The sewage treatment plant Obere Pleichach in Lower Franconia (Bavaria) was the last site where we tested our RoS 3Q 440 before winter 2006/07 arrived. At this site, the screw press dewatered aerobically stabilized sludge that had been gravity thickened to 6 – 8 %DS and included 45 % volatile solids. The achieved cake solids concentration of around 25 %DS and the solids capture rate of 97 % were within the expected range, but we were really surprised by the low polymer consumption of only 5 – 7 g active polymer per kg dried solids.
In February 2007, the plant’s management sent us their order for a container-mounted RoS 3Q system. A screw conveyor should forward the dewatered sludge cake out of the container and directly into their solar sludge dryer. Our customer was impressed by the low investment costs, the compactness and small footprint of our system, and by the screw press’ ease of operation. In April 2007, only 10 weeks later, we supplied and started up the 20’ container and the included pumps, polymer system, screw press and control panel.
We expected somewhat better results than during our previous test trials because we had improved a few details of the RoS 3Q design after our testing. But we were surprised by the result of our improvements. The performance of the supplied container system was far better than our guaranteed values. While we fed 140 kg/h dry solids, we achieved a cake solids content of over 29 %DS right after start-up; and after some optimization we achieved even 33 %DS. The solids capture rate of 98 % was also slightly better than during our prior testing. The polymer consumption was 7 – 8 g active polymer per kg of dried solids, slightly higher than before. Our screw press exceeded the performance of a belt filter press that was also tested on site and had achieved cake solids in the range of 28 – 30 %DS, and also the performance of a plate and frame press that had achieved a maximum of 32 %DS.
For almost a year now our screw press has been operated for 3 days, or 24 hours, per week without any problems. Our customers now operate our press with a polymer dosage of only 3 – 4 g / kgDS. They do not need very high cake solids because they have more than enough waste heat from cogeneration available that they use for dryer heating. It is sufficient if they feed their solar dryer with a 25 %DS sludge cake. In this way they save substantial polymer costs.
Since start-up, the sewage treatment plant Obere Pleichach has become a Mecca for other interested operators and consulting engineers who come to visit this very successful reference installation. During the entire year 2007 we have continued to perform on-site demonstrations and tests. In Germany alone we conducted 11 on-site tests and received 8 orders through this activity; the staff of the remaining 3 other plants were also impressed, but could not yet get a decision about their investment. Among the 8 sold presses, 3 are mobile systems, installed in containers or mounted on car trailers.
All our customers were convinced by the same benefits:
- Our screw press meets, or even exceeds, the performance of other dewatering machines that are far more expensive,
- Moderate investment costs,
- Minimal operation and maintenance costs,
- Consistent and reliable operation without any noise or vibration,
- Entirely enclosed and self-cleaning system without odour nuisance.
We would be happy to demonstrate the performance of our RoS 3Q press on your site and with your sludge. This year we have two more mobile units available for testing.