2nd International Conference on Recycling and Reuse, İstanbul, Turkey, 4 June - 06 July 2014, pp.241-242
Marine outfall disposal is a widely used domestic wastewater removal method. These special mostly multiport diffuser including open ended pipeline systems discharge wastewater into the marine environment in order to decrease its pollutant level by dilution and using natural recovery capacity of the receiving water body beyond the protected shoreline areas. One of the most important pollutants in the domestic wastewater is total coliform bacteria, which is accepted as an indicator of pathogenic ingredients of the sewage effluent. Untreated and pre-treated domestic effluents have total coliform bacteria ingredient typically in the range of 107-109 MPN/100mL. Because of its excessive amount of concentration, total coliform commonly needs the highest dilution level in marine outfall systems in order to obey environmentally protective regulation concentration limits.
In some cases, highly steep bathymetric profiles, such as Southeastern coast of the Black Sea, enables only shorter outfall systems. Under this condition, dilution levels could be enough for other pollutants, except for total coliform. Disinfection and disinfectant removal (e.g. dechlorination etc.) could be partly applied for total coliform concentration decrease. Thus, decreased total coliform concentration could be properly diluted in such limited conditions. However, disinfection increases operational cost of outfalls, which is an undesired choice. On the other hand, total coliform removal via dilution is directly related to far field dilution parameter T90, which is the time of 90% reduction in bacteria due to mortality. T90 value could not only be affected by sunlight, but also temperature, and salinity. Experimental studies clearly show that increased level of receiving water salinity decreases T90 value, hence far field dilution value increases. This also shows that increased level of salinity could be a disinfectant factor for total coliform in a domestic wastewater. Extra salt added initial condition of the domestic wastewater could increase the salinity of the effluent and could reduce bacterial content. Adding salt directly into wastewater could be expensive. However, some industrial wastewaters, such as textile dye process wastewaters, which have high sodium chloride concentration, could be mixed with domestic wastewaters before discharge. Increased high salinity exposure time of bacteria could increase pre-dilution level before the mixed effluent reaches to the receiving water thorough outfall diffuser. This mixing method should also be recycling method with a suitable dilution for especially textile dye process wastewaters discharges. In this study, the possible bacterial pre-dilution effects of increased salinity on sodium chloride added domestic wastewater dilution levels were theoretically investigated. Sodium chloride contents of were supplied by adding solid or textile wastewaters with various NaCl concentrations. An experimentally obtained T90 equation was used for total coliform removal calculations with various salinity contents then final dilution capacity values were evaluated considering flow rate and size of marine outfall systems.