KAMPALA, UGANDA—I stepped outside an NGO in downtown Kampala and was proverbial smacked with a familiar odor: the smell of a sewage treatment plant. It was not the smell of fresh human waste but rather the more refined smell of sewage aged in the sun for many moons. To me, someone researching poorly operating sewage treatment plants, this was gold and I decided that I would have to visit. But as you can see from the photo above, the waste treatment facility (where the photo was taken) is quite far from downtown Kampala. I still do not know what was causing the odor in town.
The treatment plant was in the best operating condition of the four sewage treatment plants I have visited in Africa so far. James gave me a tour of the plant and showed me a window into the future of NWSC. . He is operations manager of the National Water and Sewage Corporation, a government company, and Head Honcho at the waste treatment plant. An ambitious young man with a Civil Engineering degree plus an MBA, James foresees a future of financial self-sufficiency for NWSC. He is not the typical government employee. With grants already approved by the KFW, GTZ, EU and African Development Bank, a €68 million plant will be constructed in Nakivubo starting at the end of 2011. Okay, so it will be financially self-sufficient AFTER they receive the grants but still. This plant would employ an anaerobic process and the biogas captured would be converted to electricity. The new plant would have a capacity of 45,000 cubic meters per day. The lower elevation of the new location would allow all of the sewage networks to flow by gravity alone. No need for pumping stations anymore. James has invested in house-to-house surveys to assess the ability to pay of different regions. “Some people cannot pay very much but others will pay anything to have their sewage removed,” he said. Charging appropriate rates is the first step to financial sustainability.
But enough about what could be. Based on my experience in Ghana, every city plans to overhaul the sewage treatment system in the next 5 years. Let’s talk about what is. Kampala has 7 treatment sites. Six are stabilization ponds at satellite locations with some coverage of the slums and the final one is the 33,000 cubic meter per day plant I will write about here. (The plant only receives 15,000 cubic meters per day. This says to me that the city is way behind in connecting houses to the sewer system if, after 30 years, the plant is only operating at half capacity.) The smell at the treatment plant was noticeable but not all that bad either. They had an odor scrubber system where the foul air around the preliminary treatment was routed to large plastic drums full of sawdust. I have never seen this kind of odor scrubbing system before. I wonder how well it works compared to the more complex chemical scrubbers in the US.
The inlet filter, James explained, was always getting clogged. Condoms were the most numerous offenders. At least people are using them, I guess.
The sedimentation tank had a thicker scum layer than I remember seeing at waste treatment plants in the US. In the photo above, the surface looks solid.
One of the causes for this is maggots. Much of the waste arriving at the waste treatment plant comes from pit latrines rather than through the sewage network. The sewage network connects to the homes of about 88,000 people. The rest of the people use latrines or open defecation. Some of these latrines are emptied by septic emptying trucks (others are emptied into the gutter—see my upcoming post on Bwaise slum). In latrines, flies can lay eggs which hatch into maggots. Much of the floating scum layer was maggots. (Dried maggots in the photo above.) In Nigeria we plan to use waste from latrines as a feedstock. I had not thought about this before, but it seems that we will have to deal with many maggots in our feedstock. I will need to do more research to see if this will be a problem.
The sludge from the sedimentation tank is sent to an anaerobic pit, covered with grass. Don’t be fooled, you would sink right into a smelly mess if you stepped on this grass. James said the grass is never cleared and instead helps keep the tank anaerobic. I do not think this is the way the tank was designed to work, but perhaps a little adaptation is necessary.
The two tanks shown here where built in 1976 as anaerobic digesters. But due to the civil war at that time, they were never, and will never be, used.
The sludge from the digesters is sent to drying beds for a few days. The sludge is sold for 10,000 USH (about 4.5USD) per cubic meter to flower farmers. James said that demand was low. The green plants in the bed are all tomato plants. Tomato seeds are one of the hardiest seeds there are and because the local diet is high in tomatoes, many tomato seeds pass through the human digestive system and through the treatment plant unscathed.
Removing the dried sludge is a hands on job. Here workers add sand to the drying beds. Afterwards, fresh sludge will be poured on top.
The liquid from the sedimentation tank is poured over a circle of rocks AKA the Trickling Filter. Bacteria further clean the water before passing the water to Lake Victoria at about 60 mg/L BOD and 15,000 coliform per 100mL, a little higher than local recommendations. The drinking water is pulled from Lake Victoria only about 5 km from the discharge site of the waste water treatment plant. I have heard that this has caused extra expense to the NWSC recently as the corporation has to spend extra money to purify the water to the desired levels for drinking.
The BIG Picture Kampala seems to be on the right path to an efficient waste treatment system for the middle and high income areas which are sewered or have the money to pay for septic emptiers. I found that I will not need to think about new waste management solutions for these areas as Kampala is already in the capable hands of James. Slums occupying the wet lands are another story.