Simulation of Inert Component Accumulation during the Recycling of Farm Dairy Wastewater

An investigation into the potential for reclamation and re-use of waste stabilisation pond-treated farm dairy wastewater was conducted. Simple mathematical models were developed to predict the buildup of soluble inert components in both fixed and variable volume treatment and storage systems. Fixed volume flowthrough system simulations with constant discharge indicated a lower rate of concentration buildup in comparison to variable volume systems in which wastewater accumulation occurred. Decreasing the capacity of fixed volume systems was also demonstrated to result in an increased rate of concentration buildup. Steady-state concentrations were shown to be a function of wastewater wastage rate and to be independent of system volume. Predicted steady-state inert total dissolved ions (TDI) concentrations in a fixed volume system for freshwater fractions of 0·1-1·0 varied from 2200 to 20 200 g m−3. These compared to an adopted upper limit for discharge to land treatment of 3500 g m−3. Times taken to reach either the limit or the steady-state concentration varied according to the freshwater fraction used. In a variable volume system simulation, times to reach the 3500 g m−3 limit ranged from 24 to 136 cycles for freshwater fractions of 0·0-0·5. At ratios of 0·5-1·0 the predicted concentrations were all below 3500 g m−3, since the pond filled before the limit was reached. This paper also discusses disinfection and land treatment issues, and proposes further model development to incorporate the effects of complex pond hydraulics, climatic variables and dynamic pond processes on conductivity and TDI accumulation.