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Charakterystyka metod zapobiegania powstawaniu bromianów(V) w wodzie przeznaczonej do spożycia

Olsińska U.

Ochrona Środowiska

2017

Vol. 39, nr 2

17--26

Bromate content following ozonation of bromide-containing water may range from 0.4 to 60 mgBrO3–/m3. Based on toxicological studies, bromates are classified as potential human carcinogens and are subject to legal regulations in many countries. In Europe, since the 25th of December 2008 their maximum permissible content in water intended for human consumption must not exceed 10 mgBrO3–/m3. As bromates are stable compounds, difficult to remove using conventional water treatment technologies, novel techniques to control their formation in water need to be developed. Technologies meant to control the bromate content in water can be divided into two groups: (1) methods allowing limitation of bromate formation and (2) methods for bromate removal. Methods that may be applied to control the bromate formation in water intended for human consumption are briefly reviewed herein. Evaluation of progress in their development was performed as well as feasibility of their application in water treatment systems was assessed. The review outlines both the well-known methods (e.g. lowering of pH, water ammonification, bromide removal in conventional water treatment processes, operational parameter optimization, multi-stage ozonation, addition of OH radical scavengers, hydrogen peroxide dosing) and the novel ones (e.g. membrane processes for bromide removal, catalytic ozonation, strong oxidant dosing). Selection of an appropriate solution to the problem of increased bromate presence in water should always be preceded by pilot studies. The main reasons include a complex mechanism of bromate formation and simultaneous effect of various water quality indicators on the effectiveness of different bromate formation prevention methods.

Zawartość bromianów(V) po procesie ozonowania wody zawierającej bromki może sięgać od 0,4 mgBrO3–/m3 do 60 mgBrO3–/m3. Na podstawie wyników badań toksykologicznych bromiany(V) zostały zakwalifikowane do grupy potencjalnych kancerogenów i są przedmiotem regulacji prawnych w wielu krajach. W Europie, od 25 grudnia 2008 r., ich maksymalna dopuszczalna zawartość w wodzie przeznaczonej do spożycia nie może przekraczać 10 mgBrO3–/m3. Ponieważ bromiany(V) są związkami trwałymi i trudno usuwalnymi za pomocą konwencjonalnych procesów oczyszczania wody, dlatego niezbędne jest opracowanie nowych technik kontroli ich powstawania w wodzie. Technologie przydatne do kontroli zawartości bromianów(V) w wodzie można podzielić na dwie grupy: (1) metody umożliwiające ograniczenie powstawania bromianów(V), (2) metody usuwania bromianów(V). W pracy omówiono metody, które mogą być wykorzystane do kontroli powstawania bromianów(V) w wodzie przeznaczonej do spożycia przez ludzi. Dokonano także oceny postępu w ich opracowaniu, jak również możliwości ich stosowania w systemach oczyszczania wody. W rozważaniach uwzględniono zarówno metody dobrze znane (np. obniżenie wartości pH wody, amonizacja wody, usuwanie bromków w konwencjonalnych procesach oczyszczania wody, optymalizacja parametrów procesowych, ozonowanie wieloetapowe, dawkowanie akceptorów rodników OH, dawkowanie nadtlenku wodoru), jak i nowsze (zastosowanie technik membranowych do usuwania bromków, ozononowanie katalityczne oraz dawkowanie silnych utleniaczy). Wybór właściwego rozwiązania problemu zwiększonej obecności bromianów(V) w wodzie, ze względu na złożony mechanizm ich tworzenia i jednoczesny wpływ wielu wskaźników jakości wody na skuteczność poszczególnych metod zapobiegania ich powstawaniu, powinien być zawsze poprzedzony badaniami pilotowymi.

Usuwanie bromków i bromianów z wody w procesie wymiany anionów przez membranę jonowymienną

Wiśniewski J. A., Kabsch-Korbutowicz M., Łakomska S.

Rocznik Ochrona Środowiska

2013

Tom 15, cz. 2

1260--1273

Bromide ions are present both in surface and ground water and their concentration ranges from several to 800 µg/L. Bromides are not reported to be detrimental to human health but their presence in the water being disinfected is a contributing factor in the formation of harmful disinfection by-products (DBP). During water disinfection with chlorine, bromides are oxidized to hypobromous acid (HOBr), which reacts with natural organic matter (NOM) to form carcinogenic brominated trihalomethanes (BrTHM). When ozone is used in water disinfection, bromides are oxidized to hypobromite ions (OBr-/) and thereafter to bromates (BrO3-). Bromates are ions exerting a carcinogenic effect on human organisms. According to the data published by the US Environmental Protection Agency, the lifetime risk of cancer disease amounts to 10-4, for a man consuming daily 2 L of water containing 5 μg BrO3-/L. The above data prove that bromides or bromates should be removed from drinking water. Among the methods used for this purpose, coagulation (for bromide removal) and granular activated carbon adsorption or reverse osmosis (for bromate removal) provide the highest removal efficiency. We proposed Donnan dialysis with anion-exchange membrane for removal of bromides or bromates from water. In this process, an anion-exchange membrane separates two solutions: the feeding solution (with harmful anions) and the receiver (with a simple salt of a relatively high concentration). Transport of the driving anions (e.g. chlorides) from the receiver to the feeding solution induces an equivalent, oppositely directed anion flow to the receiver. In this way the harmful anions that occur in the solution being treated (bromides or bromates) are replaced with neutral ions from the receiver (i.e. chlorides). Donnan dialysis was performed in a laboratory dialytic set-up containing 20 cell pairs with anion-exchange membranes, Selemion AMV (Asahi Glass) or Neosepta ACS (Tokuyama Corp.). The working area of the membranes amounted to 0.140 m2. The feed was natural water enriched with bromide salt (500 µg Br-/L) or with bromate salt (50 µg BrO3-/L). The receiver was NaCl solution with concentration ranging from 50 to 300 mM. It was found that Donnan dialysis with the anion-exchange membrane Selemion AMV enables high removal efficiency of bromides from natural water containing 500 µg Br-/L. The efficiency of bromide removal amounts to 86% at a relatively low NaCl concentration in the receiver (100 mM). The exchange of bromide ions for chloride ions is paralleled by the exchange of associated anions: sulphates (with 76% efficiency) and bicarbonates (with 70% efficiency). Compared to the anion-exchange process with Selemion AMV, the process involving Neosepta ACS (an anion-exchange membrane of a compact surface structure) provides a higher efficiency of bromide removal that amounts to 90%. In this process, retention of the associated anions is relatively high: sulphates are exchanged for chlorides with the efficiency of 3% and bicarbonates – with the efficiency of 43%. The anion-exchange process with the membrane Selemion AMV offers complete removal of bromates from natural water (containing 50 µg BrO3-/L), when salt concentration in the receiver is low (100 mM NaCl). There is aconcomitant exchange of other anions for chloride ions: sulphates are exchanged for chlorides with the efficiency of 93% and bicarbonates – with the efficiency of 73%. The anion-exchange process also provides complete removal of bromates from natural water, when use is made of the Neosepta ACS membrane. However, the exchange of sulphate ions and bicarbonate ions for chloride ions is poor (3% efficiency and 47% efficiency, respectively). Such treatment approach may be recommended for implementation, when the concentration of anions (especially that of bicarbonates) in the water to be treated is low.