Anastasios G. Kapagiannidis

Denitrifying polyphosphate accumulating organisms population and nitrite reductase gene diversity shift in a DEPHANOX-type activated sludge system fed with municipal wastewater

Enhanced biological phosphorus removal (EBPR) is a widely applied method for nutrients removal, although little is known about the key genes regulating the complex biochemical transformations occurring in activated sludge during phosphorus removal. In the present study, the nitrite reductase gene (nirS) diversity and the denitrifying polyphosphate accumulating organisms (DPAOs) population, grown in a bench scale, two-sludge, continuous flow plant, operating for biological anoxic phosphorus removal (DEPHANOX-type), fed with municipal wastewater, were examined by means of physicochemical analyses and the application of molecular techniques. The DEPHANOX configuration highly influenced biomass phosphorus as well as polyhydroxyalkanoates content and facilitated the enrichment of the DPAOs population. The application of double probe fluorescent in situ hybridization (double probe FISH) technique revealed that DPAOs comprised 20% of the total bacterial population. Based on clone libraries construction and nirS gene sequencing analysis, a pronounced shift in denitrifying bacteria diversity was identified during activated sludge acclimatization. Moreover, nirS gene sequences distinct from those detected in any known bacterial strain or environmental clone were identified. This is the first report studying the microbial properties of activated sludge in a DEPHANOX-type system using molecular techniques.

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.

Comparison between aerobic and anoxic metabolism of denitrifying-EBPR sludge: effect of biomass poly-hydroxyalkanoates content

Biomass with denitrifying phosphate uptake ability was tested under sequencing anaerobic-aerobic and anaerobic-anoxic conditions. The initial dose of acetate, under anaerobic conditions varied to achieve different PHA (poly-hydroxyalkanoates) saturation of PAO (polyphosphate accumulating organisms) cells. Increased acetate dosage under anaerobic conditions led to higher phosphate release and increased PHA storage by PAOs and, also, to greater phosphate uptake rates under the following aerobic and/or anoxic conditions. The experimental results also indicated that when organic carbon is limited under anaerobic conditions, more internal glycogen supplementary to polyphosphate cleavage is utilized by the biomass, resulting in less phosphate release and more PHA stored per acetate taken up. In the subsequent aerobic and/or anoxic phase PAOs demonstrate an improved EBPR (enhanced biological phosphorus removal) performance, with regard to PHA consumption per phosphate taken up, for reduced initial biomass PHA content under both aerobic and anoxic conditions. The examination of EBPR biomass under controlled operational conditions, where experimental analysis of the relevant compounds in the bulk phase (PO(4)(3-), NO(3)(-) and/or O(2)) in conjunction with the biomass intracellular products (PHA, glycogen), contributes to an improved understanding of the PAOs metabolic behavior, with regard to organic substrate availability.

Sewage Sludge Solar Drying: Experiences from the First Pilot-Scale Application in Greece

Increasingly strict regulations governing sludge management have raised interest in drying technologies. The feasibility of sewage sludge solar drying was experimentally evaluated in a 66-m2 pilot-scale greenhouse plant under typical weather conditions in Greece. The greenhouse was equipped with ventilation fans to maximize the drying process efficiency and a turning drum for efficient sludge mixing. The obtained results proved the applicability and the high performance of the solar drying technology. The time necessary to achieve a dry product with a dry solids content up to 95% ranged between 8 and 31 days, depending on the weather conditions. During drying, sludge organic matter was reduced by 5–21%, and total and fecal coliform content was also decreased up to three orders of magnitude. By taking into consideration the sludge content in heavy metals, the final product can partially or totally replace commercially available inorganic fertilizers in agricultural applications, in accordance with the restrictions imposed by national and European regulations. Based on a preliminary cost analysis concerning the construction of a solar drying facility covering a sum of 80,000 population equivalent (PE), a corresponding capital cost of 24 €/PE is anticipated.

Metabolic behavior and enzymatic aspects of denitrifying EBPR sludge in a continuous-flow anaerobic-anoxic system.

The metabolic aspects of enhanced biological phosphorus removal (EBPR) were investigated for the first time in a continuous-flow anaerobic–anoxic plant fed with acetate, propionate, or substrates which are involved in the tricarboxylic acid and/or glyoxylate cycle, i.e., fumarate, malate, or oxaloacetate, as the sole carbon source. Although the polyphosphate-accumulating organisms (PAOs) population remained stable with any carbon source examined, no typical EBPR metabolism was observed during fumarate, malate, or oxaloacetate utilization. Specific enzymatic activities related to EBPR were determined in activated sludge homogenates and directly correlated with the nutrient metabolic rates. The experimental results indicated the direct involvement of alkaline phosphatase, pyrophosphatase, and exopolyphosphatase in the denitrifying EBPR process. Metabolic aspects of glyoxylate cycle enzymes are discussed with regard to the biomass anaerobic and anoxic activity. Process performance was highly influenced by the kind of substrate utilized, indicating that specific metabolic pathways should be followed to favor efficient EBPR.

Performance and metabolic aspects of a novel enhanced biological phosphorus removal system with intermittent feeding and alternate aeration

A novel enhanced biological phosphorus removal (EBPR) system, which combined the intermittent feeding design with an anaerobic selector, was examined using on-line oxidation reduction potential (ORP), nitrate and ammonium probes. Two experimental periods were investigated: the aerobic and anoxic phases were set at 40 and 20 minutes respectively for period I, and set at 30 and 30 minutes for period II. Chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and P removal were measured as high as 87%, 96% and 93% respectively, while total Kjeldahl nitrogen (TKN) and NH4(+) removal averaged 85% and 91%. Two specific denitrification rates (SDNRs), which corresponded to the consumption of the readily biodegradable and slowly biodegradable COD, were determined. SDNR-1 and SDNR-2 during period I were 0.235 and 0.059 g N g(-1) volatile suspended solids (VSS) d(-1) respectively, while the respective rates during period II were 0.105 and 0.042 g N g(-1) VSS d(-1). The specific nitrate formation and ammonium oxidizing rates were 0.076 and 0.064 g N g(-1) VSS d(-1) for period I and 0.065 and 0.081 g N g(-1) VSS d(-1) for period II respectively. The specific P release rates were 2.79 and 4.02 mg P g(-1) VSS h(-1) during period I and II, while the respective anoxic/aerobic uptake rates were 0.42 and 0.55 mg P g(-1) VSS h(-1). This is the first report on an EBPR scheme using the intermittent feeding strategy.

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.

Inhibition of the respiratory chain reactions in denitrifying EBPR biomass under simultaneous presence of acetate and electron acceptor

In this study, the deterioration of the typical EBPR (Enhanced Biological Phosphorus Removal) process due to the simultaneous presence of electron donor (external substrate) and electron acceptor (oxygen or nitrate) was investigated by using a PAOs (Polyphosphate Accumulating Organisms)-enriched biomass grown in a modified DEPHANOX system. Intracellular and extracellular constituents were monitored in batch tests under different electron donor and acceptor conditions and specific oxygen and nitrogen uptake rates were evaluated. Results showed that phosphorus uptake was inhibited during the simultaneous presence of electron donor (acetate) and acceptor (O2/NO3-) in the mixed liquor. In the presence of acetate, PHAs and glycogen were produced under both aerobic and anoxic conditions irrespectively to the PHAs amount already stored intracellularly. The Krebs cycle reactions and oxidative phosphorylation provided the reduced coenzymes and energy required for PHAs synthesis when biomass polyphosphate content was low. On the contrary, polyphosphate cleavage provided the ATP required for PHAs synthesis in the presence of high biomass polyphosphate content. Inhibition of the respiratory chain reactions was observed when biomass with high polyphosphate and low PHAs content was subjected to simultaneous presence of electron donor and acceptor. PHAs utilization rather than glycogen degradation appears to favor phosphate accumulation since no polyphosphate synthesis occurred in the absence of PHAs reserves.