The effects of temperature and mean cell residence time (MCRT) on biological nitrogen and phosphorus removal were investigated by operating two pilot‐scale continuous‐flow reactors in parallel over a range of temperatures and MCRTs. One system was operated as a high‐rate Virginia Initiative Plant (VIP) biological nutrient removal (BNR) process, and the other was operated as a conventional, fully aerobic activated sludge process for comparison. Results showed that less aerobic volume was needed for complete nitrification in the BNR process than in the conventional process when conditions of temperature and MCRT were suitable for complete nitrification. However, the BNR system was more prone to nitrifier washout than the conventional system. Nitrification rates and the degree of nitrification achieved by the BNR system and the conventional system were equal when compared on the basis of aerobic MCRT. Enhanced biological phosphorus removal (EBPR) was adversely afFected by colder temperatures, with lower MCRTs being most affected. EBPR was not possible at a 5 day system MCRT and 10°C. Nitrification, however, was more sensitive to MCRT and temperature effects than EBPR under all conditions studied. Operation of the BNR process at the lowest MCRT that provided complete nitrification provided the best combined nitrogen and phosphorus removal when EBPR was chemical oxygen demand (COD)‐limited. Higher MCRTs were considered optimal when EBPR was limited by phosphorus because of lower sludge productions.
The role of potassium (K) and magnesium (Mg) in enhanced biological phosphorus removal (EBPR) by activated sludge was studied using a bench-scale continuous-flow A/O system. A synthetic wastewater containing all the nutrients required for EBPR was used as the influent feed for the control phase of the experiment. The influent feed to the test phase of the experiment was changed to totally limit specific cations. The results clearly indicated that both K and Mg were absolutely required for successful EBPR. Failure of EBPR occurred when either K or Mg were eliminated from the influent. The molar ratio of K:P during anaerobic release and aerobic uptake was observed to be 0.22 mol/mol, while Mg:P was 0.30 mol/mol. Calcium was not required for successful EBPR. Neither calcium, iron, nor sodium were co-transported with phosphorus during release and uptake.
The objective of this study was to determine the availability of phosphorus contained in different wastewater sludgesand sludgesoil mixtures. The sludges studied included raw and aerobically digested sludges from activated sludge treatment plants using four different methods of phosphorus removal: alum addition, ferric chloride addition, anaerobic/oxic biological phosphorus removal, and no provision for excess phosphorus removal.Test methods used to determine phosphorus availability of the sludges included the equilibrium phosphorus concentration test and soil-incubation tests. The soil-incubation studies consisted of soil and soil-sand mixtures spiked with sludges. Testing on the pots compared initial pots to final pots after leaching with distilled water. Results showed that based on most measures, phosphorus was the most available from fertilizer. Phosphorus was also highly available from sludges generated without using chemical addition for phosphorus removal. Phosphorus availability of digested sludges versus raw sludges varied, depending on the method of analysis. Water Environ. Res .. 67, 282 (1995).
Nitrification kinetics as a function of mixed liquor temperature were compared for a conventional fully-aerobic activated sludge system and a system accomplishing biological nutrient removal (BNR) by incorporation of anaerobic and anoxic zones using the UCT configuration. The systems treated the same municipal wastewater and both had flow rates of 151 L/day. The nitrification rates were greater in the nutrient removal system compared to the conventional system as long as the aerobic MCRT was above the minimum for complete nitrification. It was concluded that BNR systems require less aerobic volume than fully aerobic systems to accomplish nitrification because the aerobic biomass concentration is greater in the BNR systems, particularly if the UCT configuration is used. Nonetheless, BNR systems require more total volume to accomplish complete nitrification than fully aerobic systems, and the volume differential increases as mixed liquor temperatures decrease.
zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Laboratory and pilot-plant scale studies were conducted to investigate the occurrence of anaerobic reduction of oxygen requirements in excess biological phosphorus removal (BPR) systems. The investigation was accomplished through application of chemical oxygen demand (COD)/oxygen-utilization mass balance techniques. Reductions of 0 to approximately 50% in the oxygen required for organic stabilization were achieved during treatment of synthetic and raw wastewaters. The reductions were attributed to stabilization occurring in the anaerobic reactors and represent a potential aeration energy savings that could be realized with BPR systems in addition to any savings associated with denitrification. Factors which influence the occurrence and magnitude of anaerobic stabilization include the composition of the influent wastewater, and the strength of the influent wastewater. It was concluded that substantial reduction of oxygen requirements can occur as a result of anaerobic stabilization and that the principal mechanism is probably metabolism by bacteria, such as fermenters, that do not accumulate phosphorus.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res., 64, 824 (1992).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.