Study On Remediation Techniques Of Organic-rich Sediments In Estuary Tidal Beach

The accelerated accumulation of organic matter in estuary sediments is a ubiquitous and significant environmental issue in the world. The excessive organic input may induce seriously negative effects which may lead to the deterioration of estuary environment. The remediation of organic-rich estuary sediments becomes increasingly prominent. The physical and chemical techniques have been currently used in the treatment of contaminated sediments. These methods, although effective, are usually with high cost and great damage to the environment. Compared with physical and chemical methods, microbial remediation has great advantages and has been applied to remove various organic pollutants. The application of microbial remediation in the removal of organic matter from organic-rich sediments is expected to be a fundamental method to solve the organically pollution problems. This study made use of biostimulation, bioaugmentation and combined Fenton-microbial treatment to eliminate excessive organic matter in the sediment. Both the effectiveness and removal mechanisms of each bioremediation method were evaluated and discussed. Results from this study may provide a theoretical basis and technical support for the in situ remediation of organic-rich sediments.In order to investigate the distribution of contaminants and the environmental bioremediation potential of indigenous microorganisms in the tidal beach of Sanba River estuary at Muping, Yantai, Shandong, the horizontal and vertical distribution characteristics of total organic carbon (TOC), oil, sulphide and microorganisms in the sediment samples collected from this area were determined. The environmental quality in this area was also evaluated using single factor pollution index method. The results showed that the pollution index was in an order of TOC > sulphide > oil. Moreover, the pollution degrees of TOC, oil and sulphide in contaminated estuary area were significantly higher than those in control site; and the further closer to the estuary the more serious pollution was found in this area. These results indicated that estuary pollution could be mainly attributed to the pollution discharge in the river. The investigation of the vertical profile of pollutants revealed that pollutant contents were highest in the subsurface layer(5-20 cm), and with the depth increasing (0-50 cm), they increase firstly but then decrease in the deep layer. For the distribution profile of microorganism, it suggested that the organic matter input could elevate the number of microorganisms and respiratory intensity of sediment. This indicated that indigenous microorganisms could improve the mineralization and output of organic material by respiration process, showing a bioremediation potential.Experiments was conducted to investigate the effects of ammonium, phosphorous and nitrate on bioremediation of organic-rich tidal beach sediment. Microbial growth and activity, dynamics of nutrients, electron acceptor, oil, sulfide, total organic carbon (TOC) and dissolved organic carbon were monitored. Infrared spectroscopy was used to study changes in structure and composition of sediment organic matter during the treatment process. After nitrate was added, oil and sulfide contents decreased due to the autotrophic and heterotrophic denitrification in the sediment. By contrast, the addition of ammonium showed negative effects on oil and sulfide removal, as well as on TOC reduction. The highest remediation efficiency was observed when 0.5 mg·g^-1 NO₃-N was amended with N:P ratio of 10:1. After 40 days of treatment, the highest removal rate for sulphide, oil and TOC were 89.7%, 90.6% and 13.8%, respectively. Infrared spectroscopy showed that fatty compounds were degraded faster than aromatic compounds after the addition of nitrate and phosphorous, the biostimulation treatment caused an increase in the degree of aromatization.The effectiveness of effective microorganisms(EM) and indigenous aerobic heterotrophicl bacteria was compared. The effect of oxygen supply was also evaluated by the addition of CaO₂. Microbial growth and activity, dynamics of nutrients, oil, sulfide, total organic carbon(TOC) and dissolved organic carbon(DOC) were monitored. The orthogonal experimental design was used to optimize the amount of microorganisms and CaO₂, as well as the interval between the two additions. Infrared spectroscopy was used to study changes in structure and composition of sediment organic matter during the treatment process. The results indicated that the addition of EM in the presence of CaO₂ could effectively accelerate the removal of organic matter, especially for the aromatic organic compounds. The optimal treatment conditions were: CaO₂ dose of 1%, addition interval of 1d and EM dose of 2×10⁷ cells·g^-1. After 40 days of treatment under optimal conditions the removal rate of oil and TOC were 44.4% and 17.8%, respectively. However, an increase of 34.8% in sulphide content was observed, indicating negative effect of bioaugmentation on environment.In order to eliminate the excessive organic matter in organic-rich tidal beach sediment, a combined treatment of Fenton oxidation based on CaO₂ followed by microbial inoculation was carried out. Experiments were conducted in phosphate buffer to investigate influences of catalyst type, initial pH, CaO₂ dose, catalyst to CaO₂ molar ratio (n_Fe/n_CaO2), and phosphate buffer concentration on the production of hydroxyl radicals (HO·). The effects of Fenton reaction parameters as pretreatment for microbial remediation were investigated using the orthogonal experimental design. The optimal parameters were: initial buffer pH = 4; phosphate buffer concentration = 100 mmol·L^-1; n_Fe/n_CaO2 = 1/20; mCaO₂/mTOC = 1/1. Infrared spectroscopy study indicated that Fenton oxidation resulted in the decrease in aromatization and the increase in biodegradability of organic matter. Best efficiency was observed when 1×10⁶ cells·g^-1 EM was added after 5 days of Fenton pretreatment. The removal rates for sulphide, oil and TOC were 46.3%, 43.8% and 31.1%, respectively.Comprehensive assessment of the three remediation techniques was carried out by comparing the treatment efficiency, economic costs and environmental negative impacts. The results indicated that biostimulation treatment showed both the lowest economic cost and the smallest negative impact on environment. Using Fenton-microbial treatment, highest pollutant removal efficiency was observed, although the environmental negative impact was greater than the other two treatments. Considering both the remediation cost and the remediation effectivness, biostimulation by adding NO₃-N and PO₄-P was suitable for the recovery of the area far from the estuary. However, Fenton-microbial treatment was also essential for the recovery of heavily polluted areas.