Slowsand Filtration (SSF) for Reducing Costs of Desalting Surface Waters
For desalting surface waters, this study evaluates slowsand filtration (SSF) and reverse osmosis (RO) (SSF-RO) to achieve breakthrough cost savings of 20-30 percent compared to using conventional water treatment (CT) with RO or microfiltration (MF) with RO. Using Reclamation's Water Quality Improvement Center (WQIC) (see ), this project addresses the question:
* Does SSF effectively remove particulates from water so that RO desalting equipment can operate with little or no fouling?
Need and Benefit
Two recent Reclamation studies: Alternatives for Using Central Arizona Project Water in the Northwest Tucson Area (2000) and the Science and Technology (S&T) Program -sponsored Pilot Investigation of Slowsand Filtration and Reverse Osmosis Treatment of Central Arizona Project Water (Reclamation 2002) have produced exciting results. These studies estimate that for the subject locality, SSF costs 75 percent less than CT or MF water treatment. For filtration prior to RO desalting equipment, the studies estimated that with SSF, SSF-RO can reduce total desalting costs (including concentrate disposal by a low-volume CASI through Yuma) by a breakthrough 20 percent compared to CT-RO and MF-RO. A short-term five-month pilot test in 2001 and 2002 demonstrated that SSF effectively removes particulates that foul RO desalting equipment. In addition, SSF provides chemical-free filtration and thereby avoids the problematic fouling and scaling of RO membrane equipment from iron and aluminum salts and organic polymer additives used in CT-RO.
Because of SSFs low-cost and the 2001-2002 successful pilot test results with SSF as pretreatment to RO, Reclamation is considering SSF for the Yuma Desalting Plant (YDP), where CH2M HILL is investigating alternatives.
The proposed study consists of three parts:
1. Conduct SSF-RO pilot tests. SSF-RO pilot tests at Reclamations WQIC in Yuma Arizona evaluate the effects of independent variables: water supply (YDP feedwater and Colorado River water [CRW]), season, roughing filter, SSF filtration rate, RO recovery, and SSF cleaning technique on performance variables: SSF filtrate quality (dissolved oxygen [DO], hetro-trophic plate count [HPC], pH, total organic carbons [TOC], turbidity, silt-density index [SDI], and RO fouling rate), filter run length and volume, and RO scaling.
2. Estimate costs for SSF-RO and to modify the 72-million gallons per day (MGD) YDP to incorporate SSF
3. Transfer technology to Tucson area water providers who are considering SSF for a 40-MGD CAP water treatment plant
The proposed partnership with Reclamation's S&T Program enables inclusion of CRW in SSF-RO pilot tests in part 1, cost estimates of SSF and SSF-RO for treating CRW in part 2, and technology transfer in part 3.
Reclamation, 2002, Pilot Investigation of Slowsand Filtration and Reverse Osmosis Treatment of Central Arizona Project Water Advanced Water Treatment Research Program Report No. 90 .
Contact the Principal Investigator for information about these documents.