Scale deposition is a difficulty encountered with water containing ions of sparingly soluble salts. A widely used technique for controlling scale deposition is by dosage of an antiscalant. Large quantities of polymeric scale inhibitors are used for scale control in cooling water systems, water desalination processes, and oil field operations. Like most conventional polymers, scale inhibitors are built for long existence and persist for many years after their disposal. Increasing environmental concern and discharge limitations have caused scale-inhibitor chemistry to move toward "green antiscalants" that readily biodegrade, have low mobility for minimum environmental impact, and are cost-effective. This review summarizes efforts to develop cost-effective ecologically benign scale inhibitors. Currently, the most promising green scale inhibitors are based on poly(aspartic acid). However, field operation data are very limited, and widespread use of poly(aspartic acid) scale inhibitors awaits field operation experience.

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This study—s objective was to investigate the effect of ultraviolet (UV) treatment on the subsequent formation of regulated and unregulated disinfection by‐products (DBPs). UV treatment of two sets of waters did not substantially change the waters— tendency to form trihalomethanes, haloacetic acids, or total organic halogen under the conditions of these tests. Evidence was found of small reductions in the formation of these DBPs, but the decreases did not exceed 10%. Formation of chloropicrin and 1,1,1‐trichloropropanone increased as a result of medium‐pressure UV treatment but remained at levels well below those of the regulated DBPs. Low‐pressure UV did not cause any detectable increase in chloropicrin formation. The authors propose that photonitration leads to the formation of new nitroorganics during UV treatment and these form halonitromethanes during subsequent chlorination. It is recommended that the effects of UV treatment on nonregulated DBPs be considered as new UV drinking water systems are brought on line.

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The objective of this study was to establish the relative rate constants for the reactions of selected pesticides (linuron, diuron, prometon, terbacil, diazinon, dyfonate, terbufos, and disulfoton) listed on the U.S. EPA Contaminant Candidate Listwith UV and hydroxyl radicals (*OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pesticides were found to be very reactive toward *OH as indicated by rate constant values above 10(9) M(-1) s(-1). Using molinate as a reference compound, kOH ranged from 2.7 x 10(9) to 12.0 x 10(9) M(-1) s(-1) for the contaminants while slightly higher values from 2.9 x 10(9) to 14.3 x 10(9) M(-1) s(-1) were obtained using nitrobenzene as a reference compound. A method was established that accounts for direct photolysis when calculating kOH using UV/H2O2 process for compounds which degrade significantly by a direct photolysis mechanism.

Decay kinetics resulting from the application of UV and UV/H 2 O 2 to the polycyclic aromatic hydrocarbons (PAHs) fluorene, dibenzofuran and dibenzothiophene was studied. Batch experiments were conducted with both low pressure monochromatic (253.7 nm) and medium pressure polychromatic (200-300 nm) UV sources alone or in the presence of up to 25 mg/L hydrogen peroxide, in a quasi-collimated beam apparatus. Degradation of all three PAHs, by both UV and UV/ H 2 O 2 , exhibited pseudo-first order reaction kinetics and low quantum yields ranging from 1.4×10 −3 to 1.8×10 −2 mol/E using both UV lamps. Toxicity testing using a bioluminesence inhibition bioassay was correlated to the decay in concentration of the PAHs as analyzed analytically using HPLC. Results demonstrated that treatment efficacy of oxidative PAH degradation measured by following the decay of the target compound is best complemented by also evaluating the toxicity of the treated water due to byproduct formation concerns.