Aqueous waste streams

Example 11.1 A process produces an aqueous waste stream containing 0.1 mol% acetone. Estimate the COD and BOD of the stream. 

Inorganic heavy metals are usually removed from aqueous waste streams by chemical precipitation in various forms (carbonates, hydroxides, sulfide) at different pH values. The solubiUty curves for various metal hydroxides, when they are present alone, are shown in Figure 7. The presence of other metals and complexing agents (ammonia, citric acid, EDTA, etc) strongly affects these solubiUty curves and requires careful evaluation to determine the residual concentration values after treatment (see Table 9) (38,39). 

Granular media filtration is used for treating aqueous waste streams. The filter media consists of a bed of granular particles (typically sand or sand with anthracite or coal). The anthracite has adsorptive characteristics and hence can be beneficial in removing some biological and chemical contaminants in the wastewater. This material may also be substituted for activated charcoal. 

We will be examining these subjects in a little more detail in the next chapter. But for now, we should cover some of the basics because of their importance to sand filtration. The process of flocculation is applicable to aqueous waste streams where... 

Flocculation and sedimentation arc two processes used to separate waste streams that contain both a liquid and a solid phase. Both are well-developed, highly competitive processes, which arc oflcii used in the complete treatment of waste streams. They may also be used instead of, or in addition to, filtration. Some applications include the removal of suspended solid particles and soluble heavy metals from aqueous streams. Many industries use both processes in the rcmowal of pollutants from their wastewaters. These processes work best when the waste stream contains a low concentration of the contaminating solids. Although they are applicable to a wide variety of aqueous waste streams, these processes arc not generally used to treat nonaqueous or semisolid waste streams such as sludges and slurries. 

The process needs input of lime and water next to the PVC waste. No energy input is needed since the organic condensate provides for the energy needed in the process. Energy needed for pretreatment can be up to 25-35 kWh/tonne. Downstream separation of the coke products needs another 30-40 kWh/toime. The process does not emit dioxins, metals or plasticisers. Due to internal recycling there are no aqueous waste streams. The reaction of lime with HCl forms some CO2. The coke product provides a calorific value. 

Making paper without pollution requires that each part of the process be nonpolluting. The chemicals most commonly used in the production of pulp are NaOH and Na2 S. In modem paper mills, sulfur-containing by-products are scmbbed from the plant exhaust, and the aqueous sodium hydroxide is reclaimed and recycled. The fillers used to make paper opaque—titanium dioxide, calcium carbonate, and kaolin (a clay)—are natural, nonpolluting minerals. The polymer binders and sizers are relatively easy to recapture from the aqueous waste stream. 

Heitkamp MA, V Camel, TJ Reuter, WJ Adams (1990) Biodegradation ofp-nitrophenol in an aqueous waste stream by immobilized bacteria. Appl Environ Microbiol 56 2967-2973. 

A very useful, but difficult, case has been reported by Smith and Barclay (1992) for the recovery of Monsanto s highly successful herbicide, glyphosphate (N-phosphonomethyl-glycine, tradename Roundup), from an aqueous waste stream. This stream contains a lot of unwanted products like HCHO, HCOOH, aminomethylphosphoric acid, and N-phosphonomethyl iminodiacetic acid (PMIDA). The removal of PMIDA and HCOOH from glyphosphate is essential as HCOOH can react to give the formyl derivative. Amberlite IRA-93 and Amberlite IRA-68 (anionic resins) were chosen to separate glyphosphate from PMIDA and HCOOH, respectively (HCHO does not get adsorbed). 1500 recovery cycles were tried, and the resin has two years plant life scale-up with a factor of 90,000 was very successful. 

Volkov (1994) has given a state-of-the-art review on pervaporation. A number of industrial plants exist for dehydration of ethanol-water and (.vwpropanol-water azeotropes, dehydration of ethyl acetate, etc. There is considerable potential in removing dissolved water from benzene by pervaporation. The recovery of dis.solved organics like CH2CI2, CHCI3, CCI4, etc. from aqueous waste streams also lends itself for pervaporation and pilot plants already exist. 

Membrane process for recovery of valuable organic chemicals from aqueous waste streams containing electrolytes... 

Acetone is to be recovered from an aqueous waste stream by continuous distillation. The feed will contain 10 per cent w/w acetone. Acetone of at least 98 per cent purity is wanted, and the aqueous effluent must not contain more than 50 ppm acetone. The feed will be at 20°C. Estimate the number of ideal stages required. 

Phytofiltration, a specific strategy of phytoremediation, is the use of plants to remove contaminants from water and aqueous waste streams. Three different systems (Figure 10.1) can be considered within this strategy (a) rhizofiltration (the use of hydroponically cultivated plant roots),31112 (b) constructed wetlands (CWs) and lagoons, and (c) bioadsorbents-based systems.1... 

This paper reports on measurements made in three areas pertaining to the processing of aqueous waste streams as follows. 

These components concentrate in aqueous streams and represent a serious pollution threat because of their toxicity. For this reason they must be recovered from any aqueous waste stream before leaving a plant. 

The results of this study are summarized in Table 4. The product is isolated by filtration of the reaction mixture through a silica column, thus avoiding an aqueous waste stream. 

Ensol is a flocculent and complexing agent that is be used for the ex situ treatment of contaminated aqueous waste streams. According to AER Labs, it works by binding with contaminants, making them precipitate more rapidly and easier to filter out of a waste stream. 

The Aeromix BREEiZE is an air stripping system for removal of ex situ volatile organic compounds (VOCs) from aqueous waste streams. The BREEZE is commercially available and has been used in numerous remediations. 

MPP extraction (MPPE) technology is applicable to aqueous waste streams contaminated with compounds with a higher affinity for the extraction liquid than for water. Water-miscible compounds such as alcohols and ketones have low affinities for the immobilized extraction... 

The INCA system can recover virtually any target metal in any aqueous waste stream containing up to 60% solids. Applications include on-site remediation of mining effluents and contaminated groundwater. The INCA system can also be used as an in-process treatment system for manufacturing processes where metals in solution are a problem. The modular unit can easily be used in tandem with other technologies, such as those that remove hydrocarbons, as part of a total treatment train. 

Phytotech also developed a related technology, called rhizofiltration, that uses adsorption by plant roots to remove metals from aqueous waste streams. This process involves the use of hydro-ponically grown plants to filter out targeted contaminants. Both technologies are commercially available through Edenspace. 

EnviroSep, Inc. (EnviroSep), has developed a thick-film absorption technology for the removal of volatile organic compounds (VOCs) from water. The technology uses a proprietary form of silicone rubber to absorb contaminants. The vendor claims the technology is effective for VOCs with less than 2% solubility in water and a boiling point of less than 200°C for the pure compound and is most efficient for use at sites with contaminant concentrations between 10 parts per million (ppm) and 2000 ppm. The technology is intended for aqueous waste streams. 

Freeze concentration processes are based on the difference in component concentrations between solid and liquid phases that are in equihbrium. Most minerals and many organics grow less soluble in water as the temperature decreases. When an aqueous solution is cooled, ice usually crystallizes as a pure material, and dissolved components in the aqueous waste stream are concentrated in the remaining brine, thereby reducing the volume of waste. 

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. 

Wet air oxidation is applicable to aqueous waste streams containing organic and oxidizable inorganic materials where ... 

ShallowTray air strippers are low-profile, transportable units for removal of volatile contaminants from aqueous waste streams and potable water supplies. Air strippers do not destroy contaminants but transfer them to the airstream, where they can be destroyed by incineration or oxidation, removed by activated carbon, or released into the atmosphere if relevant emissions criteria are met. 

The Polylonix Separation Technologies, Inc., polymer filtration is a separation technology that removes metals from aqueous waste streams. Specialized, water-soluble polymers are added... 

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