GRANULAR MEDIA, CLOTH FILTERS AND MICROFILTRATION AS PRETREATMENT FOR UV DISINFECTION OF SECONDARY WASTEWATER
Abstract:To investigate the feasibility of a filtration/UV system to meet existing and future discharge requirements, pilot studies of different filtration / UV systems were conducted at the Sacramento Regional Wastewater Treatment Plant (SRWTP). The filtration technologies investigated included sand filtration, cloth (disk) filtration, and microfiltration. The comparison of the effectiveness of the different filtration / UV systems was measured by testing the following parameters: total and fecal coliform, enterococcus, cryptosporidium, giardia, TSS, COD, TDS, turbidity, total organic carbon, metals, trace organics, and endocrine disruptors. Four small-scale filtration systems were constructed and operated on site at SRWTP: (1) a continuous backwash downflow sand filter; (2) a disk filter with cloth at an initial pore size of 10×18 microns and later with a pore size of 11×11microns; (3) a pressurized microfilter with membrane pore size of 0.1 microns; and (4) a vacuum operated microfilter with a pore size of 0.4 microns. The sand filter and the disk filter were followed with low pressure/high intensity UV disinfection systems. The response of coliform bacteria in the effluent from the microfilters to UV light was evaluated using a low pressure collimated beam apparatus.
The filtration systems that were found to consistently remove particles greater than 10 ∝m include the size exclusion disk filter equipped with the 11×11 ∝m and the microfiltration units. The UV dose required to meet the coliform discharge requirements in the effluent from the disk filter was 100 mW·s/cm2. The vacuum operated microfilter requires a downstream UV dose of 20 mW·s/cm2 to meet the coliform discharge limits. The pressurized microfilter may not require any downstream UV treatment as it removed coliform to below the 23 MPN/100 ml discharge limit. Removal of other parameters followed a similar pattern with the order of increasing removal being disk filtration, sand filtration, vacuum operated microfilter and pressurized microfilter. Significant findings included the ability of all filtration technologies to reduce metals concentrations and persistent pathogens.
Document Type: Research Article
Publication date: 2000-01-01
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