Backwashing disposal

Preparation of filter body feed (diatomaceous earth) and precoat Verification of proper dosages Periodic backwashing Disposal of spent filter cake... 

Similar to filter backwash, the concentrate from these membranes requires treatment before it can be disposed of with the membrane concentrate. However, the total amount of solids produced after the treatment of filter backwash can be 60-80% greater than MF and UF concentrate due to the addition of coagulants prior to the granular media filters (Bergman 2007). 

However, because both acids and bases are used in cleaning, it may be possible to store these chemicals in a stirred buffer tank to allow the solution to neutralise. This solution may then may be slowly added to the concentrate waste to dilute it and allow for a safe disposal (Mauguin and Corsin 2005). Note that the volume of this discharge is much lower than both the concentrate and filter backwash discharges. 

After treatment has proceeded for a period of time, either the coating reaches its maximum capacity to remove metals or the filter requires backwashing. At this time, the column can be backwashed to recover particulate metals from the column, and an acidic solution can be used to recover the adsorbed metals, thereby regenerating the column. Because the ferrihydrite is trapped on the sand particles, only the contaminant metals and nonferrihydrite are released. Thus the need to dispose of large amounts of iron oxide with the metal sludge, one of the main drawbacks of a conventional treatment process, is eliminated. 

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. 

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. 

The desulfurized slurry from both processes is pumped to a filter press. Soluble sodium sulfate and carbonate/hydroxide (depending on the reagent used) are removed through a series of backwashing and rinsing cycles. The solid product, once dried, is ready to be charged to the furnace whilst the soluble sodium sulfate is either disposed of via the plant s effluent system or is reclaimed as a solid product, similar to that in the caustic soda/acid neutralization process outlined above. 

Several plate and frame MF units have been installed in Japanese nuclear power plants. The units operate with automatic periodic backwash using accumulated filtrate. Typically, the units backwash every 3 hours at a back pressure twice that of the final forward pressure. The backwashed crud is removed from the system as concentrated RAD wastes. In this sense, these back-wash systems are not dissimilar to cross-flow units using MF or UF-membranes. In either case, a reject stream containing concentrated crud must be disposed of. 

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. 

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... 

Porous carbon filters for mercury usually operate at pressures up to 8 bar. The housings are nickel or nickel-coated carbon steel. The pores in the tubes have diameters less than 50 xm. Filtration face velocities range from about 0.5 to 2.0mhr . The content of suspended mercury is reduced from 10-30 ppm to less than 0.5 ppm. Results are better with lower velocity, lower caustic temperature, and the recycle of some of the filtrate. Many plants use multiple filtrations, perhaps with higher unit rates in the second step, and achieve lower mercury content in the effluent. Leaf filters packed with specially treated activated carbon are an alternative. These usually operate at lower temperature (60-65°C) and sometimes are used as two stages in series. The mercury concentration is reduced to 1-5 ppm in the first stage and to less than lOppb in the second. The spent carbon is backwashed from the filters and allowed to settle in a hold tank. The supernatant weak caustic can be used in brine treatment or pH control, and the carbon itself is stripped in a mercury furnace before disposal. 

Regeneration/Filter Backwash Waste Disposal Area... 

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. 

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. 

Regeneration/Filter Backwash Uaste Disposal Area Grouping ... 

Submit 216 Application for 100-N Sanitary Waste Disposal Facility and 183-N Filter Backwash June 1994... 

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