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"Everyday Engineering"

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O^ Nhie^~m Nu+o+'c Nga^`m Ta.i Ca'c DDo^ Thi. DDang Pha't Trie^?n

Bi`nh Anson (U'c)

LTS: VPS/GDD** xin ddu+o+.c gio+'i thie^.u dde^'n quy' ddo^.c gia? ba`i vie^'t cu?a Tie^'n Si~ Bi`nh Anson. O^ng hie^.n cu+ ngu. ta.i Perth, mie^`n Ta^y nu+o+'c U'c DDa.i Lo+.i\. TS Bi`nh Anson hie^.n ddang phu.c vu. trong nga`nh Thu?y Lo+.i\. O^ng dda~ quan ta^m va` co' nhie^`u ddo'ng go'p trong nhu+~ng sinh hoa.t chuye^n mo^n ta.i ha?i ngoa.i\.

oOo

Va^'n dde^` o^ nhie^~m nu+o+'c nga^`m ta.i ca'c sie^u ddo^ thi. (da^n so^' tre^n 1 trie^.u) trong ca'c nu+o+'c ddang mo+? mang la` mo^.t mo^'i lo nga.i tu+` la^u cu?a ca'c nha` ba?o ve^. su+'c kho?e va` mo^i sinh. Hie^.n nay, va^'n dde^` na^`y ddang ba`nh tru+o+'ng dde^'n ca'c ddo^ thi. co+~ trung (da^n so^' du+o+'i 1 trie^.u), va` ca'c ddo^ thi. na^`y ddang co' chie^`u hu+o+'ng ddi va`o ti`nh tra.ng o^ nhie^~m nhu+ ca'c sie^u ddo^ thi. kha'c. Ca'c tha`nh pho^' ddo' ddang thu hu't da^n chu'ng dde^'n sinh so^'ng, tu+` ca'c vu`ng tho^n que^, va` ca'c ddie^?m tu. thu+o+`ng la` vu`ng ven ddo^, ngoa.i tha`nh vo+'i nhu+~ng ddie^`u kie^.n ca^'p nu+o+'c va` ve^. sinh ra^'t nghe`o na`n, thie^'u tho^'n.

Va^'n dde^` co+ ba?n la` vo+'i da^n so^' gia ta(ng qua' nhanh, vu+o+.t qua' kha? na(ng cung ca^'p nu+o+'c va` kha? na(ng cung ca^'p phu+o+ng tie^.n ve^. sinh, ca'c ddo^ thi. na^`y vo^'n phu. thuo^.c va`o nguo^`n cung ca^'p nu+o+'c nga^`m, ddang pha?i ddo^'i pho' vo+'i su+. gia ta(ng ca'c ha^`m ca^`u xi' tie^u tha^'m ta.i cho^~, va` tu+` ddo', su+. gia ta(ng ca'c nguo^`n o^ nhie^~m co' phu+o+ng ha.i dde^'n pha^?m cha^'t nu+o+'c nga^`m. Vi` ca'c pha't trie^?n ddo^ thi. thu+o+`ng kho^ng ddu+o+.c qui hoa.ch ro~ ra`ng, hie^.n tra.ng hu?y hoa.i nu+o+'c nga^`m trong lo`ng dda^'t thu+o+`ng kho^ng ddu+o+.c dda'nh gia' dda^`y ddu?.

Vi` va^.y, co+ quan Qua?n tri. Vie^.n tro+. Ha?i ngoa.i (Overseas Development Administration - ODA) cu?a Anh quo^'c dda~ ta`i tro+. mo^.t du+. a'n 3 na(m, kha?o cu+'u ca'c ta'c ddo^.ng cu?a ddo^ thi. ho'a le^n ca'c ma.ch nu+o+'c nga^`m [*]. Ba ddo^ thi. ddang pha't trie^?n ddu+o+.c cho.n lu+.a dde^? thu+.c hie^.n du+. a'n. DDo' la` Merida o+? Mexico (da^n so^' 525,000), Santa Cruz o+? Bolivia (650,000), va` Hat Yai o+? Tha'i Lan (140,000).

Merida la` mo^.t tha`nh pho^' thie^'t la^.p tre^n ta^`ng dda' vo^i karst, trong khi Santa Cruz va` Hat Yai na(`m tre^n dda^'t phu` sa cu?a so^ng ra.ch. Mo.i sinh hoa.t trong ba tha`nh pho^' na^`y dde^`u tu`y thuo^.c va`o nguo^`n nu+o+'c nga^`m. 100% nguo^`n nu+o+'c cung ca^'p cho tha`nh pho^' Merida va` Santa Cruz la` tu+` nu+o+'c nga^`m, trong khi Hat Yai du`ng 40% nu+o+'c ma(.t va` 60% nu+o+'c nga^`m.

Ca^'u tru'c ddi.a cha^'t tu+`ng vu`ng thu+o+`ng co' a?nh hu+o+?ng lo+'n trong vie^.c ba?o ve^. ca'c ta^`ng nu+o+'c, gia?m thie^?u hay nga(n cha^.n mu+'c ddo^. o^ nhie^~m ma.ch nu+o+'c. Lu+u lu+o+.ng cha?y nhanh cu?a mo^.t ta^`ng nu+o+'c co' the^? giu'p pha loa~ng no^`ng ddo^. o^ nhie^~m. Ca^'u tru'c ddi.a cha^'t co' the^? ha^'p phu. ca'c cha^'t ddo^.c ha.i\. Ta.i Santa Cruz va` Hat Yai, dda^'t phu` sa giu'p nga(n cha^.n su+. di chuye^?n ca'c vi tru`ng trong ma.ch nu+o+'c ca.n, do co+ che^' ga.n lo.c cu?a ca'c ha.t ca't mi.n. Trong khi ddo', ca'c khe nu+'t cu?a ca^'u tru'c dda' vo^i o+? Merida dda~ giu'p cho vi sinh va^.t di chuye^?n va` ba`nh tru+o+'ng nhanh ho+n. Ke^'t qua? la` co' no+i mu+'c ddo^. vi tru`ng dda~ le^n dde^'n 1,000 E\. Coli trong 100 mL nu+o+'c nga^`m o+? Merida\.

Ti`nh tra.ng o+? tha`nh pho^' Hat Yai cu~ng gio^'ng nhu+ ti`nh tra.ng cu?a ca'c tha`nh pho^' Vie^.t Nam o+? ven so^ng va` ven bie^?n. O+? nhu+~ng no+i na^`y, vie^.c tie^u tha^'m nu+o+'c tha?i trong dda^'t ra^'t kho' kha(n vi` co' ma(.t nu+o+'c nga^`m cao, ca'c ddo^.c to^' trong nu+o+'c tha?i di chuye^?n tha(?ng dde^'n ma.ch nu+o+'c nga^`m ma` kho^ng pha?i qua ca'c tie^'n tri`nh ga.n lo.c va` hu?y hoa.i tu+. nhie^n trong dda^'t. The^m va`o ddo', ca'c tha`nh pho^' na^`y thu+o+`ng ddo^? nu+o+'c tha?i tha(?ng ra ca'c ke^nh ra.ch, so^ng, ho^`, va` bo+` bie^?n.

DDo^ thi. ho'a vo+'i ca'c gia ta(ng die^.n ti'ch ma(.t ddu+o+`ng va` ma(.t lo^. dda~ kho^ng la`m gia?m lu+o+.ng tha^?m tha^'u xuo^'ng dda^'t. Tra'i la.i, ro` ri? tu+` ca'c he^. tho^'ng o^'ng da^~n nu+o+'c, tie^u tha^'m tu+` ca'c ha^`m ca^`u xi', va` vie^.c tu+o+'i ca^y co? ta.i ca'c vu+o+`n hoa, sa^n cho+i co^ng co^.ng dda~ la`m gia ta(ng dda'ng ke^? lu+o+.ng nu+o+'c bo^? sung va`o ma.ch nu+o+'c nga^`m, va` tu+` ddo' mang theo ca'c cha^'t ba^?n va`o lo`ng nu+o+'c. No^`ng ddo^. nitra't, clorua, va` sulpha't dda~ gia ta(ng, ba('t nguo^`n tu+` nu+o+'c tha?i trong nha`, va` tu+` ca'c hoa.t ddo^.ng co^ng nghie^.p.

Lu+o+.ng cha^'t hu+~u co+ gia ta(ng trong nu+o+'c nga^`m la`m gia?m no^`ng ddo^. oxygen ho`a tan. Vie^.c na^`y ddu+a dde^'n su+. gia ta(ng cha^'t sa('t trong nu+o+'c, tuy kho^ng co' ha.i su+'c kho?e, nhu+ng se~ la`m va`ng o^' qua^`n a'o, va` ta.o mo^.t mu`i vi. kho' chi.u trong nu+o+'c du`ng.

Ngay ca? vie^.c kie^'n ta.o ca'c vu`ng gie^'ng khai tha'c nu+o+'c o+? ngoa.i tha`nh cu~ng co' the^? bi. nhie^~m ba^?n vi` ddo^. bo+m nu+o+'c qua' cao co' the^? hu't ca'c cha^'t o^ nhie^~m dde^'n vu`ng gie^'ng. The^m va`o ddo', vie^.c khai tha'c qua' ta?i co' the^? ta.o ra ca'c hie^.n tu+o+.ng su.p lu'n dda^'t nhu+ dda~ quan sa't ddu+o+.c o+? Bangkok, Tha'i Lan.

Ta.i Hat Yai, gia ta(ng khai tha'c nu+o+'c nga^`m dda~ la`m ha. ma(.t nu+o+'c va` thu hu't nhie^`u cha^'t ba^?n. Trong tru+o+`ng ho+.p nhu+ the^', ngu+o+`i ta la.i khoan gie^'ng khai tha'c o+? ddo^. sa^u ho+n, ta.o nhie^`u khe nu+'t, gia ta(ng va^.n to^'c tha^?m tha^'u tu+` ta^`ng nu+o+'c ca.n xuo^'ng ca'c ta^`ng nu+o+'c sa^u\. Khai tha'c nhu+ the^' tha^.t ra chi? la` dde^? tri` hoa~n mu+'c ddo^. o^ nhie^~m, kho^ng co' lo+.i gi` trong va^'n dde^` ba?o ve^. nguo^`n nu+o+'c, nha^'t la` khi ca'c nguo^`n nu+o+'c sa^u la.i co' mo^.t pha^?m cha^'t cao, ca^`n pha?i ddu+o+.c ba?o ve^. dde^? su+? du.ng la^u be^`n.

Ha^.u qua? chung cu?a dda` gia ta(ng kie^'n ta.o ca'c ha^`m ca^`u xi' tie^u tha^'m ta.i cho^~ la` mu+'c ddo^. cao cu?a ca'c cha^'t nitra't va` clorua trong nu+o+'c nga^`m, vo+'i nitra't vu+o+.t qua' mu+'c tie^u chua^?n gio+'i ha.n cho nu+o+'c uo^'ng. Va^'n dde^` na^`y dda~ thu+o+`ng xa^?y ra ta.i ca'c nu+o+'c ddang mo+? mang. Tuy nhie^n, ke^'t qua? nghie^n cu+'u cho tha^'y ra(`ng ca^`n pha?i hie^?u ro~ ca'c ye^'u to^' ddi.a cha^'t cu.c bo^., dde^? co' the^? tha^?m ddi.nh chi'nh xa'c pha^?m cha^'t nu+o+'c nga^`m ta.i mo^~i tha`nh pho^'. Kho^ng pha?i ta^`ng nu+o+'c nga^`m na`o cu~ng de^~ bi. nhie^~m ba^?n bo+?i ca'c hoa.t ddo^.ng ddo^ thi..

Vo+'i ca'c gia ta(ng ve^` vie^.c su+? du.ng ho^' xi' tie^u tha^'m ta.i cho^~, chu'ng ta ca^`n pha?i xa'c ddi.nh tha`nh pha^`n cu?a nitrogen dda~ di chuye^?n va` tha^'m va`o ma.ch nu+o+'c nga^`m tu+` ca'c nguo^`n o^ nhie^~m ddo'. DDa^y la` mo^.t va^'n dde^` kho^ng ro~ ra`ng va` nhie^`u kho' kha(n, nhu+ng ddie^`u tra so+ kho+?i dda~ cho tha^'y trong ta^`ng dda' vo^i karst, ca? 100% lu+o+.ng nitrogen dda~ tha^'m va`o nu+o+'c nga^`m (Merida). Trong khi ddo', trong ca'c ta^`ng dda^'t phu` sa, lu+o+.ng na^`y chi? co' 10 - 20% ma` tho^i (Santa Cruz va` Hat Yai).

O^ nhie^~m tu+` ca'c hoa.t ddo^.ng ky~ nghe^. ta.i ca'c quo^'c gia ddang mo+? mang thi` thu+o+`ng kho' tha^?m ddi.nh ho+n. Ca'c pha't trie^?n hoa.t ddo^.ng co^ng nghie^.p na^`y thu+o+`ng kho^ng co' kie^?m soa't va` theo do~i cha(.t che~. Vi` the^' mo^~i khi co' pha't hie^.n va^'n dde^` nhie^~m ba^?n, ra^'t kho' ma` xa'c ddi.nh ca'c cha^'t ta.o nhie^~m ba^?n va` ca'c nguo^`n ta.o nhie^~m ba^?n na^`y\. Su+. hu?y hoa.i ca'c cha^'t hu+~u co+ ho`a tan thu+o+`ng gia?i pho'ng khi' carbonic, va` tie^'p theo la` su+. ho`a tan carbona't calcium va` magnesium trong ca^'u tru'c ta^`ng nu+o+'c nga^`m. Tu+` ddo', nu+o+'c nga^`m se~ co' ca'c no^`ng ddo^. bicarbona't ra^'t cao\. Ta.i mo^.t va`i ddo^ thi., lu+o+.ng carbonic na^`y se~ ta.o ra ca'c loa.i nu+o+'c nga^`m co' ddo^. acid cao\. Trong mo^i tru+o+`ng acid, ca'c kim loa.i ddo^.c ha.i se~ de^~ bi. ho`a tan trong nu+o+'c ho+n, va` do ddo' dda~ co' nhie^`u quan nga.i la` ca'c loa.i nu+o+'c nga^`m co' ddo^. acid cao se~ ta?i ca'c kim loa.i ddo^.c ha.i ddi nhie^`u no+i\. Vi` vie^.c theo do~i su+. lu+u chuye^?n ca'c ddo^.c to^' na^`y ra^'t kho' kha(n, ne^n dde^'n nay va^~n chu+a co' nhie^`u tho^ng tin, du+~ lie^.u dde^? tha^?m ddi.nh chi'nh xa'c. Do ddo', ca^`n pha?i co' the^m ca'c nghie^n cu+'u xa'c ddi.nh ro~ ra`ng ca'c tho^ng so^' ca^`n thie^'t, dde^? theo do~i mu+'c ddo^. la^y lan cu?a ca'c ddo^.c to^' na^`y\.

Ke^'t qua? ddie^`u tra tu+` 3 tha`nh pho^' tre^n cho tha^'y va^'n dde^` ddang dde do.a pha^?m cha^'t nguo^`n nu+o+'c nga^`m ta.i ddo' cu~ng la` va^'n dde^` chung cho ca'c no+i kha'c, trong ca'c nu+o+'c ddang pha't trie^?n. Ca'c hoa.t ddo^.ng ddo^ thi. ho'a ddang ddu+o+.c thu+.c hie^.n o+? nhie^`u no+i, nhu+ng la.i i't co' ai quan ta^m nhie^`u dde^'n ca'c ha^.u qua? ta'c ddo^.ng le^n mo^i tru+o+`ng nu+o+'c nga^`m. Tuy nhie^n, so^' pha^.n cu?a ca'c nguo^`n nu+o+'c nga^`m na^`y co' le~ se~ la` mo^.t ye^'u to^' quan tro.ng nha^'t dde^? ddi.nh ddoa.t tu+o+ng lai cu?a ca'c tha`nh pho^' ddo'.

Bi`nh Anson, Perth, Western Australia Tha'ng 02 - 1995.

[*] "Medium-sized cities follow mega-cities into crisis", Water and Environment, July 1994.

** Ho^.i Chuye^n Gia Vie^.t Nam (Vietnamese Professionals Society) http://www.webcom.com/~hcgvn/

oOo


Binh Anson, Ph.D.
anson@saigon.com

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