Using runoff slope-break to determine dominate factors of runoff decline in Hutuo River Basin, North China

摘要

Piggery wastewater is characterized by its high content in nitrogen and phosphorus, as well asnby a low C/N ratio. This type of wastewater is traditionally spread to croplands (with itsnsubsequent leaching to groundwater) or rarely discharged into natural water bodies, whichnultimately cause severe episodes of eutrophication in aquatic ecosystems. In this context,nactivated sludge systems constitute a robust and efficient treatment option. The performance ofnan activated sludge process using a pre-denitrification configuration treating both sieved andnflocculated swine slurry at a hydraulic retention time (HRT) of 7.7 days was evaluated. In ordernto avoid bacterial wash-out, sludge from the settler was recirculated to the anoxic tank tonaccomplish denitrification. Once the biomass was acclimatized, the reactor was fed with swinenslurry containing 19, 2.6, and 0.27 g/L of total chemical oxygen demand (COD), total Kjeldhalnnitrogen (TKN), and soluble P, respectively. Nitrogen removal showed a clear dependency onnthe influent composition. When the influent TKN/total COD and soluble COD/total COD ratiosnwere respectively 0.12–0.15 and 0.7, the reactor exhibited good removal efficiencies (up to 99nand 91 for N-NHtn4 , TKN, respectively) while PO32n4 was removed up to 65%. However, when theninfluent TKN/total COD ratio rose to 0.26 and soluble COD/total COD decreased to 0.3, thendenitrification process was severly hindered concomitant with and accumulation of nitrite.nNevertheless, organic matter degradation was not affected by influent composition. At the lastnstage of the experiment, removals of dissolved phosphorus fell to 40% when the redoxnpotential (ORP) profile showed a constant value of 2400 mV, likely due to phosphate releasednfrom bacterial slugde.