Plant Solutions - Minerva W.W.T.P

The Village of Minerva is just east of Canton, Ohio on Route 30. Our W.W.T.P. is an activated sludge, extended aeration plant with a 930,000 g.p.d. design. Typically we get a 2% solids concentration sludge from the digestors and for many years we were able to land apply. Unfortunately, a few years ago we had to stop this land application due to problems with our sludge. This article deals with the way we coped with that problem and how, at the end of the day, we have come out ahead.

The Way It Was:

We were in trouble - that’s the way it was! We had metal in our sludge and the EPA told us we could no longer land apply. Hauling the sludge to a local disposal treatment facility became our only option. At 10 cents a gallon, however, we all knew it was only a very short term option. Meanwhile, we were slowly building up the amount of sludge we had in storage. When we got to the point of 550,000 gallons of stored sludge, it became apparent that something had to change!!

The Way It Changed:

In order to get out of the immediate jam we found ourselves in, we borrowed a 1.0 meter belt press. Then to tackle the long term problem, we hired CTI Environmental Inc., an engineering company based in Uniontown. Our aim was reasonably simple - dispose of our sludge and lower our costs. Their job was to conduct a feasibility study on the most efficient method of getting rid of sludge for the plant.

Various options were looked at including centrifuges, plate and frame presses and belt presses. After careful examination, the 20 year feasibility study produced by our engineering company concluded that a belt press would be the best option. We would be able to de-water our sludge and send it to a landfill for disposal.

However, another problem now presented itself. We had a small two story pump building with an even smaller door. It was the case of build a bigger building (more money!) or get a belt press to fit into our existing building. Something none of the belt presses we had looked at so far would do. Then the company who had loaned us the belt press offered to build us a press, disassemble it and then reassemble it inside our building After much consideration and adding and subtracting, it was agreed that this was the best route to take.

The 1.5 meter belt press we bought was manufactured by a company called OR-TEC, Inc. which is based in Bedford, just outside Cleveland. The entire system was delivered disassembled and then assembled as promised in the building. The stainless steel belt press, chemical dosing system and wash water pump are located upstairs in the building. The progressive cavity sludge pump was put in the basement to save space (I told you it was a small building!). It is controlled by an on/off/auto switch and speed selector on a control panel. The panel is mounted to the wall upstairs. The same panel controls all equipment related to the press in a manual or automatic mode.

Basically, this is how it works. Polymer is fed from a 55 gallon drum, activated by the automatic chemical dosing system and injected into the sludge. It is de-watered on the gravity drainage area of the belt with the aid of a series of ploughs, and then squeezed by two squeezing rollers before being removed from the belt by a scraper blade. A stainless steel auger moves the now de-watered sludge through a newly designed hole in the wall and discharges it into a hopper. The belt is continually cleaned by any automatic wash water system.

The Way It Is:

The belt press was started up on November 7, 1997 by OR-TEC and they spent two days training us in the use of the equipment. It took a surprisingly short amount of time to become familiar with the belt press and learn to operate it. Although we had begun to chip away at the backlog with the loaner unit, we were now anxious to de-water as much sludge as possible with our new press. We did this by coming in on weekends at first. Once we had the sludge down to a reasonable level we started to operate on a regular schedule. We anticipate that we will be running the machine approximately 16 hours per week once we have completely dealt with the stored sludge.

An in-line flowmeter fitted to the sludge line has proved an invaluable tool. We can tell from a digital LCD display beside the control panel exactly how much sludge we are running at any given time. This allows us to report to the gallon how much sludge we have processed. An hour meter on the panel tells us how long we have been running and we have kept an accurate record of our polymer usage.

The following performance summary is based on data we have collected and recorded since day one. From November 7th to February 24th, we processed 557,000 gallons of sludge at an average inlet solids concentration of 2%. This took a total of 334 hours. Taking into account the price of the hopper, the cost of emptying the hopper at the landfill and the price of polymer, it now costs us 2 cents a gallon to dispose of our sludge. That’s down from 10 cents a gallon! The other good news is that we no longer have metal in our sludge.

The Way It Will Be:

The next step will be to start land applying the de-watered sludge and save the landfill costs. We will be able to use an ordinary farm manure spreader for this. This is also a lot less likely to cause concern among people living close to areas designated for spreading, compared to the concern caused by spraying liquid sludge.

In Conclusion:

All in all, sludge de-watering has worked very well for us. We no longer dread long winters nor do we find ourselves at the mercy of wet springs. We decide when and how much sludge we de-water. Bring on the rain we say ... I’m having another coffee!!!

reprinted from From Hauling to De-Watering August 1998 Buckeye Bulletin