A few months ago there was some discussion about brown water coming from the Negril River and encrouching on the beach. Well, I visited the negril treatment plant in December and can positivly say it was not coming from there. I have worked in wastewater treatment for over 20 years and have experience in what is called an "activated sludge" plant. The Negril plant is what I would call a "lagoon" or "pond" plant, howqever the workers there called them "pans". Basically, wastewater treatment works on the concept of decompostion and speeds it up much faster than nature by optimizing conditions. For instance the plant I work at takes raw wastewater and turns it into near quality drinking water in about 36 hours. We have many mechanical devices (blowers, pumps, mixers etc) to achive maximum results in a short period of time. Of course we are servicing about 2.5 million gallons per day in an area of about 4 acres. The Negril plant has no mechanical devices. Granted, there are about 14 mechanical pump stations along the cliff and beach roads that pump the raw sewage to the treatment plant which is located next to the Golf Course just outside of town on the road to Sav. But once the raw wastewater reached the plant (called the "headworks" in the business) everything flows by gravity. The way that a "pan" plant works is by exposing the raw wastewater to sunlight for extended periods of time to disenfect the water. I took ball park measurement of the pans and guestimated the flow at the headworks and came up with an estimated detention time of 29 days. That means that water that is entering the plant today will not leave the plant for nearly a month! However if the flow coming into the plant is tripled during a tropical storm, detention time drops to about 10 days, a hugh difference. Also, during storm events there is little if any sunlight, so less disenfection is taking place. The pan system works okay and is designed for places that have a lot of land and little money. The Negril plant is on a 40 to 50 acre plot. The treatment plant consits of 2 sets of 3 pans. each pan is about twice the size of an American football field. At the headworks is a manual bar screen which is cleaned off daily by the workers. This collects mostly non treatable products such as tampons and condoms. More specifically once the water leaves the headworks it flows by gravity to the first two side by side pans. About a third into the pans is a baffle that holds back any floatables and the heaviest of sludge which the workers occasionally clean out. At the far end of the pans is a weir or a gateway to allow the water to flow into the next set of pans. At the far end of the second set of pans is a gateway into the third set of pans. At the end of the third set of pans the flows combine and flow into the Negri River, I don't know, maybe a mile or two upstream. As the water travels from pan to pan it becomes noticably cleaners. The workers told me there are plenty of big fish in the final pans and indeed I did see a fish at least a foot long crest the water. That is basically how the plant works.
The Upgrades. I visited the plant about 1.5 years ago when they were in the middle of "upgrades'. Cosmetically much was done. The entire plant is now completely fenced in. There is signage around to warn people and also saftey signage for the workers. The headworks was redone and is a bit more effieient. A few other things were done that MAY inprove the water quality. There is now blacktop rather than dirt between the pans. This means that during heavy rains dirt will not be washing into the pans. Also, the system that passes water from one pan to the next has been modernized and is more efficient. However, there was talk a year and a half ago about making the pans deeper. I'm not sure that this was done, and even if it was I'm not sure it would be effective. Pans should only be about 2.5 or 3 feet deep at most to be effective. What is more effective is cleaning out the pans of any sludge that accumlulates on the bottom. I am not sure if this is done, and if it is how often. I will try to show before and after photos of the plant.
Finally, what does this all mean to the Negril River, the ocean, the reef and the swimmers? Good question. The workers at the plant had no knowledge of any effluent parameters or lab results. They said that someone came weekly from Montego Bay to collect samples. I noticed that there was no chlorine or disinfection at the point where the water enters the river. The pan system is supposed to disinfect, but I'm not sure to what extent. A fecal coliform would have to be taken to find out how well it is working. For instance, Ocean City, New Jersey has a maximum fecal coliform of 200. If a 200 count is found on any of the beaches they are sut down. At the plant I work at our maximum is also 200, however our twice a week samples average less than 5. I would have to do more research, but I don't think that the pans do much to lower phosphate (from soaps), ammonia or nitrates (from urine). In fact a byproduct of pans are the massive amounts of algae that they produce. If someone will do the research and find test results for: fecal coliform, pH, turbidity, Dissovled oxygen, Phosphates, Nitrates, Nitrites, and BOD, I will compare them to US standards to find out how well they are doing.
Regards,
Bob
