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EFFECT OF HYDRAULIC LOADING AND CHEMICAL ADDITION ON FILTER PERFORMANCE AND PROTOZOA REMOVAL; A SIDE-BY-SIDE COMPARISON

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Giardia and Cryptosporidium are two protozoan parasites that have initiated concern due to their presence in wastewater and their ability to cause gastrointestinal illness. Results of our previous studies indicate that significant populations of these organisms exist in secondary treated effluents particularly with Giardia. Due to their resistance to disinfection processes utilized in water reclamation treatment, removal of these pathogens is dependent in part on filtration. Reclamation facilities have historically used media, such as sand and anthracite for removal of suspended solids and turbidity. Our filtration studies have shown up to 3-log10 removal of Cryptosporidium and Giardia by sand filtration. New filtration technologies are now available that allow for higher loading rates and increased throughput. Disk filters utilizing cloth media have efficiently reduced turbidity and Total Suspended Solids (TSS) to meet permitting requirements when operated under design conditions.

The primary goal of this study was to compare the removal of Cryptosporidium oocysts and Giardia cysts and indicator bacteria by two different filtration technologies: a cloth media disk filter and a dual-media (sand/anthracite) traveling bridge filter. The two types of filters were tested under various hydraulic loading rates with and without the use of chemical coagulants and received post secondary clarifier effluent from the same treatment train. Through a series of independent events, the hydraulic loading rate of each filter was increased from the design surface loading rate to two times the design rate. A polyaluminum chloride coagulant (PAC) was added to each filter at various doses to evaluate the effect on filtration in relation to the loading rate. Operations staff cleaned each filter prior to each event and carefully controlled the flow to each filter to insure uniform loading. Samples were collected at three sites: post secondary clarifier effluent (influent to filters), cloth media disk filter effluent and dual-media traveling bridge filter effluent. All samples were analyzed for Cryptosporidium, Giardia, fecal coliforms, total suspended solids (TSS), turbidity, ammonia, Total phosphorus, and total kjeldahl nitrogen (TKN) and N-nitrosodimethylamine (NDMA).

The initial study was conducted to establish background data for both filters at recommended loading rates. When the cloth media disk filter was loaded at 4.13 gpm/ft2, turbidity and suspended solids were reduced from 1.60 NTU and 3.33 mg/L to 1.40 NTU and 2.50 mg/L respectively. The dual media sand filter was loaded at 2.12 gpm/ft2 with the same quality influent and reduced turbidity and suspended solids to 0.74 NTU and 1.50 mg/L. For the pathogens a 1-log10 removal for Cryptosporidium and Giardia was found with a 90.29% removal of Cryptosporidium and a 66.85% removal of Giardia on the cloth filter and a 93.51% and 89.12% removal on the sand filter. This paper will present a report of the on-going project and discuss the various parameters used to optimize cloth and sand filter efficacy.

Further studies will be performed to determine the removal of Cryptosporidium oocysts and Giardia cysts under normal operating conditions, where filter-loading rates may vary due to the plant's flow rate.
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Document Type: Research Article

Publication date: 01 January 2004

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