Dynamics of nitrogen in a PAHs contaminated soil amended with biosolid or vermicompost in the presence of earthworms.

Nitrogen mineralization in PAHs contaminated soil in presence of Eisenia fetida amended with biosolid or vermicompost was investigated. Sterilized and unsterilized soil was contaminated with PAHs, added with E. fetida and biosolid or vermicompost and incubated aerobically for 70 days, while dynamics of inorganic N were monitored. Addition of E. fetida to sterilized soil increased concentration of NH(4)(+) 100> mg N kg(-1), while concentrations in unsterilized remained <60 mg N kg(-1) except for soil amended with biosolid plus PAHs where it increased to >80 mg kg(-1). Addition of PAHs had no significant effect on concentration of NH(4)(+) compared to the unamended soil, except in the soil added with biosolid. Addition of E. fetida to sterilized soil increased concentration of NO(2)(-) 15> mg N kg(-1) while concentrations in unsterilized soil remained <7.5 mg N kg(-1) except for soil amended with biosolid where it increased to >20 mg kg(-1). Addition of PAHs had no significant effect on concentration of NO(2)(-) compared to the unamended soil. Addition of biosolid and vermicompost increased concentration of NO(3)(-), while addition of E. fetida decreased concentration of NO(3)(-) in biosolid amended soil. It was found that NH(4)(+) and NO(2)(-) oxidizers were present in the gut of E. fetida, but their activity was not sufficient enough to inhibit a temporarily increase in concentrations of NH(4)(+) and NO(2)(-). Contamination with PAHs induced immobilization of N in biosolid or vermicompost amended soil, as did feeding of E. fetida on biosolid or vermicompost.

Bioremediation of polycyclic aromatic hydrocarbon-contaminated saline-alkaline soils of the former Lake Texcoco.

Polycyclic aromatic hydrocarbons (PAHs) such as phenanthrene, anthracene and Benzo[a]pyrene (BaP) are toxic for the environment. Removing these components from soil is difficult as they are resistant to degradation and more so in soils with high pH and large salt concentrations as in soil of the former lake Texcoco, but stimulating soil micro-organisms growth by adding nutrients might accelerate soil restoration. Soil of Texcoco and an agricultural Acolman soil, which served as a control, were spiked with phenanthrene, anthracene and BaP, added with or without biosolid or inorganic fertilizer (N, P), and dynamics of PAHs, N and P were monitored in a 112-day incubation. Concentrations of phenanthrene did not change significantly in sterilized Acolman soil, but decreased 2-times in unsterilized soil and >25-times in soil amended with biosolid and NP. The concentration of phenanthrene in unsterilized soil of Texcoco was 1.3-times lower compared to the sterilized soil, 1.7-times in soil amended with NP and 2.9-times in soil amended with biosolid. In unsterilized Acolman soil, degradation of BaP was faster in soil amended with biosolid than in unamended soil and soil amended with NP. In unsterilized soil of Texcoco, degradation of BaP was similar in soil amended with biosolid and NP but faster than in the unamended soil. It was found that application of biosolid and NP increased degradation of phenanthrene, anthracene and BaP, but to a different degree in alkaline-saline soil of Texcoco compared to an agricultural Acolman soil.

Composting of tannery effluent with cow manure and wheat straw.

Wastewater from the leather industry in León (Guanajuato, México) is discharged into the Turbio river without treatment. Tannery wastewater contains utilizable nutrients, but also toxic organic compounds which might affect soil processes and plant growth, and pathogens, which might pose a threat to the local farming community. Tannery effluent was composted with cow manure and wheat straw for 90 days to reduce pathogens and toxic organic compounds and monitored. The compost was characterized by an electrolytic conductivity (EC) of 28.1 ms cm(-1), cation exchange capacity of 17.7 meq 100 g(-1), an absorbance at 645 nm of 0.0175, a respiration rate of 0.062 mg CO2-C kg(-1) compost-C day(-1), pH 8.5 and C:N ratio 7:1 with a germination index for cress (Lepidium sativum) of 48% after 90 days. Less than 10 faecal coliforms and no Salmonella sp., Shigella sp. or eggs of helminthes were detected in the compost while total coliforms decreased by log10 of 2. Total concentrations of lead (Pb) were 8.9 mgkg(-1) dry compost, chromium (Cr) 77 mg kg(-1) dry compost, cadmium (Cd) 0.4 mg kg(-1) dry compost, copper (Cu) 10.3 mg kg(-1) dry compost and sodium (Na) 14,377 mg kg(-1) dry compost. The compost characteristics indicated that it was mature, but the germination index for cress of less than 50% suggested possible remaining phytotoxic compounds. However, the large salt concentrations (especially Na), might have inhibited cress development and thus reduced the germination index. The large salt concentration might thus limit the use of this kind of compost.