Secondary Liquid Waste Streams

Treatment systems such as the RRS and EDS that rely on chemical neutralization of agents produce secondary liquid waste streams of two types ... 

There appear to be a number of viable options for treatment of secondary liquid waste streams from systems such as the RRS, SCANS, and EDS, although further development work will be required (see the discussion of plasma arc systems, chemical oxidation, and wet air oxidation of neutralents and rinsates in Chapter 2 and Finding and Recommendation 2-11). 

The committee wishes to stress that this report is a supplemental evaluation that is focused on the destruction of EDS liquid waste streams. Nothing discussed here should be interpreted as the committee s evaluation of the EDS as a complete operating system. Such an evaluation would have to examine issues such as the structural integrity of the EDS with repeated use, operational procedures, and the EDS s process chemistry, and would have to assess whether a secondary vapor containment structure is needed. A broader discussion of the system itself could be considered in a future report on systems for the destruction of nonstockpile materiel. 

Liquid Waste Streams. Liquid waste streams may create disposal problems in Stretford systems (Tallon et al., 1984). Secondary reactions produce a limited quantity of thiosulfate and sulfate soluble salts. The concentration of dissolved salts in the circulating liquor increases until an equilibrium is reached between the amount of salts being formed and the amount of salts being removed in the sulfiir-cake. If conditions are such that the dissolved. salt concentration in the circulating solution reaches 25 wt%, some liquor has to be bled from the system. 

The DirCon freeze crystallization process is a technology that can be used to purify aqueous waste streams and concentrate liquid waste by the freezing and subsequent melting of the liquid. This technology is a type of direct-contact secondary-refrigerant freeze crystallization and operates on the principle that when water freezes, the crystal structure that forms naturally exudes contaminants from its matrix. The terms freeze crystallization and freeze concentration are often used interchangeably. 

Noncombustible or toxic liquid wastes that do not lend themselves to disposal by any of the means just outlined are the most difficult to dispose of safely. These kinds of wastes provide the strongest incentive for a producer to develop a use of the waste stream to minimize ultimate disposal costs. Thus, acidic pickling plant wastes, which contain iron plus unused sulfuric or hydrochloric acids may be used to precipitate phosphate from secondary sewage effluent (e.g., Eq. 5.25). Or they may be blended with aqueous alkaline wastes containing phenolate and unexpended sodium hydroxide to neutralize the pH extremes of both streams. 

A number of regulatory issues were raised by the Army s test results for the MCG/PLASMOX technology that must be resolved before it could be permitted in the United States. These include improvements to the gas scrubber system, more complete knowledge of the fate of key components of the non-stockpile CWM (e.g., phosphorus), and better characterization of the solid, liquid, and gaseous secondary waste streams. 

Some treatment options, such as the use of stockpile incinerators, would destroy the non-stockpile item directly. Others, especially those involving chemical neutralization, generate liquid secondary waste streams that require further treatment before disposal. This secondary waste treatment could take place in a commercial treatment, storage, and disposal facility (TSDF) or could employ one or more of the individual alternative technologies, such as chemical oxidation, either at the site where chemical neutralization takes place or at an off-site location. If secondary waste is defined as hazardous waste, such treatment would need to be conducted at a commercial TSDF permitted or approved by the appropriate regulatory authority under the Resource Conservation and Recovery Act (RCRA). 

Chemical oxidation Low-temperature technology potentially applicable to destruction of liquid secondary waste streams produced by the RRS, EDS, and other systems... 

The use of chemical oxidation to treat liquid secondary waste streams from the RRS and EDS has been discussed extensively in previous reports by this committee (NRC, 2001a, 2001c). 

Provided that chemical oxidation can be demonstrated to be effective in destroying NSCWM liquid secondary waste streams, no particular problems are anticipated in obtaining the necessary regulatory approvals. 

The use of batch supercritical water oxidation (batch SCWO) to treat liquid secondary waste streams of the EDS was reviewed in a previous report by this committee (NRC, 2001b). 

Finding 2-12a. The Army s plan to destroy highly organic neutralent waste streams by incineration is appropriate. Plasma arc systems are also adaptable to destruction of highly organic neutralents when incineration is not available or acceptable. Use of such high-temperature processes to destroy aqueous secondary wastes would be inefficient, although it may be expedient in some cases. If such aqueous liquids cannot be disposed via publicly or federally owned treatment works (POTW or EOTW), chemical oxidation or wet air oxidation may be attractive alternatives for this purpose. 

The radiation monitors associated witii the steam generator blowdown system provide a means of recognising when the secondary side becomes radioactively contaminated, an indication of a steam generator tube mpture. The blowdown flow and the ion exchange waste stream (brine) flow are both continuously monitored for radioactivity. If such radioactivity is detected, the liquid radwaste system is aligned to process the blowdown and ion-exchange waste effluent. If radioactivity should exceed a preset level, the blowdown flow control valves and the isolation valves would automatically close. 

The WRS includes two clarifiers, two thickeners, two filter presses, and auxiliary equipment. The ICB effluent is transferred to the WRS clarifiers, where a polymer will be injected to provide chemical coagulant for enhancing removal of suspended solids. The clarified effluent will be transferred to the BRS. The clarifier sludge will be pumped to the WRS thickeners, where a polymer may be added to enhance thickening. Thickener overflow is recycled to the clarifiers, and underflow is pumped to the dewatering filter presses. The Alter press separates the solids from the liquid stream. The liquid is recirculated to the clarifiers, and the filter cake, containing 20-25 percent dry weight sohds, is a secondary waste. 

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