Wastewater is any liquid waste that is discharged from such places such as residential areas, industries and agricultural areas. Though the water is negatively affected by human impacts on the environment and may contain a large number of contaminants, it mostly consists of pure water, up to 95%.
Throughout the world, an increase in the discharge of wastewater is causing a major impact on our environment. Wastewater pollution is more and more a danger to our planet because of rapid population growth, and increasing demand in water supply and sanitation provision.
According to research, every liter of wastewater pollutes up to 8 liters of freshwater. Hence, each year, around 12,000 km3 of the globe’s water resources may not available to us. By 2050, the anticipated population of the world is thought to rise to 9 billion and if the wastewater pollution keeps on with the same speed with the population growth, the world’s water resources could see a drastic reduction by around 18,000 km3 annually.
For now, in developing countries, around a tenth of the overall domestic wastewater is collected and only about nine-tenth of the existing wastewater treatment plants do not operate reliably or efficiently.
Adverse effects or inadequate wastewater handling:
increased illness and mortality lead to loss in terms of finance
4 million lost person-years annually
cost of production of drinking and industrial water increases; water tariffs increases
$56 billion annually – World Panel on Financing Water Infrastructure US, March 2003
loss of income in fisheries and aquaculture sector
tourists are deterred by the poor water quality
loss of valuable biodiversity, both in the water and land surrounding the affected water
70% of coral reefs
real estate values fall in value because quality of the surroundings is deteriorated
Wastewater
Local Overview
In Mauritius, there are about 100 industrial units engaged in several activities resulting in some kind of water pollution. When liquid effluents are discharged from industries, they tend to go into the hydrological cycles and thus adversely affect the ecosystems and the quality of water reaching the consumers. Moreover when looking at the small size of our island, we can deduce that those effluents can very easily and rapidly pollute most of our water sources, from rivers to the seas.
Many of the industries that pollute most of our water are basically found in 3 main industrial zones which are:
Plaine Lauzun
Coromandel
Vacoas-Phoenix
Firstly, the Plaine Lauzun zone includes the galvanizing, food canning, dye houses, ethanol distilleries, soap, detergent and chemical manufacturing industries. Their daily water consumption is approximately 5000m3 and they discharge their respective wastewater effluents to the Fort Victoria Sewerage treatment in Port Louis whereby only a pre treatment is carried out. Moreover the pre-treated wastewater is discharged 800m into the sea which will in turn find its way in the nearby beach named Bain des Dames where high fish mortality rate have been reported due to the release of heavy polluted water.
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Secondly, the Coromandel Industrial zone comprise of industries such as food processing, dye houses and soap industries. Their daily water consumption is about 3000m3 and they discharge their untreated wastewater by means of a 600m outfall into the sea at Pointe aux Sables to Port Louis. As a result, these effluents have been the cause of the total death of the reef opposite Pointe aux Sables.
Thirdly, the Vacoas-Phoenix zone consists of about 30 industries including one edible oil refinery and six dye houses. Their daily water consumption is about 2000m3 and they discharge their untreated wastewater into the local sewerage network which leads to the St Martin treatment plant whereby a primary treatment is carried out before it is then discharged to the sea at Pointe Moyenne. Moreover there exists a potential for health effects to crop up since during the rainy season, overflowing of water can cause a considerable amount of effluents to be discharged into river Du Mesnil which in fact is joined up to Grand River North West and from which water is extracted for domestic purposes.
On the other hand, there exist several other industries which are distributed all around the island and that in turn contribute to the pollution of water and these consist of galvanizing, dyeing, battery manufacture, leather tanning and washing industries. However since these industries do not generally carry out any onsite treatment of their effluents before they discharged it in surface waters or pits and caverns, hence there is a high possibility of aquifers being contaminated by such methods of discharge.
Disposal routes of wastewater
Rivers
All around the world, rivers are the most often used as pathways of wastewater discharge. If not rivers, then canals and tributaries are used which eventually end up in a river.
Sea
Many industries found near to the sea use the sea as their dump for wastewater. Further wastewater is added to the sea through rivers.
Sewers
Industries direct their wastewater through sewers to the nearest treatment plant.
On-site treatment
Industries treat their wastewater as far as possible to make it comply with the country’s legislation. Sometimes the water may be reused by the industry itself.
Carting away
The wastewater is carried away in specialized dedicated vehicles to be disposed off somewhere more appropriate. This method is used when the water is of a kind that cannot be discharged in the nature even if treated and hence it is sent somewhere its potentially negative effects can be neutralized.
Irrigation
The wastewater is used for irrigation if it non-toxic and is considered suitable for the task.
Major sources of wastewater in Mauritius
Sugar Industry
Since the sugar industry is one of the main pillars of our economy, we ensure it will still be one in the near future and thus limit its negative effects on our environment. Standards for effluent limitation have been introduced by Mauritian authorities to sugar factories and these norms have been in force since October 1999. But many sugar mills in Mauritius are not yet equipped with a conventional secondary or advanced treatment.
For factories that can not dilute their wastewater before discharge or that cannot use their wastewater for irrigation, an appropriate treatment technique should be found for treatment of their medium to high strength wastewater so as to comply with the existing environmental law. Wastewater from sugar factories is considered as non-toxic organic source of pollution so it would be acceptable to have a biological treatment system.
The sugar industry produces at least 5 million meter cube of wastewater per year (2001).
What produces wastewater in the sugar industry?
Cooling water: mainly used for condenser, bearing cooling, sulphur/lime houses and crystallizer for formation of crystal.
Process water: used in the sugar making process.
Parameters
Standards
Chemical Oxygen Demand (COD)
90
Biochemical Oxygen Demand (BOD)
30
pH
5-9
Conductivity
2000
Total Suspended Solids (TSS)
45
Oil & Grease
No visible oil
SAR
6
Cl-
250
SO42-
500
The above table shows the standards of effluent (wastewater) according to the Standards of Effluent for Discharge Government Notice 2003.
Major sources of wastewater in Mauritius
Textile Industry
The textile industry is another important pillar of our economy and textile factories can be found all around the island. Due to the various processes (sizing, bleaching, dying) existing in the textile industry, a considerable amount of water is being used and thus a very large amount of wastewater for discharge is produced. Unfortunately, not all the textile factories are equipped enough to cater for their wastewater treatment and many of them discharge toxic and untreated wastewater in nearby rivers and canals.
Textile wastewater may consist of:
Natural fibers: wool, hair, silk, cotton, flax
Synthetic fibers: rayon, nylon
Chemicals: dyes, de-foamers, bleaches, detergents, optical brighteners, equalizers
In the past recent years, many incidents concerning discharge of untreated wastewater by textile industries directly into natural water bodies have taken place such Mon Désert Alma canal pollution by the Compagnie Mauricienne de Textile Ltee (Verdun).
Major sources of wastewater in Mauritius
Breweries
Brewery has become a very important industry in Mauritius since it has a so vast market now. Brewery operations tend to produce considerable amounts of wastewater as waste products. Even by implementing new technological improvements in the past, it is estimated that around 3 to 10 liters of wastewater is generated for every liter of beer produced in breweries. The quantity of brewery wastewater produced will normally depend on the production and the water usage.
Brewery wastewater may contain:
Wort and beer wastes, spent grain and grain dusts.
Fermentation solids, yeast wastes.
Waste water of CIP equipment (cleaning and disinfection equipment.
Sodium wastes from the CIP equipment.
Acid solution from CIP equipments.
Caustic soda from PVPP filters.
Waste water with kieselguhr.
Alkaline cleaning water.
Alkaline waste water from bottle cleaning system.
Insoluble substance, paper and cardboard, aluminium and ferrous metals.
Soluble substance like adhesive, metals salt and conveyer lubricant.
Oil and grease track from the equipments lubrication.
Beer wastes from returned bottles and kegs.
Even different lubricants cannot be eliminated so they finish in water. Such substances increase the percentage of contamination of waste waters.
Many of the above substances, such as yeast, sodium, caustic soda & alkaline water, may lead to negative consequences if let without treatment in natural water bodies.
Major sources of wastewater in Mauritius
Hotels
Tourism is the third most important sector in Mauritius. Tourists come to Mauritius for its sand, sun and sea. But now the seas, and eventually the sand, are in danger of deterioration. This is because of the mismanagement of wastewater by some hotels. Hotels with more than 75 rooms are now required to be equipped with treatment plants so as to render their wastewater of a quality according to the norms. To ensure this, frequent monitoring should be carried out by the Waste Water Management. There are approximately 44 wastewater treatment plants in hotels all over the island which produce 7000 m3 of sludge every day. The treated water is then used for irrigation by the hotel itself.
Discharging wastewater which is out of the regulatory norms may cause negative effects such as the degradation of our seas and coastal regions where foul smell will emanate eventually, the death of marine animals and vegetation. These problems directly affect the tourism industry as well as the lives of fishermen.
Agro-industry (chemicals)
It is only with important amounts of fertilizers, insecticides and pesticides that modern agriculture in Mauritius can increase its yield. But intensively using agro-chemicals is not an unmixed blessing since its repercussions can be seen at a later stage. 48% (90,100 hectares) of the island is under cultivation and up to 57,500 tons of fertilizer is used each year, which is well above the norms.
The problem with excessive use of agro-chemicals is when they are washed away by rain and reach surface water bodies or underground water. The acceptable level of nitrate in water is 45mg/l. Excess nitrate in water causes fast-growing plant life like algae and weeds and the water body becomes clogged all over.
Impacts of wastewater on the environment
In Mauritius, wastewater comes from mainly industrial processes, sewage consisting of human wastes, organic wastes, and from the agricultural sector pollutants such as animal wastes, pesticides and fertilizers. Today, due to a real change in terms of development in many areas in industrial and agricultural practices, our rivers and other water bodies are the most affected.
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Mauritius consists of four main aquifers namely as Curepipe aquifer, the Northern, Southern and Eastern aquifers. Taking into account the National Physical Development Plan (volume I p 134) it has been found that our aquifers have been badly polluted due to a lack of proper sanitation which can be described as sewage, wastewater, refuse disposal and bad practices in agriculture.
Effects on aquatic wildlife
Our sea, lakes, rivers and groundwater are the greatly affected by water pollution, much of it coming from wastewater. Pollution not only affects the quality of the water but also the lives of the species inhabiting it.
Change in temperature
A change in temperature (e.g hot water from sugar factories) affects the aquatic ecosystem. Although the temperature is increased by only few degrees, this may affect many varieties of fishes and plants. This causes a problem in the food cycle because some fishes that prey on other fishes and plants will have difficulties in finding their food they need. In their turn, they will have to move elsewhere or very often will lead to extinction of some plants and species. Furthermore, an increase in the temperature level of the water causes a reduction in the oxygen percentage in the water and thus resulting in chemical and biological reactions due to this unnatural process. With time, the movement of living organisms, respiration process and metabolism of aquatic plants and animals within the water itself will be at high risks.
Pollutants in the wastewater
On the other hand, another main water pollutant is the wastes generated by industrial processes which are discharged into rivers. It has been found that if wastes in lesser amounts are discharged in rivers, they can self-purify themselves but if the concentration and amount of wastes are high, then their impacts also will be high. Thus, excessive amounts of wastes chemicals discharged into rivers will not only disrupt the ecosystem but also causes the death of much aquatic life and will lead to bad odors. Sometimes some aquatic animals might not die when exposed to these pollutants but consuming these toxic animals not only will cause poisoning to the consumer but also will have an impact on the reduction of food processing and consumption.
Potable water becomes scarce
Moreover, consumable water for human beings and animal farming might indirectly bear severe consequences. Because Mauritius is a small island, wastewater released by industries can flow easily across many rivers and resulting in rapid pollution. The problem does not end here because if untreated wastewater reaches underground water reserves and contaminates it, we will be in lack of potable water for consumption.
Eutrophication
This occurs when a water body becomes abnormally enriched with nutrients. This might be caused by fertilizers run-off into nearby water. Excess nutrients causes phytoplankton to grow and reproduce much more rapidly than they would normally, thus resulting in algal blooms which disrupts the normal ecosystem functioning. The large amount of algae exhausts the oxygen in the water thus depriving it from other marine life. This is why many aquatic organisms end up dead but the process of eutrophication continues; the excess algae blocks the sunlight from marine plants which use photosynthesis to live. Furthermore, some algae might produce certain toxins that can be harmful to other animals and even to man. This effect can destroy the entire food chain of the ecosystem affected.
Impacts of wastewater on the health of people exposed
Consumption of contaminated wastewater
In Mauritius it is very rare for people to consume any kind of contaminated water. However, a continuous exposure to low level of contaminants for a long time may cause diseases such as
Cancer
Liver and kidney damage
Nervous system disorders
Immune system disorders
Birth defects
But consumption of high concentration of contaminants may cause the following immediate health effects:
Nausea
Lung irritation
Skin rash
Vomiting
Dizziness
Death
When exposed to odors emanating from wastewater
Wastewater often has bad odor due to contaminants like sulfur. The following health effects might be seen on people exposed:
Coughing / Sore throat
Lung problems
Headaches
Eyes related diseases
Examples of wastewater mismanagement
The Rivière du Rempart polluted because of untreated wastewater
Mon-Loisir sugar factory was at the centre of a controversy concerning the pollution of the Rivière du Rempart. The problem has been that the sugar factory discharged dirty and untreated water (wastewater) directly into a tributary river to the Rivière du Rempart.
But according to Joseph Vaudin, the CEO of Mon-Loisir sugar factory, the problem was that the tank farm with foam and bagasse to be used in the fields during the sugarcane cutting periods, which was close to the tributary of the Rivière du Rempart, ruisseau Chevrette overwhelmed with the heavy rains we had earlier this year. And thus this wastewater discharge was unintentional.
rempart.jpg
More contribution to the discharge into the river sewage, composed of mud and scum, was brought by a faulty irrigation pipe. But this was detected and repaired within an hour.
Jean-Luc Harel, plant manager, stated that the other end of the pipe which is normally concrete will be replaced with steel to avoid this kind of problem in the future.
The local inhabitants, of whom several were very irritated, had several complaints pertaining to the discharge of dirty water from the factory directly into the river used by so many.
Impacts on the inhabitants:
The foul unbearable odor from the river once it is contaminated.
The negative effects such as breathing problems to people inhabiting near the river.
The water is no more usable for purposes such as irrigation.
No more recreation site (people used to swim in the river).
Fishing in the river is no more safe.
A kind of vegetation seems to be proliferating on the surface of the water, contributing to pollution by; blocking organic materials and all kinds of waste thrown by man, and thus leading to the death of aquatic animals such as fish & shrimps.
Wastewater from Consolidated Fabrics Ltd, Balaclava
Consolidated Fabrics Limited (CFL) factory at Solitude has been, since a few years, dumping toxic wastewater illegally in Rivière Citron. The norms of the Standards of Effluent for Discharge (Second Schedule) Government Notice 2003 and those of the Guidelines for Inland Surface Water Quality have not been respected. Ending its course in the Turtle Bay sea, this river runs through Balaclava and thus residents of Balaclava have been seriously affected by the bad odour that emanates from the illegal chemical.
cfl2.jpg
Fig. 03
Despite having voiced out their grievances and the potential health threat many times, the Balaclava Residents Association (BRA) members have seen no action being taken by CFL. Many residents have noticed that these odors are ten times more frequent than before.
Impacts on local residents:
Many are experiencing a suffocating smell of ‘rotten egg’ across the morcellement.
Almost every resident has complained of nausea, giddiness, sore throats, coughing, vomiting and headaches. One person has even reported of her baby having a rash.
People most affected by the smell have to close their windows and doors even at times when the weather was very hot.
Impacts on the environment:
The river is an eyesore to people. It is not worthy of a ‘paradise island’.
Aquatic life is being ruined. Fish & eels can no more survive in such a polluted river.
The water can no more be used for irrigation.
The river ends its course in the sea and hence marine life is no more safe.
People have reported that their pets have started to cough.
cfl3.jpg
Fig. 04
Examples of wastewater mismanagement
Unbearable odor at Bain-Boeuf beach
Bain-Boeuf beach was very much appreciated by everyone until people started complaining about an unbearable odor on the beach and its vicinity. Bain-Boeuf beach is surrounded by many hotels of which some have treatment plants to treat their wastewater. One of the hotels has been discharging its untreated wastewater into the sea. Furthermore, wastewater from agricultural lands might have been washed into the seas bringing in nitrates, phosphates and sulfates.
The chemicals above cause a surplus of nutrients in the sea and cause the algae to grow to an abnormal proportion. This process is called eutrophication. The problem is further aggravated with the death of these algae. This causes more harm to the marine life and is also the cause of the foul smell experienced by people around. Furthermore when the algae starts to decompose, it produces hydrogen sulfate, a toxic gas, which when inhaled at high concentrations may cause death. In addition to water and air pollution, there is also land pollution since the dead algae is washed on the shore and is clearly an eyesore. Bain-Boeuf beach has not been practicable as long as the problem has persisted.
Conclusion
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