The main objective of the project is to develop procedures and techniques to sustainably improve the water quality of polluted surface waters in tropical and subtropical areas. For this, within the project TAPIOKA, a pilot plant for treatment of tapioca starch wastewater and a numerical expert system for sustainable and innovative water pollution control management are developed and tested. By that, evaluation modules for water pollution control management are extended and low-cost measures for the rehabilitation of surface waters can be derived.
The objective of the subproject “wastewater treatment” was to develop and to optimize an innovative treatment concept for highly concentrated wastewater from the production of Tapioca starch. Despite existing regulations in Vietnam, this type of wastewater is often not treated sufficiently so far. For the investigation, a pilot plant was set up and operated for 24 months in Tây Ninh province. The plant consisted of a dissolved air flotation unit, an anaerobic reactor and a vertical flow constructed wetland (line 1), and a flotation unit followed by a two-stage vertical flow constructed wetland (line 2), respectively.
The process combination has proven to be suited for removing the major wastewater components of concern from Tapioca starch wastewater, namely BOD5 and Cyanide, according to the Vietnamese Guideline values for direct discharge into surface waters. A particular advantage of the concept is that several sustainability aspects are fulfilled: The plant components can be operated safely and need no chemicals (expect some sodium hydroxide for pH adjustment), the residuals can be utilized in agriculture, and biogas is produced that can substitute fossil fuel in the starch production process. The long operation period of the pilot plant also verified that the plant components are robust and work reliably under the conditions encountered in Vietnam. Thus the treatment concept can be transferred directly into practical application on a technical scale.
In a numerical expert system, the water balance, the transport of pollutants into the river from different sources as well as instream water quality are simulated. In addition, the experimental results from the pilot plant operation were accounted for. Because of the topographic characteristics and the strong anthropogenic influences, the water balance of the Tay Ninh and the Saigon catchment is very complex. The catchments are characterized by a very flat topography with gentle slopes. This character complicates a clear delineation of sub-catchments and flow path. Broad flood areas, ponds, irrigation channels, and rice fields are responsible for a large retention potential of water in the catchments. In consequence, a large amount of precipitation comes delayed to runoff. In the dry season, the water balance is strongly influenced by irrigation measures, in particular for the cultivation of rice and the low flow augmentation. The dynamics of the water and mass balance of both catchments were simulated with the SWAT model. The hydraulics and water quality of the Tay Ninh river were simulated with the 1D-HEC-RAS model. For the Dau Tieng reservoir and the tidal influenced Saigon river, the 2D-CE-QUAL-W2 model was applied. In this study, the water quality comprised sediment, nutrients, dissolved oxygen, and biological oxygen demand (BOD5). Good to very good calibration results could be achieved for all stations for the water level, discharge, and water quality parameters, respectively.
Using the coupled models and the results of the pilot plan mentioned above, an expert system was developed within the project. The task of the expert system is to reduce or to compensate the anthropogenic influences to a minimum necessary degree to ensure the natural state of the water bodies. The expert system can be used as a tool to identify necessary measures based on given water pollution control targets. It can predict the effect of wastewater discharges and can evaluate protection measures economically and ecologically. Restoration measures can be optimized with the help of the expert system.