Evaluation and testing of fine mesh sieve technologies for primary treatment of municipal wastewater B. Rusten* and H. Ødegaard** *Aquateam-Norwegian Water Technology Centre, P.O. Box 6875 Rodelokka, N-0504 Oslo, Norway (E-mail: bjorn.rusten@aquateam.no) **Norwegian University of Science and Technology (NTNU), Dept. of Hydraulic and Environmental Engineering, S. P. Andersens vei 5, N-7491 Trondheim, Norway (E-mail: hallvard.odegaard@ntnu.no) Abstract Fine mesh sieve technologies were tested in full scale at several municipal wastewater treatment plants. A screening test was used to characterize wastewater and establish the design criteria for the sieves. To achieve high removal efficiencies it was crucial to operate the sieves with a filter mat. Rotating belt sieves performed best in the full-scale tests. A small dose of cationic polymer and a static flocculator ahead of a rotating belt sieve achieved excellent results on a wastewater that was originally found unsuitable for primary treatment with fine mesh sieves. Simple screw presses dewatered the sludge from the sieves to typically 25 – 30% total solids. Using fine mesh sieves with ,500 microns openings was found to normally be the most economical process for primary treatment. Keywords Filter mat; fine mesh sieves; municipal wastewater; primary treatment Introduction Due to the European Union (EU) requirements for wastewater treatment, the Norwegian State Pollution Control Agency (SFT) took an initiative to evaluate and test several different technologies for primary treatment. This R&D program was carried out with contributions from the Norwegian University of Science and Technology (NTNU), the national R&D organizations SINTEF and NIVA, the consulting companies Asplan Viak, Rambøll Norge and Aquateam, the cities of Bergen and Tromsø, and the regional water and wastewater utility company IVAR (Ødegaard, 2005). The goal was to find dependable and cost efficient technologies that fulfilled the strin- gent EU criteria for primary treatment. The primary treatment requirements are at least 20% removal of organic matter (measured as BOD 5 ) and 50% removal of suspended solids (SS). For treatment plants with 12 control samples per year at least 10 samples must fulfill the requirements. For treatment plants with 24 control samples per year at least 21 samples must fulfill the requirements. This is a lot stricter than looking at aver- age removal efficiencies and the R&D program showed that an average SS-removal of about 65% was necessary for enough samples to pass the 50% removal requirement. Several types of sieves, large septic tanks, clarifiers, dissolved air flotation (DAF) and deep bed filtration were initially evaluated. Of the technologies that were considered fully developed, clarifiers and different types of fine mesh sieves were found most suitable for primary treatment. These technologies were then tested in full scale at several treatment plants, for both primary treatment and chemically enhanced primary treatment. Historically, primary treatment has been synonymous with sedimentation in clarifiers. The R&D program revealed, however, that most primary clarifiers are unable to achieve primary treatment according to the EU requirements. Surveying of data from five treat- ment plants showed that only one plant fulfilled the EU requirements for primary Water Science & Technology Vol 54 No 10 pp 31–38 Q IWA Publishing 2006 31 doi: 10.2166/wst.2006.710 Downloaded from https://iwaponline.com/wst/article-pdf/54/10/31/431033/31.pdf by guest on 17 June 2020