MODELING FOR OPTIMAL MANAGEMENT OF AGRICULTURAL AND DOMESTIC WASTE-WATER LOADING TO STREAMS

A simulation/optimization (S/O) model to aid managing multiobjective w astewater loading to streams while maintaining adequate downstream wat er quality is presented. The conflicting objectives are to maximize th e human and dairy cattle populations from which treated wastewater can be discharged to the river system. Nonindustrial municipal (domestic) wastewater undergoes primary and secondary treatment by a sewage trea tment plant (STP) before entering as a steady point source. Dairy wast ewater is treated by overland flow (OLF) land treatment before enterin g the stream as a controlled steady diffuse source. Maximum dual-sourc e loading strategies which do not degrade downstream water quality bey ond specified limits are developed. For each computed loading strategy , an optimal OLF system design is also determined. The E constraint me thod is used to obtain sets of noninferior solutions. Sets of noninfer ior solutions are represented graphically to show the trade-off betwee n human and bovine populations that can be maintained. Each set is com puted for a different upstream flow rate to illustrate sensitivity to nondeterministic upstream flow rates. The nonlinear constraints utiliz ed restrict downstream concentrations of 5-day biochemical oxygen dema nd, dissolved oxygen, nitrogen (organic, ammonia, nitrite, and nitrate ), organic and dissolved phosphorus, and chlorophyll a. Concentrations are described via regression equations. The new regression expression s, surrogates for the complex advective-dispersive equation, permit ra pid and feasible solutions by this unique S/O model.