Effects of effluents from wastewater treatment plants on the abiotic and biotic uptake of phosphorus by streambed sediments

PURPOSE: Sustained inputs of nitrogen and/or phosphorus from wastewater treatment plants (WWTPs) to aquatic environments lead to an increased risk of eutrophication. The purpose of this study was to analyze the relative proportions of biotic and abiotic processes in the uptake of phosphorus by streambed sediments and their response to exogenous carbon (sodium acetate) concentration gradients, as well as explore the effects of WWTP effluent discharges on the biotic and abiotic uptake potential of phosphorus by streambed sediments in the receiving streams. METHODS: Experiments were undertaken with streambed sediments collected from four different sites in different seasons, with or without the addition of a chloroform solution (biological inhibitor), to which were added different concentrations of a source of carbon (sodium acetate). After completing the indoor simulation culture, the total uptake potential (SPUₗᵢᵥₑ), abiotic uptake potential (SPUₐbᵢₒₜᵢc), and biotic uptake potential (SPUbᵢₒₜᵢc) of phosphorus by the sediments were calculated. RESULTS: The SPUₗᵢᵥₑ values of the sediments in the receiving section of the WWTP effluent were higher than those at the control site and gradually decreased with the flow direction. A larger amount (c. 79.04–98.11%) of the added phosphorus was taken up abiotically by the sediments with no added carbon. The SPUbᵢₒₜᵢc value of all sampling sites increased with the increase in exogenous carbon concentration by the addition of acetate, and accordingly the maximum contribution rate of the biotic uptake of phosphorus in sediments was 14.83–36.40%. CONCLUSIONS: Although WWTP effluents can increase the risk of release of phosphorus from sediments to the overlying water, the abiotic and biotic uptake potential of phosphorus by sediments is significantly increased by sediment–nutrient interactions. There may be more serious carbon limitations in the uptake of phosphorus by streambed sediments downstream of WWTPs than those at the reference site.