Investigation of influent COD/TAN ratio and loading rate effects on carbon and nitrogen removal via aerobic granules

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Environmental Engineering, Turkey

Approval Date: 2014




Aerobic granulation serves as a promising treatment technology over the conventional systems due to its advantages such as high biomass retention capacity, high settleability, ease of separation from the effluent, toxicity resistance, capacity to handle high organic loading rates and suitability for high chemical oxygen demand (COD) wastewaters. The scope of the thesis is to investigate the influent COD/total ammonifiable nitrogen (TAN = NH4-N + NH3-N) ratio and loading rate effects for the removal of carbon and nitrogen from wastewaters by aerobic granular SBR operation. Firstly, the effects of influent COD/TAN ratios (1 to 30) were investigated. The optimum influent COD/TAN ratio leading to both the highest COD (75%) and TAN (90%) removal efficiencies and maintenance of granular stability under the studied conditions was determined as 7.5. It was speculated that the influent COD/TAN ratio affected the aerobic granular composition via enrichment of heterotrophic bacteria at higher ratios (10-20-30) and nitrifiers at lower ratios (5-3.5-2-1). Secondly, the effects of increasing organic loading rates from 0.75-12 g COD/Lday, and nitrogen loading rates from 0.1-1.6 g TAN/Lday were investigated at vi a constant influent COD/TAN ratio of 7.5. The optimum loading rates were determined as 1.5 g COD/Lday and 0.2 g TAN/Lday, regarding the provision of the highest COD (85±1%), TAN (87±2%) and total nitrogen (TN) (49±17%) removal efficiencies, as well as formation of granules with high stability. The utilization of aerobic granular systems for sugar beet processing wastewater treatment, and the effect of this wastewater on aerobic granules were also investigated. It was found that the raw sugar beet processing wastewater with high solids content (2255±250 mg/L total suspended solids, i.e TSS) could be treated successfully via aerobic granular sludge with removal efficiencies of 65±5% total chemical oxygen demand (tCOD), 87±1% soluble chemical oxygen demand (sCOD), 58±10% TSS and 61±4%TAN. Results of this study are expected to be used for the determination of the suitable influent COD/TAN ratio and the loading rates that provide high carbon and nitrogen treatment efficiencies and maintenance of granular stability in the upcoming studies employing aerobic granular systems.