Written by Tom Welch, September 10, 2015
The Springfield, IL, Metro Sanitary District (SMSD) Sugar Creek Plant is going to be expanding over the next two years. They currently have no dewatering capability and they treat their liquid sludge with lime and liquid land-apply on their own fields onsite at the plant. In June of 2013, Schwing Bioset was invited to run a dual demo of their screw press and Bioset systems. The pilot study was conducted for two weeks where the Waste Activated Sludge (WAS) was dewatered with the screw presses and then converted to a Class A EQ product through the advanced alkaline stabilization Bioset process. Crawford, Murphy, and Tilly Engineers coordinated the pilot study for the District.
Prior to the pilot study, the plant operations team was leaning toward using belt presses for their future dewatering needs. They had familiarity with belt presses and they were concerned that screw press technology did not have the capability to meet their requirements of 2660 dry pounds per hour without having to install a large number of screw press machines. They were basing their concerns on historical screw press throughput capability based on their market research.
(Pilot Study Setup at SMSD Sugar Creek Plant)
During the pilot study, the Schwing Bioset team brought their FSP 600 screw press machine to dewater the partially aerobically digested WAS. The goal was to dewater the material to the highest percent solids, with an excellent capture rate, and also with the least amount of polymer consumption. The dewatered product would then be passed along to the mobile Bioset operation, which is an advanced alkaline stabilization process that can produce a Class A EQ Biosolid end product that can be utilized as a fertilizer or a soil amendment.
The first week of the demo was utilized to optimize the screw press performance, and the second week to monitor continued performance of the screw press while utilizing the Bioset operation to produce a Class A EQ product. The purpose of this was to monitor the product over a couple month period to determine the stability of the Class A EQ product at the Springfield plant. Over the two weeks, the FSP 600 screw press unit produced a dewatered product of 30% solids on average, even while operating the machine at 130-150% of design throughput capability. After polymer optimization, the end result was realized with 14 pounds of active polymer per ton and the capture rate was above 95% during the entire two week period. During the second week of the pilot, the Bioset system was utilized the entire time and was successful in producing the Class A EQ product.
Based on the successful results of the pilot, SMSD gave Crawford, Murphy, and Tilly the direction to design the new biosolids handling facility to include two high-performance screw presses, each capable of dewatering 1330 dry pounds per hour. Although they liked the simplicity of the Bioset Class A operation, they were uncertain if the need for Class A was justified for the new facility. They settled on a Class B Bioset system that utilizes all of the components of the Class A design, except for the reactor. Space was left in the building to install the reactor in the future should Class A become necessary. The job bid in December of 2014 and Schwing Bioset received an order for the two high-performance screw presses and the Class B alkalization system in early 2015.
These FSP 1102 screw presses showcase the capabilities of high-performance screw presses and offer larger plants an appealing alternative to traditional belt filter press or centrifuge dewatering.
(Class A EQ product at 44% solids)
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