Nitrification and denitrification in a rotating biological contactor.

摘要

This thesis is an investigation of nitrogen removal in a rotating biological contactor (RBC). Nitrogen compounds are increasingly becoming a source of concern in wastewater management because of the many effects that nitrogenous material can have on the environment. Nitrogen, in its various forms, can cause adverse effects because they require oxygen for nitrification, fertilise aquatic plant growth, exhibit toxicity toward aquatic life, affect chlorine disinfection efficiency and present a public health hazard. With these concerns in mind, the government has current regulations to reduce these concentrations to strict levels. As a result, stringent limitations on nitrogen discharge can exceed the ability of traditional wastewater treatment plants to produce high quality effluents at a reasonable cost. Consequently, economic and innovative wastewater treatments are needed to satisfy the demand for nitrogen control. Rotating biological contactors (RBCs) meet these requirements; it combines advantages not only regarding biochemical oxygen demand (BOD) removal, but also nitrification and denitrification all in a reduced plant area. In spite of the large number of studies investigating nitrification and denitrification in RBCs, there are still controversies regarding different approaches to optimise these two complex processes. In this thesis, nitrification and denitrification processes are investigated in an RBC of 5,000 L/day of capacity at the School of Chemical Engineering at Ryerson University. The experimental design was planned in two phases. In the first phase, oxygen transfer, from air to water, was measured to de-oxygenated tap water in order to establish the favourable rotational velocity that satisfy the minimum oxygen requirement for nitrification. Two RPM was the rotational speed that met those requirements. In the second phase, the RBC was modified and divided into two sections; an aerobic section where synthetic wastewater was nitrified, and an anoxic section where the nitrified influent was denitrified. The experiment was performed once the biofilm had been well developed in both sections. In this system, the nitrogen was removed successfully achieving 96% at an ammonia-nitrogen loading rate of 0.87 g NH₃-N/m2 day and 25 mg NH ₃-N/L.