Removal of Herbicides

Sigworth, E.A. Identification and removal of herbicides and pesticides, J. Am. Water Works Assoc., 57 1016-1022, 1964. 

The treatment of s-triazine herbicides constitutes a clear application of the combined use of ozone and hydrogen peroxide. At the end of the eighties, this system was investigated to remove triazines in several pilot plants in France and the United Kingdom [228], The successful results obtained led to the implementation of this system in some water-treatment plants, such as those owned by the Compagnie Generale des Eaux in Paris [228], Since then, the 03/H202system has been used in many waterworks to improve the removal of. v-triazines. It should be noted, however, that ozone processes may not be appropriate for the removal of herbicides from water because of the potential formation of very low concentrations of harmful intermediates. 

L 1 and 0.6 jag L, respectively. Due to photolysis, nitrate present in the water at a concentration of 55 mg L 1 was reduced to nitrite generating an additional problem (see section II.D.l). This is because nitrite is thought to be involved in the formation of nitrosamines. Experimental conditions in this plant have been investigated to provide the optimum operating conditions for the removal of herbicides and to minimize the impact of nitrate photolysis. The results obtained in this plant led to concentrations of atrazine and nitrite in the effluent lower than 0.1 and 100 pg L 1, respectively. It must be said, for safe operation of the plant, that an equivalent ozone dose higher than 3 kW energy and a radiant power for the UV lamp between 20 and 35 kW were needed. 

Donner, C., Remmier, F., ZuUei-Seibert, N., et al. (2002). Enhanced removal of herbicides by different in-site barrier systems (GAC, FAC, anthracite, lignite coke) in slow sand filtration.FFijier Sci. TechnoL-. Water Supply, 2(1), 123-8. 

The laboratory study procedure and results are presented in this section to demonstrate the electrokinetic removal of herbicides from soils. 

Supercritical CO2 has also beea tested as a solveat for the removal of organic contaminants from sod. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlotinated biphenyls (PCBs), may be removed from sod samples (77). Supercritical CO2 can also extract from sod the foUowiag hydrocarbons, polyaromatic hydrocarbons, chlotinated hydrocarbons, phenols, chlotinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

Herbicides. An array of herbicides are registered for use in aquatic sites, but copper sulfate and diquat dibromide are of additional interest because they also have therapeutic properties (9,10). Copper sulfate has been used to control bacteria, fungi, and certain parasites, including Jchthjophthirius (ich). Diquat dibromide can control columnaris disease, but it also exhibits fungicidal properties (9,10). EPA recentiy proposed to limit the amount of diquat dibromide, endothaH, glyphosate, and simazine that can be present in drinking water therefore, the use of these compounds may be reduced if they cannot be removed from the effluent. 

E. A. Hogendoorn, E. Dijkman, B. Baumann, C. Hidalgo, J. V. Sancho and E. Hernandez, Strategies in using analytical restricted access media columns for the removal of humic acid interferences in the trace analysis of acidic herbicides in water... 

The following brief account identifies only major groups of herbicides not mentioned elsewhere in the text, and is far from comprehensive. Their mode of action is only dealt with in a superficial way. From an ecotoxicological point of view, there has not been as much concern about their sublethal effects upon plants as there has been in the case of mammals, and there has not been a strong interest in the development of biomarker assays to establish their effects. The major concern has been whether weeds, or nontarget plants, have been removed following herbicide application—a rather easy matter to establish as plants are fairly sedentary. For a more detailed account of herbicide chemistry and biochemistry, see Hassall (1990). 

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. 

The recovery of these herbicides was checked by adding known volumes of standard solutions to lOg portions of the ten air-dried soil types followed by removal of solvent by a gentle stream of air. The soils were allowed to stand for 24h and then treated as described above. The results obtained are shown in Table 9.20. Blank determinations carried out on these soils showed that any herbicide present was below the limit of detection. 

Oxidative coupling involves condensation reactions catalyzed by phenol oxidases. In oxidative coupling of phenol, for example, arloxy or phenolate radicals are formed by the removal of an electron and a proton from an hydroxyl group. The herbicide 2,4-D is degraded (Fig. 15.5) to 2,4 dichlorophenol, which can be oxidatively coupled by phenol oxidases (Bollag and Liu 1990). 

The accomplishment of these objectives involved two different research grants Grant No. R 805 466010, "Collection and Treatment of Wastewater Generated by Pesticide Applicators", from the Oil and Hazardous Spills Branch, U.S. Environmental Protection Agency and "Removal of Five R-PAR and Near R-Par Herbicides from Wastewater", from North Central Regional Pesticide Impact Assessment Program. 

Table IV. Removal of Three Herbicides by the Complete System... 

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