Môi trường ngày càng ô nhiễm nặng, việc chung tay bảo vệ là việc của tất cả mọi người trên trái đất này. Sau đây Dịch thuật Hồng Linh dịch thuật tiếng anh giá rẻ xin giới thiệu một số thuật ngữ tiếng anh ngành môi trường. > English Việt Nam absorptionabsorbent (sự, quá trình) hấp thụchất hấp thụ absorption field mương hấp thụ xử lý nước từ bể tự hoại acid deposition mưa axit acid rain mưa axit
Mobility of pollutants in soil and groundwater near waste disposal sites J Hoeks Abstract A considerable amount (50 to 60 per cent) of municipal refuse is d u m p e d in or on the soil in the Netherlands In the humid climate the soluble components of t h e dumped refuse are leached into the underlying soil and groundwater Leachate from a waste disposal site is a seriously polluted waste water T h e flow path of these pollutants in soil is governed by the flow path of the carrier, i.e water This m e a n s that hydrologeological parameters determine the pathway of the pollutants through t h e groundwater towards the surface water The mobility of the pollutants in soil largely d e p e n d s on processes like cation exchange, chemical solubility equilibria and biochemical reactions Cation exchange processes play an important role with respect to inorganic cations including h e a v y metals Phosphates, carbonates and sulphides of iron, aluminium, calcium, magnesium a n d heavy metals are involved in chemical processes Biochemical processes are important with respect to nitrogen compounds and organic substances Information about the rate of these r e a c t i o n s is needed for predicting the mobility of different pollutants in the soil To a certain extent, control of pollution is possible, e.g by carefully selecting the sites for waste disposal, by controlling the infiltration of water into the dumped refuse a n d , if necessary, by collecting and treating the polluted leachate La propagation des polluants dans le sol et les eaux souterraines près des décharges publiques Résumé Aux Pays-Bas, une grande partie des ordures municipales (50 a pour cent) sont mises en décharge soit en surface du sol, soit en dessous du niveau du sol D a n s un climat humide tel que celui de la Hollande, les parties solubles des ordures se dissolvent dans l'eau d'infiltration Il en résulte que l'eau sortant de ces décharges est contaminée Les polluants ainsi mobilisés entrent dans le cycle hydrologique Comme c e sont les conditions hydrogéologiques qui déterminent la phase suivant laquelle les eaux d'infiltration rejoignent les eaux de surface ce sont elles qui déterminent en majeure partie la propagation des polluants En traversant'les différentes couches du sol et du sous-sol, les polluants sont s o u m i s des réactions physiques chimiques et biochimiques Pour les cations inorganiques, y compris les métaux lourds, c'est l'adsôrption qui joue le plus grand rôle Les phosphates, les carbonates, les sulfites de fer, d'aluminium, de calcium, de magnésium et de métaux lourds, jouent un rôle d a n s les réactions chimiques Les processus biochimiques sont la base de la transformation et d e la decomposition des combinés de l'azote et des matières organiques La propagation des polluants est également influencée par la vitesse avec laquelle se déroulent ces différentes réactions Parmi les différents moyens de contrôler la contamination et sa propagation, on peut citer un choix attentif des sites de décharge et le contrôle de l'eau d'infiltration et, en cas de besoin, la collecte et le traitement des eaux contaminées INTRODUCTION Little quantitative information is available about the mobility of components present in leachate from waste tips In principle the mobility of solutes in soil is controlled by the flow velocity of the water (i.e the carrier for solutes) and by interaction processes in the soil, as cation exchange reactions, solution-precipitation reactions, complex formation and biochemical reactions The transport of water in soil depends on hydrogeological factors and is reasonably predictable Because the pollution source is a point source, one has to consider specific flow lines in the aquifer This means that downstream of a waste disposal site pollution 380 Mobility of pollutants near waste disposal sites 381 TABLE Chemical composition of leachate from newly dumped refuse Components COD [mg/1.] BOD [mg/1.] CI [mg/1.] S [mg/1.] HCO4 [mg/1.] Kjeldahl-N [mg/1.] Inorganic NH4-N [mg/1.] NO3-N [mg/1.] Total P [mg/1.] Ortho P [mg/1.] Total Fe [mg/1.] Ca [mg/1.] Mg [mg/1-ï Na [mg/1.] K [mg/1.] Zn [mg/1.] Ni [mg/1.] Cd [mg/L] Cr [mg/L] Pb [mg/L] Cu [mg/L] pH EC (25°C) [/LtS/cm] SVA (1974) Zanoni (1973) Mead and Wilkie (1972) 63 900 - _ - 33100 810 560 32 400 240 630 - - 320 790 550 845 _ - 950 740 14 430 390 1410 _ 25.5 6.8 1590 625 450 990 800 30 1.05 0.25 0.12 0.30 0.30 5.7 32 400 9.6 270 2190 340 1470 115 _ - 305 805 860 _ _ _ - of groundwater can only be traced at a certain depth in the aquifer where the flow path from the waste disposal site is present (Hoeks, 1975; Hoeks et ai, 1975) The effect of dilution or mixing of leachate with groundwater is small, especially in deep aquifers An assumption of complete mixing in the aquifer as made by Oakes(1976) for his model study, oversimplifies the real situation In this study results of some column experiments will be discussed and compared with field experiences GENERATION OF POLLUTED LEACHATE FROM WASTE TIPS Water soluble components are leached from the refuse by percolating rainwater Microbial reactions in the refuse may cause the breakdown of complex inorganic compounds to soluble organic products, mainly free volatile fatty acids The leachate of waste tips often is seriously polluted with a large number of components as is illustrated in Table The COD (chemical oxygen demand) of the leachate is very high Gaschromatographic research showed that about 75 per cent of this value is a result of the presence of low molecular fatty acids (C2 to C^-acids) Concerning the heavy metals in the leachate, especially Fe is present at high concentrations and to a lesser extent also Zn and Ni Other heavy metals may be present at high levels particularly if large amounts of chemical wastes are dumped at the disposal site The amount of leachate depends on the annual precipitation surplus, the amount of surface runoff and the water storage capacity of the tip Rainwater may infiltrate into the waste tip, but on a sloping surface with a low infiltration capacity, it may be partly discharged over the surface as runoff Thus minimizing the amount of leachate may be achieved by compaction of the waste with a sloping soil cover low in permeability on top of it(Schoder, 1975; Mesu, 1976) A large storage capacity in combination with high evaporation (promoted by a plant cover) also can limit percolation 382 J Hoeks FUNDAMENTAL ASPECTS OF TRANSPORT IN SOIL The transport of waste leachate in the soil below waste tips is mainly vertical as far as it concerns transport in the unsaturated zone above the groundwater table Below the groundwater table, however, vertical as well as horizontal gradients in w a t e r pressure determine the direction of flow For the linear case the flow equation for transport of solutes is found as (equation of continuity) 5c 8F - S (1) ev t 8x where e w is the soil moisture content; c is the concentration of solute ; t is time; S is a 'sink term' resulting from chemical or biochemical reactions (S is negative if for example precipitates already present in the soil dissolve) The solute flux, F, can be written as F = vc - D-^(2) ox where v is the Darcy flow velocity, vc represents the convective flux and — D8c/8x the dispersive flux Here the dispersive flux combines the effect of diffusion and dispersion (D includes the diffusion coefficient) The contribution of dispersive flux to the total flux is often limited to 10 per cent or less So for rough estimates about the velocity of a solute front in soil one may consider the convective flux as the dominant component of the total flux (Bolt, 1976) When the sink term, S, can be neglected (e.g for CI) this means that the solute front moves with the same velocity as the percolating water For components which are involved in interaction processes (S ¥= 0) equation (1) cannot readily be solved Only for a few simplified cases are analytical solutions available Assuming for instance linear adsorption and ignoring dispersive flow, the velocity of a solute front in soil can be derived from equations (1) and (2) as ' (3) l+R where vs is the velocity of the solute front; v* is the effective water flow velocity (v* = vjew);R is the distribution ratio indicating the amount adsorbed (