JEDDAH, 12 November 2006 — As an advertisement of excellence and quality, restaurants in France with absolute confidence in their own cooking display a small sign: “Le patron mange ici.” (The owner eats here.) Deep in the bowels of Jeddah’s Hilton hotel, far from the eyes of guests and the public, are two remarkable pieces of engineering — a desalination plant and a sewage plant. Tucked into one corner of the desalination plant is a small bottling plant providing hotel employees with 25 liters of free water a day. They drink their own desalinated water. “Les patrons boivent ici.” (The owners drink here.) What better way to guarantee the quality of the water you make than to drink it?
Kieran Hughes, chief engineer at the Hilton since 2001, is a fit-looking hard-driving character who lives and breathes statistics and machines. He is particularly proud of the two water treatment plants that supply the Hilton and dispose of the waste. He regards the quality of the output as a challenge that he is completely involved with. “Even the irrigation water,” he said, “is cleaned to standards that are very nearly drinking quality.”
Why go to such extremes to desalinate seawater to bottled water standards and clean the waste water? “We do that not only for the guests but also for our team members — we have to make sure it is safe to drink,” he said. “Anyone who comes to the Hilton expects certain standards and fulfilling them is what we are about.”
From anyone else, that would sound like PR but from Hughes, it is sincere commitment by an engineer who loves his job which is to get the best from the immensely complex machines in his charge.
The process of supplying the hotel with all its fresh water requirements begins in five 30-meter deep wells in the grounds. The sea’s hydrostatic pressure initially forces — and filters — the water through the fringing reef of the Corniche into the wells. Water is pumped into the first stage of the desalination process at a rate of 8,000 cubic meters a day into sand filters. “And we return 5,000 cubic meters a day of excess brine from desalination to the sea a lot cleaner than we get it.”
Although fairly debris-free from the effect of the reef, the sand filters remove the microscopic particulate still in suspension before the seawater moves on to pre-chlorination to sterilize it and chemical dosing. Once clean and pure, but still very salty — 47,000 mg/liter of total dissolved solids (TDS) — the water enters the first pass of two reverse osmosis (RO) desalination processes. First-stage pumps bring the pressure up to about 700psi; however, as the process does not work efficiently below 980psi due to the Toray Membrane design specifications, a second-stage pump — in effect a turbocharger operated by reject pressure from the reverse osmosis cartridges — operates a second-stage pump that raises the pressure to 980psi. “As the turbo pump is operated by the backpressure of excess water,” said Hughes, “we can avoid using bigger pumps and thus save energy.”
Not all the water that enters the banks of RO cartridges passes through the membranes. The remaining brine concentrate, now clean and filtered, is pumped back into the sea through pipes which are 30 meters below the surface. The partially desalinated water goes on to a second bank of RO cartridges where the process is repeated. At the final stage, called RO second pass, when the water emerges, the TDS count has dropped from 47,000 mg/liter to a mere 40.
“At this level,” Hughes explained, “the water is very pure but low in nutrient minerals and taste. So we blend it with some of the first pass water to bring the TDS levels up to that of the best bottled water, about 140-180 mg/liter.”
That process is constantly monitored by pre-set systems monitoring probes that are checked and re-set at the beginning and end of the working day. “If anything goes wrong,” said Hughes, “the plant automatically shuts down.” To ensure the water quality is high, it is independently monitored both by Aramco who conduct spot checks and a contracted water analysis laboratory.
All water from any outlet in the hotel — bathrooms, laundry, kitchen and even the fountains in the lobby — is drinkable and of the same standard as bottled water. “Once the system is in place, it is a fairly easy thing to achieve,” said Hughes, “and it ensures the minimum risk to our guests and team.”
With an average daily production capacity of 1,000 cubic meters a day, the desalination plant supplies both the Hilton complex, Qasr Al-Sharq, and the staff quarters with room to spare. However, when the Jeddah water supply was put under pressure and shortages occurred, the Hilton boosted the output to 146 percent of normal and supplied a large local compound with its water. “We had the capacity,” said Hughes, “and we wanted to help out if we could.”
The other side of the equation — what happens to the waste when the water has been used — is taken care of by Hughes as well. All the waste systems — from bathrooms, kitchens, laundries and even the storm drains — supply huge underground storage tanks through a gravity-piped network. The effluent is then pumped into the hotel’s own high-tech 1,500-cubic-meter-a-day treatment plant. Operating at just 900 cubic meters a day, the extra capacity is called into play during major functions and conferences when there may be up to 3,000 guests on site at one time. “We have to be able to handle the possibility of their using all public and guest bathrooms simultaneously,” smiled Hughes.
The raw effluent is pumped to aeration chambers where compressed air is forced through, killing off the anaerobic bacteria (non-oxygen breathers) that produce odors.
“If the sewage treatment plant is run properly, there should never be any smell,” explained Hughes. Still it was a considerable surprise to be surrounded in a closed room by six tanks full of effluents without a trace of an odor!
The effluent travels from the aeration tanks to equalization chambers, on to the settling tanks to the clarification chamber — where the clean water is taken off — and sent through another bank of sand filters. Finally, it is chlorinated and subjected to ultraviolet sterilization before being stored for irrigation.
Clean irrigation water has a benefit as aerosol distribution is a common vector for the distribution of water-borne diseases by inhalation. Clean water reduces to almost zero the chances of that happening to guests and staff alike.
The remaining sludge is collected, allowed to settle where the benign bacteria reduce it to a silky black powder that is mixed with water and tankered away for use as fertilizer.
“It is a very efficient process,” said Hughes; efficiency is what he, as an engineer, wants to achieve. Clean water returned to the environment and solids recycled through agriculture: For an engineer, perfect.
