Η προστασία του περιβάλλοντος και της δημόσιας υγείας στις μέρες μας είναι επίκαιρες όσο ποτέ άλλοτε. Μία από τις κύριες αιτίες μόλυνσης η οποία μάλιστα συνεχώς αυξάνεται λόγω και τις ολοένα αυξανόμενης αστικοποίησης είναι η απόθεση των υγρών αποβλήτων. Γι αυτό το λόγο τα τελευταία χρόνια γίνονται ερευνητικές προσπάθειες με στόχο τη μείωση των ρυπαντικών φορτίων σε περιβαλλοντικά αποδεκτά επίπεδα, για να μπορέσουν τα λύματα να διατεθούν χωρίς να αλλοιώνουν σημαντικά τα χαρακτηριστικά του φυσικού αποδέκτη. Η βιολογική επεξεργασία λυμάτων είναι μία σύνθετη διαδικασία που πραγματοποιείται μέσω περίπλοκων βιολογικών, φυσικοχημικών και βιοχημικών αντιδράσεων. Η βιολογική απομάκρυνση του αζώτου πραγματοποιείται με τις διεργασίες της νιτροποίησης και της απονιτροποίησης. Η νιτροποίηση πραγματοποιείται κάτω από αερόβιες συνθήκες με την συνδρομή αυτότροφων βακτηρίων, που μετατρέπουν την αμμωνία σε νιτρώδες άζωτο και στη συνέχεια ακολουθεί οξείδωση των νιτρωδών σε νιτρικό άζωτο. Η απονιτροποίηση συνίσταται στην αναγωγή του νιτρικού αζώτου σε αέριο άζωτο, με τη βοήθεια προαιρετικά αερόβιων ετερότροφων μικροοργανισμών. Η προσομοίωση της διεργασίας σε Η/Υ με τη χρήση μαθηματικών μοντέλων, παίζει σημαντικό ρόλο στην περιγραφή, τον έλεγχο και την πρόβλεψη των αλληλεπιδράσεων των συστατικών που συμβαίνουν σε μια εγκατάσταση επεξεργασίας λυμάτων. Στην παρούσα εργασία έγινε η χρήση ενός τροποποιημένου μοντέλου με βάση το ASM3 για την ακρίβεια του ASM3 2N για την προσομοίωση μιας οξειδωτικής τάφρου. Σκοπός της παρούσας εργασίας είναι να διερευνηθούν μέσω προσομοιώσεων οι συνθήκες αερισμού σε μία τυπική εγκατάσταση οξειδωτικής τάφρου, κάτω από τις οποίες επιτυγχάνεται απομάκρυνση του αζώτου από τα απόβλητα σε τιμές εντός των επιτρεπτών ορίων της νομοθεσίας για διάθεση στο φυσικό αποδέκτη. Ειδικότερα μελετήθηκε η επίδραση των σημαντικών λειτουργικών παραμέτρων οι οποίες επηρεάζουν την απόδοση του συστήματος με σκοπό τον προσδιορισμό εκείνο μέσω του οποίου επιτυγχάνεται ελαχιστοποίηση του κόστους λειτουργίας μιας τέτοιας εγκατάστασης. / -

The discharge of point- and non-point source pollutants into surface waters resulting from industrial and/or municipal activities is a major focus of environmental regulation in the United States. As a result, the National Pollutant Discharge Elimination System (NPDES) permit program was established in 1972 in an effort to regulate discharges from industrial or municipal sources, including wastewater treatment plants (WWTP). To further protect Florida water quality, in 1978, State legislation enacted the Grizzle-Figg Act for Tampa Bay, which requires advanced wastewater treatment for any discharge into sensitive water bodies. A common use of wastewater effluent in the Tampa Bay area is for reclaimed water for irrigation. This leads to an estimated 90% reduction of total nitrogen (TN) load to the bay in comparison to direct discharge (TBEP, 2016). One type of wastewater treatment process that has been shown to have low aeration and chemical requirements is simultaneous nitrification denitrification (SND), which can be carried out in an oxidation ditch. SND is a biological process for nitrogen removal where nitrification and denitrification occur at the same time within the same reactor. An oxidation ditch is a race-track type reactor that promotes the occurrence biological conversion of reactive nitrogen to nitrogen gas (N2) and additionally can provide enhanced biological phosphorus removal (EBPR). Many theories exist as to the mechanisms that allow SND to occur, but the literature is inconclusive as to whether the presence of different zones within the floc, within the reactor itself, a combination of the two or unique microorganisms are responsible for SND. Advantages of SND include efficient (80-96%) nitrogen removal, with significant reductions in energy, chemical, equipment and spatial requirements. Specifically, oxygen requirements are reduced and dedicated aerobic/anoxic zones, internal recirculation and supplemental carbon and alkalinity are not required. Despite these advantages, widespread use of SND is limited because of a lack of understanding of SND kinetics as well as interactions between factors affecting SND performance. This research was carried out at the Falkenburg Advanced Wastewater Treatment Plant (AWWTP) in Hillsborough County Florida, which carries out SND, biological and chemical phosphorous removal in an oxidation ditch system. Although this facility continually meets and exceeds its permit requirements, improvements in process control strategies have the potential to improve energy efficiency, as well as decrease chemical use, sludge production, greenhouse gasses (GHG) emissions and costs. Therefore, the overall goal of this research was to investigate mechanisms of nitrogen and phosphorus removal at the Falkenburg AWWTP. These goals were achieved through bench scale SND studies carried out at varying temperatures. Kinetic parameters were determined using a simple kinetic model of nitrification/denitrification. Additionally, carrying out sampling campaigns completed the investigation of the fate of phosphorus in the Falkenburg AWWTP. The results were combined with information on alum dosing and sludge wasting to determine the overall fate of phosphorus in the system and make additional recommendations regarding the addition of alum. To mimic an oxidation ditch at Falkenburg AWWTP, bench scale bioreactor experiments were set up in glass beakers at 22°C and 29.5 C. Influent wastewater and return activated sludge (RAS) for these experiments were collected from the Falkenburg AWWTP. Bioreactors were constantly mixed and aeration was controlled to maintain a target dissolved oxygen (DO) concentration based on measurements of DO at the facility. Three phosphorous sampling campaigns (October, November and December) were also carried out to understand the fate of phosphorous, nitrogen and organic carbon at the facility. In these campaigns, samples were taken at six locations at Falkenburg AWWTP and samples were analyzed for filtered and unfiltered total phosphorus, orthophosphate and polyphosphates, filtered and unfiltered total nitrogen, soluble, total and readily biodegradable COD (rbCOD), volatile acids, cations, anions, alkalinity, total suspended solids (TSS) and volatile suspended solids (VSS). pH and DO were also measured on site. In the nitrification batch reactors, in four hours, 50% of ammonia was successfully removed at a rate of 6.31 mg-N/L/hr indicating that four hours is not sufficient time to achieve complete removal. In the denitrification batch reactors, in six hours, there was successful removal of nitrate and nitrite at a rate of 23.70 mg-NO3-/L/hr and 3.6 mg-NO2-/L/hr. In an SND batch reactor experiments at 22° C, ammonia oxidation successfully occurred in 12 hours but denitrification was inhibited due to insufficient rbCOD in the reactor. In an SND batch reactor at 29.5° C, no accumulation of nitrate or nitrite was observed, indicating successful SND. At a higher temperature, sludge bulking occurred in the reactor resulting in variations in TSS and VSS concentrations. Results from the sampling campaigns at the treatment plant indicate that successful phosphorus removal was achieved. Alum addition varied before each sampling and a relationship between alum addition and sulfate can be made. rbCOD was consumed throughout the treatment process as expected and noticeable results can be noted when rbCOD was low in terms of phosphorus removal. The results of the bench-scale experiments showed that the SND was successfully achieved at the Falkenburg facility and that temperature, DO and rbCOD are all important factors controlling biological nutrient removal at SND facilities. DO is much more difficult to maintain and control at a higher temperature further supporting the idea that stricter operator control is needed in warmer months. Additionally, because SND removal still occurred with poor DO control at 29.5°C, it further supports the idea that SND occurs because of zones within the floc, the reactor or that novel microorganisms exist that allow denitrification to occur above ideal DO concentration and nitrification to occur below ideal concentrations of DO. A variation in rbCOD in the influent wastewater at the treatment plant caused nitrification and denitrification to be inhibited in different trials. With too much rbCOD, nitrification was inhibited and with too little rbCOD, denitrification was inhibited. Additionally, alkalinity consumption was minimal which supports the idea that supplemental alkalinity is not needed in SND processes. The results from the phosphorous sampling campaign show how important influent COD is for successful phosphorus removal in the system. The objectives were achieved and overall, the plant is achieving SND and EBPR and the plant is performing as designed. The addition of alum should continue to be studied to determine a better dose and save the county ratepayers money while still meeting permit regulations. Jar tests should be used to determine the proper dosing that will not hinder the settling properties further in the treatment train. Additionally, alum feed pipe sizes should be investigated at the plant to ensure no clogging occurs with a decrease in alum flow and automated aeration based on ammonia concentrations should be considered to remove the manual operation of aerators.

The treatment of water for human consumption results in the production of residual waste flows that vary depending on source waters and water treatment technologies. Water treatment plant residual waste is defined as a pollutant that requires treatment either on site or through other means. Due to strict and evolving regulatory requirements, treatment of water treatment plant residual waste several common methods of disposing of water plant residuals exist including discharge to surface waters, discharge to sanitary sewers, and sanitary landfill disposal of dewatered wastes. Although originally discharged to the neighboring City Reservoir, the Carbondale Water Treatment Plant (CWTP) conducted an initial study to determine if plant residual waste could be treated at one of the City’s two wastewater treatment plants. No negative impacts were identified as part of this study and infrastructure was put in place to divert CWTP residual waste from the City Reservoir to the Carbondale Southeast Wastewater Treatment Plant (SEWWTP). This study focused on accessing and quantifying any impacts of Carbondale Water Treatment Plant (CWTP) residual solids sewer discharge on biological treatment processes, effluent water quality, and sludge production at the SEWWTP. The Carbondale SEWWTP treats raw water influent through a number of physical and biological processes including screening, clarification, nitrification/denitrification, and aeration. Of the tests run as part of this study daily samples were collected of SEWWTP influent, mixed liquor, return sludge, and effluent and measured for changes in pH, biochemical oxygen demand (BOD), solids, sludge volume index (SVI), dissolved oxygen (DO), and nitrogen. No significant changes were documented other than percent BOD removal did improve after the introduction of the residuals. Anions were also tested weekly. Samples were collected from the SEWWTP’s oxidation ditch to monitor biological life using biological activity reaction tests (BART) for nitrifying, denitrifying, and heterotrophically active bacteria. BART testing showed no decline in biological activity and increased populations of denitrifying bacteria. Additionally, both metals and acute toxicity of SEWWTP effluent were tested by outside testing facilities to confirm that CWTP residual solids sewer discharge did not interfere with discharge limits established as part of the plant’s permits. No significant changes were observed during testing but plant staff did indicate that more extensive cleaning of the basins was implemented post-introduction. Overall, the case study confirmed that the treatment of CWTP residual solids sewer discharge did not negatively impact treatment processes at the SEWWTP and is sustainable.