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Technology Deep Dive - Want Higher Solids Content in Biosolids Products? Consider This Alternative to Applying the Heat

Technologies like belt presses, screw presses, rotary fan presses andcentrifuges dewater biosolids and water treatment sludges effectively.

But what if circumstances require material with higher solids content than those devices can provide? For example, what if a landfill suddenly requires material at 40% solids instead of 20%? Or what if the cost of hauling material at 20% solids becomes too high to sustain?

One option is to add a thermal dryer to the process, essentially boiling off some of the excess water. Another option, new to the United States, is an electro-osmosis dehydrator, a technology that uses electric fields to pull the water out of the material.

That’s the ELODE system, distributed by Charter Machine Co. It removeswater at much lower cost than thermal drying. The system comes in a compact footprint and is easily installed downstream of a facility’s mechanical dewatering process. Walter Kuehnrich, vice president and owner, and Christopher Boyd, director of sales, both of Charter Machine, talked about the technology in an interview withTreatment Plant Operator.

What is the background of this technology?

Kuehnrich:This is a proprietary technology that has been on the global market for about 15 years.

ELODE is the manufacturer, based in South Korea. Charter Machine has the distributorship rights for the technology in the United States. We also manufacture a variety of dewatering equipment. 

Where does this product fit into the water and wastewater market?

Kuehnrich:Presses and centrifuges all operate in the range of about15-23% solids. After that, traditionally, the next level of technology was dryers, achieving 60% solids and up. There was nothing in that in-between range. The capital equipment cost and the footprint for dryers is enormous.We fit into a niche beyond presses and centrifuges, but before thermal dryers.

Where is the market niche for this technology?

Boyd:It is not a stand-alone dewatering system. It is an enhancement to an existing dewatering system, and it is retrofittable to any application. The main concept is that you are doubling the cake solids content. If you are at 15% solids, we can get at least 30% out of it. If you’re at 20%, we can get to at least 40%.

What is the basic business case for ELODE technology?

Boyd:It is completely economic-based. If you’re paying $60 or $70 a wet ton to landfill cake solids, you can cut your cost in half by using our equipment. After paying for the equipment and the electricity, there is a very short payback. If you are applying material to a farm one mile from your treatment plant, this would not be a cost-effective solution. But for large cities paying high rates for landfilling, it can be very attractive.

What payback times are achievable?

Boyd:It all depends on the application, but we have seen payback as low as less than a year, in some cases three or four years, or in other cases pushing five years. At payback beyond five years, most facilities would not consider this technology.

Is this technology ever used ahead of a pelletizing process?

Boyd: No. Pelletizers require a very specific cake solids content comingin. They don’t function well at more than 23-24% solids, because there needsto be a wetted product that can be molded into pellets as the material is drying.ELODE is more for a facility that is getting 16-17% cake solids, and all of a sudden the landfill says it will not take materials as less than 20%. We can take that material at 16% and make it 30%.

What makes this solution more energy efficient than traditional drying technology?

Boyd:We’re not using heat and we’re not boiling off the water, which is very inefficient. It takes almost nine times as much energy to boil away waterthan to heat it from room temperature to the boiling point. We use an electricfield to drive the water out of the material. Our technology generates some limited heat, but that is not the principal technique for removing the water.

Please describe in basic terms how this technology works.

Boyd:The dewatered cake is fed into the unit, which includes a distribution chamber where it is flattened onto a belt. It then enters the dewatering system where the material is trapped between the belt and the surfaceof a drum. The tension on the belt is just enough to hold the material in contact with the drum and keep it moving through the unit. There we apply a DC current that realigns the molecules in the water and the solid material, so that the water can be released. In two or three minutes inside the machine, the solids content is doubled. The water drains off through the belts into a sump and is returned to the facility headworks.

How much energy does this process require?

Boyd:It uses roughly 120 kWh per 2,000 pounds of wet material, or 120 kW per ton of wet cake, on average. That is more energy than for mechanical dewatering, but nowhere near as much as for a thermal dryer.

What is involved in an installation?

Boyd:It depends on the plant layout. Is there space behind a belt press or next to a centrifuge? If not, they just have to put in some conveyance from the dewatering equipment to a hopper that feeds the ELODE unit, which is about the same size as a belt press.

How are you demonstrating this technology to prospective users?

Kuehnrich:We take a full-scale unit on a trailer to customer sites. The neat thing about this equipment is that it only takes three minutes to get a result. Once you fire it up, you just feed in buckets of material, and within three minutes the dewatered samples come out the other side.

Is there a need for any polymer or other thickening agent?

Boyd:No. You just put the cake in and take the dewatered cake out.

Are there any differences in performance with, say, primary or waste activated sludge, or a mixture of the two?

Boyd:We haven’t seen any difference. We run a conductivity test of the sludge, as conductivity dictates the amount of amp draw required. You do need to build the electric field and have some of the electricity go through the cake solids. With about 95% of sludges, there is no issue.  

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As a leading U.S. manufacturer of wastewater and bio-solids management equipment, CMC offers unmatched capabilities to meet the diverse needs of this critical industry. Our extensive experience and expertise allow us to work closely with operators and engineers, ensuring our equipment delivers optimal functionality and reliability. Our comprehensive approach, from design and engineering to installation and after-sales support, establishes CMC as your trusted full-service supplier.