Alexandros Aivasidis

Comparison between UCT type and DPAO biomass phosphorus removal efficiency under aerobic and anoxic conditions

Two different types of biomass, capable for Enhanced Biological Phosphorus Removal (EBPR), a UCT (University of Cape Town) type and a sludge enriched with DPAOs (Denitrifying Phosphorus Accumulating Organisms) were tested in batch reactors under specific operational and environmental conditions, in order to achieve a direct comparison of their phosphorus removal capability. Three types of batch reactors were operated, Anaerobic/Oxic (AO), Anaerobic/Anoxic (A2) and Anaerobic/Anoxic/Oxic (A2O), under controlled temperature and pH conditions. Maximum anaerobic specific phosphate release, substrate utilization, as well as denitrification and phosphate uptake rates under aerobic and anoxic conditions were determined and compared for the two different microbial populations. Experimental results indicated no significant difference between the anoxic and the aerobic phosphorus (P) uptake rates, respectively for DPAO and UCT sludge. The UCT sludge was also found to achieve anoxic P uptake, however to much less extend compared to the DPAO sludge. It has also been proved that anoxic P uptake seems to negatively affect the total P removal efficiency of this type of sludge, even under following aerobic conditions. Based on these findings, denitrifying phosphorus removal systems are proved comparable to conventional EBPR configurations (UCT), concerning phosphorus removal efficiency, while their operation is accompanied by potential advantages.

Biotechnological Methods for Nutrient Removal from Wastewater with Emphasis on the Denitrifying Phosphorus Removal Process

Phosphorus is an essential element for all living cells. It is also one of the nutrients that can cause serious problems, such as eutrophication of water bodies if discharged into the environment. The main technologies developed for phosphorus removal from wastewater streams can be categorized as chemical or biological processes. The latter are considered more suitable from an economical as well as an environmental point of view and are more commonly used in practical implementations. Enhanced biological phosphorus removal (EBPR) has well proved its feasibility as well as exceptional efficiency in nutrient removal. However, because of its complex biological nature, EBPR often becomes unreliable in wastewater treatment. Additionally, the conventional EBPR methods, where phosphorus removal takes place under aerobic conditions, are quite sensitive to several environmental conditions, often encountered in full-scale plants. This article focuses on nutrient removal by biological means, which is still of great scientific interest. Emphasis is given to anoxic phosphorus removal, which is accompanied by important advantages when compared to the conventional aerobic process, such as reduction in energy demands and improved performance in the treatment of low-organic-strength wastewater.

Upflow anaerobic clarification tank (UACT) to upgrade existing anaerobic effluents

The Upflow Anaerobic Clarification Tank (UACT) is of interest as a post-treatment step for high-rate anaerobic wastewater treatment systems. The UACT contributes to extra capture of methane from the raw wastewater. It also significantly facilitates the reuse of the treated water. The efficiency of the UACT process is demonstrated in this study using laboratory-scale reactors. The water produced by the UACT had a low total COD, in most cases below 145 mg/L and a soluble COD below 60 mg/L at surface loading rates between 0.1-0.4 m(3)/(m(2) h) and hydraulic retention times between 5-6 h. The sludge bed of the UACT was characterised by 6-10 times higher substrate affinity (for ethanol, acetate and propionate) compared to the parent UASB and similar specific activity. The results suggest that a UASB followed by the UACT can, upon subsequent application of a rapid filtration, qualify as a total COD removal, no longer necessitating aerobic treatment.

Anaerobic digestion of thermal pre-treated emulsified slaughterhouse wastes (TESW): Effect of trace element limitation on process efficiency and sludge metabolic properties

Slaughterhouse solid wastes, characterized by a high lipid content, are considered a valuable resource for energy production by means of anaerobic digestion technologies. Aim of this study was to examine the effect of trace element limitation on the mesophilic anaerobic digestion of thermally pre-treated emulsified slaughterhouse wastes (TESW). Under two distinct experimental periods (Period I - low and Period II - high trace element dosage respectively) a CSTR with sludge recirculation was operated at increasing organic loading rate (OLR) from 1.5 to 10 g L-1 d-1. Under optimum conditions, COD removal was higher than 96%, biogas yield equal to 0.53 L g-1 COD feed and the biogas methane content 77%. Trace element limitation however, resulted in a dramatic decline in process efficiency, with VFA accumulation and events of extreme sludge flotation, despite that the soluble concentration of Ni, Co and Mo were between 12 and 28 μg L-1. This is indicative of mass transfer limitations caused by lipids adsorption onto the anaerobic biomass.