Anaerobic Biodegradation Technology Of Hexachlorocyclohexane

Hexachlorocyclohexane (HCH) is a typical organochlorine pesticides, because of its highly efficient insecticidal effect has been widely used in the agricultural sector. Because of persistence, semi-volatile, bio-accumulation and high toxicity, HCH has been the focus of attention. HCH can exist in soil, air and water for long time. HCH adsorbed by crops, vegetables and animal can enter the body through the food chain, accumulate and do harm to human health. HCH is easy to accumulate in the sediments when it enters the water environment because it is hardly dissolve in water. Therefore, further study of the anaerobic microbial degradation of HCH is very necessary.Firstly, on the basis of review of related literature at home and abroad, this article overviews the pollutant, hazards and existing removal techniques of Persistent Organic Pollutants; summarizes the nature, hazards, environment behavior and biodegradation of HCH; discusses the application status of Life Cycle Assessment on the pollution remediation.This paper selected four major isomers (α-、β-、γ-、δ-HCH) as the target pollutants, cultured the anaerobic sludge could degrade HCH. We carry out a series of serum bottle experiments for biodegradation of HCH:with different electron donors, with different concentration of nitrate; with different concentration of sodium chloride, study the anaerobic biodegradation characteristics and kinetics of HCH by anaerobic sludge. In addition, a life cycle assessment (LCA) was conducted using the IMPACT2002+method to evaluate the environment effects of HCH bioremediation with the electron donors. The following main conclusions were obtained:(1) The degradation of HCH under different electron donors follows pseudo-first-order kinetics. After28days of anaerobic biodegradation, by comparing the degradation efficiency and degradation rate, draw the order of effect of five electron donors:ethanol≈methanol>methanol plus glucose>glucose>acetate. Ethanol series, the half-life of α-、β-、γ-、δ-HCH are as follows:1.81days,6.29days,6.01days,4.13days; for methanol series, the half-life of HCH isomers:2.67days,9.14days,5.04days,4.65days; for methanol plus glucose:4.82days,5,94days,8.80days,9.58days; for glucose:4.21days,6.37days,4.49days,7.24days; for acetate:14.62days,46.74days,15.15days,34.68days. The degradation rates are between90%-100%, when ethanol and methanol were added, but degradation rates of the acetate series only between30%-70%. Glucose after a lag period of4-8days before it can be used by microbes, after, the promoting effect for degradation is obvious.(2) HCH anaerobic degradation process by adding sodium nitrate satisfies the quasi-first-order kinetics equation. Under the influence of different concentrations if nitrate (<25mM), the relationship of degradation rate about four kinds of HCH isomers are:Ko mM>K5mM> Ko mM> K25mM.This result shows that accession of natrate can inhibit HCH degradation, the higher the nitrate concentration the weaker of the anaerobic sludge activity. With25mM nitrate, the half-life of α-、β-、γ-、δ-HCH are45.90days,77.45days,68.36days,71.31days, respectively. When the nitrate content was more than50mM in150ml liquid, HCH degradation did not occur in35days of acclimation.(3) HCH anaerobic biodegradation in line the first order equation under the influence of different concentrations of sodium chloride. The degradation rate constant of a-HCH is K0g/L=4.006d-1> K5g/L=0.4540d-1>K3g/L=0.4284d-1> K10g/L=0.2757d-1> K15g/L=0.0882d-1; the degradation rate constant of β-HCH is K3g/L=0.3569d-1> K5g/L=0.3473d-1> K0g/L=0.2832d-1> K10g/L=0.1941d-1> K15g/L=0.1429d-1; the degradation rate constant of δ-HCH is K5g/L=0.3334d-1>K3g/L=0.2705d-1Kog/L=0.2029d-1> K15g/L=0.1469d-1> K10g/L=0.1098d-1. Seen from the kinetic rate constant, appropriate increase in concentration of sodium chloride can promote the anaerobic degradation of HCH. When the concentration of sodium chloride exceeds lOg/L, it would inhibition anaerobic sludge.(4) LCA score results showed that the methanol scenario have the lowest impact for HCH bioremediation. For all the series, the effects on respiratory inorganic, land occupation, global warming, and non-renewable energy categories had an important contribution. For all the series, the electron donor production phase was the most important (responsible for over90%of adverse effects). The upper bound on electron donor application increased with increasing HCH concentration, the methanol scenario exhibited the highest upper bound on electron donor application.