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098<br />
UNIT 4: ENVIRONMENT MANAGEMENT SYSTEMS<br />
systems may be expensive, and a cost-benefit analysis must be conducted to<br />
determine if the effort is worthwhile.<br />
The level to which grey water needs to be treated depends on the level of biological<br />
oxygen demand, or BOD, of the wastewater and the purpose for which it will be<br />
reused. The BOD level is the level of oxygen extracted from the water by bacteria<br />
when pollutants decompose. The more organic materials there are in wastewater,<br />
the more oxygen is needed for pollutant decomposition.<br />
In most hospitality businesses, grey water can be reused for irrigation or flushing<br />
toilets, and in this case it may be enough to pass the wastewater through a sand<br />
filter. To maximise sand filter efficiency, it is important to minimise the suspended<br />
solids in the wastewater. Bathroom, laundry and kitchen outlets should therefore<br />
be fitted with filters, and additional grease traps should be added to kitchen<br />
outlets.<br />
But if grey water is to be used for drinking, it must go through a complete<br />
biological treatment process:<br />
• Preliminary filtration process to remove grit and large suspended<br />
solids;<br />
• Preliminary sedimentation process during which 55% of suspended<br />
solids are allowed to settle and are subsequently removed from the<br />
wastewater;<br />
• Biological treatment process, either activated sludge or a percolating<br />
filter to oxidise the effluent, and reduce BOD;<br />
• Secondary sedimentation process to remove all suspended matter and<br />
render the effluent suitable for reuse.<br />
Good Practice Tip<br />
The treatment of wastewater should not be undertaken without the services of<br />
wastewater treatment specialists. Plumbing codes and discharge regulations<br />
should also be consulted.<br />
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Examples of Good Practice<br />
At the Cama Rajputna Club Resort, Rajasthan, India, ten to twenty thousand<br />
litres of grey water are first passed through a gravel and sand filter bed and<br />
then used for watering the garden. Water use and water bills have further<br />
decreased by changing towels and bed linen every three days.<br />
At the Steigenberger Kurhaus Hotel, Amsterdam, Netherlands, a calibrated<br />
water pressure control system together with water-saving pressure nozzles on<br />
washbasins, sinks, and toilet cisterns is bringing substantial water savings. The<br />
new dishwasher unit is programmed to reuse water from the previous wash.<br />
A wastewater treatment works has been installed at the Taj Residency, Indore,<br />
India, through which 40,000 litres of wastewater are treated and reused every<br />
day. The treated water is used to water the garden. Further water conservation<br />
was made possible by changing watering times from during the day to dawn<br />
and dusk. Losses from evaporation, which used to account for 8,000 litres per<br />
day, are thus reduced.