[Effect of particulate size and composition on the biodegradation of PAHS in nature waters].

Effect of particulate size and composition on the biodegradation of polycyclic aromatic hydrocarbons(PAHs) in nature waters was examined. Experimental study was carried out for the Yellow River. The results showed that the biodegradation of benzo[a] pyrene and chrysene in water system could be fitted with one-order kinetics and the existence of particulates promoted the biodegradation. When the particulate content was 4 g/L, the sequence of increasing trend in the PAH biodegradation rates was: water system with middle size particulates (7-25 microm) > water system with small size particulates (<7 microm) > water system with large size particulates (>25 microm). The biodegradation rate constants for benzo[a]pyrene in water systems with middle, small and large size particulates were 0.0248 d(-1), 0.0212 d(-1), 0.0192 d(-1), respectively, and that for chrysene were 0.0288 d(-1), 0.0261 d(-1), 0.0218 d(-1), respectively. The mechanisms regarding the effects of particulate size on the biodegradation of PAHs include several aspects. First, the particulate size and composition affected the PAHs degraders level in water system as well as the distribution of PAHs degraders in water and particulate phases. The population of PAHs-degraders in water systems with middle and small size particulates was higher than that with large size particulates. Second, PAHs tended to be sorbed on the particulate phase, and the desorption of PAHs from the particulate phase would lead to a higher concentration of PAHs in the interface between water and particulate phases. Since the PAHs-degraders also tended to grow in the interface between water and particulate phases, this would result in a higher contact chances for PAHs and PAHs-degraders. Therefore, the existence of particulates stimulated the biodegradation of PAHs in water system. Third, the sorption capacity of PAHs and PAHs-degraders on the middle and small size particulates was higher than that on the large size particulates. Consequently, the biodegradation rates of PAHs in water systems with middle and small size particulates were higher than that with large size particulates. However, the desorption capacity of PAHs from middle size particulates was higher than that from small size particulates, leading to that PAHs concentration in the water/particulate interface of the former system was higher than that of the latter system. Therefore, the biodegradation rates of PAHs in water system with middle size particulates were higher than that with small size particulates.

[Adsorption and partition of PAHS on particles of the Yellow River].

Experiments were carried out to study the sorption of PAHs Benzo(a)pyrene, chrysene and Benzo(g, h, i)perylene on particles of the Yellow River. The contributions of adsorption and partition to the sorption of PAHs were investigated. Several significant results were obtained from the study: (1) The total sorption capacity increases with the particle content while the sorption capacity of unit weight particle decreases; the isotherms of Benzo(a)pyrene depend on the particle content. (2) Isotherms of Benzo(a) pyrene can be fitted with the Dual Adsorption-Partition model under different particle content; the measured value of the adsorption and partition are in accord with the theoretical value of the Dual Adsorption-Partition model. (3) The adsorption is predominant in the sorption of Benzo(a)pyrene. When the particle contents are 3, 8 and 15 g/L and the liquid equilibrium concentrations are 2.84, 2.35 and 3.4 microg/L, respectively, the contributions of adsorption are 67.8%, 65.6% and 62.69%, respectively. In addition, the contributions of adsorption have a decreasing trend with the increase of the particle content. (4) The sorption capacity of Benzo (a) pyrene being alone are bigger than that with other PAHs chrysene and Benzo(g, h, i)perylene coexisting in the water system, this also proves that the adsorption is predominant in the sorption of PAHs.

[Influence of humic substance in solids on CODMn of the Yellow River].

Experiments were carried out to study the influence of humic substance in solids (Loess soil) on CODMn in the Yellow River. Several significant results were abtained from the study: (1) The total CODMn of water sample including liquid and solid phases increased significantly with the increase of solid content; The CODMn of liquid phase of water sample under pre-treatment with acid (LPWSPC) also increased significantly with the increase of solid content while that without pre-treatment did not increased significantly. (2) With the increasing of solid content, the total BOD5 of water sample increased much slower than the total CODMn and the CODMn of LPWSPC. (3) The humic substances with the content of 0.76% in solids (Loess soil) contributed greatly to the total CODMn of water sample. When the solid contents were 7.5 g/L and 15.0 g/L, the humic substances in solids accounted for 15.9% and 21.7% of the total CODMn of water sample, respectively. (4) When solid contents were 7.5 g/L and 15.0 g/L, fulvic acid,one of the main compositions of humic substance contributed to 23.6% and 50.6% of the CODMn of LPWSPC, respectively. Since the fulvic acid can hardly be biologically oxidized under natural conditions, the CODMn of LPWSPC in water quality monitoring exaggerates the oxygen-consuming organic contamination of the Yellow River.