Risk-based management approaches are more and more used in the water sector and are promoted by the WHO. As a first step towards an overall risk-based management approach of the agricultural wastewater reuse concept of Braunschweig this thesis conducts quantitative microbial risk assessment (QMRA) and quantitative chemical risk assessment (QCRA) of heavy metals. Scenarios for microbial risks are conducted for fieldworkers, nearby residents and children ingesting soil using a 1000 trial Monte Carlo Simulation. As a tolerable value of risk an additional disease burden of 1 µDALY is set following the current WHO guidelines. For heavy metals impacts on the terrestrial and aquatic ecosystems as well as on human health are assessed using the methods outlined in the European Union Technical Guidance Document on Risk Assessment (TGD). Concerning microbial risks risk-based targets are set in terms of additional required pathogen reduction in the STP Steinhof. Based on the model results an additional reduction of 1.5log units is derived for viruses, for which the highest annual risks of infection per person per year (pppy) is calculated in all scenarios. Concerning heavy metals the model indicates an increasing tendency of soil concentrations over time and identifies Cd as the only metal which is currently of concern. Risk reduction measures should be considered for this metal. Recommendations are given concerning necessary validation and additional monitoring for eliminating uncertainties within the model.