Disposal backwash water

Filter runs will vary with influent load and filter rate. Generally, however, the filters are designed to operate in the range of IS to 30 hours so that backwash water percentages are usually 2 percent or less. This minimizes disposal problems of the backwash water. Automatic operation of the filters is also suggested to reduce operator attention requirements. Backwash is generally initiated on filter hcadloss or on time. 

According to the TCLP Method 1311 (EPA SW 846) (40), for a liquid waste containing less than 0.5% solids, the liquid portion of the waste after filtration is defined as the TCLP extract. For a microfiltration system operated at a 2.5 mg Fe(III)/L dose, 2.8 gpm flow rate (1.4 gpm/m ), and 29-min backwash interval, and assuming that all the solids are removed from the filter upon backwash, the backwash water (assuming a backwash volume of 1.8 gal/m ) will have a solids content (calculated) of 0.01% (by wt). Arsenic concentration in such a filtered backwash water (average of 20 filtered samples) was determined to be 2.6 2.4 ug/L. The backwash water can thus be directly disposed as a nonhazardous waste assuming that the arsenic TCLP limit stays at its current value of 5000 fig/L. 

The regeneration/filter backwash waste disposal area grouping includes those units that have received corrosive regeneration wastes from the 163-N demineralization plant and filter backwash water from the 183-N filtered water plant. This area has five potential sources. 

In many countries the regulations for disposal are very exigent, and in this way treatment plants must treat the backwash water that is used during the normal operation. In the United Kingdom, there is a drinking water plant that used two units of ultrafiltration in its process. The first one is a pretreatment for RO units, and the second one is to treat the water used in the cleaning of the membranes. 

A number of major disposal areas for backwash water exist The source water from which it came, the nearest wastewater pollution control plant, and a sanitary landfill or other means of land disposal. The choice of ultimate disposal option will dictate the type of treatment required and the degree of concentration needed to prepare it for that method of disposal. 

Table 8.3 compares performance parameters or multimedia pressure filters and HEFs. The higher throughput of HEFs reduces the footprint of the system required when compared to multimedia filters. Also, the lower backwash flow requirements for HEFs leads to less waste water to dispose of and smaller backwash components, on these filters. 

This is suitable for treatment of water containing considerable amounts of dissolved solids. The fraction of water rejected can be on the higher side (depends on the treated water quality desired) and one should check if there is any problem at site for disposal of the wastewater generated due to backwashing of sand filter, active... 

N-l Filter Backwash Discharge Fond. The 130-N-l filter backwash discharge pond 1s a percolation pond used for disposal of effluents generated during backwash of the sand filters In the 183-N filtered water plant. The pond Is a natural basin, marsh-like In appearance, located about 0.8 km (0.5 ml) southeast of the N Reactor building. 

The filter backwash discharge pond was placed In service In early 1983 following reconstruction of the 120-N-l percolation pond, which was formerly used for disposal of the backwash effluent. The pond Is fed via a 25- to 30-cm (10- to 12-1n.) burled line from the 183-N filtered water plant. Approximately 1,100,000 L/day (300,000 gal/day) of backwash effluent were disposed of at the unit. The 183-N filter backwash effluent has a neutral pH and contains low concentrations of several anions and cations (DOE-RL 1990). Aluminum sulfate (alum) Is used as a flocculent and polyacrylamide Is used as a filter ald/coagulant In filtered water production (DOE-RL 1990). Analysis of the filter backwash effluent Indicates that It does not contain any listed dangerous wastes or dangerous waste sources, or exhibit any dangerous waste characteristics or criteria per WAC 173-303 (DOE-RL 1990). Table 5-9 shows representative analyses of the filter backwash effluent. 

The disadvantage of this system is that filtered water must be stored and then pumped through the filter. The resulting backwash fluid must then be directed to another storage medium. A method and equipment for disposing of the backwash fluid, which can be contaminated with oil or acid used in the backwash cycle, must also be provided. 

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