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| | | Junior Member
 
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Last Login: 12/23/2007 9:29:28 PM
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| | Hi. Can anyone suggest what is the best way to dewater primary sludge and WAS mixture. It is very difficulty to process it in our belt presses. Even with higher polymer dosage, the output is minimal and the pressed cake is very soft. Our clarifier level is steadily increasing and we have to take the sludge out of the system faster. We have tried reducing the WAS flow but the problem is solids build up. We also tried diverting some of the WAS back to the WWTP but we encountered more problems in the primary clarifier. The WAS seemed to have decayed, floated and caused septicity in the clarifier. Do we need other equipment to process the WAS alone so that the primary sludge will solely go the belt presses? |
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| | | Supreme Being
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| | | Supreme Being
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| | Is the settleability of the activated sludge in your plant generally good or bad? Regards TerryF |
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| | | Junior Member
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| | No, we don't have a digester. |
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| | | Junior Member
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| | Settling is generally good. |
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| | | Junior Member
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| | I know of three ways of dewatering pure WAS. These are; DAF, Gravity Drainage Deck and Centrifuge. They are all high tech options. DAF has the advantage of not requiring polymer, whilst the other two do. You can contact Smith and Loveless for Gravity Drainage Decks. Have you considered co-settling in the primary sed tanks (assuming you have sufficient ret'n time) and then a gravity thickener. This is a way to upgrade anaerobic digesters at the limits of capacity (retention times of 18 days). Thickeners usually require odour control.
Regards
Grant H, Australia |
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| | | Forum Newbie
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| | You may want to look into Rotating Drum Thickeners. They do use polymer but have a small foot print, uses less energy than centrifuges, and you can control the odor better than a DAF process. There are a couple of manufacturers that I know of. |
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| | | Supreme Being
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| | I saw a Huber press in Tremonton Utah running more or less the same kind of sludge you are talking about, looked good. They took the "dry" sludge to a compost facility and seemed happy with the results. Me, I like centrifuges. But I got to run them at a place that could afford them, not every place can. Since you are not putting the stuff in a digester, I am guessing you need 18% or better to put into a dump truck. DAF, RST and GBT are out. So what about a rotary fan press? Prime solutions and Fournier make them. Or a screw press? The FKC screw press is built like a tank. Excluding the fan press, I have run some brand of each piece of equipment mentioned and a few more. Anyone remember a coil filter? Oh, and I hate belt presses! The rotary fan press seems to be the up and coming unit for smaller plants looking for 16-20% solids. Mark |
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| It's always better to thicken the WAS separately, if possible. You can blend it afterwards with Primary to improve the WAS dewatering. Problem is that you will reduce the Primary's final dryness.
My recommendation of an optimal installation would be:
Stream A: Thicken WAS using DAF or GBT (in 2%, out 8% solids), dewater belt press (in 8%, out 14% solids) and final dewatering using Elcotech electro-dewatering (in 14%, out 40% solids).
Stream B: Thicken Primary using GBT (in 3-4%, out 10-12%), dewater Fournier Rotary Press (in 10-12%, out 35-40%).
Your final product would be in the range of 35 to 40% solids, a great product for co-generation. Automated operations, very slick, cutting-edge technology and affordable if operated automated long hours.
Would this fit with your situation?
Scott
smckay@elcotech.ca
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| | | Forum Member
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| | Since you already tried to route some of your WAS through your primary treatment process I would not suggest trying that again. How are you thickening your WAS is my question. I worked at a plant that thickened its WAS via DAF's with polymer to around 4-6% solids. We stored it in an aerated, covered tank. Later we combined thickened primary with thickened WAS sludge and added polymer to it. This mixture went into a rotating conditioning drum before going to the belt press and then to an incinerator. We were able to get 20% solids off of the belt press at around 4 tons per hour to the incinerator. The older the secondary sludge the harder it is to dewater it later. Otherwise, there shouldn't be any problems unless you use an improper polymer for your particular sludge. ~Egadz |
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