Biochemical Oxygen Demand Relationships in Typical Agricultural Effluents

Understanding the variables controlling biochemical oxygen demand (BOD) of effluents from agricultural systems is essential for predicting and managing the water quality risks associated with agricultural production. In this study, short- and long-term oxygen demand behaviors of waters from primarily agricultural sources and their relationships with other parameters were evaluated. A total of 46 water samples were generated from diverse organic sources commonly associated with agricultural activities and analyzed for BOD and other various water quality parameters. Short-term BOD (BOD2 and BOD5) were significantly correlated with total organic carbon (TOC), particulate organic carbon (POC), and dissolved organic carbon (DOC) (R (2) = 0.62-0.77, p < 0.001), likewise to total nitrogen, total Kjeldahl nitrogen, and nitrite-nitrogen (NO2-N) (R (2) = 0.40-0.55, p < 0.001). Long-term BOD (BOD60) was generally poorly correlated with these C and N fractions. Phosphate (PO4-P) exhibited a positive and linear relationship with both short- and long-term BOD, whereas chloride (Cl) tended to inhibit oxygen demand. Multivariate combinations of each of TOC, POC, and DOC with NO2-N, and Cl or PO4-P improved the predictions of both short- and long-term BOD. The ultimate BOD (BODu) derived from the first-order kinetics was highly correlated with BOD60 (R (2) = 0.81, p < 0.001) whereas BOD60 was correlated with BOD5 (R (2) = 0.60, p < 0.001). Overall the results indicated that C and N forms along with PO4-P and Cl were the dominant factors controlling the oxygen demand behaviors of agricultural effluents.