Application Of Bioaugmentation To Hypersaline Wastewater Treatment By Inoculating Intermittently Aerated Biological Filter With Halophilic Marine Bacteria

With the rapid growth of industrial activities and ocean exploitation as well as the development of coastal cities the discharge amount of hypersaline wastewater is increasing with years. Generally, in addition to salts (mainly NaCl), many varieties of hypersaline wastewater is rich in organic matter, nitrogen and phosphorus, which belong to nutrient pollutants. The generally high cost restricts the application of physico-chemical approaches to the removal of nutrient pollutants from wastewater, especially under conditions that wastewater was treated on a large scale. Thus biological treatment processes which are generally efficient and cost-effective are currently preferred methods and treatment unit playing the major role in the treatment of wastewater rich in nutrients on a large scale. However, conventional biological treatment is greatly impaired in hypersaline environments because of the inhibiting effect of high concentrations of inorganic salts on microorganisms. To avoid the adverse effect of high salinity on biological treatment system, desalinisation of hypersaline wastewater before the biological treatment process is considered. However, at present it is difficult to be achieved that the hypersaline wastewater rich in organic matter and suspended solids is desalted efficiently and economically. Since predesalination is not feasible, improving the performance of biotreatment in hypersaline environments has become a research focus in the field of hypersaline wastewater treatment.In this study, the technology of bioaugmentation was applied to the biological treatment of hypersaline wastewater by inoculating biological reactor (biofilter) with halophilic marine bacteria. The functional bacteria were immobilized in the biofilm attached to the filter media in the biofilter. Compare the performance of the biological filter enhanced with halophilic bacteria to the performance of the filter with an ordinary salinity-acclimatized biofilm in removal of organics, nitrogen and phosphorus from synthetic hypersaline wastewater with a wide range of salinity and investigate the feasibility and applicability of utilizing halophilic marine bacteria in enhancement of biological hypersaline wastewater treatment.In this study four species of marine halophilic bacteria with capability of decomposing organics as well as denitrification or accumulating phosphorus were used to improve the performance of microbial treatment system in pollutants removal.To achieve the treatment of wastewater and the immobilization of microorganisms, biological aerated filter systems were designed and set up. The effect of operational parameters on the removal of organics, nitrogen and phosphorus was investigated. To improve the removal of nitrogen and phosphorus, the aeration mode was changed from continuance to intermittence. The enhancement of biofilter performance caused by intermittent aeration was examined and the optimal cycle time of intermittent aeration was determined. Under the optimal operating condition, the removal efficiency of CODCr, total nitrogen and phosphorus were92.1%,77.9%and70.3%, respectively. The intermittently aerated biological filter showed reasonable salt tolerance and efficiency in nutrients removal from saline wastewater (salinity0-3%). The removal of CODcr was less sensitive to salinity than nitrogen and phosphorus removal. In comparison to the other studied biological processes, the intermittently aerated biofilter removed nutrients more efficiently at identical salinity and consequently has superiority and better application prospect.Bioaugmentation was applied by introducing marine halophilic bacteria into an intermittently aerated biological filter (IABF) to improve the removal of nutrient pollutants from hypersaline synthetic wastewater (salinity:3-13%). The bio-enhanced IABF showed improved performance on nutrient removal in the salinity range of4-10%compared with the control IABF. The enhancement of eliminating chemical oxygen demand, total nitrogen and total phosphorus peaked at salinities of7-10%,7-9%and5-7%, respectively, where the corresponding removal efficiencies were increased by about8.6%,15.7%and17.3%, respectively. Inoculation with marine bacteria improved the degradation of nitrogenous organics and denitrification in nitrogen transformation. In hypersaline environments biofilter recovery after backwashing was significantly prolonged whereas the time required in the bio-augmented IABF was comparatively short. The results of dehydrogenase activity assays demonstrated that inoculation with marine bacteria improved the activity of biofilm in hypersaline environments.