More than 96% sludge volume reduction: Big HUBER Screw Press units convince international customers

Schematic diagram of a RoS 3Q Screw Press
Schematic diagram of a RoS 3Q Screw Press

Screw presses for sludge dewatering have become an accepted and well-proven alternative for decanters. HUBER RoS 3Q screw presses have previously been used mainly on wastewater treatment plants smaller than 20,000 PE. Recently, however, also more and more operators of bigger plants have become aware of the advantages screw presses offer in terms of operating reliability, dewatering results and energy efficiency.

RoS 3Q 800 installation in Georgia
RoS 3Q 800 installation in Georgia

HUBER could win the contract for the supply of a sludge dewatering plant for a new 140,000 PE wastewater treatment plant to be built on the Georgian Black Sea Coast where statically thickened and aerobic stabilised (10 m³/h each) with 3% solids content should be dewatered to at least 20% to reduce sludge volume prior to solar drying. HUBER supplied two RoS 3Q 800 Screw Press units.

Measurements during plant start-up showed that the sludge had a solids content of only 0.7 – 1%, i.e. it was not statically dewatered. The results achieved by the screw presses were therefore all the more surprising: Dewatering degrees of 29 – 33% were achieved right from the beginning with a throughput of 15 m³/h. The local operators optimised polymer dosing and could thus reduce coagulant agent consumption from initially 12 to 8 kg/t DR. Even with these low polymer doses the dewatering degree measured was still continuously 33%. The screw presses reduce sludge volume prior to solar drying by 97%. Even with this extraordinary sludge volume reduction power consumption of the screw press unit lies still below 1 kW.

Installation with two RoS 3Q 800 units in the USA
Installation with two RoS 3Q 800 units in the USA

It was less surprising, however, that another installation with two RoS 3Q 800 units in the Northeast of the USA achieves also dewatering degrees in excess of 30% with an inlet solids content of only 1%. This high dewatering efficiency was already proven before through extensive on-site testing with the RoS 3Q 880 in 2009. The customer’s old belt filter press achieved only 15% at the same time. Furthermore, the belt filter press caused high repair costs and incalculable expenses for personnel because the press had to be cleaned very often when it was flooded due to strongly varying solids contents in the sludge inlet. With the closed design of the HUBER Screw Press and its automatic dewatering pressure control machine flooding or breakthrough is impossible. The decisive factor why the customer decided to buy our screw press was not just the excellent dewatering result but rather the fully automatic self-monitoring operation of the HUBER RoS 3Q.

What was more unusual was the customer’s request to guarantee 26 m³/h throughput with a redundant system design. On the basis of the scale-up of the RoS 3Q 280 test results only 18 m³/h could have been expected for the big Q 800 unit. When the customer finally agreed to a reduced dewatering degree of 25%, two RoS 3Q 800 units were installed. The performance test revealed again positive surprises: Dewatering degrees in excess of 30% are achieved with 26 m³/h throughput. Polymer consumption is the same as during on-site testing of the small RoS 3Q 280, namely 9 kg/tDR. The screw shaft of the big RoS 3Q 800 operates with a speed of only 0.6 rpm, it could therefore handle even higher volume flows if it was run at the maximum speed of 1 rpm. With 3 kW, also this screw press needs less electric energy than the upstream thin sludge pump.

 
Both RoS 3Q 800 twin installations achieve a sludge volume reduction in excess of 96% with only minimum energy consumption. Furthermore, direct dewatering of the thin sludge avoids all additional costs that would incur for the operation of an upstream mechanical thickening system.