal or settleable.

It has been observed that out of 0.45kg total solids that may be present in Im 3 of domestic waste-water, approximately 0. 0225kg are in solution, 0.0 1 12kg in suspension and the rest are settleable.

The amount of suspended solids can determine the need for, and design of primary sealing-tanks in plants employing biological treatment processes. In the long-run, all suspended solids are considered to be settleable solids, when time is not a limiting factor. Hence, the need for limited allowable solids in effluents is of great importance. If left unchecked, suspended solids will eventually render treatment plants ineffective and other water bodies receiving the same filled with unwanted solids/sludge will increase levels of pollution.

(iii) Biochemical oxygen demand (BOD)
This test involves the measurement of oxygen consumed by living organisms (mainly bacteria) utilising organic matter present in the waste, under conditions as similar as possible to those that occur in nature.

Since a quantitative relationship exists between the amount of oxygen required to convert a definite amount of organic compound to carbon dioxide and water, the amount of oxygen required thus, can serve as a measure of biodegradable organic carbon. Theoretically, a very long time is required for the biological oxidation of organic matter to complete.

It has been observed that a reasonably
large percentage of BOD is exerted in 5 days, consequently the test carried out on a 5 day incubation period at 20 ° C is more or less, a median value, as far as natural water bodies are concerned.
When assuming aerobic conditions, the test is very useful in determining the strength of domestic and industrial waste-water pollutants, in terms of oxygen that will be required when discharged in natural water courses. The test is also greatly useful in assessing the performance of municipal and/or industrial wastewater treatment plants.

(v) Chemical oxygen demand (COD)

Chemical oxygen demand is also a term which indicates the strength of polluting water, in measuring the amount of oxygen which will be required, like BOD, for oxidising the organic matter. But, unlike BOD, the process is not limited to the biological activities (bacteria) only. This test does not differentiate between biologically oxidisable and non- oxidisable materials. The ratio of COD to BOD, however, does not change significantly for any particular waste.

The major advantage of the test is the short time required for evaluation. The determination of COD can be made in about 3 hours rather than 5 days as required for measurement of BOD.

For this reason, sometimes it can also be used as a substitute for the BOD test especially when the basic characteristics of waste do not fluctuate a great deal.

The variation in COD to BOD ratio of waste-water from an industry, may indicate change of raw materials or chemicals used in manufacturing processes.

(vi) Kjeldahl Nitrogen (N)

The faeces of animals contain appreciable amounts of unassimilated proteins. These are converted in large amounts to ammonia by the action of saprophytic bacteria under aerobic or anaerobic reactions. The ammonia
released by the bacterial action may be used by plants directly to produce plant proteins.

All biological treatment processes employed by environmental engineers are dependent upon reproduction of organisms involved in the treatment process. In planning waste treatment facilities it becomes important to know
whether the waste contains sufficient nitrogen for the organism. If not, any deficiency must be supplied from an outside source. The outstrophic conversion of ammonia to nitrates requires oxygen, and so discharge of excess organic nitrogen and its subsequent oxidation can seriously
deplete the oxygen levels in rivers. Thus, measurement of organic nitrogen available in wastewater is of considerable environmental significance.
The Kjeldhal method employing sulphuric acid as the oxidising agent is a standard method of measurement of organic nitrogen in a waste-water samples.

(vii) Total phosphorus (P)

Phosphorus is known to be vital factor in life processes. The growth of algae in water is influenced greatly by the amount of phosphorus present. When nitrogen and phosphorus are plentiful, algae blooms may occur, which may produce a variety of nuisance conditions. The organisms involved in biological processes of waste-water treatment require phosphorus for reproduction and synthesis of new cell tissues.

Many industrial effluents, however, may not contain sufficient quantities of phosphorus for optimum reactions in the biological treatment unit. In such cases, inorganic phosphorus has to be added from an outside source in order to meet the requirements of the biological process at optimum level.

Thus, phosphorus determination are extremely important CHAPTER n assessing the potential biological productivity of surface water; while on the other hand, limits are required in many areas so as to avoid unwanted growth of certain biological species like algae blooms in lakes and other reservoirs.

(viii) Heavy Metals

Originally, the phrase 'heavy metals' was used to mean metals with atomic weight higher than that of iron. The trend now is that 'heavy metals' is used in a wider sense to mean 'poisonous metals'. Some of these 'heavy metals,'
like arsenic are not actually metals but are accepted in the same group.

The activities of mankind have resulted in an increase in the concentration of heavy metals in much of the environment, to a level where harmful effects on humans or the environment can be registered or anticipated.

Since heavy metals are elements, they cannot, in principle, be degraded and removed from our environment. The accumulation of heavy metals in the environment can only be halted by preventive efforts based on the concept of use cleaner technology.

Each heavy metal has its characteristics and related harmful effects. Those considered to be potentially more dangerous have been documented. Again, this is because the limiting factors are resources which include: equipment, personnel and finance needed when enforce standards. Below is the brief explanation of each heavy metal proposed to be included in the standard:

(a) Lead:

In Tanzania, lead and its products are widely used. Leaded tins, pipes, lead acid batteries, alloys and paints are just but a few products which contain lead.
Leaded gasoline is also widely used in this country. Lead is rated among the most dangerous heavy metal.

In human beings, lead is known to cause for mental retardation. It is mainly concentrated in the bones. Lead presence in the form of lead ions, Pb", in the body, interferes with the action of chemical compounds necessary for production of haemoglobin.

Lead is also known to cause both acute and chronic toxic effects on plants, animals and micro - organisms.

(b) Mercury:

The metal flows at room temperature and is used in some chemical industries. In Tanzania it is also extensively used by artisanal gold miners, especially
in areas around Lake Victoria. Although the damaging action of mercury in the body is not fully understood, it is clear that all mercury compounds are poisonous.

(c) zinc:

This metal is one of the essential micro-nutrients, particularly for tropical crops. When present at relatively high concentrations, however, especially
resulting from leaching processes, many harmful effects occur and thus, have been recorded.

Zinc is widely used in a number of ways. It is found in many agricultural chemicals such as pesticides and is a common impurity in fertilisers. It is also widely used in the electrical and electronics industry, in the making of semi-conductors, batteries, among others. Other uses include polymer stabilisation, and the making of pigments and paints.

This metal mainly enhances hytotoxicity, and has relatively low toxicity to animals and human beings.
Most zinc sources/mines are associated with cadmium as a guest element, hence whenever zinc is detected, it is reasonable to suspect the presence of the more toxic metal such as cadmium.

(d) Aluminum:
Aluminum is not a heavy metal. Nevertheless, for the purposes of considering its toxicity, is placed under this same group.

When compared to other heavy metals, aluminum doses do not pose as a big danger. In fact, some of its salts are extensively used in the treatment of water.

Aluminum is widely used as an alternative to steel for dadding structures, and as an alternative to copper in electricity conduction. Aluminum-oxide (alumina) is extensively used in industry as an abrasive.

Aluminum acetate is regarded as weak sensitizer, but may cause dermatitis on contact with the side. It is also regarded as a mild irritant. Patients under- going kidney dialysis could develop dementia as a result of the accumulation of aluminum in water" Some investigation on the brains of human beings who had died from Alzheimer's disease (senile dementia) revealed high concentrations of aluminum.

(e) Cobalt:

Cobalt has a wide range of uses, especially in the making of various alloys.

Cobalt salts produce polycythemia in animals while in humans it causes liver and kidney damage. Cobalt has also been shown to produce dermatitis and some investigators have been able to demonstrate hypersensitivity of the side due to cobalt. There have also been reports of hematologic, digestive, and pulmunary changes in humans. The metal is a suspected carcinogen of the connective tissue and lungs.

(f) Barium:

The soluble salts of barium, such as the chlorides and the sulphides, are poisonous when taken orally.

Barium benzoate is a deadly poison, while barium phosilicate is used as an insecticide.

In natural waters and least polluted areas, barium is normally detected in the ranges of mg/l (parts per billion).

4.1.2 Limits in Drinking Water

As already stated, the aim of putting limits is to protect different waters for the intended uses, be it for irrigation, sports, among others. Special attention, however, is always given to water used for drinking purposes. The limits discussed in the previous section on waste-water, are normally set against this background; that is waste-water may eventually be treated, diluted and finally find its way to drinking water sources.

The limits set for water intended for drinking purposes are more stringent for obvious reasons. The Tanzanian Bureau of standards has just finalised preparing a national standard for requirements in drinking water. The standard, TZS 574: 1997 is expected to be published soon.