Book Description

This dissertation, "Autotrophic Denitrification of Synthetic Wastewater in Biological Activated Filter (BAF) Reactors With Sulfur Media" by Ka-man, Tam, 譚家雯, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled AUTOTROPHIC DENITRIFICATION OF SYNTHETIC WASTEWATER IN BIOLOGICAL ACTIVATED FILTER (BAF) REACTORS WITH SULFUR MEDIA Submitted by TAM Ka Man for the Degree of Master of Philosophy at the University of Hong Kong in December 2006 Denitrification is an important process in wastewater treatment for controlling nitrate induced environmental problems. Autotrophic denitrification using elemental sulfur is applicable to wastewaters with a low carbon to nitrogen ratio. Nitrate is reduced to nitrogen gas with the help of Thiobacillus denitrificans while oxidizing sulfur to sulfate with the consumption of alkalinity. Though it has a slower reaction rate, autotrophic denitrification may be more economical than the commonly applied organic carbon utilizing heterotrophic denitrification. Biological Activated Filter (BAF) systems with fine media are commonly used in heterotrophic denitrification. However, the application of BAF with backwash for autotrophic denitrification has been rarely reported so far. The objectives of this study were (i) to evaluate the efficiency of sulfur-utilizing BAF reactors using synthetic wastewaters; (ii) to determine the effect of backwash, and, (iii) to identify the microbial characteristics in the sulfur-utilizing BAF reactors. Two pilot scale BAF reactors with sulfur media of 2-4mm in diameter and cultivated with autotrophic denitrifying bacteria were continuously fed in upflow mode with adjustable flow rate for more than one year. Synthetic wastewaters with concentrations of 220, 300 and 60mg NO -N/l were utilized to study the denitrification performance. Methanol and sodium benzoate at 25% and 50% of the stoichiometric requirement for heterotrophic denitrification were then added into the synthetic wastewater of 60mg NO -N/l to investigate their effects in autotrophic denitrification. Ten backwashes were carried out on the two reactors in upflow direction for 15-30min each with either water scour or combined water and air scours for 75%-100% bed expansion. The experimental results demonstrated that (i) sulfur-utilizing BAF reactors with 2- - 3 4mm diameter media can achieve a volumetric removal rate of 725g NO -N/m .d without the addition of organic carbon; (ii) addition of methanol and sodium benzoate at 25% and 50% stoichiometric requirement increases the volumetric - 3 - 3 removal rates to 928g NO -N/m .d and 1584g NO -N/m .d respectively with 3 3 reductions in alkalinity consumed and sulfate produced, but more frequent backwash was required; (iii) backwash can reduce the internal resistance with the reduction of headloss, rearrangement of media and removal of excess biomass and biofilm. Proper backwash with less than 60% biomass removal can improve the volumetric loading rate; in contrast, excessive backwash reduces the removal rate with accumulation of nitrite; and (iv) Thiobacillus denitrificans-like and Thiomicrospira denitrificans-like bacteria are the dominant species in the reactors. The diversity of bacteria in the biofilm is similar along the media bed and not significantly affected by backwash and the addition of organic carbon compounds. The application and engineering significance of sulfur-utilizing BAF reactors are discussed. DOI: 10.5353/th_b3878922 Subjects: Sulphur Denitrific