Technological characteristics of reject waters from aerobic sludge stabilization in small and medium-sized wastewater tr
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ORIGINAL RESEARCH
Technological characteristics of reject waters from aerobic sludge stabilization in small and medium‑sized wastewater treatment plants with biological nutrient removal Zbigniew Mucha1 · Jerzy Mikosz1 Received: 26 June 2020 / Accepted: 5 September 2020 © The Author(s) 2020
Abstract Most studies on the impact of reject waters recycled from sludge processing in the multi-phase activated sludge process focus on anaerobic sludge treatment in large wastewater treatment plants, leaving apart the processes of aerobic sludge stabilization often used in smaller facilities in rural and suburban areas. The article presents the results of tests carried out in three small and medium-sized wastewater treatment plants with biological removal of biogenic compounds that use aerobic stabilization to process sludge. The research concerned the quantity and quality of reject waters generated in the process of aerobic stabilization and dewatering of sewage sludge and their impact on the multi-phase activated sludge process. The results showed that the average volume of generated reject waters ranged from 3.2 to 5% of the incoming wastewater volume. The average share of organic compounds and total nitrogen loads contained in reject waters did not usually exceed 5–10% of the loads in raw wastewater but reached almost 50% in the case of total phosphorus. Studies indicated that the composition of the supernatant from aerobic stabilization is strongly dependent on the course of the process. The best quality was obtained for cyclic operation of the aerobic stabilization tank with 16 h of aeration and 8 h of settling. The results also showed the negative impact of sudden discharges of reject waters from sludge processing to a multi-phase biological reactor, which can be reduced by using an appropriate equalization tank and pretreatment of the side stream to reduce the recirculation of phosphorus. Keywords Small wastewater treatment plant · Biological nutrient removal · Aerobic stabilization · Sludge processing · Reject water
Introduction Sludge treatment should ensure the elimination of odour nuisance (stabilization) and a reduction of sludge volume (thickening and dewatering) [1]. These processes lead to the generation of large volumes of reject waters. In the past, the problem of the impact of reject waters on biological treatment processes concerned rather large wastewater treatment plants (WWTPs) in which anaerobic digestion was used to stabilize the sludge [2–4]. However, the European Union’s requirements for the quality of treated wastewater imposed * Jerzy Mikosz [email protected] 1
Division of Environmental Technologies, Faculty of Environmental and Power Engineering, Cracow University of Technology, ul. Warszawska 24, 31‑155 Cracow, Poland
on agglomerations with a population equivalent (PE) above 10,000, resulting from the implementation of Directive 91/271/EEC concerning urban wastewater treatment, also make it necessary to remove nitrogen and phosphorus in small and medium-sized WWTPs located in such agg
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