Humic flocculation

In some systems, such as lake and river waters, the suspended inorganic particles may be coated by biological polymers, termed humic substances, which prevent flocculation by either steric or electrostatic mechanisms. These can also interact with added inorganic salts (31) that can neutralize charged functional groups on these polymers. 

In the area of municipal and iadustrial wastewater treatment, the principal environmental issue is the toxicity of residual flocculating agents ia the effluent. Laboratory studies have shown that cationic polymers are toxic to fish because of the iateraction of these polymers with giU. membranes. Nonionic and anionic polymers show no toxicity (82,83). Other studies have shown that ia natural systems the suspended inorganic matter and humic substances substantially reduce the toxicity of added cationic polymer, and the polymers have been used successfully ia fish hatcheries (84—86). Based on these results, the EPA has added a protocol for testing these polymers for toxicity toward fish ia the presence of humic acids (87). The addition of anionic polymers to effluent streams containing cationic polymers to reduce their toxicity has been mentioned ia the patent Hterature (83). 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Schofield RK, Samson HR (1954) Flocculation of kaolinite due to the attraction of opposite charged crystal faces. Discuss Faraday Soc 18 135-145 Schofield RK, Samson HR (1953) The defiocculation of kaolinite suspensions and the accompanying change-over from positive to negative chloride adsorption. Clay Miner BuU 2 45-51 Schulten HR (2001) Models of humic structures association of humic acids and organic matter in soils and water. In Qapp CE et al. Humic substances and chemical contaminants. Soil Science Society of America, Madison, Wl, pp 73-88... 

Laor, Y., and M. Rebhun. 1997. Compexation—flocculation A new method to determine binding coefficients of organic contaminants to dissolved humic substances. Environmental Science and Technology 31 3558. 

Kretzschmar, R., Hesterberg, D., and Sticher, H. (1997). Effects of adsorbed humic acid on surface charge and flocculation of kaolinite. Soil Sci. Soc. Am. I. 61,101-108. 

Although mechanisms of DOM removal by physical/chemical processes in the mixing zone of estuaries are not well understood, they are believed to be important processes affecting the composition of riverine/estuarine DOM. Some of the earliest work on DOM removal processes noted that iron is important in the initial steps of flocculating humic substances across an estuarine salinity gradient and that much of this humic material was composed of humic acids (Swanson and Palacas, 1965 Eckert and Sholkovitz, 1976 ... 

Sea water contains a much lower concentration of dissolved organic matter than river water. More than half of this dissolved organic load is of a humic nature. These dissolved organic acids tend to flocculate as the salinity increases (10). Hair and Bassett (11) have observed an increase in the particulate humic acid load of an estuary as one approaches the sea. Although no studies of the distribution of humic materials throughout an estuarine system have been performed, it would appear that estuaries and their sediments in particular, act as a major sink for the dissolved and particulate humic materials. Nissenbaum and Kaplan (12) have observed that terrestrial humic materials are not deposited at great distances from shore in the marine system. A study of the flux of particulate carbon through the Chesapeake Bay comes to a similar conclusion (13). 

Sholkovitz (14) has shown that a large portion of the flocculated material is of a humic nature with large concentrations of... 

Not only are accurate data for trace metals in rivers sparse, there are complications that exist at the river-sea interface. The increase in salinity occurring at the river-sea water interface, with its concomitant increase in the concentrations of the major seawater cations, can lead to flocculation and sedimentation of trace metals such as iron (Boyle et al., 1978 Sholkovitz and Copeland, 1983) or to desorption from suspended riverine particles of trace metals such as barium (Edmond et al., 1978). In organic-rich rivers a major fraction of dissolved trace metals can exist in physiochemical association with colloidal humic acids. Sholkovitz and Copeland (1983) used product-mode mixing experiments on filtered Scottish river water, and observed that iron removal was almost complete due to the flocculation of strongly associated iron-humic acid colloids in the presence of the increased... 

Four types of colloids were considered in the WIPP program intrinsic actinide colloids, mineral colloids, microbes, and humic acid colloids (US DOE, 1996). Intrinsic actinide colloids, consisting of polymerized hydrated actinide hydroxides, are not stable in the neutral to moderately basic pH conditions expected in the WIPP, and were assumed not to contribute to the total actinide concentrations in solution. Mineral colloids are destabilized and tend to flocculate in the high-ionic-strength WIPP brines (Kelly et al., 1999). In the performance assessment calculations for the WIPP, a highly conservative value of 2.6 X 10 mol actinide per liter, for each actinide, was assumed to be bound to mineral colloids and to contribute to the mobile fraction. Actinides sorbed onto microbes and humic acids were estimated to contribute significantly to the concentration of mobile actinides in WIPP brines as discussed above (Section 9.06.3.2.2). 

Flocculation BOD removal, 113 COD removal, 113 fulvic acid removal, 187 humic acid remival, 187 mechanism, 273 process, 273 turbidity removal, 113... 

SPE methods for organic environmental pollutants, including PAA (Table 1) and HA A (Table 2.B), coupled with electrophoresis end analysis were reviewed126. Analysis of PAA in environmental waters requires preconcentration and cleanup to remove interfering substances such as humic acids from the samples. This may be accomplished by several methods, for example (a) derivatization of the PAA by the Bratton-Marshall method followed by HPLC-UVD measuring at 460 nm (Section III.B.2) (b) flocculation of the water sample with Al3+ ions to selectively remove humic compounds before SPE (c) a... 

Our results show that the adsorption on suspended matter is increased in the presence of suspended humic acid (Figure 10). This is supported by the finding of other authors (53,54) showing that organic flocculant coatings greatly affect the cation exchange capacities of sediment and suspended matter. 

Figure 3.22. "Random coil" model of humic substances in soil, showing the flocculated (low pH) and dispersed (high pH) forms of the organic polymers.

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